ISS Massbalance2018 2Hr for Website.Key

Glacier summer school 2018, McCarthy, Alaska

What is mass balance ? Regine Hock

Claridenfirn, Switzerland, 1916

1914 • Terminology, Definitions, Units • Conventional and reference surface mass balance • Firn line, snow line, ELA • Glacier runoff • Global mass changes PART I Terminology

Claridenfirn, Switzerland, 1916

1914 Background General reference for mass-balance terminology has been Anonymous,1969, J. Glaciology 8(52). in practice diverging and inconsistent and confusing use of terminology new methods, e.g. remote sensing, require update Working group (2008-2012) by GLOSSARY International Association of OF GLACIER Cryospheric Sciences (IACS) MASS BALANCE aims to update and revise Anonymous (1969) AND and to provide a consistent terminology for all RELATED glaciers (i.e. mountain glaciers, ice caps and

ice sheets) TERMS

Cogley, J.G., R. Hock, L.A. Rasmussen, A.A. Arendt, A. Bauder, R.J. Braithwaite, P. Jansson, G. Kaser, M. Möller, L. Nicholson and M. Zemp, 2011, Glossary of Glacier Mass Balance and Related Terms, IHP-VII Technical Documents in Hydrology No. 86, IACS Contribution No. 2, UNESCO-IHP, Paris. Can be downloaded from: http://www.cryosphericsciences.org/mass_balance_glossary/ massbalanceglossary Glacier mass balance Mass balance is the change in the mass of a glacier, or part of the glacier, over a stated span of time: =mass budget t . • SPACE: study volume needs to be ‘mass imbalance’ ΔM = ∫ Mdt defined t1 • mass balance is often quoted for volumes other than that of the whole glacier, for example a column of unit cross section • important to report the domain ! •TIME: the time period (esp important € for comparison with model results) • mass change can be studied over any period Net gain of mass • often done over a year or winter/summer seasons --> Annual mass balance (formerly ‘Net’) Firn line Long-term ELA Accumulation area: acc > abl Net loss of mass

Ablation area: acc < abl

Equilibrium line: acc = abl t . ΔM = ∫ Mdt t1 t . . Δmb= c+ a = ∫ (c+ a)dt t ACCUMULATION, (c, C) 1 € • Snow fall ABLATION (a, A) • Deposition of hoar, freezing rain •Melting • Windborne blowing snow/ •Sublimation drifting snow •Loss of windborne blowing • Avalanching snow/drifting snow € •Avalanching •Calving, submarine melt ...

internal acc internal melt Calving

Submarine melt basal freeze-on basal melt Mass balance components: It’s more than snowfall and melt

Total mass budget: sum of climatic balance and frontal ablation

Accumulation - Net accumulation - Net acc is a balance, acc is not

What is measured in ice cores?

Ba = Bw+Bs = Acc + Abl

Bw= Accw Bs= Ablw Implications for comparison of field measurements with model results? C, A can be modeled, but what is measured often is Bw, Bs Mass balance components Precipitation - Surface accumulation precipitation includes rain; rain water is not accumulation; water is not considered to be part of the glacier

Accumulation - Net accumulation - Net acc is a balance, acc is not

Melt - meltwater runoff Melt water may refreeze and does not contribute to meltwater runoff

Meltwater runoff - Runoff Runoff includes rain water

csfc

LAYERS asfc surface

ρ snow? compressible? internal ρ firn? ai c h i

qin qout

basal

cb ab

!11 What is mass balance? Change of the mass over a stated span of time

Mass balance of a column c = accumulation a = ablation (is negative)

Δmb= csfc + asfc + ci + ai + cb + ab + qin + qout

csfc Surface internal basal flux divergence

LAYERS asfc surface ρ € snow? compressible? internal ρ firn? ai Surface c h i

qin qout internal qin qout

basal

!12

cb ab basal Terminology ‘mess’

Mass balance of a column c = accumulation a = ablation

Δmb= csfc + asfc + ci + ai + cb + ab + qin + qout

Surface internal basal flux divergence

Continuity equation € Mass balance ? SMB ? Surface . . . → q internal q h = b− ∇Q in out

Thickness change basal € What is mass balance?

