Lake Viverone the Lake

Alpine Lakes Survey on climate change Survey on climate change

AUTHORS Cartographic elaboration Lucia Borasi, Alberto Maffiotti - Arpa Piemonte Rocco Pispico, Lucia Borasi - Arpa Piemonte

INTERNATIONAL WP4 WORKING GROUP PHOTOS Alberto Maffiotti, Lucia Borasi - Arpa Piemonte Giuseppe Cadrobbi, Nicola Cuzer, Barbara Zennaro - Provincial Gabriel Fink, Thomas Wolf, Bernd Wahl - Landesanstalt für Agency for Environmental Protection of Trento Umwelt, Messungen und Naturschutz Baden-Württemberg Bernd Wahl - Landesanstalt für Umwelt, Messungen und Maurizio Siligardi, Barbara Zennaro - Provincial Agency for Naturschutz Baden-Württemberg Environmental Protection of Trento Julia Lorber, Gabriele Weiser - Kärntner Institut für Liselotte Schulz, Georg Santner, Roswitha Fresner - Regional Seenforschung Government of Carinthia, Department Environment Annecy Tourisme Till Harum, Albrecht Leis, Christian Reszler - Joanneum Gw.P./SILA Research, Forschungsgesellschaft mbH, Institute of Water, Kärntner Institut für Seenforschung Energy and Sustainability Passagers du Vent Silmas pictures library For their active involvement in providing data, the authors would Archivio Arpa Piemonte like to thank the following people: Damien Zanella (Syndicat Mixte du Lac d’Annecy), Pierluigi Fogliati e Francesca Vietti (Arpa Aldo Blandino - Comune di Avigliana Piemonte), Daniele Magni (Regione Lombardia), Tina Leskosek and Anton Brancelj (National Institute of Biology). EDITORIAL COORDINATION Roberta Meotto - Arpa Piemonte REFERENCES FOR LAKE MONITORING AND MODELLING

Past trends GRAPHIC CONCEPT AND DESIGN Lucia Borasi, Alberto Maffiotti - Arpa Piemonte Pomilio Blumm Srl, Pescara Climatic scenarios Porteur d’image - Annecy Cedex Daniele Cane - Arpa Piemonte

Ecological model ISBN 978-88-7479-113-2 Antonello Provenzale, Jost von Hardenberg - CNR - ISAC Alberto Maffiotti, Lucia Borasi - Arpa Piemonte Thermodinamic model

Gabriel Fink, Thomas Wolf, Bernd Wahl - Landesanstalt für Copyright © 2012, Arpa Piemonte Umwelt, Messungen und Naturschutz Baden-Württemberg Via Pio VII, 9 - 10135 Torino - Italia Hydrological modelling and isotope investigations www.arpa.piemonte.it Liselotte Schulz - Regional Government of Carinthia, Department Environment, Till Harum, Albrecht Leis, Christian Reszler - Joanneum Research, Forschungsgesellschaft mbH, Institute of Water, Energy and Sustainability Survey on water temperature and water circulation Liselotte Schulz, Georg Santner, Roswitha Fresner - Regional Government of Carinthia, Department Environment

II Introduction Index

The lake ecosys- Monitoring and modelling, associated to the in- The SILMAS project: the activities of Work Package 4 4 tems are extremely vestigation of the lake evolution (from the point of The participants and the lakes 5 sensitive to hu- chemical, physical and biological view), developed man impacts and during SILMAS at each lake pilot site, provided use- The lakes and climate change: Impacts... 6 climate change ful decision making tools. Here, summary diagrams ...and adaptation 7 (Skjelkvaele and and tables of these studies, are provided. Guide to consult lake sheets 8 Wright, 1998) and they are character- This publication offers a framework of the evolution Lake Annecy 10 ized by numerous feedback mechanisms between of the lakes alpine status, in the context of climate Lake Avigliana Grande 14 biological processes, external forcings and circula- change. It is dedicated to the general public better Lake Sirio 18 tion hydrodynamics, which can be modified by cli- understand how our alpine lake areas have been im- mate change and sometimes contradictory effects pacted by climate change, in order to increase envi- Lake Viverone 22 (IPCC assessment report, 2001), causing changes ronmental awareness. But it contains also detailed Lake Constance 28 in water quality and biodiversity and leading to the technical information helping scientists and decision possible occurrence of «Catastrophic shifts» in the makers. Lake Caldonazzo 32 ecosystem (Scheffer et al. 2001). Lake Levico 36 A rise in temperature (Mooij et al. 2005; Johnk et al. Further information and details can be found in the fi- Lake Ossiacher See 40 2008) can for example facilitate the development of nal reports of the Work Package 4 of SILMAS project, phytoplanktonic bloom due to increased stability available on the project website (http://www.silmas. Lake Wörthersee 46 of the water column and the dependence of algal eu) or on the Alpine Space projects website (http:// Lake Klopeiner See 54 growth rate on temperature. www.alpine-space.eu). Conclusions 62 Bibliography 63 proach and the physical/chemical approach, speci- fying lakes bodies and trends by collecting and in- The SILMAS tegration of ecosystem indices, related to climate variability, and characterizing hydrological impacts of 5 climate change on lakes and catchments by apply- project: ing hydro and thermodynamic models and isotopic analysis. 10 8 9 the activities The biological approach concerns the collection of chemical, physical and biological historical data useful to analysed the trends, the significant ecological 6 of Work events and to observe the ecological effects of cli- 7 4 mate change on the Alpine lakes. In order to do this, 1 3 the Regional Agency for Environmental Protection of Package 4 Piedmont (ARPA) collected a maximum of data on 2 climate change from across Alpine Space. Trough this analysis, it has been possible to produce appro- Sustainable Instrument for Lakes Management in priate practical tools intended to help local decision- Alpine Space (SILMAS) project, co-funded by Euro- makers take the decisions necessary to curb the ef- pean Regional Development Fund (ERDF) within the fects of climate change. Alpine Space Programme, involved 14 partners of 5 countries (Italy, France, Austria, Slovenia and Ger- The physical/chemical approach concerns the de- many) leaded by Region Rhône-Alpes (France). termination of climate change on lakes and in the Within SILMAS project, Work Package 4 “Alpine catchment areas from a point of view of hydrologi- tion Baden-Württemberg; for Austria, Regional Gov- Lakes running changes” (WP4), leaded by ARPA cal and thermodynamic aspects, mixing conditions, ernment of Carinthia, Competence Centre Environ- residence times. Applying hydrological and thermo- The ment, Water and Nature Protection and Joanneum Piemonte (Italy), worked on analysis of effects on climate change on lakes ecosystem, sharing methods dynamic models and isotopic analysis delivered data Research, Forschungsgesellschaft mbH, Institute of and frames of references, and testing models in main of past and scenarios of future hydrological and mix- Water, Energy and Sustainability. ing conditions. participants Syndicat Mixte du Lac d'Annecy/INRA for France, types of lakes, to identify likely scenarios in which lakes could be involved. Regione Lombardia for Lombardy (Italy) and the Through the integration of biological and hydrologi- National Institute of Biology for Slovenia provided cal data into scenario in relation with main alpine and the lakes data. Within one’s own territory, each project part- WP4 was designed as a virtual laboratory producing a dynamic vision of each situation, positioned into lakes types, it has been possible to describe likely ner selected a series of lakes and provided for each identified general trends and related to environmen- scenarios to be expected from climate change, The authorities directly involved in Work Package 4 one historical series of chemical, physical and bio- tal requirements. linked to the main types of lakes encountered in the are: for France, Rhône-Alpes Region (project lead logical data: the data analysis permitted to apply Since lakes are complex dynamic systems, inter- alpine space. Adjustment strategies have been out- partner); for Italy, Piedmont Regional Agency for statistical analysis and to provide lakes trends. In acting with local environment and connected to the lined for stakeholders, according to challenges every environmental protection (WP4 lead partner) and particular, the lakes observed are indicated in the water cycle, WP4 followed first two parallel ways to networking lake will have to meet, in terms of water Environmental Protection Agency of Trento; for Ger- following table, and in the map it is possible to con- throw light on lakes evolution factors due to human resource management and ecosystems preservation many, Institute of Lake Research, State Institute for sult their geographical position: activities and climatic variability: the biological ap- or restoration. Environment, Measurements and nature Conserva-

Regione/Provincia (Stato) Nome del lago

Rhône-Alpes (France) 1 Lake Annecy Piedmont (Italy) 2 Lake Avigliana Grande 3 Lake Sirio 4 Lake Viverone Baden-Württemberg (Germany) 5 Lake Constance Trento (Italy) 6 Lake Caldonazzo 7 Lake Levico Carinthia (Austria) 8 Lake Ossiacher See 9 Lake Wörthersee 10 Lake Klopeiner See 4 5 A larger historical survey of rivers and lakes across the whole of the Northern Hemisphere from 1846 to …and adaptation The lakes 1995 by Magnuson et al. (2000) revealed significant trends towards earlier break-up and later formation Adapting to climate change is a process that, as a of lake ice providing further evidence for sytematic complement to mitigation process, reduces the con- and climate global warming over the past 150 years. sequences of global warming (IPCC, 2007). Many The timing of lake ice break-up is of ecological im- impacts of climate change on lake ecosystem can be portance because the disappearance of ice cover af- effectively addressed through adaptation, in particu- change fects the production and the composition of the phy- lar short term impacts, while increasing the magni- toplankton community and the occurrence of winter tude of the climate change impact the options for an fish kills (Weyhenmeyer, 2006). effective adaptation diminish, while associated costs Even the nutrients cycle in aquatic systems are al- increase. Adaptation will require technical know-how, Impacts… tered by warmer temperature, as the period of algal funding and substantial businesses, requires coor- bloom that happens 1 month early in the ‘90 com- dination between individual actions (e.g., farmers) pared to ‘70 in the large Swedish lakes (Weyhenmey- and public policies (e.g., water management), and Climate change will alter the hydromorphological er, 2001). requires political will and the presence of adequate conditions of the lakes; the magnitude of change The impacts of climate change on lake areas will institutional structures (e.g., risk management). induced by climate change is still relatively small in cause, in turn, impacts on human activities, such as Adaptation of a lake ecosystem to climate change comparison with the impact of anthropogenic land fisheries, water supply, tourism, hydropower, naviga- can be either natural (resilience) or there may be op- use, but, in future, climate change will may cause tion. tions for adapting human activities. Among them significant change in hydrology and, at the same Higher water temperatures lead to the progressive there are those named «hard», i.e. infrastructure and time, impose land use changes in catchments. reduction of thermal habitats for fish, which will move technology, characterized by long times and more In lakes, hydrological change are expressed in terms toward of an habitat more suitable. A reduction in investments, and those named «soft», that is non- of more dynamic fluctuations as well as overall rainfall can lead to water deficit stress, and conse- structural systems based on optimization of resource changes in water level and their impacts on eutrophi- quently lead to issues related to water supply in agri- management and risk prevention. For example the cation (Kernan et al., 2010). culture, navigation and port management. adaptation options for water supply from one hand Climate warming caused changes in the thermal re- In addition, extraordinary weather events can cause could be the water reuse, the water transport, the gime of lake waters and in the course of glacial phe- damage in terms of erosion of soil, carrying nutrients building of dams and water storage (hard adapta- nomena in the northern hemisphere (Magnuson et waters and sediments of lakes, damage them. A tion), and from the other hand the demand manage- al., 2000) including among others: most extraordinary weather event could also lead to ment and the changing dam operational rules (soft • earlier water warming in spring (Gronskaya et al., damage forestry located on the shores of lakes, es- adaptation). 2001) pecially in parks or other areas of great natural value. In general adaptation can be efficient to reduce • increase in water temperature both on the surface The lakes in the Alps are used in particular for tour- (some) climate change impacts. and at deeper levels in lakes (Endoh et al., 1999) ism and recreation; on one hand longer summers will But adaptation is not an easy task: in several eco- • lengthening of the period in summer when lake wa- lead to greater use of tourist facilities, from the other nomic sectors, climate change should already be ter temperatures exceed 10°C (Jarvet, 2000); hand will have to pay more attention to water quality, included in decision-making frameworks, especially • shortening of periods with ice cover and decrease and the diffusion of invasive species. in its thickness (Todd and Mackay, 2003) where infrastructures are being constructed. Because of uncertainty, inadequate adaptation strat- egy can worsen the situation. Innovative strategies that improve robustness to climate change situation could be proposed. Soft adaptation strategies are often better able to manage uncertainty than hard adaptation strategies. Actually, soft adaptation strategies should be considered very seriously and be the topic of more research, as, responding to needs of local authority, imply environmental benefits, even on a large scale, creating significant synergies with the environmental sustainability policies. These forms of adaptation, if on the one hand are more easily achievable, require the formation of an active social and cultural context, together with the capacity of governance.

