Changes in glacial lakes in the Poiqu River Basin in the central Himalayas

Abstract. The Poiqu River Basin contains 162.2 km² of ice and 19.9 km² of glacial lakes. The remote sensing data over the last 40 years have been used to identify 147 glacial lakes in the basin and clearly revealed the retreat of glaciers and the growth of glacial lakes at accelerating rates, in parallel to warming climate in the Himalayas. Based on remote sensing images and digital elevation model (DEM) analysis, the area and water changes in glaciers and glacial lakes are analyzed in detail, and a water balance equation (WBE) is proposed to account for the mechanism of lake growth. The WBE includes water supplies from rainfall runoff, ice and snow ablation, glacial retreat, and water losses due to infiltration and evaporation. As each water contribution item specifically depends on local weather and morphology, the WBE provides a direct link between glacier and glacial lake changes and climate changes under local conditions. Operation of the WBE for five major glacial lakes in the Poiqu River Basin has revealed that water from glaciers and snow cover dominates the growth of lakes. Lakes are found to vary in different ways even with similar backgrounds, depending strongly on local weather and geomorphology conditions. The WBE is not only applicable for predicting future changes in glacial lakes under climate warming conditions but is also useful for assessing water resources from rivers in the central Himalayas.