Reconciling high-altitude precipitation in the upper Indus basin with glacier mass balances and runoff

摘要

Mountain ranges in Asia are important water suppliers, especially ifdownstream climates are arid, water demands are high and glaciers areabundant. In such basins, the hydrological cycle depends heavily on high-altitude precipitation. Yet direct observations of high-altitudeprecipitation are lacking and satellite derived products are of insufficientresolution and quality to capture spatial variation and magnitude ofmountain precipitation. Here we use glacier mass balances to inversely inferthe high-altitude precipitation in the upper Indus basin and show that theamount of precipitation required to sustain the observed mass balances oflarge glacier systems is far beyond what is observed at valley stations orestimated by gridded precipitation products. An independent validation withobserved river flow confirms that the water balance can indeed only beclosed when the high-altitude precipitation on average is more than twice ashigh and in extreme cases up to a factor of 10 higher than previously thought.We conclude that these findings alter the present understanding of high-altitude hydrology and will have an important bearing on climate changeimpact studies, planning and design of hydropower plants and irrigationreservoirs as well as the regional geopolitical situation in general.