Mass balance of a column c = accumulation a = ablation

Δmb= csfc + asfc + ci + ai + cb + ab + qin + qout

surface Surface internal basal flux divergence

q internal q Climatic balance, bclim in € out Climatic-basal balance, b

basal (Total) mass balance, Δm . . . → h = b− ∇Q

€ What do you measure with GPS vs with a stake?

Δmb= csfc + asfc + ci + ai + cb + ab + qin + qout Surface internal basal flux divergence Climatic balance Climatic-basal balance € (Total) mass balance

GPS

Stake . . . → h = b− ∇Q

€ What do you measure with GPS vs with a stake?

Δmb= csfc + asfc + ci + ai + cb + ab + qin + qout Surface internal basal flux divergence Climatic balance Climatic-basal balance € (Total) mass balance

GPS

Stake •GPS --> total mass balance (but partitioning in components unknown) •Stake --> only surface mass balance, measurement relative to top of the stake What do you measure with GPS vs with a stake?

GPS Point/part of glacier Glacier-wide Interpolating point data over entire glacier •GPS --> total mass •total mass balance balance --> geodetic balance Stake •Stake --> only surface •total mass balance mass balance, (for land-terminating non- measurement relative to calving glaciers) top of the stake Why does the geodetic method work? Surface - Does not need any ice velocity measurements internal q qout Over an entire glacier (no ice in flowing into another ice mass) the flux divergence is zero, i.e. height changes equal the climatic-basal basal mass balance (accounting for density); assuming no changes at the glacier bed

Does an elevation change at point always indicate a change in mass? • changes in elevation dVh dMm dSL can occur without ≠ ≠ changes in mass or dt dt dt visa versa Calving flux • only includes mass loss due to calving •BUT: >50% of the mass loss at the glacier front can be due to submarine melting (even if grounded)

---> frontal ablation • mass loss at the glacier front (includes calving, submarine melting, arial melt/ sublimation ...)

What is ice discharge? Mass flux or volumetric flux of ice through a glacier cross- section or “gate”. The gate can be anywhere on the glacier, but is often at the glacier terminus. Time systems: Annual mass balance, i.e. balance over (roughly) one year

• stratigraphic system • fixed-date system • floating-date system • combined system Ablation area Accumulation area Accumulation area Ablation fixed-date fixed-date fixed-date system system system

Summer Summer Winter Winter

stratigraphic system • End winter snow probing: What system? • Stratigraphic system: dates are unknown

!21 Time Systems of Annual Measurements of Mass Balance Reported to World Glacier Monitoring System WGMS (Cumulative to 2008)

No information provided 1519

Fixed-date system 917

Stratigraphic system 931

Combined system 265

Other 188

Total of reported annual measurements 3820 --> comparing observations with model results problematic if time system not known What is specific mass balance ?

1. The mass balance at a specific location ? 2. The mass balance of the entire glacier ? 3. The mass balance expressed in m w.e. ?

Definition: Mass balance expressed per unit area, that is, with dimension [M L–2] or as a rate [M L–2 T–1] often kg m–2 or m w.e.

The prefix “specific” is not necessary. The units make clear whether or not it is specific.

