Implications of glacier change to Upper Indus River streamflow

In recent years, many of the world's mountain glaciers have shown negative mass balance and rapid decreases in glacier area and volume. Accelerated glacier recession trends have also been reported for the Greater Himalayan region, based largely on studies in Nepal and India. Recent studies carried out in the Western Karakoram Himalayas suggest an expansion of glaciers and a reduction in summer streamflow, however. Snow and ice melt from these glaciers is the primary input to the discharge of the Indus River of Pakistan, providing a perennial water supply for agriculture, hydroelectric power and drinking water for millions of people. The impact of observed and projected glacier changes on sustainable water supply and flood hazards are largely unknown. In this study, the Variable Infiltration Capacity (VIC) hydrology model, modified to represent the downslope movement of glacier ice, is used to assess the hydrologic response to glacier change in the region. Changes in streamflow seasonality and the mass balance of glaciers in the Western Karkoram Himalaya region were determined for the period 1961-1990 and future climate period 2071-2100 using precipitation and temperature data from the high resolution FVGCM-RegCM3 climate model. Changes in glacier mass balance for the base period compare well with observed glacier changes from remotely sensed data. Spring and summer streamflow in the southern watersheds of the Upper Indus Basin (UIB) increased dramatically in the later period, while northern, more glaciated watersheds showed little change.