Swiss!Climate!Summer!

! ! ! ! 14th!Swiss!Climate!Summer!School! ! Extreme!Events!and!Climate! ! ! Congressi!Stefano!Franscini,!Monte! Verità! ! 23!–!28!August!2015! ! ! ! ! ! ! ! ! ! Supporting!bodies! ! ! Center!for!Climate!Systems!Modeling! ETH!Zurich! CHN!L12.2! Universitätsstr.!16! CH98092!Zurich! http://www.c2sm.ethz.ch/! ! ! Monte!Verità! ! Via!Collina!! ! CH96612!Ascona! ! http://www.csf.ethz.ch!! ! ! ETH!Zurich! Rämistrasse!101! 8092!Zurich! https://www.ethz.ch! ! ! University!of!Bern! ! Oeschger!Centre! Zähringerstrasse!25! CH93012!Bern! http://www.oeschger.unibe.ch! !

!!!!! Swiss!Reinsurance!Company! ! Mythenquai!50/60! P.O.!Box! CH98022!Zürich! http://www.swissre.com! ! ! Federal!Office!of!Meteorology!and! ! Climatology! Meteoswiss! Operation!Center,!B.O.!Box!257! CH98058!Zurich9Flughafen! http://www.meteoswiss.ch! ! ! The!Global!Energy!and!Water!Cycle! Experiment! http://www.gewex.com! ! ! World!Climate!Research!Programme!! 7bis!Avenue!de!la!Paix,!! Case!postale!2300!Nations! CH91211!Geneva! http://wcrp9climate.org! ! ! ! Table of Contents

Cloud Radiative Effect depending on Cloud 1 Aebi Christine Type and Cloud Fraction

Exploring the Dynamical Causes of Northeast Agel Laurie 3 US Extreme Precipitation

European summer heatwaves and North Alvarez-Castro M. Carmen Atlantic weather regimes in the last 5 Millennium

Probabilistic Estimates of Marine N2O Battaglia Gianna 6 Emissions

Flood damage claims of houseowners Bernet Daniel promise insights about surface runoff in 8 Switzerland

Bevacqua Emanuele Statistical Modelling of Compound Floods 10

Extreme Winter Cyclones in the North Atlantic Blumer Sandro R. in a CESM1.0.1 Last Millennium Climate 12 Simulation”

Borodina Aleksandra Robust changes in extreme events 13

FROZENFIRE – a contribution to Paleo Fires Brugger Sandra O. from high-alpine ice cores over the last two 14 millennia Blocking detection with observations from Brunner Lukas 16 radio occultation: A case study

The importance of including the globe Buzan Jonathan temperature (radiation) in the Wet Bulb Globe 17 Temperature index

Evaluation of Mechanisms of Extreme Colfescu Ioana Temperatures over Europe and North 19 America

Impact of Arctic Sea Ice on Circulation Crasemann Berit 20 Patterns, Planetary and Baroclinic Waves

Estimation of flood-adaptation indices in Doroszkiewicz Joanna 22 varying climatic conditions

The role of the ocean on the development of 24 Duchez Aurelie European weather extremes

Understanding the Characteristics and Emerton Rebecca Predictability of 26 Flood Events at the Global Scale

What controls atmospheric particle sizes over Erhardt Tobias the Greenland ice sheet? – Influence of 28 changing deposition regimes

Synoptic variability in the CMIP5 models over Gibson Peter B. Australia: implications for the simulation of 30 extreme heat

Exploring nearly on-in-a-millennium scenarios Gómez-Navarro Juan José of extreme rainfall through dynamically 32 downscaling palaeoclimatic simulations Hydrological climate change impact Hakala Kirsti 34 assessment – addressing the uncertainties

Role of soil moisture vs. recent climate Hauser Mathias 35 change for heat waves in western Russia

Crop failures and extreme climate events in Huhtamaa Heli 36 historical Finland

Predicting the June 2013 European Flooding Ionita Monika based on Precipitation, Soil Moisture and Sea 38 Level Pressure

Response surfaces of Swiss flood events to Keller Louise 39 enable and evaluate robust adaptation

Analysis of extreme precipitation indices in Kis Anna the Carpathian Region using regional climate 41 model simulations

The role of atmospheric blockings in central Lenggenhager Sina 43 European flood events – A casestudy

Interannual variations of NPP in European Lienert Sebastian 45 forests

Projecting high-resolution extreme climate Lo Shih-how 47 indices with observational constrain

The Influence of Climate Variability on Loughran Tammas Australian Heat Wave Frequency, Duration 49 and Intensity Statistical Evidence of the Influence of Solar Activity on Atlantic Multi-decadal Oscillation Malik Abdul (AMO) and All Indian Summer Monsoon 50 Rainfall (AISMR) in Climate Model Simulations

Consideration of risks, connected to extreme Matko Maruša weather events, in spatial planning of energy 52 infrastructure

Nonstationary Precipitation Implication on precipitation maximum propability Curves for Meresa Hadush K. 54 Hydraulic Infrastructure Design in a Changing Climate

Past, present and future impact of Vb- Messmer Martina cyclones on extreme precipitation over 56 Central Europe

Understanding Extremes: A Multi-proxy, High Resolution Record of Wildfire and Miller Daniel 58 Precipitation History from Basin Pond, Maine, USA

Understanding the Development of Deep Mohd Nor Fadzil Convection over the western Malaysian 60 Peninsula during Inter Monsoon

HEPS4Power – Extended-range Hydrometeorological Ensemble Predictions Monhart Samuel 62 for Improved Hydropower Operations and Revenues

Nicolai-Shaw Nadine Drivers of soil moisture at the global scale 64

Uncertainties in measured extreme O Sungmin 66 precipitation events

Assessing hydrological regime sensitivity to climate change in a convective rainfall Peleg Nadav 68 environment: a case study of medium-sized eastern Mediterranean catchments Probabilistic Modeling of the European Pistotnik Georg 70 Severe Thunderstorm Climate

Extreme Weather Events Impact Modelling: a Pregnolato Maria 72 Transport Case Study

A review on regional convection-permitting Prein Andreas climate modeling: Demonstrations, prospects, 74 and challenges

Evaluation of heat-related mortality and Ragettli Martina 76 adaptation measures in Switzerland

Exploring eight millennia of climatic, vegetational and agricultural dynamics on the Rey Fabian 78 Swiss Plateau by using annually layered sedimentary time series

Richardson Doug Drought forecasting using statistical methods 80

A climatology of synoptic-scale Rossby wave Rothlisberger Matthias 82 triggering events

Atmospheric and oceanic warming patterns Rugenstein Maria 84 depend non-linearly on the forcing magnitude

Development of a hybrid finite-element Cloud Savre Julien 85 Resolving Model including grid adaptivity

Added value of very high resolution model simulations for the coasts of Northern Schaaf Benjamin 87 Germany using the example of two case studies of extratropical cyclones Exploring the causes of rare extreme precipitation Schröer Katharina 88 events in the south-eastern Alpine foreland region

A global regionalization of NCEP-Reanalysis Schubert-Frisius Martina using a high resolution general circulation 90 model

Analysis of solar influence on tropospheric Schwander Mikhaël weather using a new time series of weather 91 types

Decadal Climate Predictions Using Strobach Ehud 93 Sequential Learning Algorithms

Hazardous thunderstorms over Lake Victoria: Thiery Wim 95 climate change and early warnings

Radar Characteristics and Patterns Related Trefalt Simona 96 to Convective Wind Gusts in Switzerland

Tuinenburg Obbe A new classification of atmospheric droughts 98

Extreme River Floods in Western Switzerland Tuttenuj Daniel and the Lake of Constance Region in the 99 Period Prior to Instrumental Measurements

Adaptation decisions and damage costs Usui Takafumi under uncertainty in an empirical general 100 equilibrium framework

Volonte Ambrogio Sting Jet analyses in extratropical cyclones 103 The impact of increased Mediterranean sea Volosciuk Claudia surface temperatures on central European 105 extreme precipitation

Remote sensing of past and recent fires: Weber Helga Assessing the accuracy of different satellite 107 products

Was the extreme storm season 2013-14 over Wild Simon the North Atlantic and the UK triggered by 109 changes in the West-Pacific Warm Pool?

Projections of Australian Regional Wilson Louise 110 Temperature Extremes from CMIP5 Models

Searching for synergies in crop rotation Zarrineh Nina management – A simulation-optimization 112 approach

Catastrophic Magdalena or not? The flood Zbinden Eveline 114 events of AD 1342 in Central Europe

Early to Mid-Holocene climate variability from Ziehmer Malin Michelle 116 multi-millennial tree ring isotope records

Swiss Climate Summer School 2015: Extreme Events and Climate

Cloud Radiative Effect depending on Cloud Type and Cloud Fraction

Christine Aebi (1,2), Julian Gröbner (1), Niklaus Kämpfer (2), Laurent Vuilleumier (3)

(1) Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Davos, Switzerland (2) Oeschger Center for Climate Change Research and Institute of Applied Physics, University of Bern, Bern, Switzerland (3) Federal Office of Meteorology and Climatology MeteoSwiss, Payerne, Switzerland

Radiative transfer of energy in the atmosphere and the influence of clouds on the radiation budget remain the greatest sources of uncertainty in the simulation of climate change. Small changes in cloudiness and radiation can have large impacts on the Earth’s climate. Depending on the wavelength range, the effect of clouds on the radiation budget can have an opposing sign. For assessing this effect and the corresponding changes, frequent and more precise radiation and cloud observations are necessary.

The role of clouds on the surface radiation budget is studied in order to quantify the longwave, shortwave and the total cloud radiative effect (CRE) depending on the atmospheric composition and cloud type. The study is performed for three different sites in Switzerland at three different altitude levels: Payerne (490 m asl), Davos (1’560 m asl) and Jungfraujoch (3’580 m asl).

On the basis of data of visible all-sky camera systems at the three aforementioned stations in Switzerland, up to six different cloud types are distinguished (Cirrus-Cirrostratus, Cirrocumulus-Altocumulus, Stratus-Altostratus, Cumulus, Stratocumulus and Cumulonimbus-Nimbostratus). These cloud types are classified with a modified algorithm of Heinle et al. (2010). This cloud type classifying algorithm is based on a set of statistical features describing the color (spectral features) and the texture of an image (textural features) (Wacker et al., 2015). The calculation of the fractional cloud cover information is based on spectral information of the all-sky camera data. The radiation data are taken from measurements with pyranometers and pyrgeometers at the different stations.

First we calculate the longwave and shortwave CRE for cases where only one cloud type is present. This calculation is performed for the two stations Jungfraujoch and Payerne and the six different cloud types separately. On the basis of case studies we get a better understanding about the influencing factors

1 of the CRE. In a second step we want to expand the study in order to calculate a climatology over a whole year of the longwave and shortwave CRE and its sensitivity to integrated water vapor, cloud cover and cloud type for the three above-mentioned stations in Switzerland. For the calculation of the shortwave and longwave CRE the corresponding cloud-free reference models developed at PMOD/WRC are used (Wacker et al., 2013). As the study is restricted to daytime data so far (due to cameras measuring in the visible), we are developing an all- sky thermal infrared cloud cam (IRCCAM), which enables nighttime measurements and analyses as well.

References

Heinle, A., A. Macke and A. Srivastav (2010) Automatic cloud classification of whole sky images, Atmospheric Measurement Techniques.

Wacker, S., J. Gröbner and L. Vuilleumier (2013) A method to calculate cloud- free long-wave irradiance at the surface based on radiative transfer modeling and temperature lapse rate estimates, Theoretical and Applied Climatology.

Wacker, S., J. Gröbner, C. Zysset, L. Diener, P. Tzoumanikis, A. Kazantzidis, L. Vuilleumier, R. Stöckli, S. Nyeki, and N. Kämpfer (2015) Cloud observations in Switzerland using hemispherical sky cameras, Journal of Geophysical Research.

2 Swiss Climate Summer School 2015: Extreme Events and Climate

Exploring the Dynamical Causes of Northeast US Extreme Precipitation

Laurie Agel (1), Mathew Barlow (1)

(1) Department of Environmental, Earth, and Atmospheric Sciences, University of Massachusetts Lowell, Lowell, MA

Extreme precipitation in the Northeast US (NE) can have devastating impacts on health, economies and infrastructure due to flooding and significant snowfall. This research examines the nature of NE extreme precipitation, and identifies the key ingredients and underlying dynamics associated with these events. Daily station precipitation data (1979-2008) from 35 sites of the United States Historical Climatology Network (USHCN; Easterling et al. 1999) are used to identify the dates of the top 1% of precipitation at each station. The extreme precipitation on these dates displays a seasonal cycle that is distinct between inland and coastal regions, and is strongly linked to synoptic storm tracks. Most NE extreme precipitation occurs embedded in precipitation events of 3-5-day duration; however extreme precipitation itself is generally confined to single-day events, suggesting a combination of synoptic and mesoscale mechanisms. A number of methods are used to determine the ingredients and underlying dynamics (synoptic and local circulation, moisture availability and pathways, stability, etc.) associated with these seasonal and regional events including composites, pattern identification, trajectories, and Q-vector analysis. In this poster, we present the results of two types of pattern identification techniques to analyze NE extreme precipitation. The first utilizes the k-means clustering technique, which employs an iterative algorithm to separate events into a set number of groups, or clusters, that minimizes the squared Euclidean point- to-centroid distance within each cluster. Because synoptic storms are strongly linked to the extremes, Modern-Era Retrospective Analysis (MERRA; Reinecker et al. 2011) blended daily tropopause heights over the domain -100°W to -60°W and 30°N-54°N, on extreme dates only, are used as input to the k-means algorithm. Objective techniques identify two preferred partitionings – one with three clusters and one with 7 clusters. The 3-cluster solution (Figure 1a) shows a deep trough with its axis aligned NE-SW from the Great Lakes into the Gulf region, an eastern ridge pattern, and a trough with its axis aligned NW-SE across the Mid-Atlantic states. The 7-cluster solution shows two variations of each of the three previous clusters, with an additional shallow trough across southern Ontario. The second technique utilizes Self-Organizing Maps (SOMs), in which the continuous pattern space occupied by a field is discretized into a two- dimensional array of pattern characteristics. Daily MERRA blended tropopause heights (1979-2008) are input to the SOM routine to create various pattern

3 mappings, including a 5x6 solution (Figure 1b). The percent of extreme days as well as the percent of each k-means cluster that is accounted for by each SOM pattern is calculated. In this manner we are able to identify the key synoptic circulation patterns that are linked to extreme precipitation in finer detail than provided by either pattern technique alone. For patterns that explain the most extreme dates, we then generate composites of other meteorological fields such as moisture convergence, vertical ascent, baroclinicity, and stability, to develop a more complete picture of the key ingredients and dynamics underlying extreme NE precipitation.

References Easterling, D. R., T. R. Karl, J. H. Lawrimore, and S. A. Del Greco, 1999: United States Historical Climatology Network daily temperature, precipitation, and snow data for 1871–1997. ORNL/ CDIAC-118, NDP-070. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN, 84 pp. Kohonen, T., 1995: Self-organizing maps, 2nd edn. Springer, Berlin. Michelangeli, P., R. Vautard, and B. Legras, 1995: Weather Regimes: Recurrence and Quasi Stationarity. J. Atmos. Sci., 52, 1237–1256. Rienecker, M. M., and Coauthors, 2011: MERRA: NASA’s Modern-Era Retrospective Analysis for Research and Applications. J. Climate, 24, 3624– 3648.

Figure 1. MERRA blended tropopause height anomalies for a) k-means clusters of extreme precipitation days only, and b) SOM patterns for all days 1979-2008. The frequency of each pattern and the percent of extreme dates accounted for by pattern are shown above each SOM panel.

4 Swiss Climate Summer School 2015: Extreme Events and Climate

European summer heatwaves and North Atlantic weather regimes in the last Millennium

M.Carmen Alvarez-Castro*, Romain Trasancos, Pascal Yiou

IPSL-LSCE CEA-Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France

*[email protected]

Abstract

The European summer heatwaves have been increasing in frequency and magnitude in the past decades. A higher conﬁdence in future changes in such extremes necessitates to have a better knowledge about extremes behavior in the past climate. The last millennium is well documented in terms of climate forcings. Modelling e↵orts have provided a wealth of climate simulations covering the last millennium. We want to exploit such data in order to assess how models simulate extreme summer heatwaves.

The surface temperature and precipitation are closely related to atmospheric patterns. It has been shown that rainy winter/spring seasons reduce the frequency of hot summer days whereas dry seasons can be followed by summers with high or low frequency of hot days. In this poster, we show the relation between winter/spring precipitation with the frequency of hot days in the 10 hottest summers in Europe and Southern Europe during the Medieval Warm Period (MWP 1150-1250), the Little Ice Age (LIA 1650- 1750), and the historical-present period (1850-2005). We ﬁrst focus on a millennium simulations with the IPSL model (IPSL-CM5). We use daily temperature, precipitation, and SLP data from CMIP5 (Coupled Model Intercomparison Project phase 5) and a couple of IPSL simulations with diferents forcings. Summer weather regimes has been computed as well for NCEP and 20th Century reanalysis data sea level pressure data in order to compare observations with the same period (1948-2005) in CMIP5 and IPSL simulations outputs.

We discuss and present the results comparing the e↵ects of hydrological deﬁcits in the preceding season, and the occurrence of speciﬁc weather regimes, during the hottest summers over Europe and SouthWestern Europe. This analysis compares di↵erents climate forcings simulations.

5 Swiss Climate Summer School 2015: Extreme Events and Climate

Probabilistic Estimates of Marine N2O Emissions

Gianna Battaglia, Fortunat Joos

Climate and Environmental Physics, Physics Institute and Oeschger Centre for Cli- mate Change Research, University of Bern, Bern, Switzerland

Nitrous oxide (N O) is an atmospheric trace gas (pre-industrial level 270 ppb, currently 325 2 ⇠ ⇠ ppb, increasing by 0.25% yr 1) that plays important roles in the stratospheric ozone cycle and as ⇠ a greenhouse trace gas that, molecule by molecule is 200 times more e↵ective than CO2 (Gruber, 2008). N2O is emitted to the atmosphere naturally from poorly constrained microbial processes 1 1 on land ( 6 Tg N yr ) and from the oceans ( 4TgNyr ) and anthropogenically ( 10 Tg 1 ⇠ ⇠ ⇠ Nyr ) as a result of, for instance, agriculture, fossil fuel or biomass and biofuel burning (Ciais et al., 2013). In the atmosphere, N O undergoes photodissociation with a lifetime of 120 yr (Ciais 2 ⇠ et al., 2013). The uncertainties in the natural emissions of N2O to the atmosphere, including their sensitivities to environmental conditions, however, are high: The latest estimates given by the 1 IPCC for marine N2O sources, for instance, range from 1.8-9.4 TgN yr citepCiais2013. It is therefore important, to better understand the processes and sensitivities controlling marine N2O emissions to the atmosphere. In the oceans, chemo-autotrophic nitrification and chemo-heterotrophic denitrification processes impact N2O. Both processes are tightly linked to the cycling of organic matter. Nitrifiers oxidize + NH3 - which is produced by remineralization of organic matter - to NO3 with oxygen as their source of energy where a small fraction of the nitrogen ends up as N2O as a side-product. This N2O yield has been proposed to depend on oxygen concentrations, but is is unclear whether it increases linearly or exponentially (Suntharalingam et al., 2000; Jin and Gruber, 2003; Nevison, 2003; Zamora et al., 2012; Zamora and Oschlies, 2014). In the denitrification pathway - where NO3 is used as terminal electron acceptor for the oxidation of organic matter in the absence of oxygen -N2O represents an intermediary product during the reduction of NO3 to N2. It is unclear, at which oxygen concentrations denitrification sets in and at which rates the individual steps proceed (Zamora et al., 2012; Zamora and Oschlies, 2014; Babbin et al., 2015). As a consequence the relative importance of the two production pathways is still debated. We implemented di↵erent N2O production schemes (Butler et al., 2000; Suntharalingam et al., 2000; Jin and Gruber, 2003; Nevison, 2003; Zamora et al., 2012; Zamora and Oschlies, 2014) accounting for the mentioned uncertainties in our cost-ecient Bern3D Earth-System Model of Intermediate Complexity. The Bern3D model features a 3-D frictional-geostrophic ocean and an OCMIP2-type marine carbon cycle (Ritz et al., 2011). We optimize the proposed parameters governing N2O production within the water column in a probabilistic, Monte-Carlo-type, Bayesian framework (Steinacher et al., 2013) by applying observed dissolved N2O data as a constraint. Dissolved N2O measurements have recently been compiled within the MEMENTO database (Bange et al., 2009). N2O emissions of the observation-constrained model ensemble will then be determined for both future and past (e.g. Younger-Dryas) environmental conditions.

1 6 Bibliography

Babbin, a. R., D. Bianchi, a. Jayakumar, and B. B. Ward (2015), Rapid nitrous oxide cycling in the suboxic ocean, Science, 348 (6239), 1127–1129, doi:10.1126/science.aaa8380.

Bange, H. W., T. G. Bell, M. Cornejo, A. Freing, G. Uher, R. C. Upstill-Goddard, and G. Zhang (2009), MEMENTO: a proposal to develop a database of marine nitrous oxide and methane measurements, Environ. Chem., 6 (3), 195–197, doi:10.1071/EN09033.

Butler, J. H., J. W. Elkins, T. M. Thompson, and K. B. Egan (2000), Tropospheric and Dissolved N2O of the West Paciﬁc and East Indian Oceans During the El Nino Southern Oscillation Event of 1987, Journal of Geophysical Research, 94.

Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, C. A., R. DeFries, G. J., M. Heimann, C. Jones, C. Le Qu´er´e,R. Myneni, P. S., and P. Thornton (2013), Carbon and Other Biogeochemical Cycles, in Climate Change 2013: The Physical Science Basis. Working Group 1 Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

Gruber, N. (2008), The Marine Nitrogen Cycle: Overview and Challenges, 1–50 pp., doi: 10.1016/B978-0-12-372522-6.00001-3.

Jin, X., and N. Gruber (2003), O↵setting the radiative beneﬁt of ocean iron fertilization by en- hancing N2O emissions, Geophysical Research Letters, 30 (24), 2249, doi:10.1029/2003GL018458.

Nevison, C. (2003), Global distribution of N2O and the deltaN2O-AOU yield in the subsurface ocean, Global Biogeochemical Cycles, 17 (4), 1–18, doi:10.1029/2003GB002068.

Ritz, S. P., T. F. Stocker, and F. Joos (2011), A coupled dynamical ocean-energy balance atmosphere model for paleoclimate studies, J. Climate, 24 (2), 349–375, doi:10.1175/2010JCLI3351.1.

Steinacher, M., F. Joos, and T. F. Stocker (2013), Allowable carbon emissions lowered by multiple climate targets., Nature, 499 (7457), 197–201, doi:10.1038/nature12269.

Suntharalingam, P., J. L. Sarmiento, and J. R. Toggweiler (2000), Global signiﬁcance of nitrous- oxide production and transport from oceanic low-oxygen zones: A modeling study, Global Bio- geochem. Cy., 14 (4), 1353–1370, doi:10.1029/1999GB900100.

Zamora, L. M., and A. Oschlies (2014), Surface nitriﬁcation: A major uncertainty in marine N2O emissions, Geophysical Research Letters, 41, 4247–4253, doi:10.1002/2014GL060556.

Zamora, L. M., a. Oschlies, H. W. Bange, K. B. Huebert, J. D. Craig, a. Kock, and C. R. L¨oscher (2012), Nitrous oxide dynamics in low oxygen regions of the Paciﬁc: Insights from the ME- MENTO database, Biogeosciences, 9 (12), 5007–5022, doi:10.5194/bg-9-5007-2012.

2 7 Swiss Climate Summer School 2015: Extreme Events and Climate

Flood damage claims of houseowners promise insights about surface runoff in Switzerland

Bernet D. (1), Prasuhn V. (2), Weingartner R. (1)

(1) Institute of Geography & Oeschger Centre for Climate Change Research & Mobiliar Lab for Natural Risks, University of Bern, Bern, Switzerland (2) Agroscope, Institute for Sustainability Sciences ISS, Zurich, Switzerland

A few case studies exemplify that surface runoff, understood as flash floods explicitly formed and propagating outside of the river network, may be responsible for a large share of flood damages in Switzerland (e.g. Bezzola, Hegg 2008). A couple of practical methodologies exist, with which the hazard of surface runoff can be estimated (Kipfer et al. 2012; Rüttimann, Egli 2010). In general, however, little is known about when, where and why surface runoff occurs.

Flash floods caused by surface runoff have very short response times, occur rather diffusely and are therefore very difficult to observe and measure directly. Furthermore, surface runoff events generally do not leave silent witnesses, which could be used to analyze the process. A promising source that might indicate surface runoff indirectly, are damage claims of houseowners recorded by Public Insurance Companies for Buildings (PICB). In 19 out of the total 26 Cantons of Switzerland, PICB hold a monopoly position and insure (almost) every building within the respective administrative zones. Therefore, each damage to buildings caused by an insured natural hazard, which includes flooding from surface runoff, are generally registered within the respective Canton.

To address the knowledge gap concerning surface runoff, all 19 PICB were inquired to provide damage claim records of houseowners. Overall, 14 approved our inquiry and delivered gapless flood damage records covering the past 9 to 35 years (22 years on average) counting over 80’000 flood related damages. The minimal provided information of each damage claim is the location (address) and the date of the damage.

