Anthropogenic, climatic, and hydrologic trends in the Kosi Basin, Himalaya

A great debate exists concerning the influence of land-use and climatic changes on hydrology in the Himalayan region and its adjacent plains. As a representative basin of the Himalayas, we studied basinwide land-use, climatic and hydrologic trends over the Kosi Basin (54,000 km(2)) in the mountainous area of the central Himalayan region. The assessment of anthropogenic inputs showed that the population of the basin grew at a compound rate of about one percent per annum during the past four decades. The comparison of land-use data between the surveys made during the 1960s and 1978-1979 did not reveal noticeable trends in land-use change. The analysis of meteorological and hydrological time series from 1947 to 1993 showed some increasing tendency of temperature and precipitation. The statistical tests of hydrologic trends indicated an overall decrease in discharge on the Kosi River and its major tributaries. The decreasing trends of streamflow were more significant during the low-flow months. The statistical analysis of homogeneity showed that the climatic as well as the hydrologic trends were more localized in nature lacking a distinct basinwide significance.