A reflection on the long-term water balance of the Upper Indus Basin

Abstract

Rapid glacier retreats due to rising temperatures have been predicted in the Hindukush–Karakoram–Himalaya (HKKH). Recent findings indicate shrinking glaciers in parts of the Himalayas, affecting ice storage and ultimately water availability. Insights on ice storage of the HKKH remain controversial, where glaciers retreat in some parts, while surging in others. In high-altitude areas only few in-situ observations are available, leading to ambiguous closure of the hydrological balance. Objective of this paper is to analyze the closure for the Upper Indus Basin (UIB). A first-order analysis using long-term flow and precipitation records, estimates of evaporation and ice storage is performed. Satellite information, atmospheric reanalyses, in-situ observations and related uncertainty are independently investigated. Trend analysis of 50-year stream flow indicates a statistically insignificant decrease of basin outflow. Analysis of 100-year precipitation data at valley stations shows no significant long-term trend, whereas temperature has increased moderately. Estimates of evaporation and sublimation in the HKKH system are notably few. Findings suggest that a substantial loss of ice in the UIB during the 1999–2009 decade is unlikely. Ice storage is probably at equilibrium or under slight accumulation, as indicated by recent altimetry studies in the Karakoram. In the UIB there is no evidence for intermediate-term risk to water supply as suggested in recent literature.