a global estimate of mountain glacier volume and mass

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1 matthias.h.braun@fau.de A Global Estimate of Mountain Glacier Volume and Mass Change and …. Neue Perspektiven der Erdbeobachtung 13.11.2019

A Global Estimate of Mountain Glacier Volume and Mass Change and its Contribution to Sea Level Rise between 60°N and 56°S

T Seehaus, C Sommer, P Malz, D Farías, M Braun

Sea level change as measured from satellite

Currently about almost a third comes from glaciers and ice caps

Sea level change and ice mass contributions

Globally ~215 000 glaciers and ice caps • 158 ± 41 * 10³ km³ (2019), ~50 -130 * 10³ km³ (IPCC 2013) • 0.32 ± 0.08 m sea level contribution (Farinotti et al. 2019),

0.41 m(IPCC 2013) • Only 2% of the glaciers

have so far any in-situ ice thickness measurement

Farinotti et al. (2019), NGEO

Gardner et al. 2013

Motivation: Mass budget worldwide…

Zemp et al. 2019

Mass budgets of glaciers worldwide so far

DEM differencing to derive dh/dt

Methods: Derive dh/dt from TanDEM-X

C-band bistatic SAR

TanDEM-X:

X-band bistatic SAR

Image: DLR

Image: NASA

Methods: Derive dh/dt from input data

SRTM input:

DEM-product Version 3.0

Res: 1 arc sec

t0 = 2000-16-02

• Create projected, non void filled mosaics of 1x1° tiles

dh/dt dataset

TanDEM-X - SRTM output:

Projected 30x30 m pixel maps of dh/dt:

Elev.(TDX) – Elev.(SRTM)

t1 – t0

TanDEM-X input:

SLC-products (archive)

Res: processed to reference (SRTM)

t1 = 2011/12/13

• Select scene pairs (>4000) • InSAR process DEMs • Adjust and mosaic

TanDEM-X DEM-processing

Differential InSAR processing: → Interferogram calculation with SRTM as reference model

Deramping and further corrections: → Minimizing systematic errors for each DEM strip (Nuth & Kääb 2011, Malz et al. 2018)

From TanDEM-X to elevation change datasets

Mosaicing, differencing, masking and error assessment → Combining data takes to a subregional result

Mass balance by geodetic method in the constraints of SRTM orbits: <60°N and >56°S

DEM differencing:

TanDEM-X SRTM

dh/dt dM/dt

Our approach:

this study

Area [km²]

Total: ~175,000

Motivation: mb by one single method

Our results: Elevation change

Aggregated mean dh/dt per 1x1° lat/lon – area scaled center points

Results: Gridded elevation change overview

DEM differencing:

TanDEM-X SRTM

dh/dt dM/dt

Aggregated results to enhance overview

Regionalized change results: Southern Patagonia Icefield

dh/dt 2000-2012

Northern Patagonia Icefield dh/dt 2000-2012

Results: South America - elevation change

• Patagonia (8 & 9) shows the most extreme negative change rates

• Dessert (5) and Central Andes (6) as well as Lake District (7) slightly negative to balanced

• Tropical Andes (1-4) heterogenous

Specific mass balance (m.w.e./a)

Mass Balance South America (Braun et al 2019): 19.4 ± 0.6 Gt a-1

Regionalized change results:

• Himalaya shows

clear depletion

• Minima in Spiti Lahaul and Nyenquentangla range regions

• Hindu Kush, Outer Tien Shan & E Tibetan Plateau show slightly negative changes

Results: High mountain Asia - elevation change

• Central Tien Shan,

Pamir, W Karakoram more or less balanced

• Kunlun Shan and W Tibetan Plateau gain height

• Large accumulation areas with positve change rates

• Kunlun Shan and W Tibetean Plateau gain height

Karakoram:

• Large areas with positve change rates

Kunlun:

Regionalized mass balance:

Results*: High mountain Asia - mass balance

negative mb

positive /neutral mb

Regionalized mass balance:

Results*: High mountain Asia - mass balance

• Positive elevation change signal needs further investigation : influence of climate vs. weather vs. penetration differences vs. SRTM related biases

• Standard processing with constant density of 900 km m-3 not yet adjusted for large gaining accumulation areas

negative mb

positive /neutral mb

Results: North America - elevation change

Overview:

North America West

Stikine Icefield dh/dt 2000-2012

Juneau Icefield dh/dt 2000-2012

Results: North America – hypsometric analysis

fields

Berthier et al. 2018 (ASTER)

Our results

Hypsometric distribution of elevation change and glacier area

-44.95 ± 1.3 Gt a-1 mass balance world wide in SRTM constraints (174,740 km²)

10,000

Our preliminary results: Mass balance (2000-2011/15)

Area [km²]

Results: „Global“ mass balance

Mass balance [Gt a-1]

-10 1+2

12 13-15

Conclusions:

• Mass balance (2000-2011/17) by the presented geodetic method results preliminarily to a total of - 44.95 ± 1.3 Gt a-1 on 174,740 km²

• Comparability of southern and northern hemispheric datasets require some assumptions on glacier surface conditions and penetration depth.

• Processing chain is almost ready for a second real global approach – i.e. the extension of our analysis to the Arctic – depend on a second global acquisition with TanDEM-X or a comparable, compatible X-Band mission Problem: data is not released

Thank you for your attention!

Acknowledgements:

TanDEM-X satellite data was kindly provided under DLR AO XTI_GLAC0264

Comparison

C-Band SRTM TanDEM-X 90m:

• SRTM positively

biased on central N to S axis of Tibetan Plateau

• Steep ranges in W and N with slight positve tendency

• Signals not overruled by artefacts (moasic, geoid correction, acquisition geometry)

Results evaluating elevation change

Comparison

C-Band SRTM

X-Band SRTM:

• Pattern is not reliably equal to TanDEM-X DEM comparison

• Gaps a decicive positions (accumulation areas)

• Mosaicing artefacts predominant

Results evaluating elevation change

Results: North america – hypsometric analysis

fields

Berthier et al.

2018 (ASTER)

Our results

• Results in accordance with published ones

• SRTM gaps negliglable

• No systematic bias for accumulation area in North America

Hypsometric distribution of elevation change and glacier area

a global estimate of mountain glacier volume and mass

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