The application of simple methods using remote sensing data for the regional validation of a semidistributed hydrological catchment model Martin Wegehenkel * , Hubert Jochheim, Kurt Christian Kersebaum Institute of Landscape System Analysis, Centre of Agricultural Landscape and Land Use Research, Eberswalder Street 84, D-15374 Mu ¨ ncheberg, Germany Received 5 July 2004; received in revised form 10 February 2005 Available online 24 August 2005 Abstract Simulation runs of a semidistributed hydrological conceptual catchment model were performed using a spatial data set from a mesoscale catchment located at the moraine landscape of North–East Germany. The simulation quality of the model was estimated by comparing measured daily actual evapotranspiration rates, soil water contents and discharge rates with the corresponding sim- ulated model outputs. Additionally, six Landsat-TM5-subsets covering the catchment were used to calculate the Normalized Dif- ference Vegetation Index (NDVI). These NDVI-distributions were compared with the corresponding simulated regional distributions of actual evapotranspiration (ETr) rates. A visual analysis of the spatial distribution patterns of the NDVI and of the simulated ETr-rates shows some correspondences. However, the spatial variability of the NDVI-patterns was distinctly higher in comparison with the variability of the ETr-rates calculated by the model. We analyzed the coefficients of correlation R between the patterns of the NDVI and the simulated ETr-rates separately for the land cover classes arable land, meadows, coniferous, decid- uous and mixed forests. For arable land R ranged within 0.77 and 0.10, for meadows within 0.79 and 0.10, for coniferous forests between 0.73 and 0.10, for deciduous forests between 0.88 and 0.10 as well as for mixed forests between 0.67 and 0.10. The spatial distributions of simulated high and low ETr-rates were mainly correlated with the spatial distributions of forest areas, arable land, water bodies and settlements. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Hydrological modelling; THESEUS; Validation; Remote sensing; Evapotranspiration; NDVI 1. Introduction One essential component of the catchment water bal- ance is the spatial distribution of the soil water storage and the corresponding actual evapotranspiration. Spa- tial and temporal heterogeneity of vegetation type and differences in available energy and water can cause a high spatial variability of the actual evapotranspiration. The use of appropriate methods to estimate this spatial variability of evapotranspiration rates is a need to im- prove the description and prediction of the hydrologic processes in catchments. This enables also a better esti- mation of the impact of potential land cover changes on the water balance of hydrologic catchments. Moreover, this estimation is essential for a sustainable catchment management. Optical remote sensing data obtained from satellite sensors like Landsat-TM5 or Spot were used to evaluate input data such as the spatial distribu- tion of land cover and of vegetation parameters such as the Normalized Difference Vegetation Index (NDVI). Furthermore, the NDVI can also be used to estimate the spatial distribution of the evapotranspiration. For 1474-7065/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2005.07.011 * Corresponding author. Tel.: +49 33432 82275; fax: +49 33432 82334. E-mail address: mwegehenkel@zalf.de (M. Wegehenkel). www.elsevier.com/locate/pce Physics and Chemistry of the Earth 30 (2005) 575–587