The delivered data are heterogeneous and, consequently, time-consuming to harmonize. Nevertheless, the large areal and temporal coverage of the provided data records promise that robust, quantitative statements about surface runoff as a natural hazard can be made. Preliminary analysis show that exploiting damage claim records of PICB to learn more about surface runoff is feasible and worthwhile.

8 References Bezzola, G.R.; Hegg, C. (Eds.) (2008): Ereignisanalyse Hochwasser 2005. Teil 2 - Analyse von Prozessen, Massnahmen und Gefahrengrundlagen. Bundesamt für Umwelt BAFU, Eidgenössische Forschungsanstalt WSL. Bern (Umweltwissen, Nr. 0825). Kipfer, A.; Kienholz, C.; Liener, S. (2012): Ein neuer Ansatz zur Modellierung von Oberflächenabfluss. In Gernot Koboltschnig, Johannes Hübl, Julia Braun (Eds.): 12th Congress INTERPRAEVENT 2012. Proceedings : 23-26 April 2012, Grenoble, France. Klagenfurt: International Research Society INTERPRAEVENT, pp. 179–189. Rüttimann, D.; Egli, T. (2010): Wegleitung Punktuelle Gefahrenabklärung Oberflächenwasser: Naturgefahrenkommission Kanton St. Gallen.

9 Swiss Climate Summer School 2015: Extreme Events and Climate Statistical Modelling of Compound Floods

E. Bevacqua (1), D. Maraun (1), M. Widmann (2), M. Vrac (3) (1) Ocean Circulation and Climate Dynamics, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany. (2) School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK. (3) Laboratoire des Sciences du Climat et de l’Environnement, IPSL, CNRS, Centre d’Etude de Saclay, Gif‐sur‐ Yvette, France.

In the recent report of the Intergovernmental Panel on Climate Change on extreme events it has been highlighted that extreme compound events (CEs) has received little attention so far (Seneviratne et al., 2012). CEs are multivariate extreme events in which the individual contributing events might not be extreme themselves, but their joint occurrence causes an extreme impact (Leonard et al., 2013). We develop a multivariate statistical model to analyse the physical mechanisms underlying CEs and to quantify the risk associated with these events, both in present and future climate. Particularly, a function describing the impact of these events is defined to quantify their associated risk. The multivariate model is based on pair-copula constructions (PCCs) and includes meteorological predictors. The key idea of the copula approach is to build the multivariate distributions modeling the marginal distributions separately from the dependence structure among variables. Copula flexibility is however limited to model high- dimensional dependence structures, so here PCCs is used. In PCC the dependence structure is decomposed into two-dimensional copulas, some of which are conditional (Hobæk Haff et al., 2015). Here is presented a first application about compound flood (joint storm surge and high runoff) for Ravenna, Italian Adriatic area. The modeled situation is that showed in the image below. Variables indicates water level of sea or rivers. Hourly data from the last 5 years during the period November-February were selected.

The X variables are used to build the multivariate statistical model using the PCC. The Impact is defined as the river level in the location of the variable

Y River1 , which is dependent on X variables. We compute the return period of the impact to asses the flood risk. The Impact function is defined as a quadratic polynomial combination of X variables such that it fits the Y variable. Bootstrapping X variables from the built model, we computed the return periods of the impact variable obtained like the combination of simulated Xs (black line in the graph below). The red line shows the return period computed directly on the empirical data from Y River1 , only to show that the results are consistent.

10 In the following table are showed the dependencies of the pair copula selected for the fitted model.

Pairs Copulas Kendall's Tau

cSea R3(uSea ,uR3) 0.19

cR3 R2(uR3 ,uR2) 0.45 0.08 cSea R2∣R3(uSea ,uR2)

Although the dependencies of the pair copulas cSea R3 and cSea R2 ∣ R3 are low, we show that they are relevant to asses the risk of the flood. In fact, substituting the cSea R3 and cSea R2 ∣ R3 with independent copulas, there is an important underestimation of the risk, due to a relevant increase of the return period (blue line in the graph). It is planned to transfer the model to validate climate models and assess the future risk of CEs.

References Seneviratne, S., Nicholls, N., Easterling, D., Goodess, C., Kanae, S., Kossin, J., Luo, Y., Marengo, J., McInnes, K., Rahimi, M., Reichstein, M., Sorteberg, A., Vera, C., and Zhang, X. (2012). Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, Cambridge University Press.

Leonard, M., Westra, S., Phatak, A., Lambert, M., van den Hurk, B., McInnes, K., Risbey, J., Schuster, S., Jacob, D., and Stafford-Smith, M. (2013). A compound event framework for understanding extreme impacts. WIREs Clim. Change, doi: 10.1002/wcc.252.

Hobæk Haff, I., A. Frigessi, and D. Maraun (2015), How well do regional climate models simulate the spatial dependence of precipitation? An application of pair-copula constructions. J. Geophys. Res. Atmos., 120, 2624–2646. doi: 10.1002/2014JD022748.

11 Swiss Climate Research Summer School on Extreme Events and Climate

Title: “Extreme Winter Cyclones in the North Atlantic in a CESM1.0.1 Last Millennium Climate Simulation”

Authors: Sandro R. Blumer, Christoph C. Raible, Flavio Lehner, Thomas Stocker

Address: Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, [email protected]

Abstract

Extreme cyclones and their associated impacts are a major threat to mankind, as they often result in heavy precipitation events and severe winds. The last millennium is closest to the Anthropocene and has the best coverage of paleoclimatic information. Therefore, it could serve as a test bed for estimating natural forcing variations beyond the recent observational period and could deliver insights into the frequency and intensity of extreme events, including strong cyclones and their dependency on internal variability and external forcing.

The aim of this study is to investigate how the frequency and intensity of extreme cyclones in the North Atlantic have changed in the last millennium, in particular during prolonged cold and warm periods and which changes might be expected for the 21st century.

We use a comprehensive fully-coupled transient climate simulation of the last millennium (AD 1000-2100) with a relatively high spatial (0.9x1.25 degrees) resolution and define six climatic periods according to prolonged cold or warm phases: Medieval Climate Anomaly (MCA), AD 1150-1200, Little Ice Age (LIA), AD 1450-1500, Maunder Minimum (MMI), AD 1645-1720, Historical (HIS), AD 1850-2005, Modern (MOD), 1960-2010 and Projection (PRO), AD 2006- 2099. Cyclones are then detected and tracked in 12-hourly output using an algorithm that is based on the geopotential height field on 1000 hPa. Additionally, two intensity criteria for extreme cyclones are defined: the 90 percentile of the mean gradient in geopotential and the 90 percentile of the precipitation within a radius of 500 km around the cyclone centre at every time step during the lifetime of a cyclone. These criteria consider two aspects of cyclone's intensity: extremes in wind and precipitation.

The results show that extremes of North Atlantic winter cyclone intensity are significantly stronger with respect to the geopotential height gradient during prolonged cold periods and weaker during prolonged warm periods. Especially, the projection for the 21st century shows a significant weakening as the mean of the 90 percentile of the geopotential height gradient decreases by 4.1 % from MOD to PRO. This intensification of extreme cyclones during relatively cold periods compared to relatively warm periods can be explained by an increased meridional temperature gradient accompanied by an increased baroclinicity. In contrast, the extremes of winter cyclones with respect to precipitation are weaker in the prolonged cold periods and stronger during warm periods, such that an increase of 4.4 % in the mean of the 90 percentile of total precipitation is estimated from MOD to PRO. This intensification is expected on the basis of the Clausius-Clapeyron relationship.!

12 Swiss Climate Summer School 2015: Extreme Events and Climate

Robust changes in extreme events

Aleksandra Borodina(1), Erich M. Fischer(1) and Reto Knutti(1) (1) Institute of Atmosphere and Climate, ETH Zurich, Zurich, Switzerland

Changes in extreme events are of particular relevance due to their potentially severe impacts on the society and ecosystems. Here we analyze how extreme events (TXx, TNn and temperature percentiles of daily averages) relate to a mean state (seasonal and yearly means) in CMIP5 models. Large internal variability obscures this relationship in present day, however for long term projections this relationship becomes clear. As a result we are able to deduce by how much the globe has to warm before we can identify regions over which observational constraint – method that uses present day observations/reanalyses to limit the range of plausible projections – can be applied. Then we use this method to narrow down the spread across models, which directly translates into reduced uncertainties associated with projections.

13 Swiss Climate Summer School 2015: Extreme Events and Climate

FROZENFIRE – a contribution to Paleo Fires from high-alpine ice cores over the last two millennia Sandra O. Brugger (1), Erika Gobet (1), Michael Sigl (2), Dimitri Osmont (2), Daniele Colombaroli (1), Margit Schwikowski (2), Willy Tinner (1)

(1) Institute of Plant Sciences and Oeschger Centre for Climate Research, Altenbergrain 21, 3013 Bern (2) Paul Scherrer Institute, OFLB/109, 5232 Villigen

Wild fires are a main ecological disturbance agent across ecosystems worldwide, driving vegetation dynamics and biomass availability. Fires also regulate the emission of important greenhouse gases in the atmosphere and hence play a key role in the global carbon budget. In recent years, devastating, uncontrolled fires have increasingly occurred on all vegetated continents, resulting in enormous economic costs (Moritz et al. 2014). Air pollution plumes related to extreme fire events are of growing concern due to their effect on human health (Peel et al. 2013). Nevertheless, the drivers for long-term biomass burning trends are still debated. For the period since 1850 a decoupling of fire activity from temperature and population density trends was proposed (e.g. the "broken fire hockey stick"-hypothesis). This may correspond to an increasing landscape fragmentation, but is unsupported by other data, suggesting that the underlying processes are not fully understood. In combination with an increasing fire severity in the recent decades this uncertainty raises major public and scientific concerns about future management strategies under climate change (Kehrwald et al. 2013). Microscopic charcoal (>10µm) as a proxy for fire activity, framboid organic particles (or soots) as a proxy for fossil fuel combustion, and pollen and spores as proxies for vegetation composition and agricultural activity preserve in ice cores over millennia (Eichler et al. 2011).The aim of this project is to reconstruct regional paleo fire and vegetation history trends in the Mediterranean realm and Europe, Western and Central Siberia, tropical Amazonia and the Arctic (see figure 1). The investigated geographical regions either contribute largely to global fire emissions or provide recent high quality data for proxy calibration. We use existing ice cores with an excellent chronological control, particularly over the last 150 years. Yearly resolution allows the linkage of modern ice core data with coinciding satellite images. Further back in time we will compare our data with existing vegetation and fire records from sedimentary sites stored in the ALPADABA and NEOTOMA databases to assess the spatio-temporal relevance of the ice-core inferred data. Climate models will be applied to better understand the proxy sources. In addition to the optical approaches described here, paleoclimatic and paleoenvironmental dynamics will be reconstructed by geochemical means (e.g. oxygen isotopes, black carbon, important ions such as K+ and Ca+ ), as done in the framework of the SNF-Synergia project Paleo Fires of which FROZENFIRE is a part. These concerted interdisciplinary and multiproxy

14 efforts will allow us to assess vegetation and societal responses to climatic change and wildfire disturbance, specifically for the last two millennia the period that experienced important climatic changes and an increasing globalization of economy. Our data will contribute to testing the “broken fire hockey stick”-hypothesis by disentangling the role of climate, vegetation and human impacts on biomass burning to significantly advance the understanding of the role of extreme wildfire events and vegetation responses under future climate change scenarios.

Figure 1 Location of the glacier sites 1 Colle Gnifetti (Switzerland), 2 Belukha (Russia), 3 Tsambagarav (Mongolia), 4 Illimani (Bolivia) and 5 Lomonosovfonna (Svalbard) with schematic indication of main source areas for air mass transport (grey arrows) overlaid on a map of the mean annual area burned (Giglio et al. 2013).

References 1) Moritz M. A., Batllori E., Bradstock R. A., Gill A. M., Handmer J., Hessburg P. F., ... & Syphard A. D. (2014): Learning to coexist with wildfire. Nature, 515(7525), 58-66. 2) Peel J. L., Haeuber R., Garcia V., Russell A. G., & Neas L. (2013): Impact of nitrogen and climate change interactions on ambient air pollution and human health. Biogeochemistry, 114(1-3), 121-134. 3) Kehrwald N. M., Whitlock C., Barbante C., Brovkin V., Daniau A. L., Kaplan J. O., ... & Werf G. R. (2013): Fire Research: Linking Past, Present, and Future Data. Eos, Transactions American Geophysical Union, 94(46), 421-422. 4) Eichler A., Tinner W., Brütsch S., Olivier S., Papina T. & Schwikowski M. (2011): An ice-core based history of Siberian forest fires since AD 1250. Quaternary Science Reviews, 30(9), 1027-1034. 5) Giglio L., Randerson J. T. & Werf G. R. (2013): Analysis of daily, monthly, and annual burned area using the fourthgeneration global fire emissions database (GFED4). Journal of Geophysical Research: Biogeosciences, 118(1), 317-328.

15 Swiss Climate Summer School 2015: Extreme Events and Climate – extended abstract

Blocking detection with observations from radio occultation: A case study

L. Brunner1,2, A. K. Steiner1,2,3, B. Scherllin-Pirscher1,3,M.W.Jury1

1 Wegener Center for Climate and Global Change (WEGC), University of Graz, Graz, Austria 2 FWF-DK Climate Change, University of Graz, Graz, Austria 3 Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics, University of Graz, Graz, Austria

Blocking describes an atmospheric situation where a persistent and stationary high pressure system weakens or reverses the westerly flow at mid latitudes. In the northern hemisphere blocking preferably occurs in the Atlantic/European and the Pacific regions and can trigger heat waves in summer and cold spells in winter. Due to its contribution to these weather extremes blocking has been under close scientific investigation in recent years.

So far most of the research focused on blocking analysis in models and reanalysis data sets. We use for the first time an observational data set based on the Global Positioning System (GPS) Radio Occultation (RO) method. RO is a satellite-based remote sensing technique utilizing GPS signals influenced by the Earth’s atmosphere. The WEGC RO retrieval delivers profiles of atmospheric parameters like pressure and geopotential height with global coverage. To validate our results we also use a reanalysis data set from the European Centre for Medium-Range Weather Forecasts (ERA-Interim).

Here, we investigate the feasibility of blocking detection in RO data for two exemplary blocking events: the blocking over Russia in summer 2010 and the blocking over Greenland in late winter 2013. We implemented an adequate sampling strategy for best data exploitation and applied a commonly used blocking detection method based on meridional geopotential height gradients. Our results show that both exemplary blocking cases are well represented in RO data. Atmo- spheric variability is well resolved and the detected blocking patterns are consistent with those in ERA-Interim. Our ﬁndings hence demonstrate that observations from RO are highly useful for blocking research.

16 The importance of including the globe temperature (radiation) in the Wet Bulb Globe Temperature index

Jonathan R. Buzan (1,2) and Matthew Huber (1,2)

(1) Department of Earth Sciences, University of New Hampshire, Durham, New Hampshire. (2) Institute for the Study of the Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire.

Heat related issues cause reductions in work capacity, and increases in injury and deaths, globally. In the Unites States, heat is the number one cause of death from natural disaster [NOAA, 2014]. Heat stress occurs when the human body is overwhelmed by internal heat production. External heat load prevents dissipation of internal heat, and quantifying external heat loads is difficult. There is a 100+ year long history of various methods to quantify heat loads with diagnostic indices [Epstein and Moran, 2006]. High wet bulb temperatures are recognized as the primary external heat load that causes heat stress [Haldane, 1905]. Short and long wave radiation are non-negligible components of heat load, as well [Brunt, 1943]. The Wet Bulb Globe Temperature (WBGT) combined temperature, humidity, winds, and short and long wave radiation to measure heat load, and was developed to reduce military training casualties [Minard et al., 1957]. WBGT is now an ISO industry standard for diagnosing heat stress in work place environments [Parsons, 2006; 2013]:

(1) (2)

Where Tw is the wet bulb temperature, Tglobe is the globe thermometer (a black copper globe that measures short and long wave radiation and sensible heat fluxes), and T is temperature, all measured in degrees Celsius. WBGTindoor is the standard for diagnosing heat stress in environments with no solar load and includes thermal radiation.

Recent applications using global datasets and Earth system models, the WBGT index is diluted by modifying the standardized equations. These applications omit the radiation term, globe thermometer, and replace the measurement with temperature [e.g. Dunne et al., 2013; Kjellstrom, 2015]. The authors justify their modification with the assumption of working conditions are indoors or in the shade, yet, the standard for indoors/shaded environments calls for measurements of thermal radiation, not temperature.

We aim to improve this situation by implementing the full WBGT into the Community Land Model version 4.5 [Oleson et al., 2013]. We calculate a theoretical globe thermometer [Liljegren et al., 2008] and wet bulb temperature using the latest accurate computational methods [Buzan et al., 2015]. The globe thermometer is calculated above and below the canopy representing all outdoor environments that workers experience. We show that in shaded forested environments, replacing the radiation term with temperature overestimates WBGT. This is significant, because human responses to heat stress is non- linear, and a change in WBGT of 0.5 to 2 increments can be the difference from heavy work restrictions to mild work restrictions. We also show the differences between a shaded environment with the long wave radiation term and a non-shaded environment with short and long wave radiation can result in differences WBGT 1-2 increments regionally, demonstrating the importance of including short and long wave radiation in all work environments.

References NOAA. "Don't Let the Heat Have You Beat!" NOAA, 18 June 2014. Last access. 9 June 2015.http:// www.noaa.gov/features/earthobs_0508/heat.html

Brunt, D. (1943), The reactions of the human body to its physical enviroment, Q.J.R. Meteorol. Soc., 69(300), 77–114, doi:10.1002/qj.49706930002/abstract.

17 Buzan, J. R., K. Oleson, and M. Huber (2015), Implementation and comparison of a suite of heat stress metrics within the Community Land Model version 4.5, Geosci. Model Dev., 8(2), 151–170, doi: 10.5194/gmd-8-151-2015.

Dunne, J. P., R. J. Stouffer, and J. G. John (2013), Reductions in labour capacity from heat stress under climate warming, Nature Climate Change, 3(4), 1–4, doi:10.1038/nclimate1827.

Epstein, Y., and D. S. Moran (2006), Thermal comfort and the heat stress indices, Industrial Health, 44(3), 388–398.

Haldane, J. S. (1905), The Influence of High Air Temperatures No. I, Journal of Hygiene.

Kjellstrom, T. (2015), Impact of Climate Conditions on Occupational Health and Related Economic Losses: A New Feature of Global and Urban Health in the Context of Climate Change, Asia Pac J Public Health, doi:10.1177/1010539514568711.

Liljegren, J. C., R. A. Carhart, P. Lawday, S. Tschopp, and R. Sharp (2008), Modeling the Wet Bulb Globe Temperature Using Standard Meteorological Measurements, Journal of occupational and environmental hygiene, 5(10), 645–655, doi:10.1080/15459620802310770.

Minard, D., H. S. Belding, and J. R. Kingston (1957), Prevention of heat casualties, Journal of the American Medical Association, 165(14), 1813.

Oleson et al. (2013), Technical Description of version 4.5 ofthe Community Land Model (CLM), 1–435, doi:DOI: 10.5065/D6RR1W7M.

Parsons, K. (2006), Heat stress standard ISO 7243 and its global application, Industrial Health, 44(3), 368–379.

Parsons, K. (2013), Occupational health impacts of climate change: current and future ISO standards for the assessment of heat stress, Industrial Health, 51(1), 86–100.

18 Swiss Climate Summer School 2015: Extreme Events and Climate

Evaluation of Mechanisms of Extreme Temperatures over Europe and North America

Ioana Colfescu (1), Simon Tett (1), Gabi Hegerl(1).

(1)School of GeoSciences, University of Edinburgh, Grant Institute, The King's Buildings, James Hutton Road, Edinburgh EH9 3FE Edinburgh

Understanding future changes in the frequency, intensity, and duration of extreme temperatures is important for devising adaptation strategies that minimize damages to humans and not only. We quantify monthly-scale changes in the location and intensity of seasonal temperature extreme events, during the first and latter half of the 20th century in the 20th Century Reanalysis. The regions of study are North America and Europe, along with some preliminary analysis over India. The regional probabilities of change in extreme events occurrence for the two periods are quantified using Probability Density Functions while composite analysis is used for studying the main synoptic weather patterns associated to the events . An assessment of the capability of CMIP5 models to simulate these extreme events and their mechanisms is also performed by comparing the model patterns with those obtained from the 20C reanalysis.

Similarly to previous studies, our results indicate that climate models simulate mechanisms associated with temperature extreme events reasonably well. Quantitative analysis of extreme temperature and circulation show that for the two periods there are changes in circulation patterns associated with extremes.

References Mechanisms of Temperature Extreme Events in Climate Models over Europe Oliver Krueger et al 2015 Environ. Res. Lett. 10 014002 doi:10.1088/1748-9326/10/1/014002

19 Swiss Climate Summer School 2015: Extreme Events and Climate Impact of Arctic Sea Ice on Circulation Patterns, Planetary and Baroclinic Waves

Berit Crasemann (1), Klaus Dethloff (1), Dörthe Handorf (1), Ralf Jaiser(1), Hiroshi Tanaka (2), Tetsu Nakamura (3), Jinro Ukita (4)

(1) Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, Research Unit Potsdam, Germany (2) Center for Computational Sciences, University of Tsukuba, Japan (3) National Institute of Polar Research, Tachikawa, Japan and Hokkaido University, Sapporo, Japan (4) Niigata University, Niigata, Japan

Arctic amplification and recent Arctic sea ice decline affect the meridional temperature gradient between Equator and North Pole and the mid-latitude circulation patterns. Many studies have used re-analysis data such as ERA-Interim and NCEP in order to investigate the influence of decreasing Arctic sea ice on the atmospheric circulation.

In this study, we additionally make use of two AGCM (atmospheric general circulation model) for Earth Simulator (AFES4.1) sensitivity experiments with different sea ice conditions in the Arctic. One sensitivity experiment uses the monthly averaged SST/ICE for a five year period from 1979-1983 (high ice, “CNTL”), the second experiment uses the SST/ICE conditions for 2005-2009 (low ice, “NICE”). The model has a resolution of T79L56 (model top at 60km), uses fixed greenhouse gases, O3, aerosols and solar incident. Each model simulation is a perpetual run over 60 years.

First, we analyse the impact of Arctic sea ice on the instability rates and amplitude of planetary and baroclinic waves using a spectral primitive equation model derived by a orthonormal basis of vertical structure functions and Hough functions. Generally, the most unstable modes in low and high ice periods exist in the synoptic domain at wave numbers 6-10. These modes appear in the middle troposphere with a wave amplitude maximum at 40-50°N and are related to synoptic scale cyclones. Februaries following autumns and winters with low Arctic sea ice lead to a weakened polar vortex and more unstable modes in the synoptic domain.

In order to focus on the synoptic scale processes, we have applied a cluster analysis for the simulated daily sea level pressure fields for low and high ice

20 phases. The cluster analyses have been performed in a reduced state space spanned by the leading EOFs (empirical orthogonal functions). We will present the detected changes in the structure and frequency of occurrence of preferred circulation patterns and subsequent changes of storm tracks.

References

Tanaka, H.L. (1985): Global energetics analysis by expansion into three dimensional normal mode functions during the FGGE winter. Journal of the Meteorological Society of Japan, 63, 180-200

Tanaka, H.L. and E.C. Kung (1989): A study of low-frequency unstable planetary waves in realistic zonal and zonally varing basic states. Tellus, 41A, 179-199

Nakamura, T., K. Yamazaki, K. Iwamoto, M. Honda, Y. Miyoshi, Y. Ogawa, and J. Ukita (2015), A negative phase shift of the winter AO/NAO due to the recent Arctic sea-ice reduction in late autumn, J. Geophys. Res. Atmos., 120, doi:10.1002/2014JD022848.

21 Swiss Climate Summer School 2015: Extreme Events and Climate

Estimation of flood-adaptation indices in varying climatic conditions

Joanna Doroszkiewicz (1), Renata Romanowicz (2)

(1) Institute of Geophysics Polish Academy of Sciences; Księcia Janusza 64, 01-452 Warsaw, Poland Hydrology and Hydrodynamics Department

(2) Institute of Geophysics, Polish Academy of Sciences; Księcia Janusza 64, 01-452 Warsaw, Poland Hydrology and Hydrodynamics Department

Adaptation to future climatic condition requires the formulation of a management strategy based on adaptation indices. Adaptation to floods under changing climate conditions requires adaptation indices specified for future floods which can be used by water management bodies and land use planners to reduce the flood risk in the future. Our work consists of several steps (Fig.1). In the first step regional/local land use (zoning) plans and flood risk plans prepared by the President of National Water Management Board are analysed. In the second step we perform rainfall-runoff modelling using available hydrometeorological observations and future climate GCM/RCM simulation obtained from the ENSEMBLES (Najafi reza M., 2012; Demargne, 2010; Cloke ,2009) and EUROCORDEX projects (Kotlarski et al., 2014; Jacob, D. et al., 2013). Bias correction of climate model projections of temperature and precipitation is performed using Quantile Mapping (Maraun, D ,2010; Boé,2007). Hydrological modelling is performed using grey-box type transfer function and HBV models (Kiczko et al. 2015; Bergström, 1995) using selected Polish catchments as case studies. Only catchments with nearly natural conditions were selected in order to separate climatic and anthropogenic influence. The third and fourth steps consist of flow routing using the SOBEK 3 software (Deltares, 2013) to model flood waves in future and present climate conditions. In this stage of work we use the mountainous Biala Tarnowska river located in Sothern part of Poland as a case study. The last two steps consist of the estimation and evaluation of flood adaptation indices. These are: (i) the length of time water levels exceed a critical value along the river; (ii) probability of inundation of risk- prone areas and (iii) flood recurrence interval. The research had been done within the project Climate Change Impact on Hydrological Extremes (CHIHE).