Specific mass balance may be reported for a point on the surface (if it is a surface mass balance), a column of unit cross-section, or a larger volume such as the entire glacier. Balances reported for a point are always specific. Mass-balance units • Mass [M] kg, Gt (=109 kg, 1 billion tonnes) • mass change per unit area [M L-2] --> kg m-2 (specific unit) • m or mm water equivalent (w.e.): -> 1 kg of water (density 1000 kg m-3) has thickness of 1 mm when distributed over 1 m2 -> kg m-2 and mm are numerically identical -> 1 m w.e. = 1000 kg m-2 / density of water • m3 w.e. or km3 w.e. (1 km3 w.e. = 1 Gt) --> important to add w.e. or i.e. (ice equiv.) • Sea-level equivalent: kg m-2 x glacier area /-(density of water x area of the ocean) (362x106 km2) Often not included: • changes in ocean area; any delay and storage in transport of water in the terrestrial water cycle • isostatic adjustment of the land surface, tectonic movements • differentiate between grounded and floating ice (floating ice does not contribute to sea-level; grounded ice contributes only to a small fraction since the ice already displaces water) Mass balance time series look different in different units

Black Rapids Glacier

-1

Gt a by Christian Kienholz

a m w.e. PART II Concept of conventional and reference surface balance

Claridenfirn, Switzerland, 1916

1914 Mass balance as climate indicator ?

Stable climate Step change in Stable climate Ba = 0 climate Ba = 0 Steady-state Ba < 0 Steady-state Glacier retreat Glaciers are indicators of climate change ?

B=V / A

• conventional mass balance glacier area/hypsometry is updated annually • reference surface balance glacier area/hypsometry is kept constant

Harrison, W., Elsberg, Cox and March, 2005. Different balances for climatic and hydrological applications. J. Glaciol., page 176. This paper is in your folder ! b=measured point Conventional mass balance balances Time 1 (t1) Time 2 (e.g. 50 yrs later)

Relevant for hydrological purposes Measurement sites 1 Note area AND 1 surface B = b(h1)dAt1 B b dA ∫ = ∫ (h2) t2 elevation At1 At2 changes Reference surface mass balance

€ €

Relevant for climatological purposes 1 1 B = b‘ dA B = ∫ b(h1)dAt1 ∫ (h1) t1 A At1 b’=measured point balance at t1 t2 on surface at t2 but adjusted to surface at t1

€ € Mass balance as climate indicator ?

Stable climate Climate change Stable climate Bn = 0 Bn < 0 Bn = 0 Steady-state Glacier retreat Steady-state

Reference surface mass balance does not go to 0 Which balance to use when? Conventional balance: Relevant for hydrological/sea level purposes • kilogramme (kg), or gigatonne (Gt; 1 Gt = 1012 kg). • m3 w.e. or km3 w.e.

Reference surface balance: Relevant for climatological purposes

1 kg m-2 = 1 mm of water equivalent, mm w.e. = specific mass balance Mass-balance feedback: Two opposing effects Retreat effect Thinning effect (Bodvardsson, 1955)

Glacier Ice cap

@V. Radic stabilizing destabilizing

glacier increased retreat glacier thinning increased retreat thinning Which one is the conventional / reference balance?

!33 Harrison et al. 2009, Ann. Glaciol. PART III Firn line, equilibrium line, snow line ... Claridenfirn, Switzerland, 1916

1914 Snow line • Boundary separating snow from ice or firn at any time t • Transient - Annual FIRN LINE FIRN Wetted snow that has survived one summer without being transformed to ice

The set of points on the surface of a glacier delineating the firn area and, at the end of the mass-balance year, separating firn (usually above) from glacier ice (usually below).

FIRN

ICE FIRN LINE can be seen on radar profiles Snow surfaceMass balance Snow line • Boundary separating snow from ice or firn at any time t • Transient - Annual

Equilibrium line • The set of points on the surface of the glacier where the climatic mass balance is zero at a given moment. The equilibrium line separates the accumulation zone from the ablation zone. • Transient - Annual Equilibrium line vs. equilibrium line altitude (ELA)

Approximate ELA ELAs from space: Remote sensing

Landsat image of Vatnajoekull (Iceland)

Accumulation zone Where is the firn line, ELA?

