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Title Upscaling hydrological processes in a Namibian savanna

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Short title Upscaling hydrological processes in savannas

Author(s) Wieczorek, M.; Tietjen, B.; Blaum, N.; Jeltsch, F.; Rossmanith, E.

Presenting author Rossmanith, E.

Institution(s) Plant Ecology and Nature Conservation, University of Potsdam

Keywords Ecohydrologic modelling; savanna; climate change; land use; hortonian overland flow

Abstract In semiarid savannas, precipitation is the most important trigger for ecological processes. Vegetation dynamics and biomass production are strongly influenced by water availability in the soil. The distribution of water depends on different factors, including soil type and vegetation cover. When events of high precipitation occur, water run-off appears, which leads to a redistribution of water in the system. For semi-arid areas, the most typical run-off type is Hortonian overland flow, also called infiltration excess run-off, which occurs when precipitation intensity exceeds infiltration rate. Thus, water may get lost from the system. Climate change scenarios predict a decrease of precipitation for semiarid savannas of Southern Africa. In order to predict the effect of climate change on rangeland profitability, we need to understand water distribution on the landscape scales. Usually, the impact of vegetation on run-off, infiltration and evaporation and the impact of water on seed germination, plant survival and other processes are studied on small spatial scales. However, decisions of land use management are made on large, regional scales. To bring the different scales together is one of the big challenges in ecology. The aim of this study is to investigate water run-off and distribution on a large spatial scale and include the results of small scale investigations. Therefore, we developed a regional landscape model, (1 ha cells, 20,000 ha grid) of a Namibian semi-arid savanna that includes vegetation dynamics and topography. With an existing hydrological model on a small scale (5x5 m cells, 25 ha grid) we analysed how redistribution within a 1-ha-cell depends on precipitation intensity and frequency, on vegetation cover, on soil type and moisture and on topography. The results were included into the landscape model in order to simulate water run-off and distribution under different precipitation scenarios.

Congress Topic Process Analysis

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Ref. No. 581