Estimation and Forecast of Components of Runoff in the River Basins of Central Asia

Abstract

Various options for method of the over long-term hydrological forecasts of annual runoff for several river basins in Central Asia (Amu Darya, Syr Darya, Tarim, Ganges, Indus, Mekong, Brahmaputra, Yangtze, Huang He) are investigated. Annual air temperature, precipitation, and normalized difference of anomalies of these variables according to data of meteostations and for gridded values having 0.5 degree increments in latitude and longitude were tested as inputs. Informative capability of each predictor for calculating runoff in river basins of Central Asia was described. Expected air temperature as a predictor for long-term forecasts of river runoff was obtained by extrapolating the proper temporal series. Simulation, calculation and forecast of glacial runoff and evaporation were performed in the ablation zone of Central Asia glaciers. The input data for the model are: precipitation, average temperature and humidity during the summer, generalized areal, altitudinal and morphological parameters of the glaciation. In order to optimize the method of calculating of regime of glaciation, the populations of glaciers in the basins of the tributaries of the Amu Darya, Syr Darya, Indus, Ganges, Yellow, Yangtze, Brahmaputra and Tarim rivers were allocated to 3815 homogeneous groups of objects. Eight values of altitude and 23 gradations of glacier area are consistently applied as classifi cation criteria. For each group the average and weighted average morphometric characteristics of glaciers were determined. Data from 53 225 glaciers with a total area of 81144 km2 in the basins of Central Asia are used to demonstrate the capabilities of the method. Modelled values of water balance components (runoff, precipitation, and evaporation) were obtained for river basins of Vakhsh, Panj, Zarafshan, Naryn, Brahmaputra.