Ablation zone Vatnajoekull Where are the firn line, equilibrium line, (Iceland) snow line relative to each other? Assuming no superimposed ice

firn

negative mass balanced year: positive mass- Lines are the same only balance balance, firn line retreats when glacier is in remaining snow equilibrium (i.e. slower becomes firn --> balance=0 over many all lines are the years and firn line = same long-term EL) PART IV ‘Sensitivities’

Claridenfirn, Switzerland, 1916

1914 Sensitivities to climate change The change in mass balance due to a change in a climatic variable such as air temperature or precipitation. Sensitivities to temperature and precipitation are often expressed as changes in response to a 1 K warming or a 10% precipitation increase.

•Static sensitivities assume constant glacier size and geometry and refer only to the change in mean specific mass balance •Dynamic sensitivities consider the volume and geometry changes following climate change and are thus more realistic

•Sensitivities vary among regions (e.g. maritime climates more sensitive) Static mass balance sensitivities using energy balance (EB) or temperature-index (TI) melt models

Static mass Static mass balance Method balance sensitivity Reference Glaciers sensitivity T +1 K (m a-1) P +10 % (m a-1)

3 Norwegian glaciers EB -0.72 to -1.11 Oerlemans (1992) 12 glaciers EB -0.12 to -1.15 Oerlemans and Fortuin (1992) 12 glaciers EB -0.40 (average) Oerlemans (1993) 3 Norwegian glaciers TI -0.54 to -1.04 +0.14 to +0.39 Laumann and Reeh (1993) 2 Svalbard glaciers EB -0.61 (average) Fleming et al. (1997) 2 Icelandic glaciers TI -0.6 to -0.9 Jóhannesson (1997) 12 glaciers TI, EB -0.4 to -1.35 Oerlemans et al. (1998) 37 glaciers TI -0.1 to -1.3 Braithwaite and Zhang (1999) 5 Swiss glaciers TI -0.44 to -0.89 Braithwaite and Zhang (2000) 6 Scandinavian TI -0.68 to -1.13 +0.26 to +0.50 Nesje et al. (2000) glaciers 61 glaciers TI -0.13 to -1.22 +0.04 to +0.37 Braithwaite et al. (2002) 9 Icelandic glaciers EB -0.49 to -0.80 +0.27 to +0.35 de Ruyter de Wildt et al. (2003) 17 glaciers TI -0.2 to -1.5 Schneeberger et al. (2003) 42 Arctic glaciers TI -0.20 to -2.01 +0.03 to +0.36 de Woul and Hock (2005) 12 Scandinavian TI -0.30 to -1.01 +0.16 to +0.41 Rasmussen and Conway (in glaciers press) Mass balance sensitivities

Global mean static mass balance

• -0.39 m a-1 K-1 (Oerlemans, 1993)

• -0.37 m a-1 K-1 (Dyurgerov and Meier, 2000)

• -0.68 m a-1 K-1 (Hock et al., 2009) What do mass balance sensitivities depend on ?

Affected by •Glacier geometry •Climate Annual mass balance sensitivity [m a-1] to a +1 K warming

Regions with high sensitivities due to

• change in rain/snow fraction has a larger effect where precip is higher • longer ablation season has larger effect on glaciers that extend down to low-lying warmer areas • greater reduction in precip in maritime regions for a given percentage change in precip

Hock et al., 2009, GRL Future volume changes using mass balance sensitivities

ST = Mass balance sensitivity to +1 K warming SP = Mass balance sensitivity to 1% precipitation increase ΔT = predicted temperature increase ΔP = precipitation increase (%)

Mass balance in speciﬁc units Assumptions:

• Assumption that glacier initially are in steady-state • Constant sensitivities with time Seasonal sensitivity characteristic

Sensitivity varies with season • applies temperature and precipitation perturbations employed individually for each month while leaving the data for the remaining months unchanged.