6 7 Residence time: the average length of time that wa- temperature, but can be sensible to the seasonal possible future lake physics. In a second step, the ter stays in a lake. changes on long-times. In order to understand better model was forced by various climate scenarios. Air Guide Fill up time: the time to fill the empty lake. the phytoplankton sensitivity to climate change, two temperature, air humidity, wind speed, and cloud Trophic state of the lake: the degree of fertility of a models have been applied: a homogeneus and a two cover were changed to get an idea of the lakes sen- lake. layer lake ecosystem model. The models are applied sitivity to a climate change. The results show a high to consult The images shows the location of the lake in the to the following lakes: Lake Annecy, Lake Viverone, sensitivity of circulation patterns in a lake. This model whole alpine space and the position of monitoring Lake Sirio, Lake Avigliana Grande, Lake Caldonazzo, has been applied to Lake Viverone, Lake Constance point in the lake and of the meteorological station, Lake Levico and Lake Wörthersee. and Lake Wörthersee. lake sheets both used for the analysis of climate change in the lake area. In lake sheets, you can find a series of information Hydrodynamic model Hydrological modelling about the lake, its own evolution and climatic scenarios for the area interested by the lake. The aggre- Climate Driven Scenarios For a better understanding of the climate change in- and isotope investigations gate information resulting from the statistical analysis duced shifts of physical properties in an Alpine lake a applied to collected data. Scenarios for precipitation and temperature from hydrodynamic, one-dimensional, and vertical model The water balance of lakes and the residence time Therefore, for further information, refer to the other 2001 to 2050 (reference period: 1961 – 2000) in the was applied to alpine lakes. First, the model was cali- of lake water are very sensitive to changes of the detailed publications or to specific publications pu- area interested by the lake, calculated using the E- brated with measured meteorological data and the meteorological parameters air temperature and pre- blished by competent authorities. obs dataset and the Multimodel SuperEnsemble respective water temperature measurements. This cipitation. Technique (Air temperature scenarios) and the Pro- guaranteed a close to reality mathematic lake des- Semi-distributed conceptual rainfall-runoff models Lakes are in geographical location order, from west babilistic Multimodel SuperEnsemble Dressing (Pre- cription and a necessary condition for projections of have been used at 3 Carinthian lakes with the aim to east. cipitation scenarios). Each sheet contains following sections: Past trends The lake Information about the main past trend climate driven This section includes a short description of the lakes, (air temperature and precipitation) and the main past main morphometric and hydrologic data featuring trend of water temperature lake parameter, showing the lake (Identity card) and its catchment basin. linear regression lines and their gradients in winter (mean of December, January and February months) Catchment area: river basin surface expressed in and in summer (mean of June, July and August square km. In case of reservoirs and if data are avai- months), except for water temperature parameter of lable, the connected basin area is indicated next to Trentino and Austrian lakes, for which this analysis natural basin dimensions. has been made using monthly data. Lake area: lake surface expressed in square km. Maximal depth: maximal lake depth expressed in m. Average depth: average lake depth expressed in m Ecological Model and calculated as the lake volume divided by its surface area. The responses of phytoplankton and zooplankton Volume: lake volume expressed in millions of cubic communities to anthropogenic pressures frequently meters. provide the most visible indication of a long term to simulate past changes and develop scenarios of years for Klopeiner See (lakes to which this survey Average altitude: lake average altitude expressed in change in water quality. The plankton community the lake volume renewal depending on land use and has been applied). The hydrological model in combi- meters above sea level. is well buffered against the sudden fluctuations of climatic conditions and of the lake evaporation. nation with isotope investigations represents a very The application of environmental isotopes gives the useful tool to estimate changes of the lake water unique possibility to get direct insights into water dy- renewal and fill up time as consequence of environ- namics and circulation behaviour of lakes. The envi- mental (climate, land use) changes and to unders- ronmental stable isotopes Oxygen-18 and Deuterium tand better the circulation behaviour in lakes. have been used to deliver information about the origin of water, mixing and evaporation processes in the lakes. Furthermore they support the modelling activi- Change in water ties by the detection of losses from lakes to springs or inflows from groundwater. temperature and water The radioactive isotope Tritium as remnant in precipitation from the atmospheric bomb tests in the 60ies circulation and 70ies of the last century in combination with its decay to Helium was used to determine the mean Detailed investigation on surface water temperature residence time of lake water in the deepest parts. and development of temperature stratification, ap- The results gave a mean residence time of 9.5 years plied to Austrian lakes (Wörthersee, Klopeiner See, for Wörthersee, 1.5 years for Ossiacher See and 6.8 Ossiacher See). 8 9 Past trend Water temperature

Summer (JJA) Winter (DJF)

Bottom 7,5 25 Surface 8 Lineare (Bottom ) Bottom Lineare (Surface ) Surface 7 7,5 Lineare (Bottom ) Lineare (Surface ) 20 7 6,5

6,5 6 15 °C °C (Surface) °C (Bottom) 6 Lake Annecy 5,5 5,5 10

5 The lake 5 4,5 5 4,5 2001 2004 2007 2001 2004 2007 1999 2000 2003 2005 2006 2008 2009 1999 2000 2003 2005 2006 2008 2002 Lake Annecy (Haute-Savoie, 74) is the second French downstream from the lake. The nutrient enrichment 2002 largest natural lake. In the late 1950s, as a result of period was therefore relatively limited and the lake YEARS YEARS the constantly increasing pressure of human activ- is now considered to be oligotrophic. It is very clear, Period: 1999 - 2010 ity, Lake Annecy, along with many other sub-alpine its water contains good oxygen levels and there is Rate: °C per decade lakes, experienced the early stages of eutrophica- a good variety and balance of the various biologi- JJA DJF tion. However, in 1962, local representatives decided cal groups (phytoplankton, zooplankton, fish). In fact, Surface + 0.009 + 0,13 to start the construction of a vast network of drains the water quality is so good that the water can be Bottom + 0,12 + 0,05 to divert waste water away from the catchment ba- used as drinking water for most of the surrounding sin. The polluted water was treated and discharged towns (30,000 m3 are pumped out every day). Precipitation

Identity Card Summer (JJA) Winter (DJF) Catchment area 270 km² 600 550 550 500

Lake area 27 km² 500 450

Maximal depth 65 m 450 400 Average depth 41 m 400 350 mm Volume 1124,5 m3 x 106 mm 350 300 Average altitude 447 m a.s.l. 300 250 250 200

Residence time 3,8 years 200 150 3 Inflow - m /y 150 100 3 Meteo monitoring 2004 2007 1994 1997 2001 1991 2004 2007 1994 1997 2001 1991 2003 2005 2006 2008 2009 2010 1993 1995 1996 1998 1999 2000 1990 2003 2005 2006 2008 2009 1993 1995 1996 1998 1999 2000 1990 2002 1992 2002 Outflow 8 m /y station 1992 YEARS YEARS Trophic state of the lake Oligotrophic Water monitoring station Period: 1999 - 2010 Cran – Gevrier Station Rate: mm per decade JJA DJF Climate driven scenarios 2001 - 2050 + 9,4 - 3,80

Precipitation Temperature

10,5

10 1900 9,5

1700 9 °c

1500 8,5 mm

1300 8

1100 7,5

900 7 2001 2011 2021 2031 2041 2001 2007 2011 2017 2021 2027 2031 2037 2041 2047 2003 2005 2007 2009 2013 2015 2017 2019 2023 2025 2027 2029 2033 2035 2037 2039 2043 2045 2047 2049 2003 2005 2009 2013 2015 2019 2023 2025 2029 2033 2035 2039 2043 2045 2049

YEARS YEARS 2020 2030 2040 2050 Precipitation scenarios (mm) - 116 - 73,2 - 118 - 27 Air temperature scenarios (°C) + 0,14 + 0,51 + 0,92 + 1,25 10 11 Air temperature Ecological model

Summer (JJA) Winter (DJF) Homogeneous model

Mean Monthly Min Air temperature Mean Monthly Min Air temperature 1,0 16,0

0,0 15,0

-1,0 14,0

-2,0 13,0 °C °C

-3,0 12,0

-4,0 11,0

-5,0 10,0 1984 1994 2004 1984 1994 2004 1976 1978 1980 1986 1988 1990 1996 1998 2000 2006 2008 2010 1976 1978 1980 1986 1988 1990 1996 1998 2000 2006 2008 2010 1982 1992 2002 1982 1992 2002

YEARS YEARS

Mean Monthly Max Air temperature Mean Monthly Max Air temperature 10,0 34,0

9,0 32,0

8,0 30,0 Two layer model 7,0 28,0

6,0 °C °C 26,0 5,0 24,0 4,0

3,0 22,0

2,0 20,0 1984 1994 2004 1976 1978 1980 1986 1988 1990 1996 1998 2000 2006 2008 2010 1984 1994 2004 1982 1992 2002 1976 1978 1980 1986 1988 1990 1996 1998 2000 2006 2008 2010 1982 1992 2002 YEARS YEARS

Period: 1976 - 2010 Cran – Gevrier Station Rate: °C per decade JJA DJF Min Air Temperature (°C) + 0,5 + 0,05 Max Air Temperature (°C) + 0,9 + 0,40

Source: Total phosphorus concentration in µg-P/L from measure- Comparison between measured total phytoplankton con- SILA INRA, for lake monitoring data ments at a depth of 10 meters (solid points and concentration (solid points and connecting line) and the phy- Meteo-France - SILA, for meteorogical data necting line) from the homogeneous model (upper panel, toplankton concentration produced by the homogeneous dashed line) and from the two-layer model (lower panel, model (upper panel, dashed line) and from the two layer dashed line). model (lower panel, dashed line). Concentrations are in µg- C/L assuming a carbon-to-biomass ratio R=0.2.

