Land-use impacts on storm-runoff generation: scenarios of land-use change and simulation of hydrological response in a meso-scale catchment in SW-Germany

The impact of land-use change impacts on storm-runoff generation is presented based on a simulation study composed of three parts: (1) generation of spatially explicit land-use scenarios; (2) spatially distributed and process based hydrological modelling of runoff generation; (3) application of this procedure and demonstration of results for a predominantly agricultural meso-scale catchment in a loessy-soil landscape in SW Germany. Land-use scenarios are a prerequisite for assessing the influence of potential changes of land-use and/or land-cover on runoff generation. The land-use change modelling kit (LUCK) provides a method for the spatial transformation of overall trends of land-use into spatially distributed scenarios of land-use patterns, taking into account their topology in a true position mode. The assignment of land-use categories to each grid cell is realised in a spatially explicit manner, dependent on an evaluation of the site characteristics as well as its neighbourhood relationships. Based on these land-use scenarios, the influence of altered land-use characteristics on flooding is simulated using a modified version of the physically based hydrological model WaSiM-ETH. In order to extend the model's capabilities with respect to adequate representation of land-use related runoff generation mechanisms, some additional mechanisms have been introduced: (1) A macropore module accounting for fast infiltration processes; (2) A siltation module decreasing hydraulic conductivity of the soil surface as a function of precipitation intensity and vegetation coverage. (3) Sub-grid variability considering the impervious and sealed portion of a grid cell. The location and lateral interaction of landscape elements within a catchment is captured by spatially explicit modelling on the basis of gridded information provided by the scenarios. The whole simulation procedure is applied to a meso-scale catchment in SW Germany. The results show that the influence of land-use conditions on storm-runoff generation depends greatly on the rainfall event characteristics and on the related spatial scale, i.e. the influence is only relevant for convective storm events with high precipitation intensities in contrast to long-lasting advective storm events with low precipitation intensities. However, convective events-and thus land-use conditions-are of very minor relevance for the formation of floods in large river basins because this type of rainfall event is usually restricted to small-scale occurrence. (C) 2002 Elsevier Science B.V. All rights reserved.