What is mass balance - University of Alaska system

Claridenfirn, Switzerland, 1916

1914

What is mass balance ?

Regine Hock

Glacier summer school 2018, McCarthy, Alaska

• Terminology, Definitions, Units • Conventional and reference

surface mass balance • Firn line, snow line, ELA • Glacier runoff • Global mass changes


1914

PART I Terminology

BackgroundGeneral 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

aims to update and revise Anonymous (1969) and to provide a consistent terminology for all glaciers (i.e. mountain glaciers, ice caps and ice sheets)

Working group (2008-2012) by International Association of Cryospheric Sciences (IACS)

Can be downloaded from:http://www.cryosphericsciences.org/mass_balance_glossary/massbalanceglossary

GLOSSARY OF GLACIER

MASS BALANCE

AND RELATED 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.

Glacier mass balance

Net gain of mass

Net loss of massAccumulation area: acc > abl

Ablation area: acc < abl

Equilibrium line: acc = abl

Firn line Long-term ELA

Mass balance is the change in the mass of a glacier, or part of the glacier, over a stated span of time: =mass budget ‘mass imbalance’

€

ΔM = M.t1

t∫ dt • SPACE: study volume needs to be

defined • 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

• often done over a year or winter/summer seasons --> Annual mass balance (formerly ‘Net’)

ACCUMULATION, (c, C) •Snow fall •Deposition of hoar, freezing rain •Windborne blowing snow/

drifting snow •Avalanching€

b= c+ a= (c. + a).t1

t∫ dt ABLATION (a, A) •Melting •Sublimation •Loss of windborne blowing snow/drifting snow

•Avalanching •Calving, submarine melt ...

Δm€

ΔM = M.t1

t∫ dt

basal freeze-on

internal accinternal melt

basal melt

Calving

Submarine melt

Mass balance components: It’s more than snowfall and melt

Total mass budget: sum of climatic balance and frontal ablation


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

Winter balance <--> accumulation Summer balance <--> ablation

Implications for comparison of field measurements with model results? C, A can be modeled, but what is measured often is Bw, Bs

Ba = Bw+Bs = Acc + Abl Bw= Accw Bs= Ablw

What is measured in ice cores?

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

What is mass balance? Mass balance of a column

!11

csfc

asfc

abcb

h

surface

internal

basal

LAYERS

ciai

qin qout

ρsnow?compressible?

ρ firn?

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

€

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

Mass balance of a column

Surface internal basal flux divergence

c = accumulation a = ablation (is negative)

Surface

internal

basal

qin qout

Δm

!12

csfc

asfc

abcb

h

surface

internal

basal

LAYERS

ciai

qin qout

ρsnow?compressible?

ρ firn?

Terminology ‘mess’

€

h. = b.−∇Q→.

€



Continuity equation


Mass balance ?

Thickness change

c = accumulation a = ablation

Surface

internal

basal

qin qout

SMB ?

Δm

€




c = accumulation a = ablation

Climatic-basal balance, b

Climatic balance, bclim

(Total) mass balance,

Δm

€

h. = b.−∇Q→.

What is mass balance?�

Δm

surface

internal

basal

qin qout

€

b= csfc+ asfc+ ci + ai + cb + ab + qin + qoutSurface internal basal flux divergence

Climatic-basal balanceClimatic balance

(Total) mass balance

ΔmWhat do you measure with GPS vs with a stake?

GPS

Stake

€

h. = b.−∇Q→.

€

b= csfc+ asfc+ ci + ai + cb + ab + qin + qoutSurface internal basal flux divergence

Climatic-basal balanceClimatic balance

(Total) mass balance

Δm

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

Stake

•GPS --> total mass balance

•Stake --> only surface mass balance, measurement relative to top of the stake

Point/part of glacier Glacier-wide Interpolating point data over entire glacier

•total mass balance--> geodetic balance

•total mass balance (for land-terminating non-calving glaciers)

What do you measure with GPS vs with a stake?

Why does the geodetic method work? - Does not need any ice velocity measurements

Over an entire glacier (no ice flowing into another ice mass) the flux divergence is zero, i.e. height changes equal the climatic-basal mass balance (accounting for density); assuming no changes at the glacier bed

Surface

internal

basal

qin qout

Does an elevation change at point always indicate a change in mass?

dVdt ≠

dMdt ≠

dSLdt

• changes in elevation can occur without changes in mass or visa versa

h m

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.