Effects of temperature and environmental changes

Left panel: comparison between the two-layer model phytoplankton concentration in the upper layer for faster winter turbulent -1 exchange between the two layers, µ0=0.2 day , and warmer summer and winter conditions (+ 3 °C) (solid line) and current conditions (dashed line). Right panel: the same for zooplankton concentration. Concentrations are in µg-C/L. Warmer conditions and more intense winter turbulent exchange lead to a decrease in the maximum phytoplankton concentration at the bloom and to higher concentrations in the inter-bloom period, while the zooplankton concentration is almost unaffected in the peak and it is increased in the inter-bloom periods. In addition, there is a significant increase in the fish compartments. 12 13 Past trend Water temperature

Summer (JJA) Winter (DJF)

Surface 8 Surface Bottom Bottom Lineare (Surface ) 7,5 Lineare (Surface ) 30 Lineare (Bottom) 8 Lineare (Bottom ) 7 7,5 25 6,5 7 6 20 6,5 °C 5,5 6 °C (Surface) 15 5,5 °C (Bottom) 5

5 4,5 Lake Avigliana Grande 10 4,5 4

5 4 3,5 2001 2001 2004 2007 2004 2007 2003 2005 2006 2003 2005 2006 2008 2009 2010 2002 The lake 2002 YEARS * 2005: estimated data YEARS Lake Avigliana Grande is located within the Parco is remarkably interesting for historical and naturalis- Naturale Laghi di Avigliana. Tourism has significantly tic reasons: north-west of the lake, there is Mareschi Period: 2001 - 2010 developed in the area around the lakes - an area that area, the most wester Italian wetland. Rate: °C per year JJA DJF Surface + 0.02 + 0,16 Bottom + 0,03 + 0,12 Identity Card Catchment area 11,5 km² Lake area 0,89 km² Precipitation Maximal depth 26 m Average depth 19,5 m Summer (JJA) Winter (DJF) Volume 17,2 m3 x 106 Average altitude 346 m a.s.l. 600 350

300 Residence time 2,3 years 500 3 Inflow - m /y 250 400 3 Meteo monitoring Outflow - m /y station 200 300 mm Trophic state of the lake Eutrophic Water monitoring mm 150 station 200 100

100 50

0 0 1991 1991 1994 1997 2001 1994 1997 2001 2004 2007 2004 2007 1993 1995 1996 1998 1999 2000 1993 1995 1996 1998 1999 2000 2003 2005 2006 2008 2009 2010 2003 2005 2006 2008 2009 2010 1992 1992 2002 2002 Climate driven scenarios 2001 - 2050 years years

Precipitation Temperature Period: 1991 - 2011 Avigliana Station

14 Rate: °C per decade 1500

13,5 JJA DJF 1300 + 17,64 - 2,18 13 1100 12,5 mm °C

900 12

700 11,5

500 11 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049

YEARS YEARS

2020 2030 2040 2050 Precipitation scenarios (mm) + 31,6 + 11,7 - 4 - 70 Air temperature scenarios (°C) + 0,42 + 0,6 + 0,96 + 1,3

14 15 Air temperature Ecological model

Summer (JJA) Winter (DJF) Homogeneous model

Mean Monthly Air Temperature Mean Monthly Air Temperature 4,5 23 4 22,5 3,5 22 3 21,5

°C 2,5 21 °C 2 20,5

20 1,5

19,5 1

19 0,5 1991 1994 1997 2001 2004 2007 2011 1993 1995 1996 1998 1999 2000 2003 2005 2006 2008 2009 2010 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 1992 2002

YEARS YEARS

Period: 1991 - 2011 Avigliana Station Rate: °C per decade JJA DJF - 0,18 + 0,43 Two layer model

Total phosphorus concentration in µg-P/L from measure- Measured chlorophycea concentrations (solid points and ments at a depth of 10 meters (solid points and connect- connecting line) and phytoplankton concentration produced ing line) and from the homogeneous model (upper panel, by the homogeneous model (upper panel, dashed line) and dashed line) and from the two-layer model (lower panel, by the two-layer model (lower panel, dashed line). Con- dashed line). centrations are in μg-C/L using a carbon-to-biomass ratio R=0.2 and assuming cells with size 10 μm.

Effects of temperature and environmental changes

Left panel: comparison between the two-layer model phytoplankton concentration in the upper layer for faster winter turbulent -1 exchange between the two layers, μ0=0.2 day , and warmer summer and winter conditions (+ 3 °C) (solid line) and current conditions (dashed line). Right panel: the same for zooplankton concentration. Concentrations are in µg-C/L. Warmer conditions and more intense winter turbulent exchange lead to a very slight anticipation of the bloom, with a smaller maximum concentration but with a significantly longer period of high phytoplankton concentrations.

16 17 Past trend Water temperature

Summer (JJA) Winter (DJF)

30 Surface Bottom 8 Lineare (Surface ) Surface Lineare (Bottom ) Bottom 25 7,5 Lineare (Surface ) Lineare (Bottom ) 7 20 6,5

°C 15 6 °C 5,5 10 Lake Sirio 5 5 4,5

The lake 0 4 2001 2004 2007 2001 2004 2007 2003 2005 2006 2003 2005 2006 2008 2002 2002 The Lake Sirio is located within the SIC (Site of river basin of Baltea. The beauty of the place is the YEARS YEARS Community Importance) «Lakes d’Ivrea,» in the main peculiarity of the lake: it is nestled on a hillside Period: 2001 - 2007 Alpine biogeographical region straddling the towns modeled in the Pleistocene from Glacier Balteo Rate: °C per year of Chiaverano and Ivrea, in northern part of the whose left lateral moraine, Serra. JJA DJF moraine Amphitheatre of Ivrea on left bank of the Surface + 0.12 + 0,08 Bottom + 0,03 + 0,08

Identity Card Precipitation Catchment area 1,4 km² Lake area 0,29 km² Summer (JJA) Winter (DJF) Maximal depth 43,5 m Average depth 18 m 300 3 6 600 Volume 5,24 m x 10 250 Average altitude 266 m a.s.l. 550 500 200 Residence time 5,7 years 450 3 Inflow - m /y 400 150 mm 350 Outflow - m3/y mm 300 100 Trophic state of the lake meso-eutrophic Meteo monitoring 250 station 200 50 Water monitoring 150 station 100 0 2001 1994 2004 2007 2004 2007 1994 1997 2001 1991 2003 2005 2006 2008 2009 2010 1993 1996 1998 1988 1989 1990 1995 1996 1999 2003 2005 2008 2009 2010 1988 1989 1990 2002 1992 2002 1992

YEARS YEARS

Period: 1988 - 2010 Climate driven scenarios 2001 - 2050 Borgofranco d’Ivrea station Rate: mm per decade Precipitation Temperature JJA DJF + 30,0 + 16,5

1900 12,5 1700 12 1500 11,5 1300 mm

°C 11 1100

10,5 900

700 10

500 9,5 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 2001 2004 2007 2010 2013 2016 2019 2022 2025 2028 2031 2034 2037 2040 2043 2046 2049

YEARS YEARS

2020 2030 2040 2050 Precipitation scenarios (mm) + 77,6 - 34,2 - 85,2 - 85 Air temperature scenarios (°C) + 0,38 + 0,63 + 1,04 + 1,35

18 19 Air temperature Ecological model

Summer (JJA) Winter (DJF) Homogeneous model

26 7

25 6

24 5

23 4 °C °C 22 3

21 2

20 1

19 0 1991 1994 1997 2001 2004 2007 1991 1994 1997 2001 2004 2007 1988 1989 1990 1993 1995 1996 1998 1999 2000 2003 2005 2006 2008 2009 2010 1988 1989 1990 1993 1995 1996 1998 1999 2000 2003 2005 2006 2008 2009 2010 1992 2002 1992 2002

YEARS YEARS

Period: 1991 - 2011 Borgofranco d’Ivrea station Rate: °C per decade JJA DJF + 0,73 - 0,15 Two layer model

Total phosphorus concentration in µg-P/L from measure- Measured chlorophycea concentrations (solid points and ments at a depth of 10 meters (solid points and connect- connecting line) and phytoplankton concentration produced ing line) and from the homogeneous model (upper panel, by the homogeneous model (upper panel, dashed line) and dashed line) and from the two-layer model (lower panel, by the two-layer model (lower panel, dashed line). Concen- dashed line). trations are in μg-C/L assuming a carbon-to-biomass ratio R=0.2. The concentration was derived from the number concentration assuming an equivalent cell radius of 10 μm.

Effects of temperature and environmental changes

20 21 Past trend Water temperature

Summer (JJA) Winter (DJF)

26,0 7,0 Surface Bottom Lineare (Surface ) 6,5 Surface Lineare (Bottom ) 25,0 6,5 Bottom Lineare (Surface ) 6,0 Lineare (Bottom )

24,0 6,0 5,5

23,0 5,5 5,0 °C °C (Bottom) Lake Viverone °C (Surface) 4,5 22,0 5,0 The lake 4,0 21,0 4,5 3,5 The Lake Viverone (or d’Azeglio) is a lake of glacial town of Ivrea. It is third largest lake in the Piedmont origin, situated between the provinces of Turin and Region. 20,0 4,0 3,0 2001 2007 2007 2003 2004 2005 2006 2008 2009 2003 2004 2005 2006 2008 2009 2010 2002 Vercelli, Piedmont region (Italy), south east of the 2002 YEARS YEARS

Period: 2001 - 2007 Rate: °C per year Identity Card Meteo monitoring station JJA DJF Water monitoring Catchment area 49,3 km² station Surface + 0.67 + 0,68 Lake area 5,3 km² Bottom + 0,11 + 0,08 Maximal depth 49 m Average depth 27 m Volume 149 m3 x 106 Average altitude 449 m a.s.l. Precipitation Residence time 3,6 years Inflow - m3/y Summer (JJA) Winter (DJF) Outflow - m3/y Trophic state of the lake Eutrophic 400 350 350 300

250 300

200 250 mm mm 150 200 Climate driven scenarios 2001 - 2050 100 150 50

Precipitation Temperature 100 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

1900 12,5 YEARS YEARS 1700 12 Period: 1988 - 2010 1500 11,5 Piverone station 1300 Rate: mm per decade mm

°C 11 1100 JJA DJF 10,5 900 - 7,25 + 3,74 700 10

YEARS YEARS

2020 2030 2040 2050 Precipitation scenarios (mm) + 77,6 - 34,2 - 85,2 - 85 Air temperature scenarios (°C) + 0,38 + 0,63 + 1,04 + 1,35

22 23 Air temperature Ecological model

Summer (JJA) Winter (DJF) Homogeneous model

-3

36 -4

35 -5 34 °C 33 °C -6

32 -7 31

30 -8 2001 1994 1997 2001 2004 2007 2004 2007 1994 1997 1995 1996 1998 1999 2000 2003 2005 2006 2008 2009 2010 2003 2005 2006 2008 2009 2010 1993 1995 1996 1998 1999 2000 2002 2002

YEARS YEARS

Period: 1991 - 2011 Two layer model Piverone station Rate: °C per decade JJA DJF + 0,66 - 0,51

Total Phosphorus concentration in μg-P/L from measure- Comparison between measured chlorophycea concentra- ments at a depth of 10 meters in Lake Viverone (solid line) tions (solid line), assuming cells with approximate equiva- and from the homogeneous model (dashed line, upper lent radius of 15 μm, and the phytoplankton concentration panel) and from the two layer model (dashed line, lower produced by the homogeneous model (dashed line, upper panel). panel) and by the two-layer model (dasched line, lower panel). Concentrations are in μg-C/L assuming a carbon-to- biomass ratio R=0.2.

