The spatial and temporal contribution of glacier runoffto watershed discharge in the Yarkant River Basin, Northwest China

Abstract

In this paper, a glacial module based on an enhanced temperature-index approach was successfully introduced into the Soil and Water Assessment Tool (SWAT) model to simulate the glacier runoffand water balance of a glacierized watershed, the mountainous region of the Yarkant River Basin (YRB) in Karakoram. Calibration and validation of the SWAT model were based on comparisons between the simulated and observed discharge with a monthly temporal resolution from 1961 to 2011 for the Kaqun hydrological station. The results reaffirmed the viability of the approach for simulating glacier runoff, as evidenced by a Nash-SutcliffEfficiency (NSE) of 0.82-0.86 as well as a percentage bias (PBIAS) of -4.5% to 2.4%, for the calibration and validation periods, respectively. Over the last 50 years, the total discharge and glacier runoffboth exhibited increasing trends with 0.031 × 109 m3·a-1 and 0.011 × 109 m3·a-1. The annual glacier runoffcontribution to the streamflow was between 42.3% and 64.5%, with an average of 51.6%, although the glaciers accounted for only 12.6% of the watershed drainage area in the mountainous YRB. The monthly contribution of the glacier runoffranged from 11.0% in April to 62.1% in August, and the glacier runofffrom June to September accounted for about 86.3% of the annual glacier runoff. Runofffrom the mountainous regions above 5000 m a.s.l. accounted for 70.5% of the total discharge, with glacier runoffcontributions being approximately 46.4%.