Aral sea basin water resources and the changing aral water balance

Abstract

This chapter deals with two related water issues: the water resources of the Aral Sea Basin and the Aral Sea’s water balance. The Aral Sea’s size is dependent on the water resources in its basin and how much these are depleted by human usage. The chief water resources are the large basin rivers Amu Darya and Syr Darya and groundwater. The author discusses the size and character of these and their sufficiency for meeting human demand. Contrary to popular belief, the Aral Sea Basin is reasonably well endowed with water resources. But the high level of consumptive use, overwhelmingly for irrigated agriculture, has resulted in severe water shortage problems (see Chap 8). Since the Aral Sea is a terminal (closed basin) lake with no outflow lying amidst deserts, its water balance is basically composed of river inflow on the gain side and evaporation from its surface on the loss side. Precipitation on the sea’s surface contributes only about 10 % to the positive side of the balance. Net groundwater input is difficult to determine with any accuracy and likely had minimal influence until recent decades when, owing to major drops in river inflow, its impact on the water balance has grown. The Aral’s water balance was very stable from 1911 until 1960. However, since then it has been consistently negative (losses more than gains) owing to very substantial reductions in river inflow caused by large consumptive losses to irrigation. This was particularly pronounced for the decadal periods 1971-1980 and 1981-1990. More river flow reached the sea over the period 1991-2000 and its water balance, although remaining negative. However, the water balance situation deteriorated during the subsequent decade (2001-2010) owing to recurring droughts. The decidedly negative water balance has led to rapid and continuing shrinkage of the sea. (See also Chaps 9 and 11).