A comparative analysis of glacier and glacier-melt runoff changes in western and eastern Himalayan river basins

Abstract

This study assesses the impact of glacier changes and their effects on glacier melt runoff over three different Himalayan river basins located in western Himalaya (i.e. Baspa and Ganga) and eastern Himalaya (Teesta). For computation of glacier melt runoff, a fully distributed snow-glacier melt runoff model viz. SPHY has been used. The glacier area changes have been computed by preparing the glacier maps for different years for all selected river basins viz. Baspa (for year 2000 & 2018), Ganga (for year 1990, 2000, 2010 and 2020) and Teesta (for year 2000 and 2020). Results showed that the glacier areas have noticeably reduced for all Himalayan river basins viz. Baspa (∼19.8%), Ganga (∼5.01%) and Teesta (∼5%). It has been observed that smaller glaciers have more significantly reduced than large glaciers. The strength of the glacier melt induced runoff computation has been evaluated with reference to observed discharge at different gauges in all selected river basins, which showed a reliable agreement between modeled and observed runoff (R2 > 0.7). To see the behavior of runoff for different glacier sized watersheds, the three basins have been divided into a number of watersheds. In Baspa four watersheds while for Ganga and Teesta basins, six watersheds have finally selected depending on quantum of glacier. As per the decadal computation of glacier melt scenarios for all river basins viz. Baspa (i.e. 2003–2010 and 2011–2018), Ganga (1986–1995, 1996–2005, 2006–2015, and 2011–2020) and Teesta (1996–2010 and 2006–2020), observations showed that watersheds having large glaciers, the melt runoff has increased, while in cases of the watersheds having small glaciers, the melt runoff has decreased due to reduced glacier cover. In case of Baspa basin, glacier melt runoff has decreased by 5% while for Ganga and Teesta basins it has increased by 1%. Similarly, for Baspa basin, snowmelt runoff has increased by 6% and for Ganga and Teesta it has decreased by 3%.