Schulz, K; Huwe, B; W├Ârlen, C; Eiden, R: Wind speed regionalization and its influence on areal evapotranspiration prediction, Regionalization in Hydrology, 254, 97-104 (1999)
Evapotranspiration as one of the basic components in the hydrological cycle plays a major role in determinining the water budget of agricultural and forestry catchments. Due to the effects of topography the controlling factors like net radiation, temperature, humidity and wind speed are highly variable in space. In this investigation, we show that spatial differences in wind speed data may result in differences in calculated potential evapotranspiration rates. The Ryan (1977) approach, to extrapolate the wind speed data of an "undisturbed" central meteorological station to any grid point within an agricultural catchment, is introduced and compared to measurements at three different locations in the Weiherbach catchment (Kraichgau, Germany). Although only information from a digital elevation model is used, it is shown that this method provides a much better estimation of the areal windfield, than using the data from the central station alone. Distributed modelling of the water budget for the years 1994 and 1995 demonstrates that neglecting the influence of topography on wind speed will result in over-estimation of the areally averaged potential and actual evapotranspiration rates.

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