The influence of the spatial structure of soil properties on water balance modeling in a microscale catchment

The study investigates the impact of the spatial variability of soil hydraulic properties on hydrologic fluxes of the microscale Berrensiefen catchment (28.6 ha). In a first step the Mualem/VanGenuchten parameters are calculated from a point data set of soil properties using a pedotransfer function. In a second step, we estimated the Mualem/VanGenuchten parameters at unsampled locations using four different regionalization procedures: multiple regression, ordinary kriging, external drift kriging and regression kriging. The regression kriging results are taken as the reference distribution for a model study. A modified version of the 3d finite element model SWMS_3d is applied to simulate the water fluxes. With the model study the importance of the spatial features of soil hydraulic properties is quantified. Four spatial concepts are tested: a choropleth map of soil units. a catchment average, a spatial random distribution and a stochastic simulation approach. We particularly investigated the influence of the spatial concept on the modeled runoff generation. We quantified the sensitivity of runoff to the frequency distribution and to the spatial structure of the soil hydraulic properties. The frequency distribution mainly affects the amounts of the fast runoff components (surface and macropore flow) while the organized spatial variability affects the modeled temporal concentration of the fast runoff components. The effect on the calculated actual evapotranspiration is rather small, (C) 2002 Elsevier Science Ltd. All rights reserved.