Extreme and Average Glacier Runoff in the Amudarya River Basin

Glaciers located in the headwaters of the Amudarya basin cover nearly 78% from the total glaciated area in the Aral Sea basin. The long-term regime of seasonal glacier meltwaters during 1935–1993 was computed by the author's model REGMOD. For this computation, glaciers in the region were divided into 138 groups. Empirical integral function probability distributions of seasonal melting were estimated for each group and averaged for all groups for each year. Finally, high and low meltwater years were determined. The spatial distribution of melting was described in extreme and average years. It was revealed that the spatial variability of meltwater volume V _M is most variable in average years and not significant in minimal and maximal years. This is most important for stabilizing the balance between inflow and outflow in reservoirs supplying hydropower and agriculture. Regional dependencies of V _M in extreme years are closely related to the spatial distribution of the firn boundary averaged for glacier groups.