Will Climate Change Impact Water Resources Development in Nepal? Case Study: Koshi Basin

2nd International Conference on the Status and Future of the

World‘s Large Rivers

21-25 July, 2014 Manaus, Amazon, Brazil

L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

Presenting Author: L. BharatiCo-Authors: U. Bhattarai, V. Dahal, P. Gurung and V. Smakhtin

International Water management Institute (IWMI)

Will Climate Change Impact Water Resources

Development in Nepal?Case Study: Koshi Basin





The Context• Nepal is one of the most water abundant countries in the

world with total mean annual runoff of 224 billion cubic meters (BCM) and per capita water availability of 9,000 m3.

• There is large temporal and spatial variation in water availability. 80-90% of rainfall is during the four monsoon months (June-Sept.)

• All this water then rushes through the system, very often creating flooding problems in the wet season and water scarcity in the dry season.

• Water resources remain a particularly under-developed sector –Nepal is currently only utilizing 7% of its annual water availability (14% in the Koshi Basin). 24% of arable land is irrigated and out of 43,000 MW hydropower potential, only 689 MW has been developed

• The impact of CC is a much discussed topic esp. on how it might affect future development

Photo: Tom van Cakenberghe / IWMI





Koshi Basin

• Koshi Basin (87,311 km2): Transboundary basin-Largest contributor to the Ganges river

• The elevation of the basin varies from about 20m in the plains in India to more than 8,000 m in the Great Himalayan Range. Mount Everest (8,848 m) is also located in the basin.

• The basin in the Nepal part is undeveloped but there are plans to build multiple water infrastructure.





Objectives• Resource assessment i.e. water availability vs.

water use at sub-basin level (SWAT and WEAP)

• Impact of CC

• Future basin development scenarios- risks, vulnerabilities, opportunities etc.





SWAT Model: Calibration and Validation

Station Index Calibration ValidationTurkeghat (#604.5) [Arun River]

R2 0.81 0.67NSE 0.81 0.61PBIAS % -6.81 25.79

Majhitar (#684) [Tamor River]

R2 0.66 0.67NSE 0.65 0.58PBIAS % 7.52 -4.31

Pachuwarghat (#630) [Sunkoshi River]

R2 0.74 0.71NSE 0.72 0.65PBIAS % -2.06 5.42

Padherodovan (#589) [Bagmati River]

R2 0.71 0.70NSE 0.71 0.67PBIAS % -7.89 -45.38

Chatara (#695) [Saptakoshi]

R2 0.86 0.83NSE 0.85 0.80PBIAS % -8.69 13.77

Model performance is satisfactory.





Water Balance: Current





Projected Climate Data for Climate Change Study:Downscaled using MarkSim Weather Generator (RCM)(http://gismap.ciat.cgiar.org/MarkSimGCM/)

- Average of CNRM-CM3, CSIRO-Mk3.5, ECHam5, and MIROC3.2

- AR4-SRES: BL, A2 and B1

- Period: 2000s (1971-2000) for BL2030s (2016-2045) for A2 and B12050s (2036-2065) for A2 and B1

- Variable: Rainfall, Temperature (Max & Min), Solar Radiation

http://gismap.ciat.cgiar.org/MarkSimGCM/





Simulated Seasonal Flow Contribution

Simulated seasonal flow contribution in annual flow under current and future climate

Under 2030s Projection

Under 2050s Projection





CC impacts are scale dependent-temporal

• In the Koshi, in 2030s, annual flow volume will decrease by 2% under A2 and will increase by 1% under the B1 projection scenario.

. Table 1: Percentage change in projected flow volume at basin outlet Chatara-Kothu

Period Scenario Pre-monsoon Monsoon Post-monsoon Winter Annual

2030s A2 -16% -1% 7% -9% -2%

B1 -12% 1% 15% -7% 1%

2050s A2 -16% 3% 20% -9% 2%

B1 -13% 3% 25% -2% 4%





Percent change in flow volume during the a)winter, b)pre-monsoon, c)monsoon and d)post-monsoon seasons under the A2 climate

projections for the 2030’s





Results: Minimum, maximum and mean precipitation in the Central mountain region of the Koshi Basin for observed, baseline, A2 and B1

projections for the 2030’s and 2050’s





Future Climate Scenarios

“…A new set of scenarios, the Representative Concentration Pathways (RCPs), was used for the new climate model simulations carried out under the framework of the Coupled Model Intercomparison Project Phase5 (CMIP5) of the World Climate Research Programme…”

RCPs are identified by their approximate total radiative forcing in year 2100 relative to 1750: 2.6 W/m2 for RCP2.6, 4.5 W/m2 for RCP4.5, 6.0 W/m2 for RCP6.0 and 8.5W/m2 for RCP8.5

RCP2.6 : mitigation scenario leading to a very low forcing level • Radiative forcing peaks and declines by 2100

RCP4.5 and RCP6.0 : stabilization scenario• Radiative forcing stabilizes by 2100

RCP8.5 : very high GHG emissions• Radiative forcing does not peak by 2100 Source: IPCC, 2013





Future Climate Data GenerationBasis for GCM selection

Model selection is based on 10th and 90th percentile values of projected changes in P and T from 1961-1990 to 2021-2050

Four corners of the dT-dP graph showing extreme scenarios for both the RCPs are selected 8 GCMs are selected





CanESM2_rcp85CanESM2_rcp45

GFDL_ESM2G_rcp85

Current

CCSM4_rcp45





Change in Future Precipitation

CanESM2_rcp45

CanESM2_rcp85

CCSM4_rcp45 GFDL_ESM2G_rcp85





Change in Future Water Yield

CanESM2_rcp45

CanESM2_rcp85

CCSM4_rcp45 GFDL_ESM2G_rcp85





Conclusions• Climate Change will not reduce the bulk water availability in the basin i.e. at annual

or basin scale

• Climate change will increase variability in the system so future water resource management needs to focus on managing variability

• Store and transfer water seasonally i.e. from the monsoon into the dry season as well as spatially i.e. from water abundant to deficit areas are good solutions for the present as well as the future

• Publications:– L. Bharati, P. Gurung, L. Maharjan and P. Jayakody. Forthcoming. Current and Future Variability in

the Hydrological Regime of the Koshi Basin, Nepal. Forthcoming in Hydrological Sciences Journal

– L. Bharati, P. Gurung, V. Smakhtin and P. Jayakody. 2014. The Impact of Climate Change on Water Resources Development in the Koshi Basin, Nepal. Mountain Research and Development 34 (2), 118-130

Will Climate Change Impact Water Resources Development in Nepal? Case Study: Koshi Basin

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