Effects of temperature and environmental changes

Comparison between the two-layer model dynamics for warmer conditions (solid lines) and model dynamics for current conditions (dashed lines). Left panel: phytoplankton concentrations in the upper layer; right panel: zooplankton concentration. All concentrations are expressed in μg-C/L. Warmer conditions lead to an anticipation of the phytoplankton and of the zooplankton blooms, and a net increase of the phytoplankton biomass. Interestingly, a similar result is obtained also when increasing only the winter temperature and, to slightly lesser extent, only the summer temperature.

24 25 Thermodynamic model

Temperatur scenarios Wind speed scenarios Air humidity scenarios Changes of the mean Changes of the mean Changes of the mean air temperature in [°C]: wind speed in [m/s]: air humidity in % of rF: 0 4 - 3 - 0.75 0.5 2.5 - 10 - 3 1 6 1 5 - 4 - 0.5 1 3 - 8 - 2 2 8 2 - 1 - 5 - 0.25 1.5 3.5 - 6 - 1 3 10 3 - 2 0 2 - 4 0 4

Surface water temperature

30 T[°C] 30 T[°C] 35 [°C] T[°C] +5 25 25 30 +4 20 20 25 +3 20 +2 15 15 +1 15 [m/s] 0 10 10 +10% -1.5 10 -1 to 5 +3 5 5 -2 -10% 0 -3 0 0 -4 -5 t t t v v v pt pt pt b b b ne ly -5 ne ly ne ly Apr Aug Apr Aug Apr Aug Jan Fe Mar May Ju Ju Se Oc No Dec Jan Fe Mar May Ju Ju Se Oc No Dec Jan Fe Mar May Ju Ju Se Oc No Dec

Mean mixing index(1)

0.4 Ind[-] 0.35 Ind[-] 0.4 Ind[-]

0.3 0.3 0.3

0.2 0.2 0.25 0.1 0.1

0 0.2 0 -5 -4 -3 -2 -1 012345 -1 0123 -10 -8 -6 -4 -2 02468 10 Change of mean temperature [°C] Change of mean wind speed [m/s] Change of mean air humidity [%]

Evaporation

800 E[mm] 750 E[mm] 600 E[mm] 700 590 600 650 600 580 400 550 570 200 500 560 450 0 400 550 -5 -4 -3 -2 -1 012345 -1 0123 -10 -8 -6 -4 -2 02468 10 Change of air temperature [°C] Change of mean wind speed [m/s] Change of air humidity [%]

If the mean air temperature increases the surface wa- results in a less mixing intensity.The higher the wind ter increases approximately with the same amount. speed the higher is the amount of evaporation. A Increasing temperature leads to a decline of circula- Change in the mean air humidity has fewer effects to tion intensity. Lower air temperatures have no effect evaporation from the lake’s surface. onto the mixing. But a decline in mean wind speed

Summer (JJA) Winter (DJF)

23 Surface 6 Bottom Lineare (Surface ) 7 21 Bottom Lineare (Bottom ) Surface 5,5 19 6,5 Lineare (Bottom ) Lineare (Surface )

17 6 5 15 5,5

13 °C °C (Surface) °C (Bottom) 4,5 5 Lake Constance 11 4,5 9 4 The lake 7 4

5 3,5 3,5 Lake Constance is a typical glacier formed perialpine Lake Constance is situated in the Alpine region, 1964 1974 1984 1994 2004 1964 1974 1984 1994 2004

oligotrophic lake. It consists of two separate basins. resulting in high water levels in summer (due to YEARS YEARS The outflow of the large and deep Upper Lake drains snow melting) and low water levels in winter. Lake at Konstanz into the smaller and more shallow Lower Constance provides more than 4 million people with Period: 2001 - 2007 Lake. Most of the hydrological catchment area of drinking water and is most attractive for tourism. Rate: °C per year JJA DJF Surface + 0.54 + 0,19 Bottom + 0,06 + 0,10 Identity Card Catchment area 11487 km² Lake area 535 km² Precipitation Maximal depth 254 m Average depth 90 m Summer (JJA) Winter (DJF) Volume 48,4 m3 x 106 Average altitude 395 m a.s.l. 950 500 850 450 Residence time 4,5 years 400 3 750 Inflow - m /y 350 3 Meteo monitoring 650 300 Outflow - m /y station 550 250 mm Trophic state of the lake Oligotrophic mm Water monitoring 200 station 450 150 350 100 250 50 150 0

Climate driven scenarios 2001 - 2050 187 4 188 0 188 6 189 2 189 8 190 4 191 0 191 6 192 2 192 8 193 4 194 0 194 6 195 2 195 8 196 4 197 0 197 6 198 2 198 8 199 4 200 0 200 6 187 4 188 0 188 6 189 2 189 8 190 4 191 0 191 6 192 2 192 8 193 4 194 0 194 6 195 2 195 8 196 4 197 0 197 6 198 2 198 8 199 4 200 0 200 6 YEARS YEARS

Precipitation Temperature Period: 1874 - 2008

1800 Histalp project – Bregenz station 11 1700 Rate: mm per decade 10,5 1600 JJA DJF 10 1500 - 0,15 + 4,20 9,5 1400

°C 9 1300 °C 8,5 1200

1100 8

1000 7,5

900 7 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049

YEARS YEARS

2020 2030 2040 2050 Precipitation scenarios (mm) - 94,4 + 15,3 + 13,2 + 102 Air temperature scenarios (°C) + 0,28 + 0,6 + 0,96 + 1,15

28 29 Air temperature Thermodynamic model

Summer (JJA) Winter (DJF) Temperatur scenarios Wind speed scenarios Air humidity scenarios

22 Changes of the mean Changes of the mean Changes of the mean 5 air temperature in [°C]: wind speed in [m/s]: air humidity in % of rF: 21 4 Trend(1) 3 - 2 - 1.5 0.5 2.5 - 10 - 3 1 6 20 3 2 0 4 - 3 - 1.0 1.0 3.0 - 8 - 2 2 8 19 1 1 5 - 4 - 0.5 1.5 - 6 - 1 3 10

°C °C 0 18 2 - 1 0 2.0 - 4 0 4 Trend(2) -1 17 -2 Surface water temperature -3 16 -4 [°C] 15 -5 30 T[°C] +5 25 T[°C] 25 T[°C] +4 25 +3 1870 1876 1882 1888 1894 1900 1906 1912 1918 1924 1930 1936 1942 1948 1954 1960 1966 1972 1978 1984 1990 1996 2002 2008 1870 1876 1882 1888 1894 1900 1906 1912 1918 1924 1930 1936 1942 1948 1954 1960 1966 1972 1978 1984 1990 1996 2002 2008 20 20 +2 YEARS YEARS 20 +1 15 15 15 0 [m/s] Period: 1870 - 2008 Trend 10 -1.5 10 +10% 10 -1 Histalp project – Bregenz station to -2 5 +3 5 Rate: °C per decade 5 -3 -10% JJA DJF 0 -4 0 0 t t t v v v pt pt pt b b b ne ly ne ly + 0,08 - 0,18 ne ly Apr Aug Apr Aug Apr Aug Jan Fe Mar May Ju Ju Se Oc No Dec Jan Fe Mar May Ju Ju Se Oc No Dec Jan Fe Mar May Ju Ju Se Oc No Dec

Mean mixing index(3)

2 Ind[-] 2 Ind[-] 1.2 Ind[-] 1 1.5 1.5 0.8

1 1 0.6

0.4 trend scenario 0.5 0.5 0.2 trend scenario 0 0 0 -5 -4 -3 -2 -1 012345 -2 -1 0123 -10 -8 -6 -4 -2 02468 10 Change of mean temperature [°C] Change of mean wind speed [m/s] Change of mean air humidity [%]

Evaporation

650 E[mm] 700 E[mm] 600 E[mm] 600 650 580 600 550 trend scenario 560 550 500 540 500 trend scenario

450 450 520

400 400 500 -5 -4 -3 -2 -1 012345 -2 -1 0123 -10 -8 -6 -4 -2 02468 10 Change of air humidity [%] Change of mean wind speed [m/s] Change of air humidity [%]

If the mean air temperature increases the surface wa- temperatures increase the circulation intensity. The ter increases approximately with the same amount. higher the wind speed and/or the dryer the air, the Increasing temperature and/or lower wind speeds higher is the amount of evaporation. lead to a decline of circulation intensity. Lower air

(1) The Trend scenario for the air temperature is a linear continuation of the trend that was observed in the past decades. (2) The air humidity scenario for the air humidity is a continuation of the increasing amplitude in the winter/summer changes (3) This mixing index describes the vertical circulation and mixing intensity in winter/spring. The higher the index, the more intensive is the mixing. 0 means no exchange between surface and bottom water layers. Maximum at Lake Constance: 1.54. 30 31 Climate driven scenarios 2001 - 2050

