The characteristics of temporal-spatial variation of water resource components in Ordos Plateau for nearly 50 years

The evaporation from ground surface (E) and precipitation (P) are two important factors for estimating the water resource. Based on the evaporation equation by Takahashi, from atmospheric available water point of view, the evaporation and the available rainfall (Δw) in Ordos Plateau have been calculated and analyzed. The datasets of the monthly precipitation and temperature at 13 stations in Ordos Plateau during the period of 1961-2007 have been examined. The results showed that the characteristics of temporal and spatial variation for every component of water resource in the last nearly 50 years. Over the last 50 years, the general trends of water resource components showed that P and Δw are declining and E is increasing. And each component has roughly experienced three changing stages in Ordos Plateau. The maximum P and Δw happened in Summer, and the maximum evaporation intensity also happened in Summer. Δw in summer was 68.9% of the annual Δw. The P and Δw in Winter showed a significantly increasing trends, however Δw in Winter showed a significantly declining trend. Spatial distribution of annual and seasonal water resource components showed that there was a gradual decreasing trend from southeast to northwest. There were also an obvious increasing center in Eastern Gully Hilly region and an obvious declined center in Northwest Otogs Heights.