Fig 1 working scheme References 1. Bergström, S., 1995. The HBV model. In: Singh V.P., ed. Computer models of watershed hydrology. Water Resources Publications, Highlands Ranch, CO,443–476. 2. Boé, J., L. Terray, F. Habets, and E. Martin, 2007, Statistical and dynamical downscaling of the Seine basin climate for hydro-meteorological studies. International Journal of Climatology, 27(12):1643–1655. 3. Cloke, H. and F. Pappenberger, 2009, Ensemble flood forecasting: A review. Journal of Hydrology, 375(3–4):613–626, 2009. 4. Jacob, D. et al., 2013 “EURO-CORDEX: new high-resolution climate change projections for European impact research” ,Springer 2013 5. Demargne, J., J. Brown, Y. Liu, D.-J. Seo, L. Wu, Z. Toth, and Y. Zhu, 2010, Diagnostic verification of hydrometeorological and hydrologic ensembles. Atmospheric Science Letters, 11(2):114–122. 6. Kiczko A., Romanowicz R. J., Osuch M., Pappenberger F., 2015, On-line assimilation of ECMWF forecasts: Biała Tarnowska case study, in: Stochastic Flood Forecasting System, Eds Romanowicz R. and Osuch M., Springer (in print). 7. Kotlarski, S.et.al., 2007,.: Regional climate modeling on European scales: a joint standard evaluation of the EURO-CORDEX RCM ensemble, Geosci. Model Dev., 7, 1297-1333, doi:10.5194/gmd-7-1297-2014, 2014. 8. Maraun, D., Wetterhall, F., Ireson, A. M., Chandler, R. E., Kendon, E. J., Widmann, M., ... and Thiele‐Eich, I.,2010, Precipitation downscaling under climate change: recent developments to bridge the gap between dynamical models and the end user. Rev.ofGeop, 48(3). 9. Najafi reza M., Moradkhami H., Piechota T. C., 2012, Ensemble streamflow prediction: climate signal weighting methods vs. Climate forecast system reanalysis, J. Hydrol., 442-443, 105- 116. 10. Deltares, 2013,SOBEK 3 Hydrodynamics Technical Reference Manual,version:3.0.1.29298

23 Swiss Climate Summer School 2015: Extreme Events and Climate

The role of the ocean on the development of European weather extremes

A. Duchez(1), J. Hirschi(1), A. Forryan(2), P. Courtois(3), A. Blaker(1), B. Sinha(1), A. New(1), A. Scaife(4), T. Graham(4) and M. Andrews(4)

(1) National Oceanography Centre Southampton, UK. (2) University of Southampton (3) University of Alberta, Edmonton, Alberta, Canada (4) Met Office Hadley Centre, Exeter, UK

Globally, current and future climate changes result in increasing frequency and intensity of droughts (AghaKouchak et al., 2014), rainfall and associated flooding (Hirabayashi et al., 2013), and storm/hurricane intensity and associated coastal inundation (Hallegatte et al., 2013). For Europe, the associated economic loss burden was €415 billion and an estimated 140 000 lives lost for 1980-2010. Key questions that arise are: Can an upward trend in natural extreme events be recognised and predicted at the European scale? What are the key drivers within the climate system that are changing and making extreme weather events more frequent, more intense, or both?

The ocean is a key driver for natural and anthropogenic climate variability. The ocean stores 1000 times more heat than the atmosphere and redistributes heat around the planet. In the Atlantic, the heat transported by the Atlantic Meridional Overturning Circulation (AMOC) makes a substantial contribution to the mild maritime climate of North Western Europe and provides a controlling 5-10°C benefit to European climate. Interest in the AMOC has been stimulated by the prospect of its gradual weakening during the 21st century as suggested by the climate model scenarios of the fourth and fifth Intergovernmental Panel on Climate Change (IPCC) assessment reports (Solomon et al., 2007; Stocker et al., 2013) and any slowdown in the AMOC is expected to have profound implications for climate change over Europe. However the role of the ocean in development of regional weather extremes is still unclear. Since 2004, the RAPID array at 26°N has monitored the AMOC (Duchez et al., 2014; McCarthy et al., 2015). Several papers have established a direct link between a substantial reduction in the AMOC (30% decrease, Bryden et al., 2014) during winter 2009-2010 and the extreme winter of 2010 when the UK experienced its coldest December for more than a century (Buchan et al., 2014).

AMOC SST Correlation (lag 5) 1

75 o AMOC anomalies impact the oceanic heat transport and N 0.8 heat content, which can affect SSTs and the atmosphere

0.6 60 o (Sonnewald et al. 2013) and Duchez et al. 2015 show that N

0.4 the AMOC can be used as a precursor for the

45 o development of North Atlantic SST anomalies and leads a N 0.2 SST dipole pattern by 5 months (Fig. 1). In this poster, 0 30 o N particular emphasis is given to the link between the −0.2 AMOC and European extreme events.

15 o N −0.4

−0.6 Fig. 1: Lagged correlations between the SST and the AMOC at 26°N. The AMOC leads the SST by 5 months. 72 o −0.8 W o 0 Black contours indicate 95% significance levels and were o o 54 W W −1 36oW 18 obtained using a composite analysis.

Using state-of-the-art coupled climate simulations from the UK Met Office (historical and future scenario runs) as well as real observations (SST data and RAPID-AMOC observations), we analyze extremes in these

24 datasets and investigate whether they are conducive to the occurrence of extreme precipitation and temperature events over Europe (like in 1969-1970 or 2009-2010).

PRCPTOT (mm) Trend (/year) (tt 0.05) 3 84oN We characterize European precipitation extremes using a subset of the 27 core indices from The Expert Team on 2 Climate Change Detection and Indices (Tank et al., 2009, Fig.

1 2) and relate them to the atmospheric modes of variability over Europe in order to establish the large-scale 72oN 0 atmospheric circulation patterns that are conducive to the Latitude occurrence of extreme precipitation events. o 60 N −1 We also assess the evolution of future frequency and

48oN intensity of extremes under climate change. −2 36oN

24oN Fig. 2: Trend in annual precipitation (1976-2115). −3 80oW 40oW 0o 40oE Longitude

References

• AghaKouchak et al., 2014: Global warming and changes in risk of concurrent climate extremes: insight from the 2014 California drought. GRL. 41(24), 8847-8852. • Bryden et al., 2014: Impact of a 30% reduction in Atlantic meridional overturning during 2009-2010. Ocean Sci. 10, 683-691. • Buchan et al., 2014: North Atlantic SST Anomalies and the Cold North European Weather Events of Winter 2009/10 and December 2010. Mon. Weather Reviews. 142, 922–932. • Duchez et al., 2014: A new index for the Atlantic Meridional Overturning Circulation at 26°N. J. Climate. 27 (17), 6439-6455. • Duchez et al., 2015: Potential for seasonal prediction of Atlantic sea surface temperatures using the RAPID array at 26°N. Submitted to Clim. Dyn. • Hallegatte et al., 2013: Future flood losses in major coastal cities. Nature Climate Change. 3, 802-806. • Hirabayashi et al., 2013: Global flood risk under climate change. Nature Climate Change. 3, 816-821. • Klein et al., 2009: Guidelines on Analysis of extremes in a changing climate in support of informed decisions for adaption. World Meteorological Organization, 56. • McCarthy et al., 2012: Observed Interannual Variability of the Atlantic Meridional Overturning Circulation at 26.5N. GRL. 39, L19609. • McCarthy et al., 2015: Measuring the Atlantic Meridional Overturning Circulation at 26°N. Prog in Oc. 130, 91-111. • Solomon et al., 2007: The Physical Science Basis. Contribution of Working Group I to the 4th Assessment Report of the IPCC. Cambridge University Press, UK and New York, USA. • Sonnewald et al., 2013: Atlantic meridional ocean heat transport at 26°N: impact on subtropical ocean heat content variability. Ocean Sci. 9, 1057-1069. • Stocker et al., 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, UK New York, USA. 1535 pp, doi:10.1017/CBO9781107415324. • Tank et al., 2009: Guidelines on Analysis of Extremes in a Changing Climate in Support of Informed Decisions for Adaptation. WMO-TD No. 1500. Climate Data and Monitoring. World Meteorological Organization, 2009.

25 Swiss Climate Summer School 2015: Extreme Events and Climate Understanding the Characteristics and Predictability of Flood Events at the Global Scale

R.Emerton (1)

(1) Department of Geography and Environmental Science, University of Reading

Flooding is the most frequent of all types of natural disaster, accounting for 40.5% of all natural disasters in 2014 (117 flood events from a total of 289 natural disasters) (Guha-Sapir et al., 2015). Flood events can be caused by a variety of natural processes, and affect millions of people every year through displacement from homes, unsafe drinking water, destruction of infrastructure, and injury and loss of life during a flood event. In 2014 alone, almost 3,000 people were killed by floods, and more than 34 million people were affected worldwide (Guha-Sapir et al., 2015).

With an increasing global population and increasing populations living in flood-prone areas, the anticipation and forecasting of flood events is key to managing, preparing for and protecting against extreme events, from local to national and international scales. Several centres now run operational flood forecasting models, many of which provide forecasts for specific locations, river basins or countries (Alfieri et al., 2012). Forecasting floods on the global scale in addition to the local/catchment scale enables a global overview of forecasted flood events, which is crucial to many areas of the globe where there is limited access to early warnings.

The Global Flood Awareness System (GloFAS) of the JRC and ECMWF provides a global overview of upcoming floods in large world river basins. The system integrates the ECMWF operational 50- member Ensemble Prediction System with the Lisflood hydrological model in order to produce Ensemble Streamflow Predictions (ESPs) on the global scale out to 45 day lead times, daily. The resulting ESP maps are compared with reference threshold maps derived from streamflow climatology, giving 2 year, 5 year and 20 year return periods, which are used as the alert thresholds for early warning. (Alfieri et al., 2013)

The first research aim of this project looks at evaluating the seasonal, annual and geographical patterns of floods in river basins across the globe through analysis of characteristics such as duration, frequency, intensity and recurrence within a season. Through use of GloFAS, the ERA-Interim (~34 years) and ERA-Clim (~110 years) extensive reanalysis datasets have been used to identify past extreme flood events and produce global and regional overviews of flood characteristics under past and present climate conditions. These datasets are currently being used to determine the atmospheric precursors to extreme events, in order to evaluate the changes in flood characteristics due to atmospheric features and teleconnections, presented here for the example of the El Nino Southern Oscillation (ENSO). These results will further lead to analysis of the predictability of flood events in regions across the globe, and any evidence for changes in extreme flood events under changing climate regimes, aiming to answer the questions of:

“Are we able to use large scale atmospheric flow features and teleconnections to understand the predictability of flood events and improve early warnings?”

“What are the potential changes in the characteristics and predictability of extreme flood events in river basins across the globe under climate change?”

26 References

Alfieri, L., P.Burek, E, Dutra, B. Krzeminski, D. Muraro, J. Thielen and F. Pappenberger, 2013: GloFAS - global ensemble streamflow forecasting and flood early warning. Hydrology and Earth System Sciences, 17, 1161-1175

Alfieri, L., P. Salamon, F. Pappenberger, F. Wetterhall, and J. Thielen, 2012: Operational early warning systems for water-related hazards in Europe. Environmental Science and Policy, 21, 35-49

Guha-Sapir, G., R. Below, and P. Hoyois, 2015: The CRED/EM-DAT International Disaster Database. Available online at www.emdat.be - Universite Catholique de Louvain - Brussels - Belgium., Last Accessed 27 January 2015

27 Swiss Climate Summer School 2015: Extreme Events and Climate

What controls atmospheric particle sizes over the Greenland ice sheet? – Influence of changing deposition regimes

T. Erhardt (1); H. Fischer (1); D. Wagenbach† (2)

(1) Institute for Climate and Environmental Physics and Oeschger Center for Climate Change Research, University of Bern, Switzerland (2) Institute for Environmental Physics, Heidelberg University, Germany

Insoluble particle concentrations and their size distributions are routinely measured in polar ice cores to reconstruct past atmospheric dust loads and are often interpreted in terms of changes in atmospheric transport. However the transfer of mineral dust particles from the atmosphere to the ice is not well understood, especially regarding the preserved particle size distributions (PSDs).

Here we present an extension to a conceptual deposition model for aerosols based on precipitation scavenging and gravitational settling including the size distribution of the particles (Davidson et al., 1996; Fischer et al., 1998). The extended model can be used to study the effect of different atmospheric PSDs and changes in accumulation rate on the preserved particle concentration and their size distribution. It can also be applied to reconstruct past atmospheric dust conditions using accumulation rate reconstructions and measured PSDs. We apply the model to previously published size distribution data from North GRIP (Greenland) (Ruth et al., 2003) to investigate the influence of the changing deposition regime during the fast transitions between cold stadial and warm interstadial conditions during the last glacial.

During the last glacial climate archives from Greenland show large oscillations between cold stadial and warmer interstadial conditions. These transitions from cold to warm states occur within decades and are associated with 5 – 16 °C changes in average temperature and increases of the accumulation rate by a factor of two (Kindler et al., 2014). The dust record exhibits coincidental changes in the particle mass concentration of a factor of 5 – 18 with accompanying changes in the PSDs, that occur on time scales faster than 30 – 200 yr, which is the temporal resolution of the PSD record (Ruth et al., 2003).

In general the transfer to the ice shifts the particle size distributions towards larger particles. This effect is more pronounced, the lower the accumulation rate. During the Last Glacial Maximum (LGM), when accumulation at NGRIP is at its lowest, geometric mean particle diameters in the ice are up to 10 % larger in the ice with respect to particle numbers and up to 25 % with respect to particle volume. The contribution of dry deposition to the number (volume) flux peaks at 25 % (50 %) during the LGM with average values around 7% (20 %).

28 Reconstructed atmospheric geometric mean particle diameters show similar but dampened variability compared to the PSDs in the ice.

Overall the model shows that size distribution information for ice core records need to be corrected for depositional effects and that some of the stadial/interstadial variability in PSD parameters can be explained by the accompanying large changes accumulation rate.

References

Davidson, C. I., Bergin, M. H. and Kuhns, H. D.: The Deposition of particles and Gasses to Ice Sheets, in Chemical Exchange Between the Atmosphere and Polar Snow, edited by E. W. Wolff and R. C. Bales, pp. 276–306, Springer, Heidelberg. 1996.

Fischer, H., Wagenbach, D. and Kipfstuhl, J.: Sulfate and nitrate firn concentrations on the Greenland ice sheet: 1. Large‐scale geographical deposition changes, JGR, 103(D17), 21927–21934, doi:10.1029/98JD01885, 1998.

Kindler, P., Guillevic, M., Baumgartner, M., Schwander, J., Landais, A., Leuenberger, M., Spahni, R., Capron, E. and Chappellaz, J.: Temperature reconstruction from 10 to 120 kyr b2k from the NGRIP ice core, CP, 10(2), 887– 902, doi:10.5194/cp-10-887-2014, 2014.

Ruth, U., Wagenbach, D., Steffensen, J. P. and Bigler, M.: Continuous record of microparticle concentration and size distribution in the central Greenland NGRIP ice core during the last glacial period, JGR, 108(D3), 4098–5000, doi:10.1029/2002JD002376, 2003.

29 Swiss Climate Summer School 2015: Extreme Events and Climate

Synoptic variability in the CMIP5 models over Australia: implications for the simulation of extreme heat

Peter B. Gibson (1,2), Petteri Uotila (3), Sarah E. Perkins (1,2), Lisa V. Alexander (1,2) , Andrew J. Pitman (1,2)

(1) Climate Change Research Centre, University of New South Wales, Sydney, New South Wales, Australia

(2) ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, New South Wales, Australia

(3) Finnish Meteorological Institute, Helsinki, Finland

Our confidence in climate model projections depends, in part, on the ability of models to capture present day climate and associated variability over a range of time scales. However, climate models are less commonly assessed at time scales relevant to daily weather systems, despite being particularly important for the realistic simulation of various extreme events. In this study we employ a self- organizing maps procedure (SOMs) to evaluate various aspects of synoptic systems in the Australian region simulated by the CMIP5 climate models.

We find that a small group of models simulate the historical frequency of synoptic systems well. A much larger group of models are well suited to simulating the persistence and transitional phases of synoptic systems. Considering all models and synoptic aspects collectively we find model performance to be related to model horizontal resolution but unrelated to vertical resolution or representation of the stratosphere (Figure 1). These findings have implications for selecting models most useful for future projections over the Australian region, particularly for projections related to climate extremes whereby day-to-day synoptic variability are important drivers of extreme heat. The finding that some models score highly across these synoptic metrics for the region is encouraging.

We further illustrate how key synoptic circulation types, attained through the SOM procedure, are related to measures of extreme heat spatially across the Australian continent. Links between synoptic variability and extreme heat are examined separately for summer and winter seasons to suggest seasonality in the forcing. We demonstrate how the use of circulation types can further aid our understanding of drivers of extreme events, beyond what is possible through simple compositing methods. Under this approach, future work will investigate the combined influence of soil moisture and synoptic variability on the nature of

30 Australian heat extremes. Understanding processes in the land-surface and atmosphere linked to heat extremes may help improve both long-term climate change projections and seasonal forecasts.

Figure 1: scatterplots showing relationship between metrics (correlation coefficients) in the various CMIP5 models and reanalysis (JRA-55), computed against 20CRv2 for the period 1958 – 2005. Models in top (bottom) panel plots are grouped by horizontal (vertical) resolution. ‘Frequency correlation’ is a measure of the model to simulate correctly the node frequencies observed in 20CRv2.

31 Swiss Climate Summer School 2015: Extreme Events and Climate Exploring nearly on-in-a-millennium scenarios of extreme rainfall through dynamically downscaling palaeoclimatic simulations

Juan José Gómez-Navarro (1,2), Christoph Raible (1,2), Sandro Blumer (1,2), Martina Messmer (1,2), Olivia Martius(1,2)

(1) Climate and Environmental Physics, Physics Institute, University of Bern (2) Oeschger Centre for Climate Change Research (3) Geography Department, University of Bern

Extreme precipitation is a natural phenomenon that can lead to severe ooding and are a threat to human activities, especially in areas densely populated such as Switzerland. On the one hand, the climatic characterisation, i.e. severity, frequency and spatial distribution of such events, is necessary to design policies that protect public assets and private property and allow reinsurance companies to accurately estimate risks. On the other hand, the study of such events can lead to process understating, which is eventually needed to develop reliable projections about the behaviour of such situations under ongoing climate change (IPCC-SREX, 2012).

However, the study of extreme situations is hampered the fact that they are, by de.nition, very rare. A proper characterisation of such events, like one-in-a-century storms, is limited by the relatively short instrumental period, which limits the available datasets and forces the extrapolation of data. This study proposes a new approach that allows to investigate storms based on a synthetic, but physically consistent database of weather situations obtained from a very long climate simulation. In particular, an 800-year simulation carried out with a comprehensive Earth System Model (ESM) is used as a surrogate of the real climate.

We use the CESM1 model run with a spatial resolution of 1 degree (Lehner et al. 2015). However this resolution is not .ne enough to reproduce realistically the spatial structure and severity of extreme precipitation events in the Alpine area, so this dataset is dynamically downscaled with the Weather Research and Forecasting model (WRF) to a .nal resolution of 2 km (Gómez-Navarro et al. 2015). However, simulating the 800 years generated by the ESM at such high resolution

32 is infeasible nowadays. Hence, a number of case studies are previously selected. This selection is carried out examining the precipitation averaged in an area encompassing Switzerland in the ESM. Precipitation is accumulated in several temporal windows: 1 day, 2 days, 3 days, 5 days and 10 days. The 4 most extreme events in each category and season are selected. This leads to a total of 336 days to be simulated.

Clearly, this database of extreme precipitation can not be used as is, since the framework of the ESM simulation followed by dynamic downscaling has to be corrected in terms of systematic biases prior applying the results back in the real world. Hence, a 20-year climatic simulation with the same con.guration in both models is carried out. The comparison of the climate reproduced by this simulation and that derived from an independent simulation driven by ERA Interim is used estimate the biases of the model chain. Finally, Quantile Mapping (Maraun, 2013) is applied, which allows to remove systematic biases in the case studies and make the simulated rainfall comparable to reality.

References

Gómez-Navarro, J. J., C. Raible and S. Dierer: Sensitivity of the WRF model to PBL parametrizations and nesting techniques: Evaluation of surface wind over complex terrain. Geoscienti.c Model Development, 2015. Submitted.

IPCC-SREX: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change, edited by: Field, C. B., Barros, V., Stocker, T. F., Qin, D., Dokken, D. J., Ebi, K. L., Mastrandrea, M. D., Mach, K. J., Plattner, G.-K., Allen, S. K., Tignor, M., and Midgley, P. M., Cambridge University Press, Cambridge, UK, and New York, NY, USA, 2012

Lehner, F., K. Keller, C. C. Raible, Juliette Mignot, Andreas Born, F. Joos, and T. F. Stocker: Climate and carbon cycle dynamics in a CESM simulation from 850-2100CE. Earth System Dynamics, 2015. In press.

Maraun, D.: Bias Correction, Quantile Mapping, and Downscaling: Revisiting the In3ation Issue. Journal of Climate, 26, 2137–2143, 2013

33 Kirsti&Hakala& Department&of&Geography& Hydrology&and&Climate& University&of&Zurich& Winterthurerstrasse&190& CHA8057&Zürich& Switzerland& & [email protected]& +41&(0)&79&1705941& http://www.geo.uzh.ch/en/units/h2k/& ! Updated!abstract!for!2015!Swiss!Climate!Summer!School:!! ! ! Hydrological&climate&change&impact&assessment&–&addressing&the& uncertainties& ! ! Abstract& & Society&needs&improved&knowledge®arding&possible&impacts&of&climate&change&on& hydrology.&The&embodiment&of&such&perturbations&includes&floods&and&droughts&of& growing&severity&and&frequency.&Quantification&of&these&threats&is&important&as&a&base& for&sensible&adaptation&measures.&This&research&will&explore&impacts&of&climate&change& on&catchment&discharge&and&will&address&the&challenge&of&better&characterizing&and& communicating&their&uncertainties.&It&will&in&particular&focus&on&the&integrated& evaluation&of&CORDEX®ional&climate&model&simulations,&using&hydrological&modeling& at&the&catchment&scale.&

34 Swiss Climate Summer School 2015: Extreme Events and Climate

Role of soil moisture vs. recent climate change for heat waves in western Russia Mathias Hauser (1), René Orth (1), Sonia Seneviratne (1)

(1) Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland

Using the framework of event attribution, anthropogenic climate change was found to have a discernible influence on the occurrence-probability of heat waves, such as the one in Russia in 2010 (Otto et al., 2012). Soil moisture, on the other hand, is an important physical driver for heat waves as its availability has a large influence on the partitioning of the available surface net radiation into latent and sensible heat flux (Seneviratne et al., 2010, Fischer et al., 2007). The presented study investigates the relative importance of both drivers on heat waves in the region of the 2010 Russian heat wave. This is done with a large number of ensemble members from climate simulations prescribing sea surface temperatures and greenhouse gas concentrations from the 1960s, the 2000s and 2010. The statistics agree well for modeled and observed annual daily maximum temperatures (TXx), and modeled soil moisture and ERA-Interim forced offline simulations. However, the extreme temperature and soil moisture conditions of 2010 were not sampled. Thus, additional climate simulations, prescribing realistic 2010 soil moisture conditions were carried out. Using the second hottest TXx since 1951 as a threshold, it was found that climate change has approximately tripled the risk of exceeding this threshold magnitude. Sea surface temperatures of 2010 led to a 1.7 fold risk, only. Given 2010 soil moisture conditions the risk to exceed the temperature threshold are 13 times higher than in the 1960s, highlighting the importance of soil moisture- temperature feedbacks for this particular heat wave.

References

Fischer, E. M., Seneviratne, S. I., Vidale, P. L., Lüthi, D., & Schär, C. (2007). Soil moisture- atmosphere interactions during the 2003 European summer heat wave. Journal of Cli- mate, 20(20), 5081-5099.

Otto, F. E., Massey, N., Oldenborgh, G. J., Jones, R. G., & Allen, M. R. (2012). Reconciling two approaches to attribution of the 2010 Russian heat wave. Geophysical Research Letters, 39(4).

Seneviratne, S. I., Corti, T., Davin, E. L., Hirschi, M., Jaeger, E. B., Lehner, I., Orlowsky, B. & Teuling, A. J. (2010). Investigating soil moisture–climate interactions in a changing climate: A review. Earth-Science Reviews, 99(3), 125-161.

35 Swiss Climate Summer School 2015: Extreme Events and Climate

Crop failures and extreme climate events in historical Finland

Heli Huhtamaa (1, 2)

(1) University of Bern, Institute of History & Oeschger Centre for Climate Change Research, Switzerland (2) University of Eastern Finland, Department of Geographical and Historical Studies, Finland

Finland is often referred to as the “most northerly agricultural country in the world” (e.g. Mukula and Rantanen 1987; Mela 1996; Hollins et al. 2004), where climatic conditions have largely influenced agricultural practices and crop variations (Holopainen and Helama 2009). Climate and weather extremes have brought crop failure and famine throughout the history. For example, during the climate-triggered famines of the 1690s and 1860s approximately every third and twelfth, respectively, Finn died from malnutrition and related diseases (Myllyntaus 2009).

