Spatial distribution of soil moisture content within catchments and its modelling on the basis of topographic data

This paper deals with the development of a model of the average seasonal spatial distribution of soil moisture content on slopes or in small catchments. The model is based on a quantitative assessment of the water and heat balances of the upper soil layer under different climatic conditions and a generalization of the field data by Romanova (1971). The ratio of soil moisture on a sloping surface and that on a flat surface is related to slope aspect by trigonometric (Fourier) series. The model estimates the average spatial distribution of relative moisture content (KW) in the upper 50 cm layer of the soil in summer as a function of the form of the relief (flat, slope), longitudinal slope profile shape (straight, concave or convex), aspect of the slope (degrees), slope gradient (dimensionless) and relative distance from the divide, which are found from a digital elevation model. The model is applicable to humid and moderately dry climate conditions. Computer simulations are performed assisted by the GIS package PCRaster (Utrecht University, the Netherlands). The test of the model was carried out using seven years (1981–1987) soil moisture data at 38 points situated within three small experimental catchments of the Boguslav Field Experimental Hydrological Base of the Ukrainian Research Hydrometeorological Institute (Kiev region, Ukraine).