Hydrological response to droughts in the Karnali basin of Nepal

The Karnali basin (40,000 sq km) in western Nepal is a pristine river basin with large potential for the development of hydropower and irrigation. The Karnali river sustains the biodiversity in the national parks downstream and supports the livelihoods of thousands of people. Any changes in the flow regime of the Karnali may therefore have far reaching consequences. This study focuses on analyzing the hydrological response of the Karnali to (multi-year) droughts. The objective is to understand how long the storages in the hydrological system, e.g. glaciers, snow, ground and soil water can buffer prolonged droughts. The hydrological model SPHY, calibrated with long-term river flow observations, is used for this purpose. We created synthetic drought time series by sampling from a 30-year historical forcing dataset based on ERA5. We then used these time series to force the SPHY model and we analyzed the change in streamflow composition as a function of drought duration. This study provides important insights in the buffering capacity of the river basin in a changing climate.