Current and future impacts of climate change on agricultural production have gained increasing interest over the recent decades. Studies of historical responses to extreme weather and climate events may provide important insight into the vulnerability of agricultural production and its fluctuations over space and time (Pfister 2010).

Therefore, the relationships between crop failures and extreme climate and weather events in Finland AD 1300–1900 are investigated. Evidence of past harvest fluctuations, crop failure history and climate variability is gathered from tree-ring proxies and documentary source materials. First, the events that caused considerable damage to crop production in historical Finland are identified. Second, the possible social responses to these events are investigated. When people succeed or failed to cope with the extreme events? Moreover, were they able to response to the changes in the frequency, intensity and duration of these events?

Past experiences help us to better understand the present and to identify vulnerabilities in a long-term context. As Finland is a marginal area of crop cultivation that is highly sensitive to variations in climate and weather, centennial long perspective may provide us with a wide spectrum of possible socio- environmental responses to climate variability.

36 References

Hollins P.D., Kettlewell P.S. & Peltonen-Sainio P. 2004. Relationships between climate and winter cereal grain quality in Finland and their potential for forecasting. Agricultural Food Science, 13: 295–308.

Holopainen J., Helama S. 2009. Little Ice Age Farming in Finland: Preindustrial Agriculture on the Edge of the Grim Reaper’s Scythe. Human Ecology, 37: 213– 25.

Mela T. 1996. Northern agriculture: constraints and responses to global climate change. Agricultural Food Science, 5: 229–234.

Mukula J. & Rantanen O. 1987. Climatic risks to the yield and quality of field crops in Finland: I. Basic facts about Finnish field crops production. Annales Agriculturae Fenniae, 26: 1–18.

Myllyntaus T. 2009. Summer frost. A natural hazard with fatal consequences in pre-industrial Finland. In: Mauch C. & Pfister C. (eds.), Natural disasters and cultural responses: case studies toward a global environmental history, Lexington Books, Lanham, pp. 77–102.

Pfister C. 2010. The vulnerability of past societies to climatic variation: a new focus for historical climatology in the twenty-first century. Climatic Change, 100: 25–31.

37 Swiss Climate Summer School 2015: Extreme Events and Climate

Predicting the June 2013 European Flooding based on Precipitation, Soil Moisture and Sea Level Pressure

M. Ionita (1,2), M. Dima (1,3), G. Lohmann (1,2), P. Scholz (1), N. Rimbu (1)

(1) Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Bremerhaven, Germany (2) MARUM, Bremen University, Bremen, Germany (3) University of Bucharest, Faculty of Physics, Bucharest, Romania

Over the past decades Europe has experienced heavy floods with major consequences for thousands of people and billions of Euros worth of damage. In particular, the summer 2013 flood in Central Europe showed how vulnerable modern society is to hydrological extremes and emphasizes once more the need for improved forecast methods of such extreme climatic events. Based on a multiple linear regression model, it is shown here that 55% of the June 2013 Elbe River extreme discharge could have been predicted using May precipitation, soil moisture and sea level pressure. Moreover, our model was able to predict more than 75% of the total Elbe River discharge for June 2013 (in terms of magnitude) by incorporating also the amount of precipitation recorded during the days prior the flood, but the predicted discharge for the June 2013 event was still underestimated by 25%. Given that all predictors used in the model are available at the end of each month, the forecast scheme can be used to predict extreme events and to provide early warnings for upcoming floods. The forecast methodology could be efficient for other rivers also, depending on their location and their climatic background.

38 Swiss Climate Summer School 2015: Extreme Events and Climate Response surfaces of Swiss flood events to enable and evaluate robust adaptation L. Keller1,2, O. Rössler1,2, R. Weingartner1,2

(1) Institute of Geography, University of Bern, 3012 Bern, Switzerland (2) Oeschger Centre for Climate Change Research, 3012 Bern, Switzerland

The multidisciplinary SNF Sinergia project “Climate Change Extremes and Adaptation Strategies Considering Uncertainty and Federalism” (CCAdapt) aims at advancing the theory of adaptation to extreme flood events by accounting for (a) uncertainty about future flood occurrence, (b) the characteristics of different adaptation measures as well as (c) the federal setting in Switzerland. As a final result feasible adaptation strategies taking into account these aspects will be evaluated. The presented study will deliver the hydrological basis for the overall project by assessing future flood frequencies in selected Swiss catchments under consideration of uncertainties about projected climate change. Instead of using the classical “top-down” approach by applying climate projections as input for a hydrological model we will make use of the “bottom- up” approach that is based on a sensitivity study of climate impacts on hydrology. This response surface method allows the consideration of a broad range of possible future climate conditions as well as readily evaluation of new climate projections and can be used as a flexible tool in planning of adaptation measures (e.g. Prudhomme et al., 2010). A crucial point in this approach is the generation of meteorological input data. Here, this task will be guided by analysis of past flood events, which will reveal the role of different flood process types and specific hydro-meteorological conditions for flood generation in the selected catchments during the 20th century. Based on this process study meteorological storylines of flood events will be generated, which will allow for an extension of the delta change approach commonly used with the response surface method to more sophisticated modifications of the climate data. Apart from varying the quantities of meteorological input variables we will include variations of their spatial and temporal patterns. Finally, the storylines will be related to specific climate projections in order to evaluate the probabilities of the obtained response surfaces under predicted future climate conditions. Additionally, the hydrological impact of storyline parameters for which there is no projection available, e.g. specific spatial precipitation patterns, will be investigated. This will shed light on uncertainties which are not reflected in climate projections. Hydrological modelling of the flood events will be adapted to the identified process types to improve simulation quality and will possibly result in a multi-parametrization approach. Overall, we expect to develop an extended response surface approach, which allows for more realistic and more comprehensive alterations of the climatic data by considering the hydrometeorological storylines identified to be crucial for flood generation in the catchments. This, in turn may to lead to a more realistic and more intuitively apprehensible climate impact assessment for adaptation planning. The poster that will be presented at the summer school will give an overview of the planned works of the PhD project and will show preliminary results.

39 References

Prudhomme, C., Wilby, R. L., Crooks, S., Kay, A. L., and Reynard, N. S.: Scenario-neutral approach to climate change impact studies: Application to flood risk, Journal of Hydrology, 390, 198–209, doi:10.1016/j.jhydrol.2010.06.043, 2010.

40 Swiss Climate Summer School 2015: Extreme Events and Climate

Analysis of extreme precipitation indices in the Carpathian Region using regional climate model simulations

Anna Kis (1), Rita Pongrácz (2)

(1) PhD student, Dept. of Meteorology, Eötvös Loránd University (2) Assistant professor, Dept. of Meteorology, Eötvös Loránd University

Extreme weather events may result in various environmental damages and economical losses. In order to reduce their potential risks and develop appropriate adaptation strategies, it is essential to make estimations for the future as reliable as possible. Precipitation data of regional climate model (RCM) simulations from the ENSEMBLES project (van der Linden and Mitchell, 2009) were used for this study. A quantile-based bias-correction method (Formayer and Haas, 2010) was applied to the raw data (Pongrácz et al., 2014), for which the CarpatClim database (Szalai et al., 2013) served as a reference. Hence, systematic errors (underestimation in summer precipitation amount and overestimation in the rest of the year) were eliminated. From the bias-corrected daily precipitation outputs of 11 RCM simulations, several precipitation-related indices defined by relative and absolute threshold values were calculated for the entire 1961–2100 period, indicating both dry (e.g., MDS, CDD) and wet conditions (e.g., RR1, RR10, RX5, R99p). Future changes by 2021–2050 and 2071–2100 relative to different reference periods (1961–1990, 1971–2000, 1981– 2010) were determined for the Carpathian Region as well as for five subregions within this domain (containing gridcells from Slovakia, Ukraine, Hungary, Romania and Serbia). The estimated seasonal mean changes of six climate indices are summarised for the late 21st century in Fig.1. According to our results, drier summers are clearly projected for the future in the Carpathian Region. More specifically the maximum number of consecutive dry days (CDD) and the mean dry spell (MDS) are both likely to increase by about 40% on average in summer, while the number of precipitation days (RR1) is projected to decrease (by 20–30% on average) according to all of the 11 simulations. More precipitation days are estimated only for winter, however, the uncertainty is quite high (some RCM simulations projects decrease of RR1). The number of heavy precipitation days (RR10) is likely to increase, except in summer; however, in the solstice seasons the sign of the change is uncertain. All the simulations indicate increasing trend in winter, the average estimated change is 36%. For winter and autumn clearly increasing trends of the highest five-day precipitation total (RX5) and the 99th percentile of daily precipitation (R99p) are projected – therefore more intense precipitation is estimated for the end of the 21st century compared to the reference period –, while in spring and summer the inter-model inconsistency is quite high. The spatial distribution of estimated changes suggests clearly that drying trends are more pronounced in the southern regions, whereas wetter conditions are estimated for the northern parts of the domain.

Fig.1. Projected multi-model mean seasonal changes of precipitation indices in the Carpathian Region for 2071–2100 relative to the reference period 1971–2000. Coloured columns indicate the multi-model mean changes of spatial average indices’ values; grey lines refer to the entire range of RCM estimations (from the minimum at the bottom to the maximum at the top).

References

Formayer, H., Haas, P., 2010: Correction of RegCM3 model output data using a rank matching approach applied on various meteorological parameters. Deliverable D3.2 RCM output localization methods (BOKU-contribution of the FP 6 CECILIA project). http://www.cecilia-eu.org/ van der Linden, P., Mitchell, J.F.B., Eds., 2009: ENSEMBLES: Climate Change and Its Impacts: Summary of research and results from the ENSEMBLES project. UK Met Office Hadley Centre, Exeter, UK, 160p. Pongrácz, R., Bartholy, J., Kis, A., 2014: Estimation of future precipitation conditions for Hungary with special focus on dry periods. – Idıjárás 118. pp. 305– 321. Szalai, S., Auer, I., Hiebl, J., Milkovich, J., Radim, T., Stepanek, P., Zahradnicek, P., Bihari, Z., Lakatos, M., Szentimrey, T., Limanowka, D., Kilar, P., Cheval, S., Deak, Gy., Mihic, D., Antolovic, I., Mihajlovic, V., Nejedlik, P., Stastny, P., Mikulova, K., Nabyvanets, I., Skyryk, O., Krakovskaya, S., Vogt, J., Antofie, T., Spinoni, J., 2013: Climate of the Greater Carpathian Region. Final Technical Report. www.carpatclim- eu.org

42 Swiss Climate Summer School 2015: Extreme Events and Climate

The role of atmospheric blockings in central European flood events – A casestudy

Sina Lenggenhager (1, 2), Olivia Romppainen (1, 2), Stefan Brönnimann (1,2), Mischa Croci-Maspoli (3)

(1) Institute of Geography, University Bern (2) Oeschger Centre for Climate Change Research (3) MeteoSwiss

Flood events are among the most devastating weather-related events in Europe and can lead to large economic losses and even fatalities. A large number of parameters are involved in the triggering of flood events. Essential parameters are the intensity, lifetime and stationarity of the flood triggering weather system and the preconditioning of the catchment basin. These parameters are largely affected by the occurrence of atmospheric blockings. Stucki et al. (2012) have found 10 out of 13 severe flood events in Switzerland to be associated with blockings over Russia. This illustrates the potentially important role of atmospheric blocking for flood events in Europe.

Atmospheric blockings, due to their longevity and stationarity, ensure extended periods of precipitation associated with extratropical cyclones in the geographical area upstream of the blocking area. On the one hand, recurrent precipitation events lead to a strong preconditioning of the catchment basin, on the other hand the progression of the upstream weather systems is slowed and thereby the precipitation period over a catchment is prolonged. Furthermore, cloud diabatic processes might be central to the establishment and maintenance of blocking anticyclones. The precipitation responsible for the flood could hence potentially extend the lifetime and strength of a blocking anticyclone located downstream of the flooded area.

The analysis of the meteorological conditions that lead to the recent flood in Ticino in November 2014 provides a first step towards the understanding of the interactions between atmospheric blockings and flood events. There have been four major precipitation events between October and November 2014. The first one has already taken place in the beginning of October and was possibly associated with an atmospheric blocking over Eastern Europe. It was essential for the preconditioning. The second one took place from November 3 to 5 and is showing a similar pattern. The last to events (November 9-12 and 14-15) were more likely influenced by the upstream flow. They followed very closely and triggered the floods.

References Grams, C. M., Binder, H., Pfahl, S., Piaget, N., & Wernli, H. (2014). Atmospheric processes triggering the central European floods in June 2013. Natural Hazards and Earth System Science, 14(7), 1691–1702. doi:10.5194/nhess-14-1691-2014

Schwierz, C. (2004). Perspicacious indicators of atmospheric blocking. Geophysical Research Letters, 31(6), L06125. doi:10.1029/2003GL019341

Stucki, P., Rickli, R., Brönnimann, S., Martius, O., Wanner, H., Grebner, D., & Luterbacher, J. (2012). Weather patterns and hydro-climatological precursors of extreme floods in Switzerland since 1868. Meteorologische Zeitschrift, 21(6), 531–550. doi:10.1127/0941-2948/2012/368

44 Swiss Climate Summer School 2015: Extreme Events and Climate

Interannual variations of NPP in European forests

Sebastian Lienert(1), Stefan Klesse(2), Renato Spahni(1), David Frank(2), Fortunat Joos(1)

(1) Physics Institute and Oeschger Centre for Climate Change Research, University of Bern (2) Swiss Federal Institute for Forest, Snow and Landscape Research WSL

Introduction We investigate interannual variability in net primary productivity (NPP) of European forests using the dynamic global vegetation model LPX-Bern. The model results are compared to estimates of annual biomass increment from a European-wide tree ring network. Methods The Land surfaces Processes and eXchanges (LPX-Bern [1,2]) model simulates terrestrial biosphere processes, including the water, carbon and nitrogen cycles and competition between different plant functional types. Monthly climate timeseries (CRU TS3.22 ([3]) as well as annual nitrogen deposition [4] and atmospheric CO2 concentrations [5] are used to force the model. The simulations use a spatial resolution of 0.5x0.5 degrees. Figure 1: Coefficient of variation (Ratio between Tree diameter reconstructions, standard deviation and mean of NPP) between 1980 allometric equations, and stand and 2009. The circles represent measurements. density measurements allow for an empiric estimate of the annual biomass increment [6]. These measurements are used to verify the model results. Results We investigated the relationship between interannual variability (i.e. standard deviation) and the mean of NPP. We find a positive correlation between the two variables across Europe meaning that increased growth generally leads to increased variability. Interannual variability is typically around 20% of mean NPP with lower than average variability in northwestern Europe and higher than average values in Southern and parts of Eastern Europe (Figure 1). The high values in certain cells are due to a lack of growth at the beginning of the simulation leading to high variability with respect to the mean. To quantify the coefficient of variation, we plot standard deviation against the

45 mean, for both measurements and simulation (Figure 2). By using linear regression a slope of about 0.23 is obtained (blue), which is in reasonable agreement with the slope from the limited number of measurements of 0.15 (yellow). If we consider grid cells, where measurement are available, the agreement is increased further (red).

Figure 2: Standard deviation of NPP in dependence of mean NPP from 1980 to 2009. The values from the simulation are indicated by blue and red dots, with the red dots designating cells where measurements are available. The yellow dots represent measurements. Also included are linear regressions for all sets of points.

Outlook In addition to the above mentioned simple relationship between interannual variability and mean NPP, we will also investigate the sensitivity of NPP to climate. References [1] Spahni R, Joos F, Stocker BD, Steinacher M, Yu ZC (2013) Transient simulations of the carbon and nitrogen dynamics in northern peatlands: from the Last Glacial Maximum to the 21st century. Climate of the Past, 9, 1287–1308. [2] Stocker BD, Roth R, Joos F et al. (2013) Multiple greenhouse-gas feedbacks from the land biosphere under future climate change scenarios. Nature Climate Change,3 ,666–672. [3] Harris I, Jones PD et al. (2014) Updated high-resolution grids of monthly climatic observations the CRU TS3. 10 dataset. International Journal of Climatology, 34, 623–642. [4]Lamarque et. al.(2013) Multi-model mean nitrogen and sulfur deposition from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP): Evaluation historical and projected changes.Atmos. Chem. Phys., 13, 7997-8018 [5]Dlugokencky E and Tans P, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/) [6]Babst F, Bouriaud O, Alexander R, et al (2014) Towards consistent measurements of carbon accumulation: A multi-site assessment of biomass and basal area increment across Europe. Dendrochronologia, 32,153-161

46 Projecting high-resolution extreme climate indices with observational constrain Shih-how Lo Cheng-Ta Chen National Taiwan Normal University, Department of Earth Sciences, Taiwan

Extreme rainfall index has been an important issue when climate change is discussed. In IPCC AR5 report, there are many researches regarding how “frequency” or “variance” will change, while intensity is barely come up. The reason why we care about the change of the intensity in future is that the government needs the absolute values of extreme rainfall index to make a threshold once a disaster policy is made. Many researches have used IPCC AR5 models to estimate the extreme rainfall index of climate change. However, those models only carry low or mid-resolution. It is difficult to capture the extreme rainfall in low resolution models. The other drawback is it will lose lots of intensity when we use different models form IPCC AR5. This study needs to remap different models at the same resolution, so it can be expected that the process will make high resolution models lose the intensity of rainfall. Figure 1 shows how many the RX5DAY index (top event) will lose in different models at T42 resolution. The intensity of rainfall decreases with the reduction of resolution in a model. In that process, the relationship between intensity and resolution is called “area factor”. In our research, we remap T.R.M.M. data into each IPCC model and compare that with original T.R.M.M. data (at 25km resolution) to obtain area factor (Figure 2). If the bias of models is not taken into account, it can easily downscale model resolution to 25km by using area factor. When the CCSM4 model (high resolution model) is remapped to T42 resolution, the global mean in RX5DAY index will decrease by 10% and 50% for the top event, as shown in Figure 3. Having used the area factor to downscale resolution to 25km, the RX5DAY index’s global mean in NorESM1 model (low resolution model) and CCSM4 model will increase to 106 mm/day and 118.4 mm/day, respectively. Both of their rainfall value get closer to 123.3 mm/day observed by T.R.M.M. after doing downscale. As a result, it is not necessary to remap a model to the lowest resolution in an IPCC AR5 model, which still can keep the characteristics of rainfall in high resolution condition, making the extreme rainfall index under climate change easier to discuss. Key words: Downscale, Extreme rainfall index, Climate change

Figure1. Bar charts of the RX5DAY index (top event) difference between original resolution and T42.

Figure2. (Left) The distribution of TRMM’s RX5DAY index at data grid sizes of (a) 1440X400, (b) 640x320, (c) 320x160, (d)144x90, (e) 128x60 . (Right) The method to create area factor from T.R.M.M. data.

Figure3. Comparison of the RX5DAY index estimated from the TRMM, NorESM1-M and CCSM4.The RX5DAY index estimated from different grids. (a),(e) original resolution, (b),(d),(g) T42 and (c),(e),(h) downscale to 25km.

Reference: Chen, C. T., and T. Knutson, 2008: On the verification and comparison of extreme rainfall indices from climate models. J. Climate, 21, 1605–1621

48 Swiss Climate Summer School 2015: Extreme Events and Climate The Influence of Climate Variability on Australian Heat Wave Frequency, Duration and Intensity

Tammas Loughran, Sarah Perkins, Lisa Alexander, Andy Pitman

Climate Change Research Centre, University of New South Wales, Sydney, NSW, Australia.

For Australia there are a number of modes of variability that influence its climate. Their influence on rainfall and temperature is relatively well established, however this influence is the result of a complex interaction of many dynamic processes and separating them out poses challenges. Furthermore, there has been very little research done on how they relate to the frequency, duration and intensity across Australia.

This study aims to identify the interannual varibility of summer heat wave characteristics using principle component analysis and relate them to three modes of climate variability for Australia: El Nino Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM). We find that the dominant climate mode for Australian summer heat wave frequency and duration is ENSO and affects the Queensland and northwest regions of Australia.

49 Statistical Evidence of the Influence of Solar Activity on Atlantic Multi-decadal Oscillation (AMO) and All Indian Summer Monsoon Rainfall (AISMR) in Climate Model Simulations

Abdul Malik1, Stefan Brönnimann1, Alexander Stickler1

1Oeschger Center for Climate Change Research and Institute of Geography, University of Bern, Switzerland

In this study, Atmosphere Ocean Chemistry Climate Model (AOCCM) simulations with SOCOL-MPIOM accompanied with observational datasets have been used to investigate the influence of solar activity on AISMR and AMO. Four different sets of transient simulations from AD 1600-2000 including all major forcings, carried out in the framework of the SNF project FUPSOL I, have been studied (L1, L2, M1 and M2 simulations of [1]). The simulations vary in solar forcing and ocean initial conditions. In all model simulations, solar irradiance reconstructions by [2] have been used, with strong Shapiro forcing (6 W/m2 mean TSI amplitude) in the L1 and L2 runs, and medium Shapiro forcing (3 W/m2 mean TSI amplitude) in the M1 and M2 runs. Runs with indices 1 and 2 have different initial ocean conditions. Initially, we have validated SOCOL-MPIOM for AISMR with respect to several observational datasets (Twentieth Century Reanalysis, 20CR, AD 1901-2000, [3]; Global Precipitation Climatology Center, GPCC, AD 1901-2000, [4]; Monsoon Asia Drought Atlas, AD 1600-2000, [5]). Figure 1 demonstrates the difference of the FUPSOL ensemble simulations (mean of L1, L2, M1 and M2) compared to GPCC and 20CR. From Figure 1 it is clear that the model simulates the monsoon season climatology of AISMR reasonably well for most parts of the Indian sub-continent, whereas large differences are found over the Western Ghats, the Himalayans, and the coastal ranges in Burma due to low spatial resolution of the model (3.75°×3.75°). Figure 2 shows a comparison of the observed (GPCC) and simulated (FUPSOL) annual cycle of AISMR. The model annual cycle for AISMR shows an RMS error of 0.60 mm/day compared to GPCC. Moreover, we have validated the relationships of AISMR with ENSO and AMO with the HadISST [6] and Kaplan SST [7] datasets. The model shows a correlation coefficient (CC) of -0.51 between AISMR and the Niño3 index which is close to the observed correlation (- 0.42) during the period AD 1901-2000. [8] found a CC of 0.50 between decadal AISMR anomalies and a decadal AMO index for 20th century. Our model is in agreement with a CC of 0.41. Further, in our analysis we have found strong statistical evidence of the influence of solar activity on AMO and AISMR both in observations and climate model simulations. We have found statistical evidence that North Atlantic SSTs are positively correlated with TSI on annual, decadal, and multi-decadal time scales in climate model simulations and NOAA reconstructed SSTs [9]. Also AMO influences the Niño3 and AISMR. We have calculated Spearman’s partial CCs, using multiple liner regression technique, between AMO & TSI, AMO & Niño3, AMO &

50 AISMR, AISMR & TSI, and Niño3 & TSI while controlling or partialling out the the effects of external factors/variables such as CO2, Tropospheric Aerosol Optical Detpth (AOD), Stratospheric AOD etc. We have tried to investigate whether the influence of TSI on Niño3 and AISMR is direct or it comes through AMO modulation by TSI. We plan to do superposed epoch analysis of AISMR anomalies for high and low solar activity during the entire simulated period (AD 1600-2000).

Figure 1. Difference of the FUPSOL ensemble simulations with GPCC (right) and 20CR (left).

Figure 2. Comparison of the observed (GPCC) and simulated (FUPSOL) annual cycle of AISMR. References 1. S. Muthers, J. G. Anet, A. Stenke et al., The coupled atmosphere-chemistry- ocean model SOCOL-MPIOM, Geosci. Dev. Discuss 7, 3014 (2014), 10.5194/gmdd-7-3013 2. A. I. Shapiro, W. Schmutz, E. Rozanov et al., A new approach to the long term reconstruction of the solar irradiance leads to large historical solar forcing, Astron. Astrophys. 529(A67), 3023 (2011), 10.1051/0004-6361/201016173 3. G. P. Compo, J. S. Whitaker, P. D. Sardeshmukh et al., The Twentieth Century Reanalysis Project, Quarterly J. Roy. Meteorol. Soc. 137, 1(2011), 10.1002/qj.776 4. U. Schneider, A. Becker, P. Finger et al., GPCC full data reanalysis version 6.0 at 0.5°: monthly land-surface precipitation from rain-gauges built on GTS- based and historic data, 2011, 10.5676/DWD_GPCC/FD_M_V6_050 5. E. R. Cook, K. J. Anchukaitis, B. M. Buckley et al., Asian monsoon failure and megadrought during the last millenium, Science 328(5977), 486 (2010), 10.1126/science.1185188 6. N. A. Rayner, D. E. Parker, E. B. Horton et al., Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century, J. Geophys. Res. 108(D14), 4407 (2003), 10.1029/2002JD002670 7. A. Kaplan, M. Cane, Y. Kushnir et al., Analyses of global sea surface temperature 1856-1991, Journal of Geophysical Research 103, 18,567(1998) 8. K. J. Manish, A. C. Pandey, Trend and spectral analysis of rainfall over India during 1901-2000, Journal of Geophysical Research 116, 1 (2011), 10.1029/2010JD014966 9. T. M. Smith, R. W. Reynolds, T. C. Peterson, et al., Improvements to NOAA's Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006), Journal of Climate, 21, 10, (2008), http://dx.doi.org/10.1175/2007JCLI2100.1

51 Swiss Climate Summer School 2015: Extreme Events and Climate

Consideration of risks, connected to extreme weather events, in spatial planning of energy infrastructure

Maruöa Matko (1), Branko Kontiæ (1), Mojca Golobiè (2)

(1,) Joûef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia (2) Biotechnical Faculty, Department of Landscape Architecture, Jamnikarjeva 101, 1000 Ljubljana, Slovenia

The research investigates how to include risks to electric infrastructure due to extreme weather events (EWE) into the spatial planning. The ultimate goal is reduction of societal cost associated to damaged infrastructure, while intermediate goal is proper siting of new infrastructure. The work covers both development and testing of a method for integrating risks and spatial planning. The possibilities of application of the method are wide, ranging from different types of extreme weather events, diverse infrastructure, as well as different geographical scales and regions.