Precipitation Temperature

1600 10 1500 9,5 1400 9 1300 8,5 1200

mm 8 1100 °C 7,5 1000

900 7

800 6,5

700 6 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049

Lake Caldonazzo YEARS YEARS

The lake 2020 2030 2040 2050 Precipitation scenarios (mm) - 51,6 - 66,6 - 102,4 - 52 Lake Caldonazzo is the largest lake entirely within the or three brooks which get down from the Mountain Air temperature scenarios (°C) + 0,24 + 0,63 + 1,04 + 1,35 provincial boundary of Trentino. Lake Caldonazzo Marzola and others of less flow from the Tenna constitutes a tourist attraction with its various hill. A big spring is born in the north-eastern part beaches (Caldonazzo, Calceranica, S.Cristoforo, of the lake, at an altitude of 463 meters; it can be etc..) and its pleasant landscape: in the background considered as the source of the lake. There are a Past trend it is possible to admire the peaks of the Brenta few artificial tributaries. One gets into the lake at San Dolomites. Situated in Valsugana, far only 15 Km from Cristoforo, another comes from the Fersina, and the Water temperature Trento, it is almost entirely encircled by mountains; Merdàr brook, deviated by man. In the eastern part the Tenna hill separates it from the near lake Levico. of the lake there is only an emissary that gives origine Month of March (mean) July - August Lake Caldonazzo originated from a blockage. The to the Brenta river together with the emissary of the perennial tributary of the lake are Rio Màndola, two lake Levico. Month of March July - August 10 30 9 Surface Bottom 8 Lineare (Surface ) 9 25 Lineare (Bottom )

Identity Card 7 8 20

°C 7 15 °C Catchment area 49,3 km² °C 6

Lake area 5,3 km² 5 6 10 Maximal depth 49 m Average depth 27 m 4 5 5

3 6 3 4 0 Volume 149 m x 10 08/08/00 30/07/01 20/08/02 25/08/03 22/07/04 17/08/05 07/08/06 18/07/07 15/07/08 12/08/09 Bottom 5,6 6,7 6 6,67 5,6 5,78 6,16 6,64 7,8 5,88 mar-04 mar-04 mar-07 mar-01 mar-01 mar-03 mar-03 mar-05 mar-06 mar-08 mar-09 mar-00 mar-00 Average altitude 449 m a.s.l. mar-02 Surface 21,9 22,9 21,3 25,73 23,4 22,04 23,12 22,69 23,5 24,17 Residence time 3,6 years MONTHS Inflow - m3/y 3 Meteo monitoring Period: 2000 - 2009 Outflow - m /y station Rate: °C per month Trophic state of the lake mesotrophic Water monitoring station Month of March July - August Surface + 0,007 + 0,13 Bottom + 0,01 + 0,07

32 33 Precipitation Ecological model

Summer (JJA) Winter (DJF) Homogeneous model

500 500

450 450 400 400 350 350 300 300 250 mm mm

250 200 150 200 100 150 50 100 0 1864 1894 1924 1954 1984 1864 1894 1924 1954 1984 1870 1876 1888 1900 1906 1918 1930 1936 1948 1960 1966 1978 1990 1996 1870 1876 1888 1900 1906 1918 1930 1936 1948 1960 1966 1978 1990 1996 1882 1912 1942 1972 2002 1882 1912 1942 1972 2002

YEARS YEARS

Period: 1991 - 2011 Histalp project Trento station Rate: mm per decade JJA DJF - 1,75 - 0,92 Two layer model

Air temperature

Summer (JJA) Winter (DJF)

26 5

25 4

24 3

23 2

22 1 °C °C

21 0

20 -1

19 -2

18 -3 Total phosphorus concentration in µg-P/L from measure- Measured chlorophycea concentrations (solid points and

1816 1824 1832 1840 1848 1856 1864 1872 1880 1888 1896 1904 1912 1920 1928 1936 1944 1952 1960 1968 1976 1984 1992 2000 1816 1824 1832 1840 1848 1856 1864 1872 1880 1888 1896 1904 1912 1920 1928 1936 1944 1952 1960 1968 1976 1984 1992 2000 ments at a depth of 10 meters (solid points and connect- connecting line) and phytoplankton concentration produced YEARS YEARS ing line) and from the homogeneous model (upper panel, by the homogeneous model (upper panel, dashed line) and dashed line) and from the two-layer model (lower panel, by the two-layer model (lower panel, dashed line). Concen- Period: 1870 - 2008 dashed line). trations are in μg-C/L assuming a carbon-to-biomass ratio R=0.2. Histalp project Trento station Rate: °C per decade JJA DJF Effects of temperature and environmental changes + 0,05 + 0,07 Since the model parameters are the same as those temperature and parameter changes as discussed used for Lake Levico, also for Lake Caldonazzo we for Lake Levico. find the same dependence of the model dynamics on

34 35 Climate driven scenarios 2001 - 2050

Precipitation Temperature

1600 10 1500 9,5 1400 9 1300 8,5 1200

mm 8 1100 °C 7,5 1000

900 7

800 6,5 Lake Levico 700 6 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 The lake YEARS YEARS 2020 2030 2040 2050 Lake Levico, situated in Valsugana (20 Km. from river Brenta which flows into Adriatic near Venetia. Precipitation scenarios (mm) - 51,6 + 66,6 - 102,4 - 52 Trento), is near the Lake Caldonazzo and separated The Lake Levico forming, owing to the blockage of Air temperature scenarios (°C) + 0,24 + 0,63 + 1,04 + 1,35 from it by the Tenna hill. the alluvial cone of Rio Maggiore and Rio Vignola, The landscape around the lake is fascinating: it is dates back to 270 A.C. This date is given by the closed in by the wooded slopes of the surrounding carbon-14 dating of a oak trunk found, still erect, on mountains and the majority of the banks are natural. the lake bottom. The only town near the lake is Levico Past trend The lake presents a fjord-shape; its tributary are the Terme, famous for its lake and the spawhich waters “Roggia’, which collects the water of the Rio Vignola, are rich in iron and arsenic minerals and have many Water temperature and the Rio Maggiore. The waters of Lake Levico therapeutic effects. It is a resort with a prestigious feeds, together with those of Lake Caldonazzo, the tourist tradition. March - April July - August

10 Identity Card 9 23 8 18 Catchment area 22 km² 7 °C

Lake area 1,1 km² 6 °C 13 5 Maximal depth 38 m 8 Average depth 11 m 4 Volume 13 m3 x 106 3 3 set-07 set-04 set-01 set-08 set-05 set-06 set-03 set-00 feb-01 feb-07 feb-04 set-02 feb-08 feb-09 feb-05 feb-06 feb-03 feb-02 mar-07 mar-07 mar-04 mar-04 mar-01 mar-01 ago-07 ago-04 ago-01 mar-08 mar-08 mar-09 mar-05 mar-05 mar-06 mar-03 mar-03 mar-00 mar-00 ago-08 ago-09 ago-05 ago-06 ago-03 ago-00 Average altitude 440 m a.s.l. ago-02

mar-02 mar-02 08/ 30/ 20/ 28/ 22/ 17/ 07/ 18/ 15/ 12/ Residence time 1,1 years 15/03 06/03 12/03 03/03 08/03 04/04 18/04 28/03 10/03 09/03 08/ 07/ 08/ 07/ 07/ 08/ 08/ 07/ 07/ 08/ 3 /00 /01 /02 /03 /04 /05 /06 /07 /08 /09 00 01 02 03 04 05 06 07 08 09 Inflow - m /y Surface 5,6 4,7 5,6 4,6 4,02 8,38 8,49 6,96 5,1 4,48 Surface (0,12 °C) 22,1 23,5 22,7 25,149 22,8 22,08 23,79 23,84 23,5 24,82 3 Meteo monitoring Outflow - m /y station Bottom 4,1 4,6 4 4,1 3,98 4,28 4,67 5,59 4,7 4,32 Bottom (0,06 °C) 5,8 5,8 5,7 5,94 5,4 5,02 5,77 5,91 7,1 6,22 Trophic state of the lake mesotrophic Water monitoring station Period: 2000 - 2009 Rate: °C per month March - April July - August Surface + 0,006 + 0,008 Bottom + 0,012 + 0,01

36 37 Precipitation Ecological model

Summer (JJA) Winter (DJF) Homogeneous model

500 500

450 450 400 400 350 350 300 300 250 mm mm

YEARS YEARS

Period: 1991 - 2011 Histalp project Trento station Rate: mm per decade JJA DJF - 1,75 - 0,92 Two layer model

Air temperature

Summer (JJA) Winter (DJF)

26 5

25 4

24 3

23 2

22 1 °C °C

21 0

20 -1

19 -2

18 -3 Total phosphorus concentration in µg-P/L from measure- Measured chlorophycea concentrations (solid points and 1816 1824 1832 1840 1848 1856 1864 1872 1880 1888 1896 1904 1912 1920 1928 1936 1944 1952 1960 1968 1976 1984 1992 2000 1816 1824 1832 1840 1848 1856 1864 1872 1880 1888 1896 1904 1912 1920 1928 1936 1944 1952 1960 1968 1976 1984 1992 2000 ments at a depth of 10 meters (solid points and connect- connecting line) and phytoplankton concentration produced YEARS YEARS ing line) and from the homogeneous model (upper panel, by the homogeneous model (upper panel, dashed line) and dashed line) and from the two-layer model (lower panel, by the two-layer model (lower panel, dashed line). Concen- Period: 1816 - 2005 dashed line). trations are in μg-C/L assuming a carbon-to-biomass ratio Histalp project Trento station R=0.2. The concentration was derived from the cell number Rate: °C per decade concentration assuming an equivalent radius of 10 μm. JJA DJF + 0,05 + 0,07 Effects of temperature and environmental changes

Left panel: comparison between the two-layer model phytoplankton concentration in the upper layer for faster winter turbulent -1 exchange between the two layers, μ0=0.2 day , and warmer summer and winter conditions (+3 °C) (solid line) and current conditions (dashed line). Right panel: the same for zooplankton concentration Warmer conditions and more intense winter turbulent exchange lead to anticipation of the phytoplankton and zooplankton blooms, with a slightly smaller maximum concentration for phytoplankton.

