Sensitivity of the Himalayan hydrology to land-use and climatic changes

Land-use and climatic changes are of major concerns in the Himalayan region because of their potential impacts on a predominantly agriculture-based ec onomy and a regional hydrology dominated by the monsoons. Such concerns are not limited to any particular basin but exist throughout the region includ ing the downstream plains. As a representative basin of the Himalayas, the Kosi Basin (54,000 km(2)) located in the mountainous area of the central Hi malayan region was selected as a study area. We used water balance and dist ributed deterministic modeling approaches to analyze the hydrologic sensiti vity of the basin to projected land-use, and potential climate change scena rios. Runoff increase was higher than precipitation increase in all the pot ential precipitation change scenarios applying contemporary temperature. Th e scenario of contemporary precipitation and a rise in temperature of 4 deg rees C caused a decrease in runoff by two to eight percent depending upon t he areas considered and models used. In the absence of climatic change, the results from a distributed water balance model applied in the humid south of the basin indicated a reduction in runoff by 1.3% in the scenario of max imum increase in forest areas below 4,000 m.