The method consists of four steps: 1. Determination of the geographic scope and intensity level of extreme weather event based on data on past occurence 2. Analysis of vulnerability of a system (electric energy infrastructure, location/area where infrastructure is situated) tospecific EWE 3. Determination of probability/frequency of occurrence of an extreme weather eventat a particular site/region where specific energy infrastructure is or is going to be located 4. Integration of the three steps towards determination of physical and other (e.g., economic, health) consequences leading to specification of risk index The steps are schematically presented in Figure 1.

Figure 1: Steps in risk analysis

The method was tested on two case studies: ∑ Siting of new transmission lines in Slovenia considering consequences of heavy sleet in 2014 ∑ Vulnerability of HPPs on the Sava river and NPP Kröko to heavy rain

52 Siting of new transmission lines in Slovenia considering consequences of heavy sleet in 2014 First, risk to electric power lines in Slovenia due to sleet was assessed. Further consideration shows that results of risk assessment can be applied in spatial planning by means of avoiding areas where the infrastructure would be most vulnerable and could be an important component of decision making.

Figure 2: The proposed corridors of planned 400 kV powerline Berièevo - Divaèa overlayed with the map of risks due to sleet - frequency of occurrence of sleet with specific intensity

Vulnerability of hydroelectric power plants to heavy rain The analysis of past interruptions of the hydroelectric power stations on three Slovenian rivers (Sava, Soèa and Drava) was carried out. An important component of the risk assessment method is the evaluation of vulnerability of HPPs associated to the erosion potential in the watersheds, which is then used in comparative evaluation between different river basins for the ultimate purpose of informing siting of future energy infrastructure, HPPs, transmission lines, and others.

Figure 3: Risk indices for the Sava, Drava and Soèa river watersheds combined with erosion model results

References IAEA. (2013).Techno – economic evaluation of options for adapting nuclear and other energy infrastructure to long-term climate change and extreme weather. CRP IAEA, first Research coordination meeting, Wienna, April 2013 Kontiæ, D., & Kontiæ, B. (2008). Introduction of threat analysis into the land-use planning process. Journal of Hazardous Materials, 163(2—3), 683-700. Pütz, M., Kruse, S., Casanova, E., & Butterling, M. (2011). Climate Change Fitness of Spatial Planning. WP5 Synthesis Report. ETC Alpine Space Project CLISP

53 Swiss Climate Summer School 2015: Extreme Events and Climate

Nonstationary Precipitation Implication on precipitation maximum propability Curves for Hydraulic Infrastructure Design in a Changing Climate

Hadush K. Meresa1 , Adane A. Awass2, Marzena Osuch1, Renata J. Romanowicz1

1 Institute of Geophysics Polish Academy of Sciences 2Arbaminch University , water technology institute

Climate change could fundamentally alter the frequency, duration, extent and/or severity of hydrological events. Extreme hydrological events are mainly depends on the extreme climatic events that are growing more severe and frequent in the world, calling into question how those changes are incorporate and formulate in our Hydraulic infrastructure design. Currently our infrastructures are designed on the bases of observed precipitation and probable maximum precipitation(PMP) curves with the assumption of stationary, that is considered the climate extremes will not vary significantly over time. However, climate change alter both the climate and hydrological extremes in time and space, which is called nonstationary. In this paper we addressed nonstationary issue b/c current PMP curves can substantially underestimate Hydrological extremes and thus they may not be suitable for hydraulic infrastructure design in a changing climate. Therefore, it is necessary to confirm considering of nonstationary of extremes climate and hydrological data are more robust and accurate estimation of design streamflow for hydraulic infrastructure projects and flood mitigation works. Generally, we compare the result from assumption of stationary and nonstationary condition in different period of future climate. As per the result, we show that a stationary climate assumption may lead to underestimation of extreme precipitation, which increases the flood risk and failure risk in infrastructure systems. The same result was also observed in the seven and fourteen days sum maximum of precipitation in all catchments. We then present a generalized framework for estimating nonstationary PMP curves and their uncertainties using Bayesian inference. The methodology can potentially be integrated in future design concepts.

Key words: climate change, nonstationary, PMP, uncertainty,

54 A B

C D

Figure. 1 Annual maximum from three days sum of precipitation maxima return level vs return period in Prosna catchment: A) under stationary condition, B) non-stationary during the period of observations 1971–2100, C) non-stationary based on median of sampled parameters, and D) non-stationary based on the 95 percentile of the sampled parameters or Low Risk (LR) non-stationary

References:

Barua, S., Muttil, N., Ng, A. W. M., and Perera, B. J. C. (2013). “Rainfall trend and its implications for water resource management within the Yarra River catchment, Australia.” Hydrol. Processes, 27(12), 1727–1738.

Halwatura D. , A. M. Lechner A.m., and S. Arnold S. (2015) “Drought severity–duration– frequency curves: a foundation for risk assessment and planning tool for ecosystem establishment in post-mining landscapes” Hydrol. Earth Syst. Sci., 19, 1069-1091, doi:10.5194/hess-19-1069- 2015

Rootzén H, Katz RW (2013) “Design life level: quantifying risk in a changing climate”. Water Resour Res 49: 5964–5972

Yilmaz A. G., and Perera B.J. (2014) “Extreme Rainfall Nonstationarity Investigation and Intensity–Frequency–Duration Relationship” J. Hydrol. Eng. 1160-1172.

55 Swiss Climate Summer School 2015: Extreme Events and Climate

Past, present and future impact of Vb-cyclones on extreme precipitation over Central Europe

Martina Messmer (1,2), Juan José Gómez-Navarro (1,2), and Christoph C. Raible (1,2)

(1) Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland (2) Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Cyclones, which develop over the western Mediterranean and move northeastward, are a major source of extreme weather and responsible for heavy precipitation over Central Europe. However, despite their importance, the relevant processes triggering these so-called Vb-events and their impact on extreme precipitation are not yet fully understood. Gaining insight into these processes is crucial to improve the projection of changes in frequency and severity of Vb-driven extreme events under future climate change scenarios. To identify prominent Vb-situations, this study applies a cyclone detection and tracking tool to the ERA-Interim reanalysis (1979-2013). Results indicate that although Vb-cyclones are rare events (2.3/year), they are present in around 15% of all extreme precipitation days (99 percentile) over the Alpine region during the analysed period. Still, only 23% of all Vb-events are associated with extreme precipitation, indicating high variability in precipitation amounts across these events. Thus, we further explore this variability and show that a major parameter in triggering heavy precipitation in such events is the large-scale dynamics, while the thermodynamic state of the atmosphere seems to be of secondary importance. Thus, precipitation amounts are closely linked to the intensity of the Vb-cyclone, although it is important to note that the impact they produce is rather local and strongly dependent on the interaction between the large-scale circulation and the complex orography around the Alps. The impact of climate change on Vb-events is also explored in this contribution. It can affect such events mostly through two mechanisms: changes in the thermodynamic state of the atmosphere through global warming, or shifts in the large-scale circulation that leave a footprint in the trajectory and intensity of Vb-cyclones. To obtain a first glance on the changes associated to modifications in the thermodynamic processes during Vb-events under climate change, we

56 perform a number of sensitivity experiments to assess the role of the Sea Surface Temperature (SST) and its contribution to the moisture content in the atmosphere. For this, we use the regional climate model WRF, which allows simulating a physical consistent response of Vb-cyclones to different SSTs, leaving the dynamical component of the problem fix through experiments. The changes in SST are designed to follow the expected temperature changes in a future climate scenario, also considering the uncertainty in such projections. The regional climate model allows simulating explicitly the diabatic processes and the influence of the Alps, which are of major relevance for the Vb-cyclones. Preliminary results indicate that an increase of up to 3 °C is needed to noticeably influence the precipitation amounts delivered over Central Europe during Vb- events. This indicates a non-linear response to the SST warming, and is in broad agreement with the previous finding indicating that thermodynamic state only plays a secondary role in triggering precipitation during Vb-events. Future studies will address the influence of climate change on the large-scale dynamics, and how this modifies the trajectory and depth of Vb-cyclones. For this, we will compute and analyse a number of transient simulations driven by comprehensive Earth System Models run under climate change scenarios.

57 Swiss Climate Summer School 2015: Extreme Events and Climate

Understanding Extremes: A Multi-proxy, High Resolution Record of Wildfire and Precipitation History from Basin Pond, Maine, USA

Miller, Daniel R. (1), Bradley, Raymond S. (1), Castañeda, Isla S. (1)

(1) Department of Geosciences, University of Massachusetts – Amherst, Amherst, MA, USA, 01003

Future impacts from climate change can be better understood by placing modern climate trends into perspective through extension of the short instrumental records of climate variability. This is especially true for extreme climatic events, as the period of instrumental records provides only a few examples and these have likely have been influenced by anthropogenic warming1. Multi-parameter records showing the past range of climate variability can be obtained from lakes. Lakes are particularly good recorders of climate variability because sediment from the surrounding environment accumulates in lakes, making them sensitive recorders of climate variability and providing high- resolution histories of local environmental conditions in the past. In some cases, such as at Basin Pond, Fayette, Maine, USA, sediment is persevered efficiently enough to produce distinguishable annual laminations (varves) in the sedimentary record. The varved record at Basin Pond was used to construct an accurate, highly-resolved age-to-depth model over the past 300 years. Using a multi-proxy analysis, including organic biomarker analysis of molecular compounds and sedimentological features preserved in the sediment record, a history of environmental change and climatic events at Basin Pond was constructed. These sedimentary analyses were compared with the record of known extreme events (from instrumental measurements and historical documents), including 129 years of high-resolution (daily) precipitation and temperature meteorological data, and two known wildfire events over the past 190 years. Polycyclic Aromatic Hydrocarbons (PAHs), a class of organic compounds that can be used to trace combustion activity2, 3, were found in abundance in the Basin Pond sedimentary record. Peaks in the abundances of two PAHs (retene and chrysene) and the ratio retene/(retene + chrysene) were found to be highly correlated with the known wildfire events occurring in the historical period, giving promise in using these compounds and ratio as a robust proxy for regional wildfire events in northeastern U.S lacustrine sediment records. Current work is underway on extending the record of regional wildfire activity over the past 1,000 years using biogeochemical analysis of sedimentary PAHs.

58 References

1 Bradley, R.S. (Ed.), 2014. Paleoclimatology Reconstructing Climate of the Quaternary, in: Paleoclimatology (Third Edition). Academic Press, San Diego.

2 Denis, E.H., Toney, J.L., Tarozo, R., Scott Anderson, R., Roach, L.D., Huang, Y., 2012. Polycyclic aromatic hydrocarbons (PAHs) in lake sediments record historic fire events: Validation using HPLC-fluorescence detection. Organic Geochemistry 45, 7–17. doi:10.1016/j.orggeochem.2012.01.005.

3 Wilcke, W., 2000. SYNOPSIS Polycyclic Aromatic Hydrocarbons (PAHs) in Soil — a Review. Z. Pflanzenernähr. Bodenk. 163, 229–248. doi:10.1002/1522- 2624(200006)163:3<229::AID-JPLN229>3.0.CO;2-6.

59 Swiss%Climate%Summer%School%2015:%Extreme%Events%and%Climate% ! Understanding%the%Development%of%Deep%Convection%over%the% western%Malaysian%Peninsula%during%Inter%Monsoon.% ! Fadzil%Mohd%Nor1,%Pete%Inness1,%Chris%Holloway1% % (1)%Dept.%of%Meteorology,%University%of%Reading% % Orography! plays! an! important! role! in! the! development! and! spatial! pattern! of! heavy! rainfall!over!the!Maritime!Continent.!This!work!is!looking!to!understand!the!mechanism! involved!in!the!development!of!severe!convection!over!the!western!Malaysia!Peninsular! during! inter! monsoon,! April?May! (AM)! and! September?October! (SO).! This! work! also! looks! at! the! role! of! orography! and! Sumatra! Island! on! the! development! of! the! severe! convection!and!the!rainfall!pattern.!The!number!of!rainy!days!is!generally!higher!over! the!western!Malaysian!Peninsula! during!inter!monsoon!periods! than!during!monsoon! seasons.!Based!on!the!gauge!data,!a!higher!number!of!rainy!days!was!observed!over!the! inland!gauge!stations!than!the!west!coastal!stations.!This!result!agrees!with!the!previous! studies!that!propose!that!the!interaction!between!sea!breezes!and!lee!waves!from!the! mountain!as!well!as!the!mountain?valley!winds!reinforced!convection!activities!over!the! mountainous!area!(Joseph!et.al.!(2008),!Qian!J.!H.!(2008),!Sow!et.!al.!(2011)).!The!same! results!were!shown!in!TRMM!and!APHRODITE!analysis,!where!higher!number!of!rainy! days! was! observed! over! the! inland! regions! rather! than! the! coast.! Diurnal! analyses! showed!most!of!the!rainfall!occurred!in!the!afternoon!until!late!evening!and!mostly!is! not!associated!with!the!active!phase!of!the!Madden?Julian!Oscillation.!For!heavy!rainfall! analysis,! days! with! daily! rainfall! rate! above! the! 90th! percentile! were! determined! and! analyzed.! Although! previous! results! showed! a! higher! number! of! rainy! days! were! observed! during! inter! monsoon,! the! number! of! days! with! the! rainfall! above! the! 90th! percentile!is!not.!More!heavy!rainfall!days!(above!90th!percentile)!were!observed!during! winter!monsoon!over!the!west!coast!and!inland,!and!more!heavy!rainfall!days!during!SO! over! the! northwestern! coast.! The! detailed! analysis! of! convection! activities! will! be! analysed!using!high!resolution!model!by!simulating!two!case!studies,!one!each!from!AM! and! SO.! These! two! events! caused! flash! floods! and! heavy! rainfall! over! the! west! coast! Malaysian!peninsula.!Limited!area!domain!model!with!12!km!outer!domain!and!1.5!km! inner!domain!were!set!up!for!the!model!run.!Sensitivity!experiments!will!also!be!done! by! removing! orography! and! removing! Sumatra! Island.! We! will! use! the! simulations! to! study!the!mechanisms!involved!in!the!development!of!severe!convection!on!these!dates! and!how!orography!and!Sumatra!Island!affects!this!development!and!associated!rainfall! over!the!western!Malaysian!Peninsula.! % % % %

1" " 60 References% Joseph,!B.!et!al.!(2008).!Sea!breeze!simulation!over!the!Malay!Peninsula!in!an!intermonsoon! period.!!Journal(of(Geophysical(Research!113.D20,!p.!D20122.! ! Sow,!Khai!Shen!et!al.!(2011).!Numerical!simulation!of!a!severe!late!afternoon!thunderstorm!over! Peninsular!Malaysia".!Atmospheric(Research,99.2,!pp.!248!! ! Qian!,!J!Hua!(2008)!Why!precipitation!is!mostly!concentrated!over!island!in!the!Maritime! Continent.!Journal(of(Atmospheric(Science,(65,(pp!1428?1441! ! ! ! ! ! ! ! !

2" " 61 Swiss Climate Summer School 2015: Extreme Events and Climate

HEPS4Power – Extended-range Hydrometeorological Ensemble Predictions for Improved Hydropower Operations and Revenues

Samuel Monhart (1,2,3), Konrad Bogner (1), Christoph Spirig (2), Mark Liniger (2), Fred Jordan (4) and Massimiliano Zappa (1)

(1) Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Mountain Hydrology and Mass Movements, Birmensdorf, Switzerland (2) Federal Office of Meteorology and Climatology MeteoSwiss, Climate Prediction, Zurich-Airport, Switzerland (3) Institute for Atmospheric and Climate Sciences (IAC), ETH Zurich, Switzerland (4) e-dric, Lausanne, Switzerland

In recent years large progress has been achieved using operational hydrologic prediction for lead times of up to ten days to manage flood events and droughts. Beside predictions of extreme events many applications in the private and the public sector would profit from hydrological forecasts exceeding the 10 day forecast horizon. In particular the hydropower community would benefit strongly from such extended-range forecasts for planning purposes and operations of multi-reservoir sites. The meteorological extended-range predictions have improved their skill during the last years. However, the operational use of such forecasts for hydrological applications at lead times of 15 to 60 days has not yet been established. The new Swiss Competence Centers for Energy Research (SCCER) are established to develop fundamental research. The subdivision investigating the supply of energy (SCCER- SoE) focuses on innovative solutions in the field of GeoEnergies and HydroPower. Within this framework the aim of the project HEPS4Power is to demonstrate the added value of an operational extended- range hydrometeorological forecasting system for fine-tuning hydropower operations. The value-chain starts with the collection and processing of meteorological data (MeteoSwiss) passed to operational application of state-of- the-art hydrological modelling (WSL) and ends with the optimization of user specific presentation of the data with an experienced partner in energy forecasting (e-dric).

62 We will provide an overview of the planned steps to establish such a hydrometeorological prediction system for alpine catchments. In a first step downscaling techniques need to be evaluated. This evaluation will be done for Europe with a focus on the alpine region with complex topography. The appropriate method will then be used to downscale ECMWF extended-range forecasts which leads to high-resolution meteorological input data tailored for the hydrological model ensemble. In the second step we will use a multi-model approach for ensemble discharge prediction. Similar to the meteorological model output, post-processing techniques will be applied to improve the quality of the forecast against observed discharge. The final step in the project then combines the hydrological predictions with energy market prices in an optimization model to increase the revenues of multi-reservoir sites and to provide management guidelines for the hydropower system operators.

63 64 65 Swiss Climate Summer School 2015: Extreme Events and Climate

Uncertainties in measured extreme precipitation events

Sungmin O (1, 2) and Ulrich Foelsche (1, 2, 3)

(1) Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics (IGMA/IP), NAWI Graz, University of Graz, Austria (2) FWF-DK Climate Change, University of Graz, Austria (3) Wegener Center for Climate and Global Change (WEGC), University of Graz, Austria

Introduction

Ground-level rain gauges provide the most direct measurements of precipitation, and therefore, despite recent advances in remote sensing observations, such rain gauge data are still utilized for calibration of radar/satellite precipitation estimates. Regional climate and hydrological models also require rain gauge data for their validation purposes. For these reasons, it is an important elementary process to understand rain gauge data and to evaluate their associated uncertainties and errors for obtaining accurate data.

My PhD research aims to assess the uncertainties in measured precipitation by a high-resolution ground-based weather network, WegenerNet (hereafter, WegNet, see ‘Materials and Planned approaches’). The research mainly addresses extreme events since these are connected with high uncertainties in the measurements and they can impact directly our societies and economies.

Research Questions

The main question of the research is ‘by how much has extreme precipitation been underestimated?’, and in detail:

What/how much uncertainty is inherent in the WegNet data? How much do national weather stations underestimate precipitation during intense convective events due to under-sampling? How can the WegNet data be utilized for calibration of remote sensing?

66 Materials and Planned Approaches

The WegNet is a dense network of 151 meteorological stations within an area of about 20 km × 15 km centered near the city of Feldbach in the southeast of Austria. The WegNet has a horizontal resolution of ≈ 1.4 km and employs ‘tipping bucket’ gauges for precipitation measurements. Regular measurements started in January, 2007, precipitation data are sampled every 5 minutes.

At first, a quantitative assessment of uncertainties in the WegNet is required to use it as a ground reference. The uncertainties can be investigated at a point but also in the whole domain. For one point study, for example, I am working on systematic differences between measurements from different gauge sensors since the WegNet data contain inherent bias due to its employment of three different sensors. It will also be necessary to study the whole spatial data of the WegNet to characterize the accuracy of grid-average precipitation.

The second part of study is planned to compare WegNet data with those derived from other observation sources. The comparison can be conducted based on scatter plots, statistical values such as bias, root mean squared error, mean absolute error and so on. There are only two Austrian national weather stations in the WegNet domain, so I could figure out how much we have been restricted to data from those only two stations especially in extreme precipitation events. The WegNet data also can be regarded as ‘true’ values for satellite estimates, for example data from NASA’s Global Precipitation Missions which have only 1 by 1 degree resolution, in other word the high-resolution WegNet data will be a good reference to evaluate error associated with the satellite estimates.

Conclusions

The results from this research will show the limitation of the current standard weather stations to catch extreme precipitation amounts which are expected to increase due to climate change. Also the feasibility of the WegNet data as a ground reference will be secured so the data can be utilized beyond my PhD research scopes.

References

Kirchengast, G., Kabas, T., Leuprecht, A., Bichler, C., and Truhetz, H.: WegenerNet: A pioneering high-resolution network for monitoring weather and climate, B. Am. Meteorol. Soc., 95, 227–242, 2014. Villarini, G., W.F. Krajewski: Evaluation of the Research-Version TMPA Three-Hourly 0.25°x0.25° Rainfall Estimates over Oklahoma. Geopys. Res. Lett., 34, doi:10.1029/2006GL029147, 2007. Villarini, G., Mandapaka, P. V., Krajewski, W. F., and Moore, R. J.: Rainfall and sampling uncertainties: A rain gauge perspective, J. Geophys. Res., 113, D11102, doi:10.1029/2007JD009214, 2008.

67 Swiss Climate Summer School 2015: Extreme Events and Climate

Assessing hydrological regime sensitivity to climate change in a convective rainfall environment: a case study of medium-sized eastern Mediterranean catchments

Nadav Peleg (1), Eylon Shamir (2), Konstantine Georgakakos (2,3), and Efrat Morin (4)

(1) Hydrology and Water Resources Program, Hebrew University, Jerusalem, Israel ([email protected]), (2) Hydrologic Research Center, San Diego, California, USA, (3) Scripps Institution of Oceanography, University of California San Diego, La Jolla California, USA, (4) Department of Geography, Hebrew University, Jerusalem, Israel

A modeling framework is formulated and applied to assess the sensitivity of the hydrological regime of catchments with respect to projected climate change. The study uses likely rainfall scenarios with high spatiotemporal resolution that are dependent on projected changes in the driving regional meteorological synoptic systems. The framework was applied to a case study in two medium-sized Mediterranean catchments in Israel, affected by convective rainfall, by combining the HiReS-WG rainfall generator and the SACSMA hydrological model. The projected climate change impact on the hydrological regime was examined for the RCP4.5 and RCP8.5 emission scenarios, comparing the beginning of the 21st century and the mid-21st-century periods from General Circulation Models simulations available from CMIP5. Focusing on changes in the occurrence frequency of regional synoptic systems and their impact on rainfall and streamflow patterns, we find that the mean annual rainfall over the catchments is projected to be reduced by 15% (outer range 2–23%) and 18% (7–25%) for the RCP4.5 sand RCP8.5 emission scenarios, respectively. The mean annual streamflow volumes are projected to be reduced by 45% (10–60%) and 47% (16–66%). Moreover, the streamflow season in these ephemeral streams is projected to be shorter by 22% and 26–28% for the RCP4.5 and RCP8.5, respectively. The amplification in reduction of streamflow volumes relative to rainfall amounts is related to the projected reduction in soil moisture, as a result of fewer rainfall events and longer dry spells between rainfall events during the wet season. The dominant factors for the projected reduction in rainfall amount were the reduction in occurrence of wet synoptic systems and the shortening of the wet synoptic systems durations. Changes in the occurrence frequency of the two dominant types of the regional wet synoptic systems (Active Red Sea Trough and Mediterranean low) were found to have a minor impact on the total rainfall.

68 References Peleg, N., Shamir, E., Georgakakos, KP., Morin, E., (2015), A framework for assessing hydrological regime sensitivity to climate change in a convective rainfall environment: A case study of two medium-sized eastern Mediterranean catchments, Israel. Hydrology and Earth System Sciences, 19, p. 567–581. Peleg, N., Bartov, M., Morin, E., (2014), CMIP5-predicted climate shifts over the East Mediterranean: implications for the transition region between Mediterranean and semi-arid climates. International Journal of Climatology, DOI: 10.1002/joc.4114.

