The contribution of glacier melt to streamflow

Ongoing and projected future changes in glacier volume and extent globally have led to concerns about the implications for water supplies. Glacier contributions to river discharge are not well known on a regional or global basis, nor are the populations at risk to future glacier changes. We estimate upper bounds on the fraction of river discharge attributable to glacier discharge on a monthly basis using a global hydrology model and glacier energy balance computations, and track this fraction through the global stream network. In general, our estimates of the fraction of river discharge attributable to glacier sources are lower than previously published values. Nonetheless, we estimate that globally 370 (140) million people live in river basins where glacier sources contribute at least 10% (25%) of river discharge on a seasonal basis. Most of this population is in the High Asia region.