SSC (Oerlemans & Reichert, 2000): Monthly perturbations in precipitation or temperature Seasonal mass balance sensitivities • applies temperature and precipitation perturbations employed individually for each month while leaving the data for the remaining months unchanged. PART IV Global mass balances

Claridenfirn, Switzerland, 1916

1914 Global glacier volume

Sea-Level Equivalent (SLE) ~66 m 58.3 m Antarctica 7.4 m Greenland 0.5 m mountain glaciers Mountain glaciers and ice caps ~200,000 glaciers 705 km2 including glaciers in the periphery of Greenland (89,700 km2 ) and Antarctica (133,200 km2)

Yakutat Glacier, Alaska 2011; photo: B. Truessel Ice volume Sea-level contribution 1992 - 2010, IPCC 2013 Mountain glaciers (1%)

Green- land Glaciers 11%

Thermal Greenland expansion Antarctica 88% Antarctica

Land water storage Global glacier mass loss (IPCC, 2007)

• based on 3 global estimates (Cogley, 2005; Dyurgerov & Meier, 2005; Ohmura, 2004) • based on spatial extrapolation of direct mass balance measurements on <200 glaciers • incomplete glacier inventory

1993-2003: SLE= 0.77±0.22 mm/yr

)

(mm yr- (mm Sea-levelequivalent

2006

Kaser et al. 2006, GRL; IPCC 2007 2010 1960 2000 Journal of Glaciology, Vol. 60, No. 221, 2014 doi: 10.3189/2014JoG13J176 537

The Randolph Glacier Inventory: a globally complete inventory of glaciers

W. Tad PFEFFER,1 Anthony A. ARENDT,2 Andrew BLISS,2 Tobias BOLCH,3,4 J. Graham COGLEY,5 Alex S. GARDNER,6 Jon-Ove HAGEN,7 Regine HOCK,2,8 Georg KASER,9 Christian KIENHOLZ,2 Evan S. MILES,10 Geir MOHOLDT,11 Nico MO¨ LG,3 Frank PAUL,3 Valentina RADIC´ ,12 Philipp RASTNER,3 Bruce H. RAUP,13 Justin RICH,2 Martin J. SHARP,14 THE RANDOLPH CONSORTIUM15 1Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA 2Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA 3Department of Geography, University of Zu¨rich, Zu¨rich, Switzerland 4Institute for Cartography, Technische Universita¨t Dresden, Dresden, Germany 5Department of Geography, Trent University, Peterborough, Ontario, Canada E-mail: [email protected] - inventoried glacierized 6Graduate School of Geography, Clark University, Worcester, MA, USA 7Department of Geosciences, University of Oslo, Oslo, Norway area (WGI) 8Department of Earth Sciences, Uppsala University, Uppsala, Sweden 9Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria - NOT inventoried 10Scott Polar Research Institute, University of Cambridge, Cambridge, UK 11Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, glacierized area before La Jolla, CA, USA 12Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, 2012 Canada 13National Snow and Ice Data Center, University of Colorado, Boulder, CO, USA 14Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada 15A complete list of Consortium authors is in the Appendix

ABSTRACT. The Randolph Glacier Inventory (RGI) is a globally complete collection of digital outlines of glaciers, excluding the ice sheets, developed to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change for estimates of past and future mass balance. The RGI was created with limited resources in a short period. Priority was given to completeness of coverage, but a limited, uniform set of attributes is attached to each of the 198 000 glaciers in its latest version, 3.2. Satellite imagery from 1999–2010 provided most of the outlines. Their total extent is estimated as 726 800 34 000 km2. The uncertainty, about 5%, is derived from careful single-glacier and basin-scale Æ Æ uncertainty estimates and comparisons with inventories that were not sources for the RGI. The main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover. These errors appear not to be normally distributed, and quantifying them reliably is an unsolved problem. Combined with digital elevation models, the RGI glacier outlines yield hypsometries that can be combined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers. The RGI has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume, and thus actual and potential contributions to sea-level rise. KEYWORDS: Antarctic glaciology, Arctic glaciology, glacier delineation, glacier mapping, remote sensing, tropical glaciology Yakutat Glacier, Alaska 2011; photo: B. Truessel

