The document summarizes a study on the downstream impacts of the Melamchi Inter-basin Water Transfer Plan (MIWTP) under current and future climate change projections. The study uses hydrological models to quantify the flow reduction in sub-basins downstream of water transfer points under current conditions and climate change scenarios for 2030s and 2050s. The results show flow reductions of less than 12% annually in the immediately downstream sub-basins. Crop water requirements are also assessed, finding no water stress issues in the future under normal or intensive water use scenarios.

1. P. Gurung and L. Bharati International Water Management Institute (IWMI), Lalitpur, Nepal Downstream impacts of the Melamchi Inter-basin Water Transfer Plan (MIWTP) under current and future climate change projections

2. Background Melamchi Water Supply Project (MWSP): 1973 (Identified) 1998 (Implemented) 2008 (Planned to Complete) 2015 (Extend to Complete) Demand of local people , political circumstances and challenges to engage private sector partner is major barrier to complete project Drinking Water Demand of Kathmandu: 220 MLD Water available in Kathmandu Valley: 90 MLD (Dry Season) 130 MLD (Wet Season) In addition, downstream hydrological impacts is another issue (Project has set minimum downstream release nearly 35 MLD )

3. Objective of the Study 1. Use of distributed hydrological model developed for entire Koshi basin to look hydrological impacts of the MIWTP until the outlet of the Koshi basin at Chatara 2. To evaluate impact of climate change on downstream hydrology under current and future climate scenario 3. To quantify impact of water transfer on agricultural command area of Melamchi river ( 289 hectare) under current and future climate scenario

4. Model used for the Study Soil Water Assessment Tool ( SWAT ) Model: - Physically based semi-distributed hydrological model - To simulate water quantity , sedimentation and water quality - Developed by Department of Agriculture of USA Soil, Water and Salt Balance ( BUDGET ) Model: - Field based model - To simulate crop water requirement (CWR) and prepare irrigation schedule - Developed by faculty of applied bioscience and engineering, Katholieke Universiteite Leuven of BELGIUM

5. Study River Reach Model developed for Koshi basin is divided into 79 sub-basins (Outlet Chatara) Ü 1 8 6 2 4 3 5 14 9 32 17 51 7 16 78 73 11 18 10 75 12 45 34 27 13 57 62 65 58 56 15 38 55 60 72 23 71 30 61 53 54 36 69 67 44 66 42 35 59 64 40 74 70 19 47 43 41 37 68 31 76 79 28 48 77 29 39 22 20 46 52 49 63 25 50 33 26 24 21 0 60 120 30 km

6. Study River Reach Downstream impact of MWSP is carried out for 11 among 79 sub-basins of Koshi basin

7. Study River Area In this study, the study river reach starts from sub-basin 35 and ends at sub-basin 79 Water Transfer Location (I) (II) (III)

8. Climate Change Projection Scenario Global Circulation Model: - Downscaled using MarkSim Weather Generator ( 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 Statistical Downscaled: - AR4-SRES: BL , A1B , A2 and B1 - Period: ( 1971-2000 ) for BL ( 2001-2100 ) for A1B , A2 and B1 - Variable: Rainfall, Temperature (Max & Min), Solar Radiation, Relative Humidity and Wind Speed

9. Melamchi Inter-basin Water Transfer Plan ( MIWTP ) [Conceptual Plan for Modeling] Conceptual Methods Stage I: Sub-basin 24 [170 MLD] Stage II: Sub-basin 25 [85 MLD] Stage III: Sub-basin 22 [85 MLD] Order of the sub-basins as per flow direction The rivers flow into Study River Reach Impact of MWSP occur in 11 sub-basins

10. Monthly Available Water at Headwork of MWSP: More than 80% of the total annual river flow occurrs within June to October Result of Current Scenario

11. Downstream Impact on River Reach of Koshi Basin: Annual Reduction: Stage I : 12% Stage II : 7% Stage III : 7% Wet Season Reduction: Stage I : 6% Stage II : 4% Stage III : 3% Dry Season Reduction: Stage I : 36% Stage II : 18% Stage III : 20% Reduction at Chatara: Annual : 0.2% Wet : 0.1% Dry : 0.6% Result of Current Scenario