69 Swiss Climate Summer School 2015: Extreme Events and Climate

Probabilistic Modeling of the European Severe Thunderstorm Climate

Georg Pistotnik (1), Henning W. Rust (2), Pieter Groenemeijer (3), Robert Sausen (4)

(1) Ludwig Maximilian University (LMU), Munich, Germany (2) Free University of Berlin, Berlin, Germany (3) European Severe Storms Laboratory (ESSL), Wessling, Germany (4) German Aerospace Center (DLR), Oberpfaffenhofen, Germany

Thunderstorms with phenomena like large hail, severe wind gusts, tornadoes and flash floods are among the most important weather-related hazards in Europe. Their small extent in space and time makes it difficult to collect large enough pairwise samples of known events and underlying meteorological conditions to examine their behavior. As a remedy, objective reanalyses provide “artificial” gridded soundings which allow the computation of covariates, or “proxies” for the probability of severe storm occurrence, consistently across space and time (Brooks et al., 2003). We computed such covariates from ERA-Interim (Dee et al., 2011) and matched them with severe storm observations from the European Severe Weather Database (ESWD; Dotzek et al., 2009) for the period 2006-2013 across central Europe, where the reporting efficiency of such events was reliably high. Logistic regressions were applied to smooth the probabilities and to extrapolate them into unprecedented combinations of given predictors. The probability of severe weather rises with increasing Convective Available Potential Energy (CAPE) and with increasing 0-6 km vertical wind shear (deep- layer shear; DLS) for each investigated type – large hail (Fig. 1), damaging winds, tornadoes and, surprisingly, also for flash floods. Applying these probabilities to the entire ERA-Interim data set 1979-2013 allows computing a synthetic European severe thunderstorm climate. Fig. 2 shows the expected annual number of large hail events per 10.000 km2. Most prominently, it rises from north to south, and it is also enhanced in the surroundings of large mountains like the Alps and the Pyrenees. The other severe weather types feature qualitatively similar patterns. Tornadoes, albeit generally less frequent, are slightly favored over coastal compared to inland areas. Among our most important results are the following: (1) CAPE and DLS are the best two predictors for large hail, while CAPE and 0-1 km vertical wind shear (low-level shear; LLS) are the best for severe wind gusts, tornadoes, and flash floods; (2) adding a third predictor by introducing the 6-hourly convective precipitation in ERA-Interim as a measure for the likelihood of convective initiation, and a fourth one by splitting CAPE into its two individual components, namely the vertical temperature gradient and low-level moisture, further improves

70 the results; and (3) linear logistic regressions are not a good enough fit and need to be generalized to additive logistic regressions. These findings are significant on a 95% level according to Chi Square and Likelihood Ratio Tests, respectively. Finally, applying these proxies to MPI-ESM decadal climate predictions allows an estimate of future trends of severe storm frequency in Europe. A weak and non- significant rising trend of severe thunderstorms from 1979 to 2013 is predicted to continue in the upcoming decade, mainly resulting from an increase of CAPE which overcompensates a decrease of vertical wind shear.

References • Brooks, H.E., J.W. Lee, and J.P. Craven, 2003: The spatial distribution of severe thunderstorm and tornado environments from global reanalysis data. – Atmos. Res., 67-68, 73-94. • Dee, D.P., and Co-Authors, 2011: The ERA-Interim reanalysis: Configuration and performance of the data assimilation system. – Q. J. R. Meteorol. Soc., 137:656, 553-597. • Dotzek, N., P. Groenemeijer, B. Feuerstein, and A.M. Holzer, 2009: Overview of ESSL's severe convective storms research using the European Severe Weather Database ESWD. – Atmos. Res., 93, 575-586.

Fig.1: Probability of >2 cm sized hail events [%] per 10.000 km2 and per six hours as a function of sqrt(CAPE) and DLS. Left: observations. Right: additive logistic regression. Black contours outline 1, 10, 100 and 1000 occurrences in the training data set (the predictors are discretized to steps of one unit each).

Fig. 2: Expected annual number of >2 cm sized hail events 1979-2013 per 10.000 km2, modeled with an additive logistic regression based on the optimum four predictors (vertical temperature gradient, low-level moisture, DLS, and likelihood of convective initiation).

71 Swiss Climate Summer School 2015: Extreme Events and Climate

Extreme Weather Events Impact Modelling: a Transport Case Study

Maria Pregnolato (1), Richard Dawson (1), Alistair Ford (1), Sean Wilkinson (1), Carmine Galasso (2)

(1) School of Civil Engineering and Geoscience, Newcastle University, Newcastle (UK) (2) Department of Civil, Environmental and Geomatic Engineering and Institute for Disaster and Risk Reduction, University College London, London (UK)

Critical infrastructures, such as transportation systems, are at risk of natural hazards worldwide, in particular in urban areas. A changing climate and a strong urbanization is posing under pressure communities, assets, and built environment. As infrastructures can be considered the backbone of cities, network resilience has become a necessary component of any structured development. A key to effective acts on road transport network is an in-depth knowledge of their exposure and vulnerability to geologic hazards, as floods, and the damage due to their impact experienced across the network. In recent years, since uncertainty trends dominate the scenario, flood management has seen a transition from scenario-based approach to risk-based approach. Therefore, risk modelling has assumed a key role in flood risk assessment (De Moel and Aerts 2011). This research addresses the challenges by focusing on the development of probabilistic methodology for managing risk by modelling urban transport networks within the context of flooding events, through a combination of climate simulations and spatial representations. By overlaying spatial data on hazard thresholds from a flood model and a flood safety function, different levels of disruption to commuting journeys on road networks are evaluated as indirect tangible damage (Jenkins et al. 2012). To calculate the disruptive effect of flooding on transport networks, a function relating water depth to safe driving car speed has been developed by combining data from experimental reports, safety literature, analysis of videos of cars driving through floodwater, and expert judgement (Figure 1).

Figure 1. Representation of the safety driving speed as a function of the flooding water depth.

A preliminary analysis has been run in the Tyne & Wear (in North-East England) region to demonstrate how the analysis can assessed the disruptions for commuter journeys due to flooding. Nevertheless, it can be applied to present conditions as well as future uncertain scenarios, allowing the examination of the impacts alongside socio-economic and climate changes As model validation is rarely performed in damage modelling and it is often evaluated as a gap in the research, an urban flood validation on real data from traffic flows is an on-going effort to assure the reliability of the method. Future research directions are likely to undertake cost-benefit analysis of adaptation measures, for an optimal employment of resources and a cost-effective risk management. This new step will involve i) flood risk estimation of events with different severity and frequency ii) a portfolio of potential risk reduction options iii) quantification and comparison of benefits and cost of the different options selected.

References De Moel, H., and Aerts, J. (2011). "Effect of uncertainty in land use, damage models and inundation depth on flood damage estimates." Natural Hazards, 57, 407-425. Jenkins, K., Glenis, V., Ford, A., and Hall, J. (2012). "A Probabilistic Risk-Based Approach to Addressing Impacts of Climate Change on Cities: The Tyndall Centre’s Urban Integrated Assessment Framework." UGEC Viewpoints, Connecting Past and Present Lessons in Urbanization and the Environment (8).

73 Swiss Climate Summer School 2015: Extreme Events and Climate

A review on regional convection-permitting climate modeling: Demonstrations, prospects, and challenges

Andreas F. Prein (1,2),Wolfgang Langhans (3), Giorgia Fosser (4), Andrew Ferrone (5), Nikolina Ban (6), Klaus Goergen (7,8,9),Michael Keller (6,10), Merja Toelle (11), Oliver Gutjahr (12), Frauke Feser (13), Erwan Brisson (14), Stefan Kollet (9,15), Juerg Schmidli (6,10), Nicole P. M. van Lipzig (16), and Ruby Leung (17)

(1) National Center for Atmospheric Research, Boulder, Colorado, USA (2) Wegener Center for Global and Climate Change (WEGC), University of Graz, Graz, Austria (3) Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA (4) Meteo-France/CNRS, CNRM-GAME, Toulouse, France (5) Luxembourg Institute of Science and Technology, Environmental Research and Innovation Department, Environmental Resource Center, Belvaux, Luxembourg (6)Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland (7) Meteorological Institute, University of Bonn, Bonn, Germany (8) Juelich Supercomputing Centre, Research Centre Juelich, Juelich, Germany (9) Centre for High-Performance Scientific Computing in Terrestrial Systems, ABC/J Geoverbund, Juelich, Germany (10) Center for Climate Systems Modeling, ETH Zurich, Zurich, Switzerland (11) Institute of Geography, Justus-Liebig Universitaet Giessen, Giessen, Germany (12) Regional and Environmental Sciences, Department of Environmental Meteorology, University of Trier, Trier, Germany (13) Institute for Coastal Research, Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research, Geesthacht, Germany (14) Institut fuer Atmosphaere und Umwelt, Goethe-Universitt Frankfurt am Main, Frankfurt, Germany (15) Agrosphere (IBG-3), Research Centre Juelich, Juelich, Germany, 16Department of Earth and Environmental Sciences, KU Leuven Leuven, Belgium, (17) Pacific Northwest National Laboratory, Richland, Washington, USA

Regional climate modeling using convection-permitting models (CPMs; horizontal grid spacing <4 km) emerges as a promising framework to provide more reliable climate information on regional to local scales compared to traditionally used large-scale models (LSMs; horizontal grid spacing >10 km). CPMs no longer rely on convection parameterization schemes, which had been identified as a major source of errors and uncertainties in LSMs. Moreover, CPMs allow for a more accurate representation of surface and orography fields. The drawback of CPMs is the high demand on computational resources. For this reason, first CPM climate simulations only appeared a decade ago. In this study, we aim to provide a common basis for CPM climate simulations by giving a holistic review of the topic. The most important components in CPMs such as physical parameterizations and dynamical formulations are discussed critically. An overview of weaknesses and an outlook on required future developments is provided. Most importantly, this review presents the consolidated outcome of studies that addressed the added value of CPM climate simulations compared to LSMs. Improvements are evident mostly for climate statistics related to deep convection (such as the summertime diurnal circle of precipitation; Figure 1), mountainous regions, or extreme events. The climate change signals of CPM

74 simulations suggest an increase in flash floods, changes in hail storm characteristics, and reductions in the snowpack over mountains. In conclusion, CPMs are a very promising tool for future climate research. However, coordinated modeling programs are crucially needed to advance parameterizations of unresolved physics and to assess the full potential of CPMs.

Figure 1. Mean diurnal cycle of (a) precipitation averaged across June, July, and August (JJA) in Switzerland; (b) July 2006 in Switzerland; (c) June, July, and August in the eastern part of the Alps; (d) annually in Southern UK; and (e) June, July, and August in Baden-Wuerttemberg, Germany. All CPM climate simulations show improvements in the shape (onset and peak) of the precipitation diurnal cycle compared to their corresponding LSM simulations. The approximate location of the model domains is shown in (f).

References

Prein, Andreas F., et al. "A review on regional convection‐ permitting climate modeling: demonstrations, prospects, and challenges." Reviews of Geophysics (2015).

75 Swiss Climate Summer School 2015: Extreme Events and Climate

Evaluation of heat-related mortality and adaptation measures in Switzerland

Ragettli Martina S. (1,2), Urbinello Damiano (1,2), Schindler Christian (1,2), Röösli Martin (1,2)

(1) Swiss Tropical and Public Health Institute, Basel, Switzerland (2) University of Basel, Basel, Switzerland

Amplified by global warming, there is a need to reduce the public health impacts of exposure to hot weather. The health risks of heat waves may vary across the globe depending on climatic, demographic and socioeconomic profiles. In Switzerland, a heat wave occurring during summer 2003 caused an estimated 7% increase in all-cause mortality (Grize et al., 2005). As a consequence, the Swiss Federal Office of Public Health provided recommendations on how to behave during hot weather periods. Our project aims to (1) evaluate implemented preventive measures to reduce heat-related mortality, (2) to assess the effect of heat waves on mortality in Switzerland, and (3) to identify meteorological parameters best describing the heat effect on mortality. First, adopted and recommended measures aiming to reduce heat-related mortality in different counties in Switzerland will be collected and evaluated. Second, Swiss mortality data (1995-2012) and meteorological data from MeteoSwiss will be used to investigate heat-related excess mortality. The hypothesis will be tested whether the effect of heat episodes on mortality has been reduced since 2003. Finally, both the results of our project and of other identified relevant epidemiological studies on the topic will be made available to agencies and stakeholders in Switzerland by means of workshops and newsletters. The project will generate evidence on the meteorological parameters of heat waves most strongly related to increased mortality. It will indicate whether an increased sensitivity to health risks of heat waves and adopted policies have reduced the extent of heat-related mortality in Switzerland. This information may contribute to limiting the public health impacts of heat waves and climate change worldwide, and will generate evidence for new potential adaptation measures within health policy programs.

76 References Grize, L.; Huss, A.; Thommen, O.; Schindler, C.; Braun-Fahrländer, C. Heat wave 2003 and mortality in Switzerland. Swiss Med. Wkly. 2005, 135, 200-205.

77 Swiss Climate Summer School 2015: Extreme Events and Climate

Exploring eight millennia of climatic, vegetational and agricultural dynamics on the Swiss Plateau by using annually layered sedimentary time series

Fabian Rey (1), Erika Gobet (1), Adrian Gilli (2), Albert Hafner (3), Willy Tinner (1)

(1) Institute of Plant Sciences and Oeschger Centre for Climate Change Research, University of Bern, Switzerland (2) Geological Institute, Swiss Federal Institute of Technology Zurich, Switzerland (3) Institute of Archaeological Science and Oeschger Centre for Climate Change Research, University of Bern, Switzerland

Annually layered lake sediment series from the Swiss Plateau are exceptionally rare. To contain annual laminations (varves), such lakes need to be deep (>20- 30 m) to prevent bioturbation due to anoxic bottom waters and the bedrock has to be carbonatic to build up light calcite summer layers. Furthermore the lakes should be small (< 0.5 km2) to possess local to regional pollen and spore signals as vegetation proxies. So far, only the two well-studied sites at Soppensee and at Faulenseemoos delivered varve sequences at low altitudes. They cover the time before the first significant increase of human impact during the Neolithic (around 6000 BP). With Moossee and Burgäschisee in Canton of Bern, we present two new sites with varved sequences covering most of the cultural phases and the transition periods in between (Neolithic, Bronze Age, Iron Age, Roman Period, Migration Period, Middle Ages and Little Ice Age). Annually layered sediments have the potential to enhance the chronological precision of sedimentary sequences via a combination of varve counts with wiggle matching of radiocarbon dates, an approach which often applied in archeology and dendrochronology. Until now, studies combining archeology and varved sediments are lacking because no varved series were available so far in Switzerland. For both Bernese lakes, Neolithic pile dwellings mainly from the Cortaillod Culture (5900-5600 BP) are known. Sometimes, these cultural phases were very short (less than 20 years) and with the high precision of the varve chronologies it may be possible to track even such short-term landnam phases. The first focus of our study will be on Neolithic cultures (6500-4300 BP) since most of the well-dated archeological findings are covering that time period. With the findings at the excavation sites and the results from the lake sediments, it will be possible to perform an on-site/off-site comparison. Our second focus will take a closer look to the short-term events and important transitions between cultural phases (e.g. Iron Age-Roman Period, Roman Period-Migration Period, and Middle Age-Little Ice Age). The aim of our study is to understand the linkages

78 between past societies, land use, climate, vegetation and fire activity more thoroughly than achieved so far.

79 Swiss Climate Summer School 2015: Extreme Events and Climate

Drought forecasting using statistical methods

Doug Richardson (1), Hayley Fowler (1), Chris Kilsby (1), Francesco Serinaldi (1)

(1) School of Civil Engineering and Geosciences, Newcastle University

Drought is a complex meteorological and hydrological phenomenon that can have severe implications for natural habitats, ecosystems, and many social and economic sectors. Generally drought is separated into four distinct operational definitions functionally separated by the time scales under which they form. These are (1) meteorological drought (below average rainfall), (2) hydrological drought (e.g. streamflow deficits), (3) agricultural drought (soil moisture deficits) and (4) socioeconomic drought (related to the demands of end-users). In the UK drought is a recurrent feature of climate (Marsh et al., 2007) with potentially large impacts on public water supply (e.g. 1975-76, 1995-96, 2010-12), yet it is rare that a drought will encompass the whole country at once. This is due to spatially varying precipitation and temperature levels and the type of primary water source at risk. South and east England relies mostly on groundwater abstraction from aquifers, whilst northern and western regions obtain water primarily from surface water (Jones and Lister, 1998). Future climate projections display some agreement that UK drought will increase in frequency, severity and spatial extent (e.g. Rahiz and New, 2013), with repeat climatic conditions driving the 1975-76 drought a distinct possibility.

Water companies’ ability to mitigate the impacts of drought by managing diminishing availability depends on forward planning and it would be extremely valuable to improve forecasts of drought on a monthly to seasonal scale. By focusing on statistical forecasting methods, this research aims to provide techniques that are simpler, faster and computationally cheaper than physically- based models. In general statistical forecasting is done by relating the variable of interest (some hydro-meteorological variable such as rainfall or streamflow, or a drought index) to one or more predictors via some formal dependence. These predictors are generally antecedent values of the response variable or external forcings. The examination of the behaviour of long-memory processes (e.g. large-scale atmospheric circulation patterns, sea surface temperatures and soil moisture content) in the time leading up to the onset, peak severity and termination points of drought events should result in the identification of suitable predictors to be included in the forecasting model, and further our understanding of the drivers of drought.

A candidate model is Generalised Additive Models for Location, Scale and Shape parameters (GAMLSS; Rigby and Stasinopoulos, 2005). GAMLSS is a very

80 flexible class allowing for more general distribution functions (e.g. highly skewed and/or kurtotic distributions) and the modelling of not just the location parameter but also the scale and shape parameters. Additionally GAMLSS permits the forecasting of an entire distribution, allowing the output to be assessed in probabilistic terms rather than simply the mean and confidence intervals.

References

Jones, P.D. and Lister, D.H. (1998) 'Riverflow reconstructions for 15 catchments over England and Wales and an assessment of hydrologic drought since 1865', International Journal of Climatology, 18(9), pp. 999-1013.

Marsh, T., Cole, G. and Wilby, R. (2007) 'Major droughts in England and Wales, 1800–2006', Weather, 62(4), pp. 87-93.

Rahiz, M. and New, M. (2013) '21st Century Drought Scenarios for the UK', Water Resources Management, 27(4), pp. 1039-1061.

Rigby, R.A. and Stasinopoulos, D.M. (2005) 'Generalized additive models for location, scale and shape', Journal of the Royal Statistical Society Series C- Applied Statistics, 54, pp. 507-544.

81 1

Swiss Climate Summer School 2015: Extreme Events and Climate

A climatology of synoptic-scale Rossby wave triggering events

Matthias R¨othlisberger1, Olivia Martius1,2 and Heini Wernli3

1 Oeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Bern, Switzerland 2 Mobiliar Lab for Natural Risks, University of Bern, Bern, Switzerland 3 Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

Extended Abstract

Synoptic-scale Rossby waves are ubiquitous in the extratropical flow and together with jets and vortices they form the building blocks of extratropical dynamics. The triggering of synoptic-scale Rossby waves and the associated mechanisms have so far not been analysed in detail. In this study a novel method is presented that automatically identifies triggering events (TEs) of synoptic-scale Rossby waves on tropopause-level waveguides. TEs are identified based on geometry changes of the 2 Potential Vorticity Units (PVU) contours on two isentropic levels (320 and 340 K). The 2 PVU contours are hereby regarded as proxies for the position and shape of the extratropical and subtropical waveguide respectively (e.g. Hoskins and Ambrizzi, 1993; Martius et al., 2010). A TE is recorded in a zonally aligned (i.e. wave-free) longitudinal contour segment if it becomes wavy over time and, additionally, the respective 2 PVU contour is wave-free upstream of the segment. In this study we focus on the mechanisms that lead to the formation of synoptic-scale Rossby waves on tropopause-level waveguides. Viewed from a PV perspective, these triggering mechanisms illustrate ways how meso- to synoptic-scale PV anomalies can be brought to or generated near a wave-free upper-level waveguide. As a proof of concept and in order to illustrate the potential of the identification algorithm, three example TEs are presented in which distinct triggering mechanisms can be identified. In the

82 REFERENCES 2

first TE, a large convective system associated with strong diabatic processes leads to the formation of an upper-level low-PV anomaly (e.g. Wernli and Davies, 1997) and triggers a Rossby wave on the extratropical waveguide. In the second case, a meso-scale lower-stratospheric high-PV anomaly (e.g. Kew et al., 2010) approaches the undisturbed extratropical waveguide from the north and acts as trigger for a Rossby wave. The third case illustrates the interaction between the two waveguides. A breaking wave on the extratropical waveguide steers a lower-stratospheric high PV anomaly into close proximity with the undisturbed subtropical waveguide and induces a wave on the latter (e.g. Martius et al., 2010). The method is applied to ERA-Interim data from 1979 to 2014 in order to produce a feature-based climatology of TEs on the two waveguides in the Northern Hemisphere during winter. Three main regions of triggering activity are identified: the Northwestern Pacific, North America and the North Atlantic, as well as North Africa and the Middle East. In future work we will expand the climatology of TEs to all seasons and both hemispheres and we will explore climatological aspects of Rossby wave triggering, such as possible linkages between major climate modes and Rossby wave triggering.

References

Hoskins, B. J., and T. Ambrizzi. 1993. Rossby wave propagation on a realistic longitu- dinally varying ﬂow. J. Atmos. Sci. 50, 1661–1671.

Kew, S. F., M. Sprenger, and H. C. Davies. 2010. Potential vorticity anomalies of the lowermost stratosphere: A 10-yr winter climatology. Mon. Weather Rev. 138, 1234– 1249.

Martius, O., C. Schwierz, and H. C. Davies. 2010. Tropopause-level waveguides. J. Atmos. Sci. 67, 866–879.

Wernli, H., and H. C. Davies. 1997. A Lagrangian-based analysis of extratropical cyclones. I: The method and some applications. Q. J. Roy. Meteor. Soc. 123, 467–489.

83 Atmospheric and oceanic warming patterns depend non-linearly on the forcing magnitude

Maria Rugenstein1 and Reto Knutti1

1ETH Zürich, Institute for Atmospheric and Climate

An understanding of the variability and extremes in a changing climate requires a robust understanding of the sensitivity of climate to dierent timescales and magnitudes of perturbations. Since I do not work directly on extreme events, I will present work on spatial patterns of global warming and its temporal variability.

I show – in an idealistic setting for CO2 step function forcings – that the strength of the atmospheric perturbation inﬂuences the ocean heat uptake and sea level rise in a non-linear fashion. The (local) rate of change of ocean heat uptake in turn will inﬂuence the (local) atmospheric warming pattern, land-sea, and low- versus high latitude warming contrast. We use the intermediate complexity model ECBilt-CLIO and up to 90 ensemble members for each of the six forcing levels ranging from 1.07 to 16 times preindustrial CO2 concentration.

Very high CO2 forcing increases the stratiﬁcation in the ocean, slowing down the channeling of heat into the deep ocean. Very low, barely noticeable atmospheric CO2 forcing, also shows high equilibration time scales, due to a very weak response of the circulation. “Standard scenarios” of CO2 increase, in the range of the RCP scenarios, shows the strongest circulation response and the fastest ocean heat uptake. Depending on the forcing scenario the heat is stored in dierent locations, which inﬂuences the sea level rise globally and locally and sets the conditions for SST warming. I would be happy to discuss whether this may have implications for the detection and attribution of extreme events.

84 Swiss Climate Summer School 2015: Extreme Events and Climate Development of a hybrid finite-element Cloud Resolving Model including grid adaptivity

J. Savre (1), M. Herzog (1), C. Pain (2), J. Percival (2)

(1) Department of Geography, University of Cambridge, Cambridge, UK (2) Department of Earth Science & Engineering, Imperial College London, London, UK

Despite the recent development of highly-scalable atmospheric models (at global, regional and cloud scales) and the emergence of extremely powerful high-performance computing centers, we are still not able to accurately resolve all the physical scales involved in the climate and weather systems. It actually now appears clear that rethinking our existing models and the numerical methods employed will be necessary to continue improving their performances while increasing the affordable spatial resolution.

To achieve this goal, the next generation atmospheric models must offer the possibility to better control the spatial resolution and numerical efforts by increasing the flexibility of the numerical grid [1]. This includes models supporting very irregular meshes and adaptive remeshing techniques. Of course, the numerical methods used to solve the flow equations must be consequently adapted to preserve some important numerical properties (accuracy, mass conservation, no spurious oscillations...).

The Cloud Resolving Model (CRM) introduced and evaluated in this work combines the use of adaptive triangular (in 2D, tetrahedral in 3D) meshes with hybrid finite-element methods (continuous/discontinuous Galerkin methods). The code is based on the Fluidity dynamical core (developed at Imperial College London [2]) which has been enhanced to include dry and moist atmospheric thermodynamics, cloud microphysics and appropriate boundary conditions to solve cloud scale atmospheric flows.

The model introduced above has been thoroughly tested under dry atmospheric conditions (dry convection, topographically forced gravity waves...) and its ability to capture moist atmospheric processes (moist convection, condensation/evaporation, precipitation generation...) has been demonstrated (see Figure 1). In particularly, it has been shown that adaptive grids are able to accurately capture the main features of buoyancy driven atmospheric flows (Figure 2), without accuracy loss, but with a substantial performance improvement (CPU time reduced by a factor up to 8 at comparable maximum resolution).

85 Future works will focus on the improvement of the cloud microphysics scheme and the application of the new modelling framework to actual cloud conditions. In particular, as part of the EU-FP7 PEARL (Preparing for Extreme And Rare events in coastal regions [3]) project, the model will be used to study the development of heavily precipitating cloud systems over the eastern coast of Denmark (Greve) which can regularly lead to severe floods.

Figure 1: Development of a 2D idealized squall line cloud system, 1h after initialization. Bold line: cloud boundaries, color shadings: precipitation eld, vectors: wind vectors.

Figure 2: Density current simulations with a uniform grid (left) and adaptive remeshing (right). Iso-contours and colors represent potential temperature perturbations from 0 K to -15 K. The maximum resolution in both cases is 6 m.

