Climatic variability and its impact on hydrology of the Karnali River Basin, Nepal Himalaya

Himalayan mountains especially western part of Nepal lacks information about the hydrological dynamics and are susceptible to the impacts of a rapidly changing climate. This research helps in understanding the fundamentals of hydrological behavior in the topographically challenging and comparatively remote Karnali River Basin. This basin has area of 45,269 sq. km. with around 12% rocky bare land. Precipitation and temperature observations of past 32 years showed that the average annual precipitation is 1456 mm/year and is increasing in the mountains but decreasing in most of the other regions. The basin has average annual minimum 13⁰C and maximum 25⁰C temperature, and the maximum temperature is increasing at faster rate than the minimum temperature with significantly higher in high elevation and pre-monsoon. A fully encapsulated, process-oriented, distributed J2000 hydrological model developed inside JAMS framework is used for further analysis. The calibrated and validated model results suggest that the J2000 model is able to represent the hydrographs. 77% of rainfall occurs in monsoon and more than 10% of the annual precipitation is snowfall. The evapotranspiration is about 33% of the precipitation and discharge is about 66%. In total discharge snowmelt contributes about 13%, the glacier melt (from glacier areas) contributes 12.6% of the total discharge whereas snowmelt (from outside of glacier areas) contributes 13%. The different runoff components area: overland flow (35%), subsurface flow (49%) and base flow (15%). The sensitive analysis in JAMS framework using the Monte Carlo approach shows that recession coefficient for overland flow is most sensitive parameter. The change in climatic elements shows that the further rise in temperature and change in the precipitation pattern will further increase vulnerability in the basin.

Himalayan mountains especially western part of Nepal lacks information about the hydrological dynamics and are susceptible to the impacts of a rapidly changing climate. This research helps in understanding the fundamentals of hydrological behavior in the topographically challenging and comparatively remote Karnali River Basin. This basin has area of 45,269 sq. km. with around 12% rocky bare land. Precipitation and temperature observations of past 32 years showed that the average annual precipitation is 1456 mm/year and is increasing in the mountains but decreasing in most of the other regions. The basin has average annual minimum 13⁰C and maximum 25⁰C temperature, and the maximum temperature is increasing at faster rate than the minimum temperature with significantly higher in high elevation and pre-monsoon. A fully encapsulated, process-oriented, distributed J2000 hydrological model developed inside JAMS framework is used for further analysis. The calibrated and validated model results suggest that the J2000 model is able to represent the hydrographs. 77% of rainfall occurs in monsoon and more than 10% of the annual precipitation is snowfall. The evapotranspiration is about 33% of the precipitation and discharge is about 66%. In total discharge snowmelt contributes about 13%, the glacier melt (from glacier areas) contributes 12.6% of the total discharge whereas snowmelt (from outside of glacier areas) contributes 13%. The different runoff components area: overland flow (35%), subsurface flow (49%) and base flow (15%). The sensitive analysis in JAMS framework using the Monte Carlo approach shows that recession coefficient for overland flow is most sensitive parameter. The change in climatic elements shows that the further rise in temperature and change in the precipitation pattern will further increase vulnerability in the basin.