The role of spatial variability of soil moisture for modelling surface runoff generation at the small catchment scale

The effects of spatial variability of soil moisture on surface runoff gener ation at the hillslope and small catchment scale were studied. The model us ed is physically based accounting for the relevant hydrological processes d uring storm runoff periods, ii case study investigating the effects on runo ff generation in a loessy small catchment is presented. In this study the s torm rainfall response was modelled using different distribution patterns o f the initial soil moisture content, and where different initial soil moist ure fields were generated by using both interpolation methods and stochasti c simulation methods. It is shown that spatial variability of pre-event soi l moisture results in an increase in runoff production compared to averaged values. It is of particular importance to note the combined organised/stoc hastic variability features, that is, the superposition of systematic and r andom features of soil moisture dominate local generation of surface runoff . In general one can sap that the stronger the organised heterogeneity is, the more important is an adequate and refined interpolation technique which is capable of accounting for complex spatial trends. The effects of soil m oisture variations are of particular importance for storms, where the produ ced runoff volume is just a small fraction of precipitation.