1. INTRODUCTION coverage that is essential for global-scale assessments. The Randolph Glacier Inventory (RGI) is a collection of However, of the few attributes attached to each RGI vector digital outlines of the world’s glaciers, excluding the outline, some are analytically valuable. For example the Greenland and Antarctic ice sheets. The RGI was developed terminus-type attribute and the complete coverage combine in a short (1–2 year) period with limited resources in order to to yield the first estimate of the global proportion of meet the needs of the Fifth Assessment Report (AR5) of the tidewater glaciers. Intergovernmental Panel on Climate Change (IPCC) for Complete coverage is desirable for a broad range of estimates of recent and future glacier mass balance. Priority global-scale investigations. Volume–area scaling (e.g. Bahr was given to complete coverage rather than to extensive and others, 1997) and other procedures to derive glacier documentary detail. The rationale of the RGI (Casey, 2003; volume (e.g. Farinotti and others, 2009; Linsbauer and Cogley, 2009a; Ohmura, 2009) is that fewer attributes and, if others, 2012) require detailed knowledge of glacier areas, unavoidable, locally reduced accuracy of delineation and in some cases a digital elevation model (DEM) as well. (Section 3) would be a price worth paying for the complete Glacier outlines are needed in geodetic estimation of IACS Activities Resources About IUGG

IACS Working group Division on Glaciers and Ice Sheets Goal of the Randolph Glacier Inventory Working Group and The Randolph Glacier Inventory (RGI) is a recently- infrastructure for glacier published, globally complete collection of digital outlines of monitoring glaciers, excluding the ice (2014 - 2018) sheets. The Working Group aims to maintain and develop the RGI as a resource for global/regional-scale WG co-chairs : and Technischemass-balance Universität assessments Dresden, Germany Relevant publications: Koji Fujitaand, University projections of andNagoya, work Japan 2014 2013 Graham Cogley, Trent University, Peterborough, Canada Alex Gardnertowards, Clark merging University, the RGI USA into Regine Hock, University of Alaska Fairbanks, USA the Global Land Ice Matthias Huss, University of Fribourg and ETH Zürich, Related Working Groups: Measure-ments from Space Switzerland Glacier ice thickness (GLIMS) database. WG members : Georg Kaser, University of Innsbruck, Austria p: Mass balance terminology Christian Kienholz, University of Alaska Fairbanks, USA Scope: Etienne Berthier, CNRS-OMP-LEGOS, Toulouse, France Anil Kulkarni, Indian Institute of Science, Bangalore, India [back to working groups page] Background Andrew Bliss, University of Alaska Fairbanks, USA Shiyin Liu, Cold and Arid Regions Environmental & Engineering Objectives Tobias Bolch, University of Zürich, Switzerland Research Institute, Lanzhou, China Deliverables and milestones and Technische Universität Dresden, Germany Christopher Nuth, University of Oslo, Norway Relevant publications: Koji Fujita, University of Nagoya, Japan Ben Marzeion, University of Innsbruck, Austria 2014 2013 Alex Gardner, Clark University, USA Takayuki Nuimura, University of Nagoya, Japan Frank Paul, University of Zürich, Switzerland Matthias Huss, University of Fribourg and ETH Zürich, Related Working Groups: Valentina Radić, University of British Columbia, Canada Switzerland Glacier ice thickness Bruce Raup, National Snow and Ice Data Center, Boulder, USA Georg Kaser, University of Innsbruck, Austria p: Mass balance terminology Christian Kienholz, University of Alaska Fairbanks, USA Akiko Sakai, University of Nagoya, Japan Anil Kulkarni, Indian Institute of Science, Bangalore, India Donghui Shangguan[back to working, groupsCold andpage ]Arid Regions Environmental & Shiyin Liu, Cold and Arid Regions Environmental & Engineering Engineering Research Institute, Lanzhou, China Research Institute, Lanzhou, China Arun Shrestha, InternationalYakutat Centre Glacier, for Integratred Alaska 2011; Mountain photo: B. Truessel Christopher Nuth, University of Oslo, Norway Development, Kathmandu, Nepal Ben Marzeion, University of Innsbruck, Austria Takayuki Nuimura, University of Nagoya, Japan [top] Frank Paul, University of Zürich, Switzerland Valentina Radić, University of British Columbia, Canada Bruce Raup, National Snow and Ice Data Center, Boulder, USABackground : Akiko Sakai, University of Nagoya, Japan Donghui Shangguan, Cold and Arid Regions EnvironmentalThe & Randolph Glacier Inventory (RGI; Arendt et al., 2013; Pfeffer et al., Engineering Research Institute, Lanzhou, China 2014) is a globally complete collection of digital outlines of glaciers, Arun Shrestha, International Centre for Integratred Mountainexcluding the ice sheets. The RGI was created with limited resources by Development, Kathmandu, Nepal an ad-hoc group of scientists in a short period to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change (IPCC)[top ]for estimates of recent and future glacier mass balance. Priority was given to complete coverage, if necessary at reduced quality, rather than to extensive attributes or documentary detail. Background : The RGI has proven highly valuable and has been used extensively since its first release in 2012. For example, the RGI has been used to compute The Randolph Glacier Inventory (RGI; Arendt et al., 2013; Pfeffer et al., regional and global glacier area (Gardner et al., 2013) and glacier volume 2014) is a globally complete collection of digital outlines of glaciers, excluding the ice sheets. The RGI was created with limited resources by an ad-hoc group of scientists in a short period to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change (IPCC) for estimates of recent and future glacier mass balance. Priority was given to complete coverage, if necessary at reduced quality, rather than to extensive attributes or documentary detail.

