Hydrological Characteristics of the Heihe River Basin in the Arid Inland Area of Northwest China

The hydrological characteristics of the Heihe River Basin in the arid inland area of northwest China were investigated. The spatial distribution of annual precipitation in the basin indicates that it decreases from east to west and from south to north, and increases with elevation by a gradient of 24.4 mm per hundred meters below 2,810 m a.s.l., but decreases with elevation by that of 37.0 mm per hundred meters above 2,810 m a.s.l. For the last 50 years, the mountain runoff of the basin has a tendency of increase. Except in the mountain area, the aridity is very high in the basin, and the aridity index ranges from 1.6 to 7.0 at the piedmont, to 9.0~20.0 in the midstream area and up to 40.0 in the downstream Ejin region. It is estimated for the last 50 years that a 1oC increment of annual temperature causes a 21.5 mm increase of evaporation in the mountain area, and the equivalent reduction of mountain runoff is 0.215×109 m3/yr at the Yingluoxia Hydrometric Station. The estimation shows also that a 1oC increment of annual temperature causes 1,842 mm increase of farmland evapotranspiration in the midstream area, an equivalent of 0.298×109 m3/yr more water consumption. The anthropogenic influence on the hydrological processes and water resources is then discussed.