Analysis of long-term water balance in the source area of the Yellow River basin

To analyse the long-term water balance of the Yellow River basin, a new hydrological model was developed and applied to the source area of the basin. The analysis involved 41 years (1960-2000) of daily observation data from 16 meteorological stations. The model is composed of the following three sub-models: a heat balance model, a runoff formation model and a river-routing network model. To understand the heat and water balances more precisely, the original model was modified as follows. First, the land surface was classified into five types (bare, grassland, forest, irrigation area and water surface) using a high-resolution land-use map. Potential evaporation was then calculated using land-surface temperatures estimated by the heat balance model. The maximum evapotranspiration of each land surface was calculated from potential evaporation using functions of the leaf area index (LAI). Finally, actual evapotranspiration was estimated by regulating the maximum evapotranspiration using functions of soil moisture content. The river discharge estimated by the model agreed well with the observed data in most years. However, relatively large errors, which may have been caused by the overestimation of surface flow, appeared in some summer periods. The rapid decrease of river discharge in recent years in the source area of the Yellow River basin depended primarily on the decrease in precipitation. Furthermore, the results suggested that the long-term water balance in the source area of the Yellow River basin is influenced by land-use changes. Copyright (C) 2007 John Wiley & Sons, Ltd.