The RGI has proven highly valuable and has been used extensively since its first release in 2012. For example, the RGI has been used to compute regional and global glacier area (Gardner et al., 2013) and glacier volume Mass changes 2003 - 2009 (IPCC 2013)

Approach: combine best available estimates for each region with new analyses based on ICESat

Glaciological ! W US/Canada, Scandinavia, North Asia, central Europe, Caucasus, low latitudes, New Zealand

GRACE Alaska

ICESat Greenland, Antarctica

GRACE+ICESat Arctic Canada, Svalbard, Russian Arctic, High Mountain Asia

Gardner, A. S., Moholdt, G., Cogley, J. G., Wouters, B., Arendt, A. A., Wahr, J., Berthier, E., Hock, R., Pfeffer, W. T., Kaser, G., Ligtenberg, S. R. M., Bolch, T., Sharp, M. J., Hagen, J. O., van den Broeke, M. R., and Paul, F. 2013: A Reconciled Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009, Science 340 Global glacier mass changes 2003 - 2009 All glaciers other than the ice sheets in Greenland and Antarctica

Mass budget (Gt a-1)

Numbers refer to region numbers Glacier area

blue = tidewater Gardner et al., 2013, Science glaciers • Largest regional contributors: Arctic Canada, Alaska, Greenland periphery, Southern Andes • Average thinning rate = 0.4 m yr -1 Global glacier mass loss = 0.71 ± 0.08 mm SLE yr-1 • --> 29% of observed global sea-level rise • Roughly equivalent to ice sheet mass loss • Global volume projections 2015 - 2100

RCP2.6 RCP4.5 RCP8.5

-14% -20% -26% -24% -33% multi-GCM mean individual GCMs -48%

Marzeion et al Giesen&Oerlemans Huss&Hock

Volume (normalized) Volume Bliss/Radic et al. Slangen et al.