What is ice discharge?

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 ...)

Time systems: Annual mass balance, i.e. balance over (roughly) one year

Abl

atio

n ar

ea

A

ccum

ulat

ion

area

• stratigraphic system • fixed-date system • floating-date system • combined system

!21

fixed-date system

stratigraphic system

fixed-date systemfixed-date

system

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

Winter

Summer SummerWinter

No information provided 1519

Fixed-date system 917

Stratigraphic system 931

Combined system 265

Other 188

Total of reported annual measurements 3820

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

--> 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

by Christian Kienholz

Black Rapids Glacier

m

w.e

. a-1

G

t a-1


1914

PART II Concept of conventional and reference surface balance

Mass balance as climate indicator ?

Stable climate Ba = 0

Steady-state

Step change in climate Ba < 0

Glacier retreat

Stable climate Ba = 0

Steady-state

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 !

Conventional mass balanceTime 1 (t1) Time 2 (e.g. 50 yrs later)

Measurement sites Note area AND

surface elevation changes

Reference surface mass balance

€

B =1At2

b(h2)∫ dAt2

€

B =1At1

b(h1)∫ dAt1

€

B =1At1

b(h1)∫ dAt1

€

B =1At1

b(h1)∫ dAt1

Relevant for hydrological purposes

Relevant for climatological purposes ‘

b=measured point balances

b’=measured point balance at t2 on surface at t2 but adjusted to surface at t1

Mass balance as climate indicator ?

Stable climate Bn = 0

Steady-state

Climate change Bn < 0

Glacier retreat

Stable climate Bn = 0

Steady-state

Reference surface mass balance does not go to 0

Which balance to use when?Conventional balance:

Relevant for hydrological/sea level purposes

Reference surface balance: Relevant for climatological purposes

• kilogramme (kg), or gigatonne (Gt; 1 Gt = 1012 kg). • m3 w.e. or km3 w.e.

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

Glacier

@V. Radic

increased thinning

glacier retreatglacier

retreat

increased thinning

stabilizing destabilizing

(Bodvardsson, 1955)

Ice cap

!33Harrison et al. 2009, Ann. Glaciol.

Which one is the conventional /

reference balance?


1914

PART III Firn line, equilibrium line, snow line ...

Snow line • Boundary separating snow from

ice or firn at any time t • Transient - Annual

FIRN LINEFIRN Wetted snow that has survived one summer without being transformed to ice

FIRN

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).

Mass balanceSnow surface

FIRN LINE can be seen on radar profiles

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

Approximate ELA

Equilibrium line vs. equilibrium line altitude (ELA)

ELAs from space: Remote sensing

Landsat image of Vatnajoekull (Iceland)

Ablation zone

Accumulation zone

Where is the firn line, ELA?

Where are the firn line, equilibrium line, snow line relative to each other?

firn=snow=EL if no superimposed ice

firn=snow=EL if no superimposed ice

firn<snow=EL if no superimposed ice

negative mass balance firn line retreats slower

balanced year: Lines are the same only when glacier is in equilibrium (i.e. balance=0 over many years and firn line = long-term EL)

positive mass-balance, remaining snow becomes firn --> all lines are the same

Vatnajoekull (Iceland)

Assuming no superimposed ice


1914

PART IV ‘Sensitivities’

Sensitivities to climate changeThe 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

Glaciers MethodStatic mass

balance sensitivity T +1 K (m a-1)

Static mass balance

sensitivity P +10 % (m a-1)

Reference

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 glaciers

TI -0.68 to -1.13 +0.26 to +0.50 Nesje et al. (2000)

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 glaciers

TI -0.30 to -1.01 +0.16 to +0.41 Rasmussen and Conway (in 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)

Affected by •Glacier geometry •Climate

What do mass balance sensitivities depend on ?

Annual mass balance sensitivity [m a-1] to a +1 K warming

Hock et al., 2009, GRL

• 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

Regions with high sensitivities due to

Future volume changes using mass balance sensitivities

Assumptions:

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

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

M

Mass balance in specific units

Seasonal sensitivity characteristic

Sensitivity varies with season

SSC (Oerlemans & Reichert, 2000):

Monthly perturbations in precipitation or temperature

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

Seasonal mass balance sensitivities• applies temperature and precipitation perturbations employed individually for

each month while leaving the data for the remaining months unchanged.


