Soil evaporation under different types of land use in southern African savanna ecosystems

For dryland ecosystems, soil evaporation is a major factor of the soil water balance. Often handled in one term with transpiration, little is known quantitatively about evaporation and impacts of soil and vegetation on it. On 12 plots at three sites in Angola, Namibia, and Botswana, potential and actual evaporation was measured using microlysimeters and parameterized. Dependencies on micrometeorological, soil, and site properties were statistically examined. In simulation runs with SWAP, the microlysimeter measurements were tried to be reproduced. Measured potential evaporation rates varied from 3.0 mm d(-1) to 8.6 mm d(-1). The evaporational parameter beta ranged between 0.9 mm(1/2) and 4.3 mm(1/2). Evaporation was found to be strongly impacted by vegetation and land use, increasing from homogeneous bush areas over heterogeneous, more open woodlands to sparsely covered dryland agricultures. Correlations of evaporation variables with temperature, humidity, shading, topsoil water content, pF, bulk density, texture, and C content were found. Relationships were non-explicit, which could be achieved by combining different factors. The simulation showed satisfying results with small deviations, confirming the model's general ability to depict the process. The application of the Boesten-Stroosnijder-model in combination with the used methods showed to be very useful to express evaporational properties, yet further research is necessary to improve consistency. A basis for evaporation prediction from known plot and soil characteristics and temporal and spatial up-scaling could be given.