Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 9 3 2005 10.5194/hess-9-225-2005 http://www.hydrol-earth-syst-sci.net/9/225/2005/ http://www.hydrol-earth-syst-sci.net/9/225/2005/hess-9-225-2005.html http://www.hydrol-earth-syst-sci.net/9/225/2005/hess-9-225-2005.pdf 225 241 2005-09-21 Comparative analysis of the actual evapotranspiration of Flemish forest and cropland, using the soil water balance model WAVE W. W. Verstraeten B. Muys J. Feyen F. Veroustraete M. Minnaert L. Meiresonne A. De Schrijver Laboratory of Soil and Water Management, Katholieke Universiteit Leuven, Vital Decosterstraat 102, 3000 Leuven, Flanders, Belgium Laboratory for Forest, Nature and Landscape Research, Katholieke Universiteit Leuven, Vital Decosterstraat 102, 3000 Leuven, Flanders, Belgium Flemish Institute for Technological Research, Centre for Remote Sensing and Earth Observation Processes, Boeretang 200, 2400 Mol, Flanders, Belgium Laboratory of Forestry, Ghent University, Geraardsbergse Steenweg 267, 9090 Gontrode, Flanders, Belgium Institute for Forestry and Game Management (IBW), Gaverstraat 4, 9500 Geraardsbergen, Flanders, Belgium This paper focuses on the quantification of the green &ndash; vegetation related &ndash; water flux of forest stands in the temperate lowland of Flanders. The underlying reason of the research was to develop a methodology for assessing the impact of forests on the hydrologic cycle in comparison to agriculture. The tested approach for calculating the water use by forests was based on the application of the soil water balance model WAVE. The study involved the collection of data from 14 forest stands, the calibration and validation of the WAVE model, and the comparison of the water use (<I>WU</I>) components &ndash; transpiration, soil and interception evaporation &ndash; between forest and cropland. <P style="line-height: 20px;"> For model calibration purposes simulated and measured time series of soil water content at different soil depths, period March 2000&ndash;August 2001, were compared. A multiple-site validation was conducted as well. Actual tree transpiration calculated with sap flow measurements in three forest stands gave similar results for two of the three stands of pine (<I>Pinus sylvestris</I> L.), but WAVE overestimated the actual measured transpiration for a stand of poplar (<I>Populus</I> sp.). <P style="line-height: 20px;"> A useful approach to compare the <I>WU</I> components of forest versus cropland is scenario analysis based on the validated WAVE model. The statistical Profile Analysis method was implemented to explore and analyse the simulated <I>WU</I> time series. With an average annual rainfall of 819 mm, the results reveal that forests in Flanders consume more water than agricultural crops. A 30 years average of 491 mm for 10 forests stands versus 398 mm for 10 cropped agricultural fields was derived. The <I>WU</I> components, on yearly basis, also differ between the two land use types (transpiration: 315 mm for forest and 261 mm for agricultural land use; soil evaporation: 47 mm and 131 mm, for forest and cropland, respectively). Forest canopy interception evaporation was estimated at 126 mm, while it was negligible for cropland.