Signature and hydrologic consequences of climate change within the upper–middle Brahmaputra Basin

Abstract

AbstractA prevailing perception is that the glaciers and perennial snow and ice covered areas (SCAP) or in the Himalayan region are fast contracting. However, systematic studies providing the quantitative estimates of SCAP as a function of time within individual river basins are lacking. The importance of meltwater in river flows varies greatly from one river basin to another, yet the actual estimates of those contributions are largely unknown. This study bridges such knowledge gaps for the upper–middle Brahmaputra Basin by using best available digital cartographic and remotely sensed snow cover data. We find that when the entire basin is considered, SCAP decreased from 7637 ± 764 in 1980 to 4298 ± 1422 km2 in 1992. However, it has increased to 7160 ± 2248 km2 in 2000. From 2000 to 2010, the SCAP has remained nearly constant around a mean of 10 052 ± 1468 km2. The same trend is observed within individual physiographic zones of the basin. Such increase in SCAP is due to the increase in the precipitation over the middle Brahmaputra Basin and the Nyainquentanglha Mountains, as observed in station records. The incursion of moist air through the Brahmaputra valley to the higher elevations within the Nyainquentanglha Mountains causes snowfall during pre‐monsoonal and post‐monsoonal seasons and an expansion of the SCAP. Glacial expansions in the Nyainquentanglha Mountains have also been observed in other recent studies. In addition to the increase in precipitation and SCAP, another manifestation of climate change observed in this basin is the increasing temperature with a mean annual trend of +0.28 °C/decade. The hydrologic consequences of the observed effects of climate change are expected to be an insignificant change in streamflows in the watersheds drained by the upper Brahmaputra River but a perceptible increase in river discharges in the watersheds drained by the middle Brahmaputra River and its tributaries, particularly within the upper and lower catchments of the middle Brahmaputra Basin. Copyright © 2012 John Wiley & Sons, Ltd.