This document summarizes a study on the potential impacts of climate change on water resources development in Nepal's Koshi Basin. The researchers used hydrological models to analyze current conditions and project future scenarios. Their key findings were: 1) Climate change is not expected to significantly reduce total annual water availability in the basin, but will likely increase seasonal and inter-annual variability. 2) By 2030, annual river flows are projected to decrease by 2% under one scenario and increase by 1% under another. 3) Adaptation strategies like seasonal water storage and transfer between areas will be important to manage future variability.

1. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
Will Climate Change Impact
Water Resources Development
in Nepal?
Case Study: Koshi Basin
Presenting Author: L. Bharati
Co-Authors: U. Bhattarai, V. Dahal, P. Gurung and V. Smakhtin
International Water management Institute (IWMI)
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

2. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
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
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin
Photo: Tom van Cakenberghe / IWMI

3. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
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.
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

4. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
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.
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

5. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
SWAT Model: Calibration and
Validation Station Index Calibration Validation
Turkeghat (#604.5)
[Arun River]
R2 0.81 0.67
NSE 0.81 0.61
PBIAS % -6.81 25.79
Majhitar (#684)
[Tamor River]
R2 0.66 0.67
NSE 0.65 0.58
PBIAS % 7.52 -4.31
Pachuwarghat (#630)
[Sunkoshi River]
R2 0.74 0.71
NSE 0.72 0.65
PBIAS % -2.06 5.42
Padherodovan (#589)
[Bagmati River]
R2 0.71 0.70
NSE 0.71 0.67
PBIAS % -7.89 -45.38
Chatara (#695)
[Saptakoshi]
R2 0.86 0.83
NSE 0.85 0.80
PBIAS % -8.69 13.77
Model performance is
satisfactory.
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

6. Water Balance: Current
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

7. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
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 BL
2030s (2016-2045) for A2 and B1
2050s (2036-2065) for A2 and B1
- Variable: Rainfall, Temperature (Max & Min), Solar Radiation
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

8. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
Simulated Seasonal Flow Contribution
Simulated seasonal flow contribution in annual flow under current and future climate
Under 2030s
Projection
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin
Under 2050s
Projection

9. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
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%
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

10. Percent change in flow volume during the a)winter, b)pre-monsoon,
2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
c)monsoon and d)post-monsoon seasons under the A2 climate projections for
the 2030’s
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

11. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
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
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

12. 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

13. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
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
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

14. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
Future Climate Data Generation
Basis 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
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin

15. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
CanESM2_rcp45 CanESM2_rcp85
GFDL_ESM2G_rcp85
Current
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin
CCSM4_rcp45

16. Change in Future Precipitation
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
CanESM2_rcp4
5
CanESM2_rcp85
CCSM4_rcp45 GFDL_ESM2G_rcp85

17. Change in Future Water Yield
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
CanESM2_rcp4
5
CanESM2_rcp85
CCSM4_rcp45 GFDL_ESM2G_rcp85

18. 2nd International Conference on the Status and Future of the
World‘s Large Rivers
21-25 July, 2014 Manaus, Amazon, Brazil
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
L. BL.Bharati, U. Bhattarai, V. Dahal , P. Gurung and V. Smakhtin