International Centre for Integrated Mountain Development

Kathmandu, Nepal

Water availability analysis for the upper Indus, Ganges, Brahmaputra,Salween and Mekong river basins

Arun Shrestha

LEG regional training workshop on national adaptation plans (NAPs) for Asian countries10-14 August 2015, Yangon, Myanmar

Acknowledgement

• HICAP Project• Arthur Lutz, Future Water• Walter Immerzeel, Future Water

& Utrecht University

Content

• The regional context• Major science questions• Global assessment - IPCC• Results• Conclusion

International Centre for Integrated Mountain Development (ICIMOD)

Programmes• Adaptation to

change• Transboundary

Landscape• River Basins• Cryosphere and

Atmosphere• Mount Information

System

• Intergovernmental International organization working in the Hindu Kush-Himalayan Region

• Established in 1983

The Hindu Kush Himalayan Region

“water tower”

Different sources of moisture

(Shrestha, 2008)

Strong seasonality

Shrestha et al.,

Major science questions

1. What are the relative contributions of snow, ice, permafrost, rainfall and groundwater to the hydrology of the sub-basins and basin?

2. How will these contribution change and what will be the impact of climate change?

3. What is the current water demand scenario and how will it change in the future?

4. How can the scientific understanding linked with policy and support planned and autonomous adaptation?

30THREE DECADES

Global assessment – IPCC AR5

Approach

• High resolution (1 km) fully distributed model for the upstream parts of the Indus, Ganges, Brahmaputra, Salween and Mekong (HI-SPHY; based on Immerzeel et al. 2010)

• Reference period from 1998 until 2007• Calibration using observed runoff• Climate change scenarios

• Ensemble of latest CMIP5 GCM output• Downscaling -change method• Transient runs until 2050

Model domain

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!( Outflow locations to downstream models0 200 400 600 800 1000

km

Upper Indus437.201 km2

Upper Ganges169.162 km2

Upper Brahmaputra372.664 km2

Upper Salween103.497 km2 Upper Mekong

77.696 km2

Basin scale model set-up and calibration

Input data

• Digital Elevation Model (HydroSheds based on NASA SRTM)

• APHRODITE and Princeton gridded data

• Runoff from 12 measurements stns in Nepal and Pakistan

• FAO Soil• MERIS Land Use

Legend> 7000 m

< 500 m0 200 400 600 800 1000

km

Soil types (FAO)0 200 400 600 800 1000

km

Land Use (GlobCover)0 200 400 600 800 1000

km

Climate change scenarios

• Use two representative concentration pathways (RCP)– RCP8.5 (8.5 W/m2 in 2100) extreme– RCP4.5 (4.5 W/m2 in 2100) less extreme

• Forcing regional and global circulation models until 2050

• 4 GCMs for RCP4.5 and 4 GCMs for RCP 8.5 spanning entire range of possible futures:– Dry & cold– Dry & warm– Wet & cold– Wet & warm

• Total 2 RCPs x 4 models = 8 sets of climate projections

• Downscaled using -change method

Model input dataRiver runoff data 1998-2007 for calibration

LegendRiver runoff data locations

0 200 400 600 800 1000km

LegendRiver runoff data locations

0 200 400 600 800 1000km

• 12 locations with river flow

data series (not all

complete)

• Data provided by DHM

Nepal, IWMI, PMD, and

WAPDA Pakistan

Basin-scale1 km grid cell scale

Glacier projections

Fractional glacier cover

Glacierhypsometry

Classification glacier

size classes

Glacier mass

balance

Volume-Area-

scaling

1 km grid cell scale

Updated fractional glacier

cover per cellDEM

Contribution to stream flow

Basin

Contribution to total runoff (%)

Glacier

melt

Snow

melt

Rainfall-

runoff

Base

flow

UIB 41 22 27 10

UGB 12 9 66 13

UBB 16 10 59 15

USB 8 28 42 22

UMB 1 33 44 22

Glacier change

Changes in hydrological regime

RCP4.5

RCP8.5

No significant change in water availability

Changes in hydrological regimes

Case study - Koshi

RCP 4.5

RCP 8.5

TamaKoshi

Dudh Koshi

Hydropower potentialFlow duration curves

Flow duration curves

Main results

• Glaciers in the five river basins – Indus, Ganges, Brahmaputra, Salween and Mekong –are likely to reduce by 20% to 55% by 2050.

• Due to melting of glaciers and increased precipitation, the overall river flows are likely to increase or remain unchanged in 2041-2050 compared to 1998-2007 for all four river basins.

• By 2050, total runoff is likely to change:

– -5% to +12% in the upper Indus basin,

– +1% to +27% in the upper Ganges,

– 0% to +13% in the upper Brahmaputra,

– + 3% to +19% in the upper Salween and

– + 2 to +20% in the upper Mekong.

Lutz, A. F., W. W. Immerzeel, A. B. Shrestha, and M. F. P. Bierkens, 2014: Consistent increase in High Asia's runoff due to increasing glacier melt and precipitation. Nature Clim. Change, advance online publication.

Thank you