References [1] J. Slingo et al., Phil. Trans. R. Soc. A., 367, 815-831, 2009 [2] R. Ford et al., Mon. Wea. Rev., 132, 2816-2831, 2004 [3] www.pearl-fp7.eu

86 Swiss Climate Summer School 2015: Extreme Events and Climate

Added value of very high resolution model simulations for the coasts of Northern Germany using the example of two case studies of extratropical cyclones

Benjamin Schaaf (1), Frauke Feser (1)

(1) Helmholtz-Zentrum Geesthacht, Germany

This study aims to analyse a range of added values for a very high-resolution climate model simulation (RCM) which permits convection in comparison to a regional model with coarser grid resolution.

Reanalysis data was dynamically downscaled with the RCM COSMO-CLM to a much higher resolution, using in addition to the conventional forcing via the lateral boundaries the spectral nudging technique in the model domain´s interior. This method 'nudges' the large spatial scales of the regional climate model towards the reanalysis, while the smaller spatial scales are left unchanged. It was applied successfully in a number of applications, leading to realistic atmospheric weather descriptions of the past.

The hindcast was calculated for the last 67 years, from 1948 until 2014. The model area is the German Bight, including Northern Germany and parts of the Baltic Sea. This is one of the first model simulations at climate scale with a very high resolution of 2.8 km, so even small-scale effects can be detected.

Two case studies were analysed, storms Xynthia (February/March 2010) and Christian (October 2013) which both moved through the model area. With a filtering and tracking program the course of individual storms was tracked and compared with observations. The high-resolution model simulation shows precipitation areas which are not present in the coarser grid simulation, especially in summer months when the maximum of convective precipitation is reached. This leads to a higher monthly accumulated precipitation, which is more realistic in comparison to observations. Also for wind speed and gusts one can see a more realistic wind field in urban areas, which is caused by a better description of surface topography. In addition return values and percentiles of wind speed and precipitation were examined.

References Geyer, B.: High-resolution atmospheric reconstruction for Europe 1948–2012: coastDat2, Earth Syst. Sci. Data, 6, 147-164, doi:10.5194/essd-6-147-2014, 2014

Swiss Climate Summer School 2015: Extreme Events and Climate

Exploring the causes of rare extreme precipitation events in the south-eastern Alpine foreland region Katharina Schröer (1, 2), Gottfried Kirchengast (1, 2, 3)

(1) Wegener Center for Climate and Global Change (WEGC), University of Graz, Austria (2) FWF-DK Climate Change, University of Graz, Austria (3) Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics (IGAM/IP), University of Graz, Austria

While there is still considerable uncertainty in how the character of precipitation will change in space and time, the “frequency or intensity of heavy precipitation events has likely increased in North America and Europe” [1], and extreme intensities of short-duration precipitation events on the daily to sub-hourly scale seem to increase unambiguously as temperatures rise [e.g., 2, 3, 4]. Statistical studies on extreme precipitation contribute substantially to the research field. Thresholds, such as percentile values are used to classify extreme events out of a given sample. Probability density functions (PDFs) are sought, fit and applied to describe frequency, magnitude or recurrence intervals of extreme precipitation events. We term such extreme events statistical extreme events - “SEEs”. These studies respond to the needs of engineering practice in e.g. infrastructure design, or trend analysis of precipitation in climate studies, but they a) often ignore outliers because of practical or statistical/data limitations (i.e. left out as “residual risk”) and b) tell us little about the underlying processes of the climate and weather system causing these outliers. We term these outliers that can only be attributed to the distribution tails via large uncertainty ranges as rare extreme events - “REEs”.

The main focus of this study is to identify and physically assess processes that potentially differentiate REEs from SEEs under the hypothesis that REEs are caused by a conjunction of specific conditions on different scales. We differentiate spatio-temporal circumstances of large-scale/long-term and regional/seasonal preconditioning that combine with specific local/short-term event conditions. In this initial study, we primarily examine precipitation records of high temporal resolution (5 and 10 min) of the Austrian Hydrographic Service (AHYD) and ZAMG (National Weather Service of Austria) meteorological station networks over the climate-sensitive south-eastern Alpine foreland region. We delineate temporally and spatially coherent precipitation events rather than treating regular observation intervals as individual instances. The most extreme events found are then systematically analyzed in depth, using a large pool of auxiliary data.

For each event, the preconditioning will be evaluated making use of extended climate and weather information such as atmospheric analyses and synoptic observations; complemented by a desk review of peer-reviewed scientific literature, extreme event reports, retrospects of weather services and others. By systematically exploring the spatio-temporal character and conditioning processes of REEs on a per-event basis we aim to overcome some of the limits of data-sparse statistics. In identifying specific patterns of processes generating REEs we intend to contribute to understanding uncertainties associated with extreme precipitation. Looking ahead to later phases of the project, a desirable outcome is to use findings from the analysis of the recent past to have valuable information to evaluate extreme precipitation in climate model scenarios of the future.

References [1] IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA [2] Trenberth, K. E. (2011). Changes in precipitation with climate change. Climate Research 47 (1-2), 123–138. WOS:000289207700014. [3] Berg, P., C. Moseley, and J. O. Haerter (2013, March). Strong increase in onvective precipitation in response to higher temperatures. Nature Geoscience 6 3), 181–185. [4] Kendon, E. J., N. M. Roberts, H. J. Fowler, M. J. Roberts, S. C. Chan, and C. Senior (2014, July). Heavier summer downpours with climate change revealed by weather forecast resolution model. Nature Climate Change 4 (7), 570–576. WOS:000338837400021.

89 Authors:)) Martina)Schubert2Frisius)and)Frauke)Feser))) Helmholtz2Zentrum)Geesthacht)(HZG),)Zentrum)für)Material2)und)Küstenforschung;)Germany.) ) ) ) Title:)A)global)regionalization)of)NCEP2Reanalysis)using)a)high)resolution)general)circulation)model) ) Abstract:) ) Long2term) reanalysis) products) represent) an) important) data) source) for) numerous) climate) studies.) However,) their)coarse)spatial)resolution)and)the)inhomogeneity)in)space)and)time)make)it)difficult)to)derive)changes)in) meteorological) variables) over) time.) Therefore,) we) use) spectral) nudging) to) down2scale) the) global) reanalysis) data)to)a)finer)resolution)with)a)general)global)circulation)model.)Besides)the)conserving)of)the)large2)scale) atmospheric)information)and)the)resulting)finer)topography,)an)added)value)of)information)in)meteorological) phenomena)of)medium)and)small)spatial)extensions)is)expected.) ) Following) this) strategy) a) global) regionalization) with) the) global) high2resolution) atmospheric) model) ECHAM6) (T255L95),)developed)by)MPI2M)Hamburg,)was)recently)performed)successfully)by)spectrally)nudging)NCEP1) reanalysis)(T62L28))for)the)time)period)from)1948)until)April)2015.)This)simulation)enables)the)investigation)of) long2term) changes) in) meteorological) phenomena;) the) focus) is) put) here) on) intense) storms.) We) found) in) preliminary)analyses)the)expected)added)value)on)medium)and)smaller)scales)compared)to)the)driving)NCEP) re2analysis)by)evaluating)them)with)observed)data)and)finer)resolved)re2analyses)from)DWD,)EOBS,)CRU)and) ERA2Interim.)Most)of)the)regional)storms)like)hurricanes)and)typhoons)are)better)reconstructed)in)ECHAM6) compared)to)NCEP1,)although)their)intensity)still)lies)below)those)of)best)track)data.))The)data)was)also)used)to) present)first)results)of)tropical)cyclones)undergoing)extra2tropical)transition)(ET).)) ) )

)

90 Swiss Climate Summer School 2015: Extreme Events and Climate Analysis of solar influence on tropospheric weather using a new time series of weather types.

Mikhaël Schwander (1,2), Stefan Brönnimann (1,2)

(1) Climatology Group, Institue of Geography, University of Bern (2) Oeschger Centre for Climate Change Research, University of Bern

Weather types describe daily atmospheric circulation variability over a given region with a simple measure. Their use can be beneficial for historical climatology, which increasingly targets day-to-day variability but lacks comprehensive atmospheric circulation fields further back than 1871 (start of the Twentieth Century Reanalysis). A new statistical method is used to generate a daily weather type classification (WTC) covering the last 250 years. The method uses an existing classification (e.g. CAP) available for a reference period and extends it back to the end of the 18th century. The CAP classification used in our study is available from 1957 onward. It has been computed by MeteoSwiss using ERA-40/ERA-Interim reanalyses (Weusthoff, 2011). In order to produce a weather types time series which covers a longer time period than the available reanalyses, we use early instrumental data from weather stations. A classification (CAP9) is taken as a reference for a determined period. Let x be a vector with information from stations 1...n for one day. x contains weather data from several stations. For example, t=temperature, p=pressure, Δp=pressure tendency.

Further, let i denote the weather type (1 to 9 for CAP9). Then, the weather type of day t is the type i that minimizes the following function (Mahalanobis distance):

∑i is the covariance matrix of x for all days in the reference period that pertain to the weather type i.

We use instrumental data form Western/Central Europe in order to cover the period 1763-2008. All the data need to be available for the reference period (1957-1998), so the whole time series is calibrated over the same period. The comparison of the new time series with the reference (obtained from ERA-40 and Interim) shows a good correlation (0.85). However, the new methods performs better for winter months than for summer.

91 This new WTC offers the possibility to analyze weather conditions over Europe for more than two centuries with objective types. In the frame of the FUPSOL-II project (Future and Past Solar Influence on the Terrestrial Climate), this new time series is used to analyze solar activity changes on weather types in Europe based on the frequency of occurrence of these types. This kind of analysis has been performed by Huth et al. (2008), but it only covers the period 1949-2003. The first results of the analysis over 245 years show a slight increase in the frequency of easterly and northerly types over Western and Central Europe under low solar activity in winter. Under high solar activity, there is a tendency towards westerly types to be more frequent (linked to an enhanced zonal flow).

References

Huth, R et al. (2008), Solar activity affects the occurrence of synoptic types over Europe. Annales Geophysicae, 26(7):1999-2004.

Weusthoff, T. (2011). Weather Type Classification at MeteoSwiss: Introduction of new automatic classification schemes. Arbeitsberichte der MeteoSchweiz, 235:46.

92 Swiss Climate Summer School 2015: Extreme Events and Climate

Decadal Climate Predictions Using Sequential Learning Algorithms Ehud Strobach (1) and Golan Bel (1) (1) Department of Solar Energy and Environmental Physics, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, 84990 Israel

Ensembles of climate models can improve future climate predictions and reduce their uncertainties. We use Sequential Learning Algorithms (SLAs) [1] in order to establish a weighted ensemble of climate models based on their past performance. This method has several advantages, including the lack of a priori assumptions regarding the ensemble members; the weight of the ensemble members can be updated upon the arrival of new measurements, and it can be proved that the prediction of the weighted ensemble is at least as good as the prediction of the best model if the learning period is long enough. Using this method, we aim to achieve two main goals: to provide better future climate predictions and to reduce their uncertainties.

We divide the predictions made by the climate models into two periods: a learning period and a prediction period. During the learning period, the weights are assigned to the climate models in a sequential manner. At the beginning, some initial weight is assigned to the models. In the case of no a priori knowledge, the models are assigned with equal weights. Then, a new observation is revealed, and based on this, the models are scored using a loss function–an evaluation metric that measures the discrepancy between the predicted value and the outcome. Finally, the loss function is used to update the weights of the previous sequence. This process is repeated until there are no new available observations, and the weights of the last learning sequence are used for future predictions–the prediction period.

The goal of SLAs is to minimize the cumulative regret with respect to each expert (i.e., climate model). This quantity is defined as: �

��,� ≡ ∑ (�(��,��) −�(��,�,��)) ≡ �� −��,� �=1 where � is a discrete time, � is the number of learning steps, �� is the forecaster’s (i.e., the weighted average) prediction, �� is the outcome and ��,� is the prediction by expert �; � is the 2 loss function, which we define to be the squared error loss – �(��,��) ≡ (�� −��) . �� and ��,� are the cumulative loss functions of the forecaster and the expert �, respectively. Using the forecaster’s strategy, it can be shown that: �→∞ max�=1,…,�(��,�) → 0, meaning that the forecaster will predict at least as well as the best expert during the learning period (provided there is a long enough learning period).

The SLAs were applied to a set of 30-year decadal experiments, from 1981-2011, of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The first 20 years were used as a learning period and the last 10 years (120 months) were used as a prediction period. Figure

93 1 shows the number of time points in which the Exponentiated Gradient Average (EGA) SLA had smaller error (upper panel) and smaller uncertainty (lower panel) than the reference climatology. White circles represent a significant improvement by the EGA algorithm, and black circles represent a significantly poorer performance. The algorithm has also been shown to improve the predictions of the simple average and the best model [2].

Figure 1: The number of time points in which the Exponentiated Gradient Average (EGA) SLA had smaller error (upper panel) and smaller uncertainty (lower panel) than the reference climatology. White circles represent a significant improvement by the EGA algorithm, and black circles represent a significantly poorer performance.

References [1] Cesa-Bianchi, N., and G. Lugosi, 2006: Prediction, learning, and games. Cambridge University Press, Cambridge, UK. [2] Strobach, E., and G. Bel, 2015: Improvement of climate predictions and reduction of their uncertainties using learning algorithms. Atmospheric Chemistry and Physics Discussions, 15 (5), 7707–7734, doi:10.5194/acpd-15- 7707-2015, URL http://www.atmos-chem-phys-discuss.net/15/7707/2015/.

94 Hazardous thunderstorms over Lake Victoria: climate change and early warnings

Wim Thiery1, Edouard Davin2, Sonia Seneviratne2, Kristopher Bedka3, Stef Lhermitte1 and Nicole van Lipzig1

1 KU Leuven - University of Leuven, Belgium 2 Swiss Federal Institute of Technology, Switzerland 3 NASA Langley Research Center, United States of America

Corresponding author’s e-mail address: [email protected]

Despite the lack of accurate statistics, fatalities among fishermen operating on the surface of Lake Victoria are estimated to rise up to several thousands per year, most of them caused by severe weather. Here we present the first dedicated high-resolution, coupled lake-land-atmosphere climate projection for the African Great Lakes region and investigate the influence of future enhanced greenhouse gases on extreme thunderstorms over Lake Victoria. Our model projections for the end-of-the-century underline the major role for Lake Victoria in modulating extreme precipitation changes. Under a high-emission scenario (RCP8.5), the 1% most extreme over-lake precipitation may intensify by 18% towards 2071-2100 relative to 1981-2010, that is about three times faster compared to the projected change over the surrounding land after isolation from the mean change. The expected Clausius-Clapeyron scaling of precipitation extremes to temperature increases holds over Lake Victoria but not over the surrounding land, confirming the lake imprint on future precipitation change patterns. Interestingly, this is in contrast to the change in average over-lake precipitation, which is projected to decrease by -6% for the same period. By further analyzing the high-resolution output we were able to explain this different response. While mesoscale circulation changes cause the average precipitation decline, the response of extremes is essentially thermodynamic.

Furthermore, a study of the controlling factors of extreme nighttime thunderstorms over Lake Victoria revealed a strong dependency of the nighttime over-lake storm intensity on the antecedent daytime land storm activity. Physically, intense daytime land storms induce a moist anomaly in the lower layers of the atmosphere, and cool the land surface. The cold anomaly limits moisture divergence from the lake (weak lake breeze) while favouring nighttime near-surface convergence (strong land breeze). Satellite-based observations of precipitation intensity or thunderstorm activity may therefore serve as a risk indicator for storm intensity over Lake Victoria the following night.

Swiss Climate Summer School 2015: Extreme Events and Climate

Radar Characteristics and Patterns Related to Convective Wind Gusts in Switzerland

Simona Trefalt (1,2), Olivia Martius (1), Alessandro Hering (2) , Urs Germann (2)

(1) University of Bern, Mobiliar Group for Climate Impact Research (2) MeteoSwiss, Division for Radar, Satellite and Nowcasting

During the convective season (April to September) severe thunderstorms often affect Switzerland, both North and South of the Alps. Heavy precipitation, large hail and wind gusts may cause damage to buildings and agriculture among many others and represent considerable costs for insurance companies. Accurate real-time point measurements of wind gusts in Switzerland are available from ~130 ground weather stations, which make up a very dense network compared to the international mean. Due to the high spatial (and temporal) variability of wind gusts the number of stations is however still not high enough to provide a full depiction of the wind gust distribution over the Swiss territory. Weather radar data, conversely, has a wide-ranging quasi-continuous spatial coverage and permits the study of the 3D development of gust-producing cells and the surrounding environment. Algorithms for wind gust detection from radar data exist for flat topographic areas, but they cannot directly be adopted for the configuration of the operational 4th generation C-Band Swiss Radar Network as well as in complex terrain. On the one hand, the radar beam visibility close to the ground, where potentially damaging wind gusts occur, is often limited by orography and the radars are too far apart to form a dual- or multiple-Doppler network. On the other hand, the prioritisation of long-range measurements such as for the Swiss Radar Network entails low Nyquist velocities, with the need for complex dealiasing procedures. Additionally, existing methods frequently focus on detection and nowcasting of mesocyclones, which are a small contributor to severe weather in Switzerland. In consequence, other approaches need to be considered. In this study, radar proxies are searched for an a posteriori detection of wind gusts to construct comprehensive wind gust maps. Possible proxies are investigated as pre-cursor signals of wind gusts as well, to contribute to severe weather warnings. In the analyses, we relate non-Alpine weather station wind gust recordings above 20m/s (i.e. a damage threshold used by insurance companies) for the convective seasons 2012-2014 to radar products in the area immediately surrounding the stations. The radar products considered are MaxEcho, EchoTop15, -45 and -50, Vertically Integrated Liquid (VIL), Probability of Hail (POH) and Maximum Expected Severe Hail Size (MESHS), which are operationally computed at MeteoSwiss. We furthermore investigate the (vertical) evolution of these radar products with time, i.e. leading up to severe wind gusts. The synoptic situation in Central Europe concomitant with severe wind gusts is examined and first results suggest that during the analysis period gust-producing cells are predominantly associated with an approaching or passing cold or warm front rather than thermal thunderstorms or convergence lines. K-means clustering analysis is employed to

statistically characterise the occurrence of wind gusts related to different patterns in radar reflectivity. Composites of the other afore-mentioned radar products are subsequently built according to the k-means clustering classes. A discussion relative to the results of these analyses will be presented in the poster.

97 Swiss Climate Summer School 2015: Extreme Events and Climate A new classification of atmospheric droughts Obbe Tuinenburg Copernicus Institute, Utrecht University, The Netherlands

This research aims to increase the understanding of droughts globally, by analysis of the atmospheric water budget during normal and drought periods.

Using an atmospheric moisture tracking model, precipitation is tracked back in the atmosphere to create a climatology of the atmospheric moisture balance. The anomaly of this balance during drought situations is determined to create a new classification of atmospheric droughts: locally dominated (no atmospheric anomaly), moisture budget dominated (anomalous moisture advection due to different evaporation in the moisture source area, but normal winds) and flow anomaly (wind field anomaly).

Figure 1 shows an example of the methodology for October periods in Spain based on ERA-interim reanalysis, which would probably be classified as moisture budget dominated. The top figures show results of the atmospheric moisture tracking. Normally, the precipitation that falls in Spain has evaporated quit nearby in the east-Atlantic, off the coast of Portugal and Morocco. During dry periods, moisture sources shift northwards. The bottom panels show that October precipitation in Spain correlates well with evaporation and temperature in the same east-Atlantic area.

Currently, the methodology is applied and analyzed globally for the current climate (1979-present) and for CMIP5 climate change scenario's.

The possible utilization of the knowledge of the type of drought and statistical tele-connections is an increased (statistical) predictability of droughts by monitoring sea- and land-surface conditions in the evaporation areas that contribute to remote precipitation.

98 Figure 1: Evaporative origin of October precipitation falling in Spain for normal and drought periods (top panels) and correlation of precipitation with surface evaporation and temperatures. Swiss Climate Summer School 2015: Extreme Events and Climate

Extreme River Floods in Western Switzerland and the Lake of Constance Region in the Period Prior to Instrumental Measurements

Daniel Tuttenuj, M. A.

Section of Social, Economic and Environmental History, Historical Institute, University of Bern

Supervisor: Prof. Dr. Christian Rohr

The floods that occurred on the Aare and Rhine rivers in May 2015 and the mostly successful handling of this event in terms of flood protection measures are a good reminder of how important it is to comprehend the causes and processes involved in such natural hazards. While the needed data series of gauge measurements and peak discharge calculations reach back to the 19th century, historical records dating further back in time can provide additional and useful information to help understanding extreme flood events and to evaluate prevention measures such as river dams and corrections undertaken prior to instrumental measurements. In my PhD project I will use a wide range of historical sources to assess and quantify past extreme flood events. It is part of the SNF-funded project “Reconstruction of the Genesis, Process and Impact of Major Pre-instrumental Flood Events of Major Swiss Rivers Including a Peak Discharge Quantification” and will cover the research locations Fribourg (Saane R.), Burgdorf (Emme R.), Thun, Bern (both Aare R.), and the Lake of Constance at the locations Lindau, Constance and Rorschach. My main goals are to provide a long time series of quantitative data for extreme flood events, to discuss the occurring changes in these data, and to evaluate the impact of the aforementioned human influences on the drainage system. Extracting information given in account books from the towns of Basel (Source 1) and Solothurn (Source 2) may also enable me to assess the frequency and seasonality of less severe river floods. Finally, historical information will be used for remodeling the historical hydrological regime to homogenize the historical data series to modern day conditions and thus make it comparable to the data provided by instrumental measurements.

99 The method I will apply for processing all information provided by historical sources such as chronicles, newspapers, institutional records, as well as flood marks, paintings and archeological evidence has been developed and successfully applied to the site of Basel by Wetter et al. (2011). They have also shown that data homogenization is possible by reconstructing previous stream flow conditions using historical river profiles and by carefully observing and reconstructing human changes of the river bed and its surroundings. Taken all information into account, peak discharges for past extreme flood events will be calculated with a one-dimensional hydrological model.

Figure 1: Processing of historical information in order to calculate peak discharges of river flow. Source: Wetter et al. 2011, 737.

References

Source 1: Wochen-Ausgabenbücher der Stadt Basel; Staatsarchiv Basel-Stadt: Finanz G 1-84.

Source 2: Seckelmeisterrechnungen der Stadt Solothurn; Staatsarchiv Solothurn: SM.

Wetter, O., Pfister, C., Weingartner, R., Luterbacher, J., Reist, T., & Trösch, J. (2011): The largest floods in the High Rhine basin since 1268 assessed from documentary and instrumental evidence. Hydrol. Sci. J. 56(5), 733–758.

100 Swiss Climate Summer School 2015: Extreme Events and Climate Adaptation decisions and damage costs under uncertainty in an empirical general equilibrium framework Takafumi Usui (1), Frank Vöhringer (1, 2) and Philippe Thalmann (1)

(1) Laboratory of Environmental and Urban Economics, École Polytechnique Fédérale de Lausanne, Switzerland. (2) Econability, Switzerland.

1 Research objectives

Mitigation measures are primary research interests in order to prevent irreversible damages on the environment attributable to anthropogenic interferences. However, due to the inertia of the climate system, there is a growing need for adaptation strategies. An ex-ante assessment of adaptation strategies is necessary, but it is methodologically abstract how to address uncertainty in the intensity and the impact of climate change in economic modeling. The goal of the project is to analyze decision rules for the implementation of adaptation measures under uncertainty within the framework of a general equilibrium model. The project focuses on extreme flood hazards in Switzerland, which could be associated with climate change. We will discuss stochastic flood damages and related adaptation decisions employing a computational general equilibrium (CGE) model. The damage costs caused by flooding will be estimated, taking into account the long-term economic developments and the impact of climate change. Through the project, we aim to show how uncertainty can be introduced into a CGE model and also to gain a better understanding of the economic nature of dierent adaptation options for flooding.

2 Methodology and current results

2.1 CGE model with uncertain flood events A CGE model is a unified framework for analyzing the eciency and the equity of economic decisions based on relative price changes. It is widely employed in various fields of applied economics and especially in the field of energy and environment; numerous policy simulations can be found. Uncertainty is of general interest for the CGE modeling community. Löschel and Otto (2009) tested the sensitivity of modeling results to uncertainties about the cost and the performance of backstop technologies such as CCS, using Monte Carlo analysis. Perfect foresight is a common assumption in dynamic CGE models, however, this seems not to be appropriate with stochastic shocks. In our simulations, we modify the modeling framework such that agents in the economy have perfect foresight for macroeconomic conditions but the timing and the intensity of floods are still uncertain. With this adjustment, the agents would be simply surprised when floods occur and the capital stock would be damaged depending on the scale of flooding. Fig.1 is an illustrative example for a capital accumulation path with a perfect foresight and a myopia assumption. As shown in panel (a), the capital stock is accumulated in a proactive way since the agent could forecast future damages by flooding. Whereas the agent is uncertain about flood events, as

1 101 4 4 Benchmark Benchmark Run 1 Run 1 Run 2 Run 2 Run 3 Run 3 Run 4 Run 4 Run 5 Run 5 3 Run 6 3 Run 6 Run 7 Run 7 Run 8 Run 8 Run 9 Run 9 Run 10 Run 10 2 2

1 1 Activity index of capital stock Activity index of capital stock Activity index 0 0 0 10 20 30 40 50 0 10 20 30 40 50 Time series Time series

(a) Perfect foresight (b) Complete myopia

Fig. 1. Eects of dierent assumptions for the agent’s behavior on the dynamic capital accumulation path. Ten independent simulation runs are extracted, where the timing and the damage scale of ﬂoods are random parameters. depicted in panel (b), severe damage on the accumulated capital stock can be expected, if there is no adaptation eort.

