Comparison of observed and modeled surface fluxes of heat for the Volta river basin

Land-surface processes and their modeling play an important role in planetary boundary modeling, due to their role of providing the surface boundary conditions to the atmosphere. In particular, processes regarding clouds and precipitation are strongly influenced by land-surface processes. To get a further understanding of those interactions we focus on the validation and calibration of a Soil-Vegetation-Atmosphere-Transfer (SVAT) model (The Oregon-State-University-Land-Surface Model) for the Volta River Basin in West Africa. This is a typical example of a semi-arid region in which studies on the interaction within soil, vegetation, atmosphere and water are still needed. For the validation of the model scintillometer measurements from three different sites in Ghana are used to calculate an areal average sensible heat flux density. The three sites show major differences concerning the vegetation, soils, land use, slopes and also climate. All data used in this study are part of long-term observations of the water- and energy balance in the Volta Basin. The calculated fluxes are compared with the output of the model. For the first step an off-line, uncoupled version of the SVAT model is used, driven by measured atmospheric forcings. These were obtained at a weather station on every research site. The second step is the adaptation of the SVAT model to the conditions in the Volta River Basin. The results from the adapted model are validated with the scintillometer measurements. Besides, a comparison with the results of the original model reveal potential shortcomings of the standard SVAT model used under semi-arid condition