1914

PART IV Global mass balances

Yakutat Glacier, Alaska 2011; photo: B. Truessel

Global glacier volume

Sea-Level Equivalent (SLE)~66 m 58.3 m Antarctica 7.4 m Greenland 0.5 m mountain glaciers

~200,000 glaciers 705 km2 including glaciers in the periphery of Greenland (89,700 km2 ) and Antarctica (133,200 km2)

Mountain glaciers and ice caps

Mountain glaciers (1%)

Green-land 11%

Antarctica 88%

GreenlandThermal expansion

Glaciers

Antarctica

Land water storage

Ice volume Sea-level contribution1992 - 2010, IPCC 2013

Global glacier mass loss (IPCC, 2007)

1993-2003: SLE= 0.77±0.22 mm/yr

1960 2000

• 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

2006

Kaser et al. 2006, GRL; IPCC 2007 2010

Sea

-leve

l equ

ival

ent

(mm

yr-1

)


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 MOLG,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, USA2Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA

3Department of Geography, University of Zurich, Zurich, Switzerland4Institute for Cartography, Technische Universitat Dresden, Dresden, Germany5Department of Geography, Trent University, Peterborough, Ontario, Canada

E-mail: [email protected] School of Geography, Clark University, Worcester, MA, USA

7Department of Geosciences, University of Oslo, Oslo, Norway8Department of Earth Sciences, Uppsala University, Uppsala, Sweden

9Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria10Scott Polar Research Institute, University of Cambridge, Cambridge, UK

11Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego,La Jolla, CA, USA

12Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia,Canada

13National Snow and Ice Data Center, University of Colorado, Boulder, CO, USA14Department 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 ofglaciers, excluding the ice sheets, developed to meet the needs of the Fifth Assessment of theIntergovernmental Panel on Climate Change for estimates of past and future mass balance. The RGI wascreated with limited resources in a short period. Priority was given to completeness of coverage, but alimited, uniform set of attributes is attached to each of the !!198000 glaciers in its latest version, 3.2.Satellite imagery from 1999–2010 provided most of the outlines. Their total extent is estimated as726 800" 34000 km2. The uncertainty, about"5%, is derived from careful single-glacier and basin-scaleuncertainty estimates and comparisons with inventories that were not sources for the RGI. The maincontributors 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 com-bined 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 ofglacier mass changes and total volume, and thus actual and potential contributions to sea-level rise.

KEYWORDS: Antarctic glaciology, Arctic glaciology, glacier delineation, glacier mapping, remotesensing, tropical glaciology

1. INTRODUCTION

The Randolph Glacier Inventory (RGI) is a collection ofdigital outlines of the world’s glaciers, excluding theGreenland and Antarctic ice sheets. The RGI was developedin a short (1–2 year) period with limited resources in order tomeet the needs of the Fifth Assessment Report (AR5) of theIntergovernmental Panel on Climate Change (IPCC) forestimates of recent and future glacier mass balance. Prioritywas given to complete coverage rather than to extensivedocumentary detail. The rationale of the RGI (Casey, 2003;Cogley, 2009a; Ohmura, 2009) is that fewer attributes and, ifunavoidable, locally reduced accuracy of delineation(Section 3) would be a price worth paying for the complete

coverage that is essential for global-scale assessments.However, of the few attributes attached to each RGI vectoroutline, some are analytically valuable. For example theterminus-type attribute and the complete coverage combineto yield the first estimate of the global proportion oftidewater glaciers.

Complete coverage is desirable for a broad range ofglobal-scale investigations. Volume–area scaling (e.g. Bahrand others, 1997) and other procedures to derive glaciervolume (e.g. Farinotti and others, 2009; Linsbauer andothers, 2012) require detailed knowledge of glacier areas,and in some cases a digital elevation model (DEM) as well.Glacier outlines are needed in geodetic estimation of

Journal of Glaciology, Vol. 60, No. 221, 2014 doi: 10.3189/2014JoG13J176 537

- inventoried glacierized area (WGI) - NOT inventoried glacierized area before 2012


Goal of theWorking Group

The Randolph GlacierInventory (RGI) is a recently-published, globally completecollection of digital outlines ofglaciers, excluding the icesheets. The Working Groupaims to maintain and developthe RGI as a resource forglobal/regional-scalemass-balance assessmentsand projections and worktowards merging the RGI intothe Global Land IceMeasure-ments from Space(GLIMS) database.