2.2 Dynamic damage cost estimation Over the last decades, the number of floods in Switzerland increased. For instance, the flood in 2005 was especially damage-intensive and caused estimated about 3 billion CHF economic loss. We start to define selected flood events and to show how damages for these empirical floods can be estimated considering long term economic growth and climate change.

3 Future research plans

The next steps of the on-going research project are:

1. To introduce speciﬁc capital with which the economy can adapt to or downscale the impact of the uncertain ﬂood damages.

2. To select regional ﬂoods in Switzerland, evaluate damages with economic growth scenarios and specify adaptation measures for selected events.

3. To implement within the existing CGE model for Switzerland, the GENESwIS.

References

Löschel, Andreas and Vincent M. Otto (2009) “Technological uncertainty and cost eectiveness of CO2 emission reduction,” Energy Economics, Vol. 31, No. SUPPL. 1, pp. S4–S17, DOI: http://dx.doi.org/10.1016/j.eneco.2008.11.008.

2 102 Swiss Climate Summer School 2015: Extreme Events and Climate

Sting Jet analyses in extratropical cyclones

Ambrogio Volonte’1, Peter A. Clark1, Suzanne L. Gray1 1 Department of Meteorology, University of Reading, UK

(a) (b)

Figure 1: Infrared satellite image from Meteosat (1a). Cloud-top brightness temperature (K) from MetUM simulation (1b). Both images refer to the storm Tini at 06z on 12th February 2014. In the images the fronts, the cloud head and the dry intrusions are highlighted; SJ stands for sting jet.

Extratropical cyclones can easily produce windstorms that have a large social and economic impact. Gener- ally, these strong surface winds are related to low-level jets occurring along warm and cold fronts but, analysing the Great Storm that affected the UK in October 1987, Browning (2004) and Clark et al. (2005) highlighted that an additional region of strong surface winds can exist on the southern side of the cyclone centre, in the frontal-fracture area located between the cold front and the bent-back front. These strong winds are related to an airstream, called a “sting jet”, that exits from the tip of the hook-shaped cloud head in the mid-troposphere and descends towards the surface, accelerating and reducing its relative humidity. In this PhD project, “Dynamics of Sting Jets and their relation to Larger-Scale Drivers” funded by the AXA Research Fund, we are investigating the large-scale factors controlling the generation and growth of sting jet airstreams. The scope of this study is to understand and highlight the dynamical basis of the sting jet, in order to provide a strong theoretical underpinning to the sting-jet related research. In particular, we aim to assess the actual role of large-scale environmental parameters (e.g. cyclone background state) and the contribution of diabatic processes and of effects such as the release of different atmospheric instabilities. The first stage of this project, that we are currently carrying out, consists of the analysis of a real casestudy, the storm Tini, that affected the UK on 12th February 2014 (Figure 1). We are looking at the evolution of this extratropical cyclone through simulations run with the MetUM, which is the operational forecast model of the Met Office, UK, and by means of post-processing programs written using the Iris-Python language. With this methodology we are verifying the presence of a sting jet in this storm and we are also analysing back- trajectories (computed with the software LAGRANTO (Wernli and Davies 1997)) and looking at instabilities’ diagnostics in order to gain further information on the sting jet dynamics. The poster will show the results of this investigation. The subsequent stage of the project, that we will soon start to undertake, regards idealised simulations to be performed in a periodic channel configuration with baroclinic lifecycles. With this more general setting it will be possible to understand more in depth the mechanisms leading to sting jets and address the main questions of the project, using sensitivity experiments and examining carefully the role of potential vorticity and related variables during the storm evolution.

103 References

Browning, K. A., 2004: The sting at the end of the tail: Damaging winds associated with extratropical cyclones. Q. J. R. Meteorol. Soc., 130, 375–399. Clark, P. A., K. A. Browning, and C. Wang, 2005: The sting at the end of the tail: Model diagnostics of ﬁne-scale three-dimensional structure of the cloud head. Q. J. R. Meteorol. Soc., 131, 2263–2292. Wernli, H. and H. C. Davies, 1997: A Lagrangian-based analysis of extratropical cyclones. I: The method and some applications. Q. J. R. Meteorol. Soc., 123, 467–489.

104 Swiss Climate Summer School 2015: Extreme Events and Climate The impact of increased Mediterranean sea surface temperatures on central European extreme precipitation

Claudia Volosciuk (1), Douglas Maraun (1), Vladimir Semenov (1,2,3,4), Natalia Tilinina (3), Mojib Latif (1), Sergey Gulev (3)

(1) GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany (2) A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russia (3) P.P. Shirshov Institute of Oceonology, Russian Academy of Sciences, Moscow, Russia (4) Institute of Geography, Russian Academy of Sciences, Moscow, Russia

Central European climate is influenced by the Mediterranean Sea, where a strong increase in sea surface temperature (SST) has been observed during the last four decades. One example of extreme weather events are cyclones following the “Vb” pathway. These cyclones are generated over the Mediterranean Sea, travel northeastwards around the Alps and then hit central European countries. These cyclones carry large amounts of moisture and cause extreme precipitation, and subsequently flooding, particularly in summer.

To investigate the impact of increased Mediterranean SST on extreme precipitation in Europe, we analyze a series of simulations with the atmospheric general circulation model ECHAM5. In the control run, we forced the model with the 1970-1999 SST climatology. In an additional run, we replaced the Mediterranean and Black Sea SST forcing with the climatology of the warmer 2000-2012 period. ECHAM5 was run at high horizontal resolution (T159) and integrated for 40 years in each experiment. 20-season return levels (RL20S) were derived as a measure of extreme precipitation for daily precipitation in JJA (June - August). These return levels are estimated as quantiles of a stationary generalized Pareto distribution, based on exceedances of the 95th precipitation percentile.

Summer RL20S are increased in central Europe along the Vb cyclone track in the warmer Mediterranean simulation, compared to the control run (see Fig. 1), although summer mean precipitation does not change much. Due to the warmer climate in the Mediterranean region, climatological mean evaporation and precipitable water in the atmosphere are increased. On extreme days, composites show an even further increase in precipitable water over the central European region and evaporation over the western Mediterranean sea. This additional available moisture is transported from the Mediterranean sea to central Europe. Over land, evaporation does not increase and, hence, moisture recycling does not appear to play a major role in the simulated increase in extreme precipitation. This finding suggests further increases in European summer

105 flooding, should Mediterranean SSTs continue to increase.

Figure 1: Simulated increase in 20-summer daily precipitation return levels due to a warmer Mediterranean sea.

106 Swiss Climate Summer School 2015: Extreme Events and Climate

Remote sensing of past and recent fires: Assessing the accuracy of different satellite products

Helga Weber (1,2), Stefan Wunderle (1,2)

(1) Remote Sensing Research Group, Institute of Geography, University of Bern, Switzerland (2) Oeschger Center for Climate Change Research, University of Bern, Switzerland

Over the last 40 years, increased levels of burning raised awareness of fire- climate-human linkages in the past to assess future interactions (Kehrwald et al., 2013). These include the relative importance of rising temperatures, climate variability, and management practices because levels of fire activity are expected to increase in many regions as e.g. droughts intensify (Moritz et al., 2012). But large uncertainties exist due to the amount, frequency, and intensity of burning biomass emissions under changing climate. Over the last 150 years, fire records showed a decoupling from fire activities of the main drivers temperature and population density. The most important drivers of this phenomenon remain debated and will be addressed by the interdisciplinary Sinergia project “Paleo fires from high-alpine ice cores”. This research framework brings together expertise of ice core analysis and interpretation, fire reconstruction from natural archives, atmospheric modelling of fire tracers, and remote sensing of fire activities to link past and recent observations.

The remote sensing subproject will identify fire events for Europe, Siberia, and Amazonia based on different satellite sensors covering a time series of the last 30 years. For the compiled data set of fire events the retrieval accuracy will differ for different satellite systems depending on the size of the fire, vegetation coverage, and atmospheric conditions. However, merging of multiple satellite products with different spatial resolutions is not widely done, but has been found to be of high value for burned area estimates (Giglio et al., 2010). Therefore, an accuracy assessment will be performed and their uncertainties analysed using existent satellite products as well as the application and modification of retrieval methods (e.g. MODIS, AVHRR, ASTER, and (A)ATSR). One of the first objectives is to compare fire products and define the size of fires/burnt areas related to vegetation coverage. This comparison and quality assessment is the topic of the poster and will be accompanied by an illustrative example of the different satellite products for one fire event. The result of the accuracy assessment will aide the compilation of a homogenous time series based on different satellite systems. Additionally, own retrievals of fires from NOAA/MetOp

107 AVHRR imagery will extend the fire time series to the last 30 years. This is the only sensor with sufficient heritage for the needed time series and its potential has been shown in several studies (e.g. Li et al., 2001). In future, this data set will be used to investigate the influence of climate change on the annual fire frequency, intensity, and size in different temperate, boreal, and tropical regions. This enables the calibration of ice core fire proxies and supports modelling of backward trajectories.

References

Giglio, L, Randerson, J T, Van der Werf, G R, Kasibhatla, P S, Collatz, G J, Morton, D C, and DeFries, R S (2010). “Assessing variability and long-term trends in burned area by merging multiple satellite fire products”. Biogeosciences 7.3, pp. 1171–1186.

Kehrwald, N M, Whitlock, C, Barbante, C, Brovkin, V, Daniau, A L, Kaplan, J O, Marlon, J R, Power, M J, Thonicke, K, and Van der Werf, G R (2013). “Fire Research: Linking Past, Present, and Future Data”. EOS 94, pp. 421–432.

Li, Zhangqing, Kaufman, Yoram J, Ichoku, Charles, Fraser, Robert, Trishchenko, Alex, Giglio, Louis, Jin, Ji-Zhing, and Yu, Xinwen (2001). “A review of AVHRR- based active fire detection algorithms: Princi- ples, limitations, and recommendations”. Global and regional vegetation fire monitoring from space, planning and coordinated international effort, pp. 199–225.

Moritz, M A, Parisien, M A, Batllori, E, and Krawchuk, M A (2012). “Climate change and disruptions to global fire activity”. Ecosphere 3(6). pp. 1–22. DOI: 10.1890/ES11-00345.1.

108 Swiss Climate Summer School 2015: Extreme Events and Climate Was the extreme storm season 2013-14 over the North Atlantic and the UK triggered by changes in the West-Pacific Warm Pool?

Simon Wild, Daniel J. Befort and Gregor C. Leckebusch

University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham, UK

In winter 2013-2014, the UK experienced exceptional stormy and rainy weather conditions. The period from December 2013 to February 2014 was the stormiest regarding frequency for at least 20 years according to the UK Met Office. While the UK was hit by several high intensity storms, surface temperatures over large parts of central North America fell to near record minimum values. One potential driver for these cold conditions is discussed to be the increasingly warm surface waters of the tropical West Pacific. It has been suggested that these increasing sea surface temperatures could also be the cause for extreme weather over the British Isles. To test this hypothesis, we investigate potential mechanisms linking SST anomalies the Western Pacific Warm Pool with European wind storm activity. We will mainly focus on two research questions. Firstly: Was a chain of anomaly patterns with origin in the West Pacific present in the winter 2013-14? And secondly: What is the role of this mechanism in explaining interannual variability of wind storms over Europe in the recent past? Our results, using ERA-Interim Reanalysis from 1979 – 2014 for December to February, show an absolute maximum of wind storm frequency for large parts of the eastern North Atlantic and coastal regions of West Europe in winter 2013-14. Wind storms are identified with a tracking algorithm based on exceedances of the local 98th percentile of surface wind speeds. We also find an absolute minimum for the surface temperature over large regions in central North America and a substantially reduced number of cyclones in the eastern North Pacific in the same season. The convective activity over the West Pacific Warm Pool and the number of cyclones in the eastern North Pacific are significantly correlated. The location of the highest cyclone density in the North Pacific, respectively the PNA, is in turn strongly related to temperature anomalies over central North America. We further find a significant anti-correlation of interannual variability between surface temperatures in North America and wind storm frequency in the eastern North Atlantic. Thus, we find indications for teleconnections between the variability of sea surface temperatures in the West Pacific Warm Pool and European cyclone activity, which supports the above suggested hypothesis.

109 Swiss Climate Summer School 2015: Extreme Events and Climate

Projections of Australian Regional Temperature Extremes from CMIP5 Models

Louise Wilson (1), Tony Rafter (1)

(1) Oceans & Atmosphere Flagship, CSIRO, Australia

Extreme heat events have major impact on Australian environment and society. From a risk assessment and impact planning perspective, projections of changes in the magnitude and frequency of these events is invaluable.

Here we present regional projections of daily temperature extremes from CMIP5 models under emission pathways RCP4.5 and RCP8.5 for Australia. We examine annual maxima of daily maximum temperatures and annual minima of daily minimum temperatures and derive 20-year return levels using extreme value theory. Distribution parameters of a Generalised Extreme Value (GEV) are fitted to data using the method of L-moments (e.g. Hosking, 1990), which is well suited to small sample sizes (Kharin et al. (2005)).

Annual and 20-year maxima and minima temperatures are projected to increase significantly over all of Australia by late in the 21st century, and projected changes are found to be strongly dependent on the RCP. The magnitude of changes in both mean and extremes are greatest over central regions for maximum temperatures, decreasing to the north and south. Projections of change in minimum temperatures are largest in northern regions and decrease in magnitude towards the south.

The response of extreme temperatures to climate forcings is shown to be spatially non-uniform over the Australian continent. In southeast Australia temperature maxima increase more than minima, while temperature minima increase more than maxima in other regions of the country (see figure 1).

We also investigate the differences in climate response of temperature extremes against changes in mean. Comparison of annual mean daily temperature minima and maxima (figure 1a and 1b) to annual (figure 1c) and 20-year (figure 1d) maxima and minima temperatures is made in figure 1. Increases in maximum temperature extremes are of greater magnitude than those for mean changes over southeast Australia, but they are more closely aligned for other regions. Relative increases of mean and extreme minimum temperatures follow a different pattern. Minimum temperature extremes are projected to increase by more than the mean over northern Australia, while elsewhere mean changes are projected to warm by more than extreme minimum temperatures.

110

Figure 1: Median and 10th to 90th percentile range of projected change in daily minimum (maximum) temperature in sub-clusters for 2080-2099 relative to 1986- 2005 for RCP8.5. Shown in each box from left to right is (a) the annual mean daily minimum (maximum) for the larger set of 37 models, (b) the annual mean daily minimum (maximum), (b) the annual daily minimum (maximum), and the (d) 20-year return level of annual daily minimum (maximum) temperature from a consistent subset of 24 models. The Australian average result is shown at bottom left of each plot (from Ekstrom et. al., 2015, p.96).

References Ekstrom, M, P Whetton, C Gerbing, M Grose, J Bhend, L Webb, et al. (including L Wilson). Projections: Atmosphere and the Land. In: P Whetton, M Ekstrom, C Gerbing, M Grose, J Bhend, L Webb, J Risbey., editor/s. Climate Change in Australia Information for Australia’s Natural Resource Management Regions: Technical Report. CSIRO and Bureau of Meteorology; 2015. 222pp.

Hosking JRM (1990) L-moments: analysis and estimation of distributions using linear combinations of order statistics. J R Stat Soc 52:105–124.

Kharin, V, FW Zwiers, and X Zhang (2005), Intercomparison of near surface temperature and precipitation extremes observations, J. Climate, 18, 5201–5223.

111 Swiss Climate Summer School 2015: Extreme Events and Climate

Searching for synergies in crop rotation management – A simulation-optimization approach

N. Zarrineha,b, A. Holzkämpera,b, J. Fuhrera,b

aAgroscope, Institute for Sustainability Sciences, Zurich, Switzerland bOeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Aim of the project The agroecosystem is an interconnected system where management interven- tions have multiple effects on a wide range of ecosystem services. In this project, we aim to investigate - in a case study region in Western Switzerland - how management of crop rotations can best be adapted both at local and regional scales in order to increase yield stability of the crop production system under more frequent climate extremes, while providing synergies between production and other ecosystem services (i.e. water regulation, soil quality, carbon sequestration) and biodiversity conservation. A biophysical simulation model SWAT is used in combination with multi-objective optimization.

Background Previous studies revealed a wide scope for adaptation through changes in the management of crop rotations (Klein et al., 2014). In particular, crop sequence and conservation soil management such as reduced tillage, maintenance of resi- due surface cover, or use of cover crops can contribute to improvements of several ecosystem services (e.g. nutrient cycling, water regulation, soil protection or carbon sequestration) (Delgado et al., 2013) while maintaining productivity. In addition, management intensity and rotation diversity – particularly the introduction of cover crops - benefits species diversity (Schipanski et al., 2014).

Specific objectives This study, which contributes to the European project “TALE - Towards multifunctional agricultural landscapes in Europe: Assessing and governing synergies between biodiversity and ecosystem services“ (BiodivERsA/FACCE-JPI) considers three main objectives. First, different crop rotations including cover crops will be assessed to identify optimal synergies between different ecosystem services at the field scale. Second, effects of spatial configurations of selected crop rotations on the provision of multiple ecosystem services will be analyzed to identify spatial patterns of cropland management providing optimum synergies at the catchment scale. Third, impacts of climatic change scenarios for around 2050 on synergies and trade-offs between ecosystem services will be studied at field and catchment scales.

112

Methodology Two SWAT (Soil and Water Assessment Tool) models operating at different spatial scales are used. After calibration and validation, the model will be applied in combination with local input data (soil, topography, climate). Simulation results will be subjected to multi-objective optimization to identify optimized land management patterns to mitigate climatic change impacts while maintaining maximum synergies and minimal trade-offs (see Figure1).

Figure1: Overview of project structure

Expected results Robust recommendations for adaptation planning will be provided at multiple scales: optimized sets of rotations providing synergies between ecosystem services under different climatic conditions at field scale, and optimum spatial patterns of land management providing synergies between ecosystem services under different climatic conditions at catchment scale.

References

Delgado, J.A., Nearing, M.A. and Rice, C.W., 2013. Conservation practices for climate change adaptation. In: L.S. Donald (Ed), Advances in Agronomy. Academic Press, pp. 47-115. Klein, T., Holzkämper, A., Calanca, P. and Fuhrer, J., 2014. Adaptation options under climate change for multifunctional agriculture: a simulation study for western Switzerland. Regional Environmental Change, 14, 167–184. Schipanski, M.E., Barbercheck, M., Douglas, M.R., Finney, D.M., Haider, K., Kaye, J.P. et al., 2014. A framework for evaluating ecosystem services provided by cover crops in agroecosystems. Agricultural Systems 125, 12-22.

113 Swiss Climate Summer School 2015: Extreme Events and Climate

Catastrophic Magdalena or not? The flood events of AD 1342 in Central Europe

Eveline Zbinden

Institute of Geography (GIUB), Hydrology Group, and Oeschger Centre for Climate Change Research, University of Bern, Switzerland

Introduction One of the most severe flood of the last centuries in Central Europe seems to be the flood of AD 1342, the "Maria Magdalena flood". It occured in the summer AD 1342 and caused extraordinary damages in many places. But did other floods occur in AD 1342? Were these damages caused mainly by just one singular flood event or by more than one? The analyzed hypothesis for the investigation area of Central Europe are: 1) There was a catastrophic flood in AD 1342. 2) It was not the only catastrophic flood event in AD 1342.

State of knowledge Several studies have been analyzed the flood event of AD 1342 in Europe during the last years (Brázdil, Elleder, Glaser, Herget, Himmelsbach, Kiss, Pfister, Rohr and Zbinden. Those scientists looked on details within their specific research area and time scale. Their methods differ and their results.

Data and methods The information on flood events has to be interpreted, combined and classified. The chosen data consists of written sources by contemporary and non-contemporary sources. They descend from the compilation by Curt Weikinn (1958), one of the most detailed collection of flood events in Central Europe. The methodological steps of source criticism can be summarized: 1. Installing a database of written sources + Dating by contemporary information 2. Mapping the cases by occurence in a place 3. Merging the places to flood events 4. Classifying the magnitude of floods (Pfister/Hächler 1991) Some source texts do not have a detailed information of season, month or day within the year AD 1342. Therefore they can not always be linked directly with a dated event. For reaching a more detailed dating, the chosen date was taken from the available contemporary sources. This interpretation can be distinguished from the documented data information.

Results and Discussion There are several flood events in AD 1342, that can be found in written sources for this year: Early February: Prague (Czech Rep.) and Dresden (Germany) - catastrophic event Early February: Rouen and Vendôme (northern France) - strong event Summer: Avignon (southern France) - strong event Late June: Hannover (Germany) - very strong event Late July: Main- and Rhine area (many places in Germany)- catastrophic event November: Lombardia (northern Italy) - catastrophic event There has been a catastrophic flood event in late July in Central Europe. And another catastrophic flood event was documented in early February in Prague and Dresden. These two extreme events must not be seen as one event. A direct connection between the floods in northern France at the same time as in Prague and Dresden can not be seen, yet.

114 Conclusion The results can answer the hypothesis: 1) YES, there was a catastrophic flood in AD 1342 – on 22nd July. The damages as well as the affected area were extreme. It reached the highest level in the classification-matrix. 2) YES, Maria Magdalena flood was not the only catastrophic flood event in AD 1342. There were catastrophic floods in February and November. In the year AD 1342, several flood events occurred in central Europe and caused severe damage. Without source criticism and a detailed analysis, there can be a confusion of events in winter and summer, especially when there's no dating in the text source.

References The main references are: Pfister, Christian; Hächler, Stefan (1991): Überschwemmungskatastrophen im Schweizer Alpenraum seit dem Spätmittelalter In: Historical Climatology in Different Climatic Zones, Würzburger Geographische Arbeiten, Heft 80). Würzburg. S. 127-148. Weikinn, Curt (1958): Quellentexte zur Witterungsgeschichte Europas von der Zeitenwende bis zum Jahre 1850. Band I (Zeitwende bis 1500). Berlin Zbinden, Eveline (2011): Das Magdalenen-Hochwasser von 1342 – der «hydrologische Gau» in Mitteleuropa. In: Wasser Energie Luft (Heft 3). Baden.

115 Swiss Climate Summer School 2015: Extreme Events and Climate

Early to Mid-Holocene climate variability from multi-millennial tree ring isotope records

Malin Michelle Ziehmer (1,2), Kurt Nicolussi (3), Christian Schlüchter (2,4), Markus Leuenberger (1,2)

(1) Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland (2) Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland (3) Alpine Tree-Ring Group, Institute of Geography, University of Innsbruck, Innsbruck, Austria (4) Institute of Geological Sciences, University of Bern, Bern, Switzerland

The investigation of the evolution of Holocene climate and its variability in the Alps mainly focuses on analyzing low-frequency archives such as glacier and tree line fluctuations. The environment of the Alps reacts sensitively to changes in climatic conditions such as variations of precipitation and temperature. For instance, the current retreat of glaciers reveals a consequence of global warming induced by global climate change. The investigated low-frequency records expose an evolution of Holocene climate from a generally warm Early and Mid to a relatively cool Late Holocene. However, the rare high resolution records often do not indicate such a general long-term trend. The causes and mechanisms behind the trends are not fully understood yet. Recent finds of wood remains of long-lived trees in Alpine glacier forefields changed the concept of Holocene glacier variability and therefore, the present understanding of Holocene climate dynamics. Those findings prove that glaciers in the Alps were usually relatively small and short in their extension during the Early and Mid-Holocene (Joerin et al., 2008; Nicolussi and Schlüchter, 2012). They further prove that the natural variability of postglacial climate is still not sufficiently known. However; such knowledge is essential for climate model input and the ability to disentangle natural from anthropogenic influences on the Earth’s climate. The study aims at establishing highly resolved isotope records from the mentioned, calendar-dated wood remains covering the past 9000 years. Samples are collected in glacier forefields in the Alps, thereby covering a large SW- NE transect. Wood samples are separated into 5-year tree ring blocks from which cellulose is extracted and is crushed by ultrasonic homogenization (Boettger et al., 2007; Laumer et al., 2009). Stable isotopes of carbon, oxygen and hydrogen are simultaneously measured using a recently developed method by Loader et al. (2015). Stable isotope records, containing of a sample replication of four

116 samples per 5-year tree ring block, allow to establish stable isotope chronologies over the Holocene. A special focus is set here on the Early to Mid-Holocene climate variability covering a time period from approximately 9000 to 6000 years BP, which opens the opportunity to analyze minima and optima periods, but also to investigate abrupt climatic changes which are most prominent in the Early and Mid-Holocene such as the well documented 8.2 ka event. The new highly resolved isotope records (C, O, H), which are combined in a multi-proxy approach with the tree ring width and the maximum latewood density of analyzed wood enable a high- resolution reconstruction of environmental conditions and of the natural variability of the Early and Mid-Holocene.

References

Boettger, T., et al. Anal. Chem., 2007, 79: 4603-4612 Joerin, U.E. et al. QSR, 2008, 27: 337-350 Laumer, W., et al. Rapid Commun. Mass Spectrom., 2009, 23: 1934–1940 Loader, N.J., et al. Anal. Chem., 2015, 87: 376-380 Nicolussi K., C. Schlüchter. Geology, 2012, 40: 819-822

117