38 39 Climate driven scenarios 2001 - 2050

Precipitation Temperature

1300 7,5

1200 7

1100 6,5

1000 6 °c mm 900 5,5

800 5

700 4,5

Lake Ossiacher See 600 4 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049

The lake YEARS YEARS

Lake Ossiacher See is the third largest Lake of the 1950s to 2 Mill. over the past years. This led to a 2020 2030 2040 2050 the southern Austrian province Carinthia. The massive increase of domestic sewage lake influx and Precipitation scenarios (mm) - 86,4 - 20,1 - 29,6 + 5,5 (holomictic: circulation of the whole water body) lake as a consequence the Lake showed eutrophication Air temperature scenarios (°C) + 0,46 + 0,42 + 0,76 + 1,1 is divided by a swell into two basins. The maximum phenomena. The first available data are from 1931. depth of the smaller eastern part (3,9 km²) is 10 m Since 1970 a continous monitoring program exists. In and of the larger western part (6,9 km²) is 52 m. The addition the lake was a target of the Lake Restoration main tributary is the River Tiebel, that enters the lake Project from 1974 to 1978. After great investments in Past trend at the east end runs through a swampy area (6 km²) – collecting and deviating the sewage from the lake, a Bleistättter Moor. In the past the moor was drained for re- oligotrophication process started and today the Water temperature agricultural purposes. The development of tourism in lake is classified between oligo- and mesotrophic. the catchment area of Lake Ossiacher See showed During summer the temperature of the lake can Month of May Month of December an increase from 100 000 overnight stays a year in reach more than 25 °C. Bottom Surface 7,5 Lineare (Bottom) 19 Bottom 7,25 Lineare (Surface) Surface 17 Lineare (Bottom ) 7 Lineare (Surface)

Identity Card 15 6,75

Catchment area 154 km² 13 6,5 °C

°C 6,25 Lake area 10,8 km² 11 Maximal depth 52,6 m 6 9 Average depth 19,9 m 5,75 3 6 7 Volume 203 m x 10 5,5

Average altitude 501 m a.s.l. 5 5,25

Mean fill up time 2,2 years 3 5 Mean residence time - m3/y dic-04 dic-07 dic-05 dic-06 dic-08 dic-09 mag-04 mag-07 of deep lake water mag-05 mag-06 mag-08 mag-09 mag-10

3 Meteo monitoring MONTHS * 2005: data estimated MONTHS Mean annual inflow - m /y station 1971-2010 Water monitoring Mean annual out flow station Period: 2004 - 2009 1971-2010 Rate: °C per month Trophic state of the lake weakly mesotrophic Month of May Month of December Surface + 0,008 + 0,025 Bottom + 0,002 + 0,008

40 41 Precipitation Hydrological modelling and isotope investigations

Summer (JJA) Winter (DJF)

700 400

600 350

300 500

250 400 200 mm mm 300 150 200 100

100 50

0 0 1813 1822 1831 1840 1849 1858 1867 1876 1885 1894 1903 1912 1921 1930 1939 1948 1957 1966 1975 1984 1993 2002 1813 1822 1831 1840 1849 1858 1867 1876 1885 1894 1903 1912 1921 1930 1939 1948 1957 1966 1975 1984 1993 2002 YEARS YEARS

Period: 1813 - 2011 Histalp Project –- Klaghenfurt - Flugafen station Rate: mm per decade JJA DJF - 1,8 - 1,5

Investigation of the actual circulation and evaporation processes using environmental isotopes Air temperature

-8,2 Outflow (Seebach) Summer (JJA) Winter (DJF) -8,4 Inflow (Tiebel) -8,6

2,0 ] Profil OS_West 22,0 -8,8 1 -9,0 1,0 ‰ 2 21,0 [ -9,2 5 0,0 -9,4 8 10 -1,0 -9,6 20,0 VSMOW 12 15 O -9,8 -2,0

18 20 -10,0

°C 30

°C 19,0 -3,0 -10,2 40 -10,4 47 18,0 -4,0 Median -10,6 -5,0 17,0

-6,0 11/09 02/10 05/10 08/10 11/10 02/11 05/11 08/11

16,0 -7,0 Date Mean residence time in the deepest part: 1.5 years Isotpoic composition of in and outflow as tracer for water 1951 1954 1957 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 1951 1954 1957 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 YEARS YEARS movement 0 Period: 1951 – 2005

Ossiach station -10 Rate: °C per decade d-Excess [‰]

JJA DJF -20 2,50 + 0,28 + 0,38 3,50 4,50 -30 5,50

Depth (m) 6,50 7,50 -40 8,50 9,50

-50 11/09 02/10 05/10 08/10 11/10 02/11 05/11 08/11 Date

Actual circulation behaviour (Deuterium excess)

42 43 Past water balance changes and trends What could happen in the future?

Trends of lake water renewal and evaporation Trend of the filling time Due to the not definable catchment area of the main Similar changes as at Wörthersee can be expected Annual lake volume renewal and evaporation on Carinthian lakes inflow a simulation of scenarios was not possible. 14000 800 Lake volume renewal Evaporation Ossiacher See Fill Up Time (years) 13000 750 5

12000 700 4 The lake is characterized by a relatively fast circula- evaporation) and consequently an increasing fill up 11000 650

10000 600 tion, the catchment is more dominant for the water time. 3 9000 550 balance as the lake itself. The past development shows, that the lake water bal-

8000 500 2 A semi-distributed conceptual rainfall-runoff model ance is very sensitive to changes in the air tempera- Filling time (years) 7000 450 lake evaporation (mm) lake volume renewal (mm) has been used with the aim to simulate past changes ture and precipitation. Therefore similar changes as 6000 400 1 5000 350 and develop scenarios of the lake volume renewal simulated for the lake Wörthersee can be expected

4000 300 0 depending on land use and climatic conditions and with percentual reductions of the lake water renewal 1971 1976 1981 1986 1991 1996 2001 2006 2011

1971 1976 1981 1986 1991 1996 2001 2006 2011 of the lake evaporation. The graphs show significant of approx. 12 to 23%. Furthermore land use changes changes in the water balance (decrease of the lake in the catchment of the lake can have important ad- Annual lake water components 13000 Inflow Tiebel Inflow direct Precipitation direct Lake evaporation volume renewal and water level, increase of the lake ditional impacts.

LAKE VOLUME RENEWAL 11000 4% 32% 9000 64% Change in water temperature and water circulation 7000 m

Lake-m 5000 Medium water temperature at surface

Inflow Tiebel Inflow direct catchment Lake surface balance (P-E) 3000 January April August November

1000 Ossiacher See: 1990 - 2010 + 0,4 °C + 1,6 °C − 0,8 °C + 0,4 °C

-1000 Development of temperature stratification 197 0 197 5 198 0 198 5 1990 1995 200 0 200 5 201 0

Trends of inflow, outflow and water level

10 9 Inflow Tiebel (stream gauge) )

/s 8 Outflow

(m 7 w 6 5 nthly flo 4

mo 3 2 Mean 1 0 0 6 2 8 4 0 6 /7 /7 /8 /8 /9 /0 /0 12/72 01/79 12/84 01/91 12/96 01/03 12/08 01 01 01 01 01 01 01

Water level Ossiacher See 200

180

160 m)

(c 140 W 120

100 There is a clear increase in surface water tempera- Lake Ossiacher See is a holomictic (totally mixing) ture in January , April and November due to global lake. The water body is circulating down to the bot- 80 4 4 9 9 4 9 warming - later cooling in winter and earlier warm- tom of the lake. The figure shows that in mixing pe- /9 /9 /7 /8 /0 ing in spring. In summer there is a decrease in water riod the cold water from the surface is transported 01 01 01 01 01 01/89 01 /0 temperature due to higher evaporation (cooling ef- down to the bottom of the lake so the temperature is fect on water surface). lower than 4 °C.

44 45 Climate driven scenarios 2001 - 2050

Precipitation Temperature

1500 9

1400 8,5 1300 8 1200 7,5 1100 °C mm 7 1000 6,5 900

800 6 Lake Wörthersee 700 5,5 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 The lake YEARS YEARS 2020 2030 2040 2050 Lake is the largest natural and meromictic lake of the for a waste water system started. In 1968 the Precipitation scenarios (mm) - 42,6 - 21,3 - 63,6 + 24 southern Austrian province Carinthia. sewage plant that collects the waste water from the Air temperature scenarios (°C) + 0,32 + 0,6 + 0,92 + 1,2 A meromictic lake is characterized by the lack of catchment area of Lake Wörthersee went on line. oxygen and the highest nutrient in the deepest water, Since that time the water quality of lake Wörthersee which must be taken into account when assessing turned better and is now considered to be between the water quality. In the late 1950s and early 1960s oligo- and mesotrophic. Now a clear lake with good Past trend the increasing pressure of human activities caused oxygen content, rich on various biological groups the development of algal blooms, a signal for (phytoplankton, zooplankton and fish) will invite Water temperature eutrophication. At this time local representatives visitors to have a bath during summer. took action, and in 1963 the construction work Month of March Month of December

Surface 10 6 Bottom Surface Lineare (Surface) 9,5 Bottom Lineare (Bottom) Lineare (Surface ) 9 Lineare (Bottom) Identity Card 5,5 8,5 8 5 7,5 Catchment area 137 km² 7 4,5 °C 6,5 °C 6 Lake area 19,4 km² 5,5 4 5 Maximal depth 85,2 m 4,5 Average depth 41,9 m 3,5 4 3,5 Volume 1001 m3 x 106 3 3 07 04 05 06 08 09 10 ma r- ma r- ma r- ma r- ma r- ma r- ma r- dic-07 Average altitude 439 m a.s.l. dic-04 dic-05 dic-06 dic-08 dic-09 Mean fill up time 15,0 years YEARS YEARS Mean residence time m3/y 9,5 Meteo monitoring Period: 2004 - 2009 of deep lake water station Mean annual inflow m3/y Rate: °C per month 3108 Water monitoring 1971-2010 station Month of March Month of December Mean annual out flow 3504 Surface + 0,01 + 0,066 1971-2010 Bottom + 0,001 + 0,003 Trophic state of the lake between oligo- and mesotrophic

46 47 Precipitation Ecological model

Summer (JJA) Winter (DJF) Two layer model

700 400 Owing to the importance of the vertical mixing in this lake, it is necessary to consider only the two layer model. 600 350

300 500

250 400 200 mm mm 300 150 200 100

100 50

Period: 1813 - 2011 Histalp Project - Klaghenfurt - Flugafen station Rate: mm per decade Total Phosphorus concentration in μg-P/L from measure- Comparison between measured Cyanophycae concen- JJA DJF ments (solid points and connecting line) and from the tration (solid points and connecting lines) and the phyto- - 1,8 - 1,5 two-layer model (dashed line). plankton concentration produced by the two-layer model (dashed line). Concentrations are in μg-C/L assuming a carbon-to-biomass ratio R=0.2.

Air temperature Effects of temperature and environmental changes

Summer (JJA) Winter (DJF)

21 3

20 1 y = 0,007x - 3,8468

19 -1 C) (° T 18 C) (° -3 T

17 -5

16 -7

15 -9 1813 1822 1831 1840 1849 1858 1867 1876 1885 1894 1903 1912 1921 1930 1939 1948 1957 1966 1975 1984 1993 2002 1813 1822 1831 1840 1849 1858 1867 1876 1885 1894 1903 1912 1921 1930 1939 1948 1957 1966 1975 1984 1993 2002

YEARS YEARS

Period: 1813 – 2008 Left panel: comparison between the two-layer model phytoplankton concentration in the upper layer for faster winter turbulent exchange Histalp Project - Klaghenfurt - Flugafen station -1 between the two layers, μ0=0.2 day , and warmer summer and winter conditions (+3 °C) (solid line) and current conditions (dashed line). Rate: °C per decade Right panel: comparison between the two-layer model phytoplankton concentration in the upper layer for slower nutrient export from the -1 JJA DJF upper layer, ß=0.05 day (solid line), and current conditions (dashed line). Concentrations are in μg-C/L. Since in this version of the model the phytoplankton growth rate is rather insensitive to temperature, an increase in the maximum sum- + 0,05 + 0,07 mer temperature leads to almost no change in the model behavior. An increase of +3 °C in winter temperatures does slightly modify the model behavior.