12. Annual Available Water at Headwork of MWSP: Result of CC Scenario Current Flow [MCM] CC Projected Range of Flow [MCM] (1976-2005) 2030s 2050s Before MWSP: Melamchi river 499 312 - 347 316 - 359 Yangri river 443 306 - 336 306 - 340 Larke river 448 302 - 342 299 - 349 After MWSP: Melamchi river 437 250 - 285 253 - 297 Yangri river 412 275 - 305 275 - 309 Larke river 417 271 - 311 268 - 318

13. Range of Change in Annual Projected Flow at Headwork of MWSP: Result of CC Scenario

14. Range of Change in Wet Season Projected Flow at Headwork of MWSP: Result of CC Scenario

15. Range of Change in Dry Season Projected Flow at Headwork of MWSP: Result of CC Scenario

16. Average Change and Standard Deviation [± µ ,(± σ )] in Projected Flow ( 2030s ): Annual Change: Stage I : -29% (±2%) Stage II : -29% (±3%) Stage III : -37% (±1%) Wet Season Change: Stage I : -33% (±2%) Stage II : -33% (±3%) Stage III : -42% (±1%) Dry Season Change: Stage I : -16% (±4%) Stage II : -13% (±5%) Stage III : -19% (±3%) Change at Chatara: Annual : - 8% (±25%) Wet : -15% (±22%) Dry : +18% (±37%) Result of CC Scenario

17. Annual Change: Stage I : -28% (±3%) Stage II : -27% (±3%) Stage III : -35% (±3%) Wet Season Change: Stage I : -31% (±3%) Stage II : -30% (±3%) Stage III : -39% (±3%) Dry Season Change: Stage I : -15% (±5%) Stage II : -12% (±5%) Stage III : -18% (±3%) Change at Chatara: Annual : +18% (±48%) Wet : +11% (±46%) Dry : +42% (±58%) Result of CC Scenario Average Change and Standard Deviation [± µ ,(± σ )] in Projected Flow ( 2050s ):

18. Existing Cropping Pattern and Calendar Source: - Field investigation - District Ag. statistics Possible Change in Cropping Pattern and Calendar Source: - Field investigation - Proposing by DoI Cropping Pattern and Calendar of Melamchi River Command Area: Result – Crop Water Requirement

19. Rainfall vs Crop Water Requirement (CWR) in present and change in cropping pattern scenario Result – Crop Water Requirement Crop Water Requirement ( CWR ) of Melamchi River Command Area: Irrigation Requirement – Change in cropping pattern scenario Irrigation Requirement – Present cropping pattern scenario

20. Comparative plot of water availability and gross irrigation requirement ( GIR ) in driest month Result – Crop Water Requirement Impact of MIWTP on Melamchi River Command Area in Current Climate Scenario :

21. Result – Crop Water Requirement Impact of MIWTP on Melamchi River Command Area in Current Climate Scenario : Comparative plot of water availability and GIR at 40% overall efficiency in driest month Intensive Water Use Scenario

22. Impact of MIWTP on Melamchi River Command Area in CC Scenario ( 2030s ): Result – Crop Water Requirement Comparative plot of water availability and GIR at 40% overall efficiency in driest month Intensive Water Use Scenario

23. Impact of MIWTP on Melamchi River Command Area in CC Scenario ( 2050s ): Result – Crop Water Requirement Comparative plot of water availability and GIR at 40% overall efficiency in driest month Intensive Water Use Scenario

24. Conclusion In past, detail quantification of the impacts in downstream sub-basins have not been done, hence this study help to fill this gap In this study, flow reduction is quantified in all three stages at sub-basin level under current and future climate projection scenario In the current scenario , MIWTP will decrease annual water availability by less than 12% on the sub-basin that is immediately downstream of the transfer points but not further downstream towards the basin outlet, the water availability will decrease by 0.2% THANK YOU !!! Average climate change result shows that no water stress problem will occur in Melamchi river command area under current and future scenario Under intense water use scenario, the Melamchi river command area can increase; < 2.2 times of the present area at current climate scenario ( < 636 hectare ) < 1.4 times of the present area at 2030s climate scenario ( < 405 hectare ) < 2.0 times of the present area at 2050s climate scenario ( < 578 hectare )