Scope:BackgroundObjectivesDeliverables and milestones

WG co-chairs :

Graham Cogley, Trent University, Peterborough, CanadaRegine Hock, University of Alaska Fairbanks, USA

WG members :

Etienne Berthier, CNRS-OMP-LEGOS, Toulouse, FranceAndrew Bliss, University of Alaska Fairbanks, USATobias Bolch, University of Zürich, Switzerland

IACS Working groupDivision on Glaciers and Ice Sheets

Randolph Glacier Inventoryand

infrastructure for glaciermonitoring

(2014 - 2018)

IACS Activities Resources About IUGG

Relevant publications:2014 2013

Related Working Groups:Glacier ice thicknessp: Mass balance terminology

[back to working groups page]

and Technische Universität Dresden, GermanyKoji Fujita, University of Nagoya, JapanAlex Gardner, Clark University, USAMatthias Huss, University of Fribourg and ETH Zürich,SwitzerlandGeorg Kaser, University of Innsbruck, AustriaChristian Kienholz, University of Alaska Fairbanks, USAAnil Kulkarni, Indian Institute of Science, Bangalore, IndiaShiyin Liu, Cold and Arid Regions Environmental & EngineeringResearch Institute, Lanzhou, ChinaChristopher Nuth, University of Oslo, NorwayBen Marzeion, University of Innsbruck, AustriaTakayuki Nuimura, University of Nagoya, JapanFrank Paul, University of Zürich, SwitzerlandValentina Radić, University of British Columbia, CanadaBruce Raup, National Snow and Ice Data Center, Boulder, USAAkiko Sakai, University of Nagoya, JapanDonghui Shangguan, Cold and Arid Regions Environmental &Engineering Research Institute, Lanzhou, ChinaArun Shrestha, International Centre for Integratred MountainDevelopment, Kathmandu, Nepal

[top]

Background :

The Randolph Glacier Inventory (RGI; Arendt et al., 2013; Pfeffer et al.,2014) is a globally complete collection of digital outlines of glaciers,excluding the ice sheets. The RGI was created with limited resources byan ad-hoc group of scientists in a short period to meet the needs of theFifth Assessment of the Intergovernmental Panel on Climate Change(IPCC) for estimates of recent and future glacier mass balance. Prioritywas given to complete coverage, if necessary at reduced quality, ratherthan to extensive attributes or documentary detail.

The RGI has proven highly valuable and has been used extensively sinceits first release in 2012. For example, the RGI has been used to computeregional and global glacier area (Gardner et al., 2013) and glacier volume

Relevant publications:2014 2013

Related Working Groups:Glacier ice thicknessp: Mass balance terminology

[back to working groups page]

and Technische Universität Dresden, GermanyKoji Fujita, University of Nagoya, JapanAlex Gardner, Clark University, USAMatthias Huss, University of Fribourg and ETH Zürich,SwitzerlandGeorg Kaser, University of Innsbruck, AustriaChristian Kienholz, University of Alaska Fairbanks, USAAnil Kulkarni, Indian Institute of Science, Bangalore, IndiaShiyin Liu, Cold and Arid Regions Environmental & EngineeringResearch Institute, Lanzhou, ChinaChristopher Nuth, University of Oslo, NorwayBen Marzeion, University of Innsbruck, AustriaTakayuki Nuimura, University of Nagoya, JapanFrank Paul, University of Zürich, SwitzerlandValentina Radić, University of British Columbia, CanadaBruce Raup, National Snow and Ice Data Center, Boulder, USAAkiko Sakai, University of Nagoya, JapanDonghui Shangguan, Cold and Arid Regions Environmental &Engineering Research Institute, Lanzhou, ChinaArun Shrestha, International Centre for Integratred MountainDevelopment, Kathmandu, Nepal

[top]

Background :

The Randolph Glacier Inventory (RGI; Arendt et al., 2013; Pfeffer et al.,2014) is a globally complete collection of digital outlines of glaciers,excluding the ice sheets. The RGI was created with limited resources byan ad-hoc group of scientists in a short period to meet the needs of theFifth Assessment of the Intergovernmental Panel on Climate Change(IPCC) for estimates of recent and future glacier mass balance. Prioritywas given to complete coverage, if necessary at reduced quality, ratherthan to extensive attributes or documentary detail.