48 49 Thermodynamic model Hydrological modelling and isotope investigations

Temperature scenarios Wind speed scenarios Air humidity scenarios Changes of the mean Changes of the mean Changes of the mean air temperature in [°C]: wind speed in [m/s]: air humidity in % of rF: 0 4 - 3 - 1.5 0 2 - 10 - 3 1 6 1 5 - 4 - 0.75 0.5 2.5 - 8 - 2 2 8 2 - 1 - 5 - 0.5 1 3 - 6 - 1 3 10 3 - 2 - 0.25 1.5 - 4 0 4

Surface water temperature

30 30 T[°C] T[°C] 30 [°C] T[°C] 25 25 +5 25 +4 20 20 20 +3 +2 15 15 15 +1 10 [m/s] 10 10 0 +10% -1.5 -1 to 5 5 +3 5 -2 -10% Investigation of the actual circulation and evaporation processes using environmental isotopes 0 -3 0 0 -4 -5 -5 -10 Lake Ossiachersee (profile 2) Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Lake Ossiachersee (profile 1) Lake Wörthersee (profile 1) -20 Lake Wörthersee (profile 2) Lake Wörthersee (profile 3)

(1 ) ) 18 O+9,376 Mean mixing index Lake Klopeiner See (shallow) δ -30 Lake Klopeiner See (deep) LMWL Klagenfurt (73-08) LMWL Klagenfurt 2 H=7,96* 1.4 Ind[-] 1.4 Ind[-] 1.5 Ind[-] (‰ Evaporation line δ W -40

1.2 1.2 MO

1.4 VS -50

1 1 H Evaporation trend 2 2 18 0.8 0.8 1.3 δ -60 δ H=4,89 *δ O-21,23

0.6 0.6 1.2 -70 0.4 0.4 1.1 -80 0.2 0.2 -11-10 -9 -8 -7 -6 -5 -4 -3 -2 18 0 0 1 δ OVSMOW (‰) -5 -4 -3 -2 -1 012345 -2 -1 0123 -10 -8 -6 -4 -2 02468 10 Mean residence time in the deepest part: 9.5 years Evaporation trend Change of mean temperature [°C] Change of mean wind speed [m/s] Change of mean air humidity [%] 0 18O [‰] δ VSMOW Evaporation -10

650 E[mm] 650 E[mm] 560 E[mm] -20 -6,6 -6,7 -30 600 -6,8 600 550 -40 -6,9 550 -7,0 -50 -7,1 550 540

depth [m] -7,2 500 -60 -7,3 500 530 -70 -7,4 450 -7,5 -80 -7,6 400 450 520 12/09 03/10 06/10 09/10 12/10 03/11 -5 -4 -3 -2 -1 012345 -2 -1 0123 -10 -8 -6 -4 -2 0246810 date Change of air humidity [%] Change of mean wind speed [m/s] Change of air humidity [%] Actual circulation behaviour (Oxygen- 18 contents)

(1) This mixing index describes the vertical circulation and mixing intensity in winter/spring. The higher the index, the more intensive is the mixing. 0 means no exchange between surface and bottom water layers. Maximum at Woerthersee: 1.26. 50 51 The lake is characterized by a relatively slow circulation, that the lake water balance is very sensitive to changes in Past water balance changes and trends the catchment is more dominant for the water balance as the air temperature. A temperature increase of 1.5 °C until Trends of lake water renewal and evaporation Trend of the filling time the lake itself. the decade 2040-2050 with stable precipitation produces a A semi-distributed conceptual rainfall-runoff model has mean reduction of the lake water renewal of 12%. In April- Annual lake volume renewal and evaporation Fill Up Time (years) 10000 800 20 been used with the aim to simulate past changes and de- May the reduction even reaches more than 30%. 9000 750 19 Lake volume renewal Lake evaporation velop scenarios of the lake volume renewal depending on The superposition with a 5% reduction of precipitation 8000 700 18

17 land use and climatic conditions and of the lake evapo- gives a mean reduction of 23%, in April-May even more 7000 650 ) 16 6000 600 ration. The graphs show significant changes in the water than 40%. Furthermore land use changes in the catchment mm ( 15 5000 550 balance (decrease of the lake volume renewal, increase of of the lake can have important additional impacts. oration p

a 14 4000 500 Filling time (years) the lake evaporation) and consequently an increasing fill Consequently a continuation of the increasing trend of the 13 lake ev lake volume renewal (mm) 3000 450 up time. filling time and residence time can be expected, param- 12 2000 400 11 The past development and the simulated scenarios show, eters which have an impact on the ecology of the lake. 1000 350 10 0 300

1971 1976 1981 1986 19911996200120062011 197 1 197 6 198 1 198 6 199 1 1996 2001 2006 2011 Percentual change of the lake water renewal Annual lake water components 6000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year LAKE VOLUME RENEWAL Inflow Reifnitz Inflow direct rest Precipitation direct lake evaporation Scenario 1 9 3 - 24 - 35 - 30 - 17 - 12 - 13 - 8 - 11 - 10 - 1 - 12 5000 11% 23% Scenario 2 - 2 - 8 - 33 - 44 - 41 - 31 - 26 - 26 - 19 - 22 - 20 - 11 - 23

4000 66%

3000 m

Lake-m Change in water temperature and water circulation 2000

Inflow Reifnitz Inflow direct catchment rest Lake surface balance (P-E)

1000 Medium water temperature at surface

0 January April August November

-1000 1970 1975 1980 198519901995 2000 2005 2010 Wörthersee: 1930 - 2010 + 1,2 °C + 1,5 °C + 1,2 °C + 1,0 °C

What could happen in the future? Development of temperature stratification

Meteorological scenarios

3 2 Mean = 1.4°C 1 0 -1 Delta T (°C) -2 60-ies to 00-ies Temperature -3 JAN FEB MAR APR MAY JUN JUL AUGSEP OCT NOV DEC 30

20 PET

10 Mean = 5.8 mm/mo.

0 Delta ET0 (mm) 60-ies to 00-ies -10 JAN FEB MAR APR MAY JUN JUL AUGSEP OCT NOV DEC

Scenario 1: Temp. and pot. evapotranspiration from HISTALP Scenarios 2040-2050: monthly distribution of the lake water trend (50 years) extrapolated renewal

Scenario 2: Scenario 1 with a decrease in precipitation of 5% equally distributed over the year

20 20 There is a clear increase in surface water temperature in went down to 80 meters indicated by the presence of oxy- Reference Scenario 1 DELTA HISTALP (DELTA ET0, T) 2040-2050 10 January, April and August due to global warming – later gen concentration in the depth. The temperature situation DELTA HISTALP (DELTA ET0, T & precip-5%) 2040-2050 15 cooling in winter and earlier warming in spring. In August and oxygen concentration is shown in the figure above for 0 the impact is lower than in April because of increasing the time period December 2009 to November 2011. The y % -10 evaporation (cooling effect on water surface). spring and winter circulation is going down to 60 meters. 10 Lake Wörthersee is a meromictic (partly mixing) lake. In the A clear indication of a deeper circulation is a decrease in -20 LVR change in Lake-mm per da 1930th the water body was circulating down to 50 meter. water temperature and an increase of oxygen concentra- -30 5 In the last decades there was sometimes a circulation that tion in the deep zone of the lake.

-40

0 -50 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR

52 53 Climate driven scenarios 2001 - 2050

Precipitation Temperature

1600 9

1500 8,5 1400

8 1300

1200 7,5 °C mm

1100 7 1000 6,5 900

800 6

Lake Klopeiner See 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 2031 2033 2035 2037 2039 2041 2043 2045 2047 2049 YEARS YEARS The lake 2020 2030 2040 2050 It is a relic of a former much lager post glacial lake. The lake is nearly egg shaped, about 1.8 km long and Precipitation scenarios (mm) - 72,8 - 19,2 - 43,2 + 31,5 The lake gets filled up by detrital of the post glacial 0,8 km wide. According to the long water residence Air temperature scenarios (°C) + 0,32 + 0,6 + 0,96 + 1,25 River Vellach until the Lake Klopeiner See and nearby time the municipality St. Kanzian as owner of the Kleinsee remained for now. The shore lost most lake, try hard to preserve the water quality. Since the of its nativeness due to settlements and tourism lake showed eutrophication in the early 1980s the infrastructure. The partly mixing lake is characterized whole catchment got a sewerage system. Since 1975 Past trend by lime marl in the eastern and western bay. It has the lake gets treated by a unique drainage of deep now noteworthy tributary, so it gets mainly feeded water in order to reduce the nutrient load. The lake is Water temperature through small inflows and ground water. The outflow used for touristic purposes; the first visitors arrived in with a low mean flow condition of 35 l/sec. is situated 1885. At that time the region had 40 beds and most Month of May Month of December in the western bay. Finally the outflow goes in the visitors came to recover from lung disease. Now a 7,5 River Drau. It is the less pervaded and therefore the day the region has nearly one million overnight stays. 25 Surface Surface Bottom 7 Bottom Lineare (Surface) Lineare (Surface) warmest lake of Carinthia. 20 Lineare (Bottom ) Lineare (Bottom ) 6,5

15 6 °C °C 5,5 10 Identity Card 5 5 Catchment area 2.40 km² 4,5 0 4 Lake area 1.14 km² mag-04 ago-04 nov-04 feb-05 mag-05 ago-05 nov-05 feb-06 mag-06 ago-06 nov-06 feb-07 mag-07 ago-07 nov-07 feb-08 mag-08 ago-08 nov-08 feb-09 mag-09 ago-09 nov-09 feb-10 mag-10 Maximal depth 48 m dic-04 dic-05 dic-06 dic-07 dic-08 dic-09 Months Months Average depth 23 m Volume 22.9 m3 x 106 Period: 2001 - 2010 Average altitude 446 m a.s.l. Rate: °C per month Meteo monitoring Month of May Month of December Mean fill up time 20.6 years station Surface + 0,02 + 0,16 Water monitoring Mean residence time station Bottom + 0,03 + 0,12 of deep lake water 6.8 years Mean annual inflow 1971-2010 23.8 l/s (mainly from groundwater) Mean annual out flow 1971-2010 (including losses 34.0 l/s to spring) Trophic state of the lake oligotrophic

54 55 Precipitation Hydrological modelling and isotope investigations

Summer (JJA) Winter (DJF)

700 400

600 350

300 500

250 400 200 mm mm 300 150 200 100

100 50 Deep profile sampling 0 0 Monthly sampling and measurements

1813 1822 1831 1840 1849 1858 1867 1876 1885 1894 1903 1912 1921 1930 1939 1948 1957 1966 1975 1984 1993 2002 1813 1822 1831 1840 1849 1858 1867 1876 1885 1894 1903 1912 1921 1930 1939 1948 1957 1966 1975 1984 1993 2002 Spring connested YEARS YEARS with the lake with monthly sampling

New gauging station Period: 1813 - 2011 Histalp Project - Klaghenfurt - Flugafen station Rate: mm per decade Investigation of the actual circulation and evaporation processes using environmental isotopes JJA DJF - 1,8 - 1,5

