Abstract
Precipitation accuracy greatly affects hydrological forecast and calculation, particularly to mountainous drainage basins where rainfall is extremely non-uniform. This paper develops a spatial model of precipitation based on relationship between the gauged rainfall at 9 sites and the DEM implemented by the GIS. The Thiessen method and the spatial model are applied and compared to estimate daily, monthly and annual basin-mean rainfall. The results show a significant difference, implying the need for a spatial model of precipitation to be used for a distributed hydrological model. The basin daily, monthly and yearly rainfalls by the Thiessen method are underestimated respectively, 40∼190%, 14∼40% and 17∼28% less than those by the spatial model. The basin storage, therefore, in the hydrological model used for flood prediction has to be overestimated largely to fit to the gauged stream flows. The basin-wide water balance in monthly interval is examined to verify the spatial rainfall based on the discharges from 2 sub-basins in high altitude, and the results illustrate that the runoff depth in a few months are larger than or equal to the rainfall estimated by the Thiessen method leading to the stored water ΔS by soil, generating the negative values in the rainy months. The surplus rainfall stored in saturated soil in the summer is drained as the surface flow which is larger than precipitation during the autumn. This is reflected on the hydrographs due to the soil frost so that the ΔS shows the maximum negative value in the autumn.