The RGI has proven highly valuable and has been used extensively sinceits first release in 2012. For example, the RGI has been used to computeregional and global glacier area (Gardner et al., 2013) and glacier volume

Mass changes 2003 - 2009 (IPCC 2013)

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

!

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

GRACE Alaska

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

ICESat Greenland, Antarctica

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

Mass budget (Gt a-1)

All glaciers other than the ice sheets in Greenland and Antarctica

Glacier area

• 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 glacier mass changes 2003 - 2009

Gardner et al., 2013, Science

Numbers refer to region numbers

blue = tidewater glaciers

-24%

-48%

-26%

-33%

Vol

ume

(nor

mal

ized

)

RCP2.6 RCP4.5 RCP8.5

Global volume projections 2015 - 2100

-20%-14%

Marzeion et al Giesen&Oerlemans Huss&Hock Bliss/Radic et al. Slangen et al.

multi-GCM mean individual GCMs

RCP = Representative Concentration Pathways (emission scenarios)

Marzeion et al Giesen&Oerlemans Huss&Hock Bliss/Radic et al. Slangen et al.

Volu

me

(nor

mal

ized

)

2100

1

2020

RCP8.50

1

0

0.6

multi-model mean individual GCMs


1914

PART V What is

Glacier runoff?

Response to warming

Short-term time scale

Long-term time scale

Period of negative mass balances

Balanced mass budget

How does runoff change as it becomes warmer?

0o E 20o E 40o E 60o E 80o E 100o E

20o N

40o N

60o N

140o W 120o W 100o W 80o W

20o N

40o N

60o N

80o W 60o W

20o S

0o N

Peak Water (year)

1980 2010 2040 2070 2100

River basin average

1980 2010 2040 2070 21000.00.20.40.60.81.01.21.4

YUKON

Gla

cier

Run

off (

-)

2000 2050 2100

PAST FUTURE

G=1.1%

0.00.20.40.60.81.01.21.4

ARAL SEA

Gla

cier

Run

off (

-)

2000 2050 2100

PAST FUTURE

G=1.2%

0.00.20.40.60.81.01.21.4

RHONE

Gla

cier

Run

off (

-)

2000 2050 2100

PAST FUTURE

G=0.9%

AMAZON(<0.1)

SANTA(1.7)

COLORADO(0.4)

RAPEL(1.5)

NEGRO(<0.1)

SANTA CRUZ(9.9)

(0.1) TITICACA

MAJES

DAULE/VINCES

(0.3)

(0.1)

BAKER(7.7)

(0.3) BIOBIO

MACKENZIE (<0.1)

COPPER (20)

NELSON (<0.1)

FRASER (1.0)

COLUMBIA (0.3)

YUKON (1.1)

KUSKO-KWIM(0.9)

OB(<0.1)

THJORSA(16)

GLOMA(0.6)

RHINE(0.1)

DANUBE(<0.1) ARAL

SEA(1.2)

RHONE(0.9)

PO(0.5)

KUBAN(0.2)

HUANG HE(<0.1)

INDUS(2.4) YANGTZE

(0.1)

MEKONG(<0.1)

BRAHMA-PUTRA

(3.2)

GANGES(1.1) SALWEEN

(0.9)

TARIM(2.3)

BALKHASH(0.9)

ISSYK-KUL(0.9)

LULE(1.0)

Huss & Hock, 2018, Nature Climate Change

later peak water in basin with larger glaciers/ice cover %RCP 4.5

What is glacier runoff?1.) All runoff from glacierized area Q = M - R - discharge a gauging station would measure

2.) Runoff from glacier net mass loss Q = M - R + P

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

•happens always, i.e. also in year where annual net balance is zero

•glacier in balance has no effect on annual runoff (but seasonal effects)

• relevant for hydrologists

• relevant for sea-level • ‘extra’ water from long-term glacier storage

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 measurementsa) 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)

What is mass balance - University of Alaska system

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