Air temperature trend Evaporation Lake water Summer (JJA) Winter (DJF)

3,0 25,0 Spring water

24,0 2,0

23,0 1,0 22,0 0,0 Mean residence time in the deepest part: 6,8 years Evaporation trend 21,0

°C -1,0

°C 20,0

19,0 -2,0 0 18,0 18 -3,0 δ O [‰] 17,0 -5 VSMOW -4,0 16,0 -10 -3,4 -3,5 15,0 -5,0 -15 -3,6 2001 2001 2004 2007 2004 1998 1999 2000 2003 2005 2006 1998 1999 2000 2003 2005 2006 2002 2002 -3,7 YEARS YEARS -20 -3,8 -3,9 -25 -4,0 depth [m] Period: 1813 – 2008 -30 -4,1 Klopein station -35 Rate: °C per decade -40 JJA DJF - 0,13 + 0,10 12/09 03/10 06/10 09/1012/10 03/11 date Actual circulation behaviour (Oxygen-18 contents) Quantification of lake losses to a spring

56 57 20 Past water balance changes and trends Reference DELTA HISTALP (DELTA ET0, T) 2040-2050 DELTA HISTALP (DELTA ET0, T & precip-5%) 2040-2050 Trends of lake water renewal and evaporation Trend of the filling time 15

Annual lake volume renewal and evaporation Fill Up Time (years) 5000 800 25 y Lake volume renewal Evaporation 4500 750 24 10

4000 700 23 Lake-mm per da 3500 650 22

3000 600 21 5

2500 550 20

2000 500 19 Filling time (years) 18 1500 450 lake evaporation (mm) 0 lake volume renewal (mm) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 1000 400 17

500 350 16

15 0 300 50 50 1971 1976 1981 1986 1991 1996 2001 2006 2011 1971 197 6 198 1 198 6 199 1 1996 2001 2006 2011 Scenario 1 Scenario 2

Annual lake water components 0 0 3000

LAKE VOLUME RENEWAL Inflow direct Precipitation direct Lake evaporation 2500

-50 -50 29% 2000 LVR change in LVR change in 71% 1500 -100 -100 m 1000 Lake-m

500 -150 -150 JAN FEB MAR APR MAYJUN JULAUG SEP OCT NOV DEC YEAR JANFEB MARAPR MAY JUN JUL AUG SEP OCT NOV DECYEAR Inflow direct catchment Lake surface balance (P-E) 0

-500 The small lake is characterized by a relatively slow cir- The past development and the simulated scenarios show, culation, the evaporation processes on the lake surface that the water balance of small lakes with small catchment -1000 1970 1975 1980 1985 1990 1995 2000 2005 2010 are more dominant for the water balance. The lake is re- areas is extremely sensitive to changes in the air temper- charged by small groundwater inflows and losses water to ature. A temperature increase of 1.5 °C until the decade What could happen in the future? a spring. The variations of the isotope contents even in the 2040-2050 with stable precipitation produces a mean re- highest depth prove together with the isotope signature of duction of the lake water renewal of 23%. In the months Meteorological scenarios the spring nearby that there exists a slow circulation in the from March to July the reduction even exceeds 30% with a

3 Scenario 1: Temp. and pot. lake and a loss of about 5 l/s of lake water to the spring maximum of 81% in May. 2 Mean = 1.4°C evapotranspiration from HISTALP which has to be taken into account in the water balance The superposition with a 5% reduction of precipitation 1 trend (50 years) extrapolated. calculations. gives a mean reduction of 40%, in May – July even more 0 -1 A lumped conceptual rainfall-runoff model has been used than 50% with a maximum of 117% in May. Furthermore Delta T (°C) -2 60-ies to 00-ies Temperature with the aim to simulate past changes and develop scenar- land use changes in the catchment of the lake can have -3 JAN FEB MAR APR MAY JUN JUL AUGSEP OCT NOV DEC ios of the lake volume renewal depending on land use and important additional impacts. 30 climatic conditions and of the lake evaporation. The graphs Consequently a continuation of the increasing trend of the

20 PET show significant changes in the water balance (decrease of filling time and residence time can be expected, param-

10 Mean = 5.8 mm/mo. the lake volume renewal, increase of the lake evaporation) eters which have an impact on the ecology of the lake. and consequently an increasing fill up time. 0 Delta ET0 (mm) 60-ies to 00-ies -10 JAN FEB MAR APR MAY JUN JUL AUGSEP OCT NOV DEC Percentual change of the lake water renewal Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Scenario 1 1 0 - 31 - 32 - 81 - 50 - 30 - 25 - 7 - 16 - 8 - 1 - 23 Scenarios 2040-2050: monthly distribution Scenario 2 - 9 - 13 - 44 - 44 - 117 - 85 - 54 - 39 - 20 - 29 - 18 - 11 - 40 of the lake water renewal.

58 59 Change in water temperature and water circulation

Medium water temperature at surface

January April August November

Wörthersee: 1930 - 2010 + 0,2 °C + 1,1 °C + 0,2 °C - 0,2 °C

Development of temperature stratification

There is a very slight increase in surface water temperature The temperature situation and oxygen concentration in the in winter, spring and summer in the period from 1990 to depth informs about the mixing period and extension of 2010. It seems that there is no influence of global warming water circulation. A clear indication for the depth of circula- on the water temperature of Lake Klopeiner See. tion is the appearance of oxygen. In general in this lake the Lake Klopeiner See is a meromictic (partly mixing) lake. oxygen limit is in the depth of 30 meters. In May 2010 the The water temperature in the stagnant water body in winter circulation went deeper and oxygen was measured down is slightly higher than in the layers above. The circulating to 40 meters. water body goes down to 30 meters as the figure above shows.

60 Conclusions Bibliography

Before the 1990s, most environmental scientists a change in growing season for plants, to an increase • Contribution of Working Group III to the Fourth • Korhonen,. J. (2005), “Suomen vesistöjen jääolot”, considered climate to exert a relatively constant in- of evaporation, evapotranspiration and a probable Assessment Report of the Intergovernmental Panel Finnish Environment 751, Finnish Environment Institute, fluence on freshwater ecosystems. In recent years, drought state in late summer, with alterations of the on Climate Change, 2007. B. Metz, O.R. Davidson, Helsinki. however, it has become clear that climate change oxygen concentrations in the water column and in P.R. Bosch, R. Dave, L.A. Meyer (eds); Cambridge • Magnuson, J. J., Robertson, D. M., Benson, B. J., exerts additional stress to surface waters and that it the food web. The authorities involved in the lakes University Press, Cambridge, United Kingdom and Wynne, R. H., Livingstone, D. M., Arai, T., Assel, R. New York, NY, USA. A., Barry, R. G., Card, V., Kuusisto, E., Granin, N., interacts with other drivers (such as eutrophication, management in the Alpine Space must take action • Endoh, S., Yamashita, S., Kawakami, M.,AND Prowse, T. D., Stewart, K. M. and Vuglinski, V. S. hydromorphological change, acidification). The main now to prepare for these impacts. This includes Okumura, Y., 1999. Recent Warming of Lake Biwa (2000), “Historical trends in lake and river ice cover in impacts of climate change on lake ecosystems re- changing the way buildings and infrastructure are Water, Jap. J. Limnol., 60, 223 – 228 the Northern Hemisphere” , Science 289(5485), 1743- sult from change in air temperature, precipitation and designed, improving our water use, rethinking the • Gronskaya, T.P., George, D.G. & Arvola, L. 2001. The 1746. wind regimes. way we develop vulnerable shore zones, or planting influence of long-term changes in the weather on the • Mooij W M ,Hülsmann S ,De Senerpont Domis L N The response of the lakes to climate change de- more drought-tolerant crops. thermal characteristics of lakes in the UK, Finland ,Nolet B A ,Bodelier P L E ,Boers P C M ,et al.The pends on their mixing characteristics, which, in turn, and Russia. –9th International Conference on the impact of climate change on lakes in the Netherlands: are influenced by their location, landscape setting, Engineering solution, upgrade of infrastructures, wa- Conservation and Management of Lakes. Session 5. a review. Aquat Ecol 2005; 39: 381–400. size and topography. ter monitoring increase, proposals for new structures Partnerships for Sustainable Life in Lake Environments: • Scheffer,M. etal. (2001)Catastrophicshiftsinecosystems. and facilities have to be applied to alpine lakes. On Making Global Freshwater Mandates Work. Shiga Nature 413, 591–596 Global warming is already having an impact on the one hand some adaptation actions, such as behav- Prefectural Government, Japan, pp. 43-46. • Skjelkvåle, B.L. and Wright, R.F. 1998. Mountain physical, chemical, biological and hydromorphologi- ioural adaptations, can be implemented at low cost • Jarvet, A., 2000. Biological consequences of global lakes; sensitivity to acid deposition and global climate warming:is the signal already apparent? Tree, 15, 56 – change. AMBIO 27:280-286. cal conditions of lake ecosystems. The magnitude of while others, on the other hand infrastructural mea- 61. • Todd M.C., and Mackay A.W., 2003: Large –scale change induced by climate change is still relatively sures will require significant investment. But the de- • Jöhnk K D ,Huisman J, Sharples J Sommeijer B ,Visser climate controls on the Lake Bajkal ice cover. J. small in comparison with the impact of anthropogen- cisions make today about management of the main P M ,Stroom J M.Summer heat waves promote blooms Climate, 16 3186-3199. ic land use, and, at the same time, impose land use uses of the lakes (irrigation, navigation, tourism/bath- of harmful Cyanobacteria. Glob Chang Biol 2008; 14: • Weyhenmeyer, G. A. 2001. Warmer winters - are changes in catchments. ing, energy power…) will have lasting consequences 495 – 512. planktonic algal populations in Sweden’s largest lakes Change in the characteristics of lake ecosystem in for our children and future generations, and to reduce • Kernan M., Battarbee R., Moss B.,2010 climate affected? Ambio 30: 565-571. the Alpine area, as illustrated here, are likely to con- the future costs of management. By considering the change impacts on freshwater ecosystems, Blackwell tinue and will become much more pronounced as future climate when making these decisions Alpine Publishing greenhouse gas emission rise. Space will be in a better position to deal with the unavoidable impacts of climate changes. These changes will have consequences in Alpine Space area such as more likely frequent and more Long data series of climatic, chemical, physical and extreme weather events, with an increased sediment biological parameters are essential to better define loads; a decline in rainfall, in particular in the west- water management and to set up decision making ern region could reduce the water level, and conse- tools. Actually, through monitoring, modelling and quently, for example, to reduce the regularity of the system analysis, SILMAS project provided an early- port, to lead to a change in location of ecosystem warning system for climate change, helping decision and of spawning and nursery areas, to increase the makers at a political level to take adjustment strat- eutrophication in shallow lakes; higher temperatures egies, in terms of water resource management and lead for example to a decrease in water supplies, to ecosystem preservation or restoration.

62 63