RCP = Representative Concentration Pathways (emission scenarios) 1

0.6

Volume (normalized) Volume 1

0 2020 2100 Marzeion et al Giesen&Oerlemans multi-model mean Huss&Hock individual GCMs RCP8.5 Bliss/Radic et al. Slangen et al. PART V What is Glacier runoff?

Claridenfirn, Switzerland, 1916

1914 How does runoff change as it becomes warmer?

Period of negative Short-term mass balances time scale

Balanced Response to warming mass budget

Long-term time scale YUKON (1.1) Peak Water (year) KUSKO- MACKENZIE KWIM 60o N (0.9) (<0.1) COPPER FRASER (20) (1.0) NELSON 1.4 G=1.1% (<0.1) 1980 2010 2040 2070 2100

1.2 1.0 0.8 River basin average 0.6 40 oYUKON N COLUMBIA 0.4 (0.3) 0.2 Glacier Runoff (-) PAST FUTURE 0.0 2000 2050 2100 1980 2010 2040 2070 2100

140o W 120o W 100o W 80o W DAULE/ LULE VINCES (1.0) (0.1) GLOMA (0.6) 1.4 G=1.2% THJORSA o o 60 N 0 N (16) 1.2 20o N 1.0 OB SANTA AMAZON (<0.1) 0.8 (1.7) RHINE (<0.1) (0.1) ISSYK-KUL 0.6 ARAL SEA (0.9) 0.4 RHONE KUBAN BALKHASH 0.2 DANUBE Glacier Runoff (-) (0.9) (0.2) ARAL (0.9) PAST FUTURE (<0.1) SEA 0.0 PO 2000 2050 2100 (0.5) (1.2) 20o S 40o N MAJES TARIM (0.3) TITICACA (2.3) HUANG HE (0.1) (<0.1)

1.4 G=0.9% RAPEL INDUS 1.2 YANGTZE (1.5) (2.4) (0.1) COLORADO 1.0 BIOBIO (0.4) 0.8 GANGES (0.3) (1.1) 0.6 SALWEEN NEGRO RHONE (0.9) o 0.4 (<0.1) 20 N BAKER 0.2 BRAHMA- (7.7) Glacier Runoff (-) PAST FUTURE SANTA CRUZ 0.0 PUTRA MEKONG (9.9) 2000 2050 2100 (3.2) (<0.1) 80o W 60o W 0o E 20o E 40o E 60o E 80o E 100o E later peak water in basin with Huss & Hock, 2018, RCP 4.5 larger glaciers/ice cover % Nature Climate Change What is glacier runoff?

1.) All runoff from glacierized area •happens always, i.e. also in year where Q = M - R annual net balance is zero - discharge a gauging station would measure •glacier in balance has no effect on annual runoff (but seasonal effects) •relevant for hydrologists

2.) Runoff from glacier net mass loss •relevant for sea-level Q = M - R + P •‘extra’ water from long-term glacier storage

3.) Runoff only from bare ice area Q = Mice

Radic V. and R.Hock, 2014. Glaciers in the Earth’s hydrological cycle. Assessments of glacier mass and runoff changes on global and regional scales. Survey of Geophysics 35, 813-837. Main conclusion • Reporting mass balance: always report – domain to which the balance refers (and area) – time period a balance refers to • if annual balance is reported report the dates and/or the time system (--> essential to compare to model results) • report which mass balance component is measured/ modeled; use proper terminology • Elevation change vs mass balance from stake measurements a) at a point (NOT equal) b) glacier-wide (equal) Summary • Specific mass balance: mass per area • surface mass balance: strictly speaking only balance at the surface -> climatic balance if internal accumulation included • annual balance instead of previous term net balance • Accumulation is not identical to net accumulation • Runoff is not identical to melt or meltwater runoff • Frontal ablation includes calving flux and submarine melting • Reporting of time systems and glacier area (area- elevation distribution) is crucial • Conventional balance (area, elevation updated) reference surface mass balance (kept constant)