Potential Impact of Climate Change on Future Water Availability in Budhigandaki River Basin, Nepal

Most of the researches carried out in Nepal found that there would be an increase in precipitation due to climate change which in turn affects not only the timing, magnitude and frequency of the high flows but also the low flows. The magnitude of the floods is particularly important when we deal with hydraulic structures like spillway of a hydropower project to dispose the flood water. The increase/decrease in low flow implies more/less energy generation in dry season, consequently increasing/decreasing revenue. Timing and duration of peak flows dictate the operation rules of the reservoir both for water use and safe disposal of flood water. Further diversion flood may also be changed as an effect of climate change. Almost 3,000 MW capacity hydropower projects are identified in Budhigandaki river basin, when Nepal is having less than 1000 MW of hydropower generation as per today. The techno-economic implications of climate change on these planned projects of this basin are, thus, going to be of prime importance for the country's aspiration of socio-economic transformation. This work aims to analyze changes in river flow regime of the Budhigandaki river due to climate change and examine its impact on water availability for hydropower generation from the planned projects lying in the basin. The climate data were prepared for three climate change scenarios i.e., RCP 2.6; 4.5 and 8.5 with three time windows for each scenario, namely i.e. immediate future (2011-2040), mid future (2041-2070) and long future (2071-2100). Flows at potential project locations for the future were generated using these climate data as the input to the calibrated and validated HEC-HMS model. The generated flows were compared with that of baseline period (1981-2010). The water availability in the basin is not likely to decrease during this century, both in the monsoon and dry seasons. The magnitude of floods and frequency of floods above a certain threshold value in all scenarios and for all time windows are found more when compared with base case scenario. Probable higher flow during lean period implies that the impact of climate change on energy generation during the dry season is likely to increase from the planned hydropower projects.