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Titre : Estimation of actual evapotranspiration and water balance using combined geostationary and polar orbiting satellite products : a case study in Spain

Auteur : Mamo, T.A. (Tadesse Alemu)

Etablissement de soutenance : University of Twente International Institute for Geo-Information Science and Earth Observation (ITC)

Grade : Master of Science in Geo-Information Science and Earth Observation 2010

Résumé
Actual evapotranspiration and rainfall are the key elements in water balance estimation that give scientifically sound information on water availability. Currently, satellite remote sensing is widely used for estimation of these two parameters. In the past decades, the quantification of daily actual evapotranspiration (AET) from remote sensing data w as mainly based on one time observation from sun synchronous satellites by scaling instantaneous evaporative fraction (EF) under the assumption of constant daytime EF. Models and data source selections for accurate estimation of AET from remote sensing observation are also continuously improving . The sources of data for this thesis were 40 ground meteorological stations in the study area an d satellite products from the European organization for the exploitation of meteorological satellites on land surface analysis, satellite application facility (EUMETSAT LSA SAF) and moderate resolution imaging spectroradiometer (MODIS). Products from EUMETSAT are mainly derived from the spinning enhanced visible and infrared imager (SEVIRI) radiometer embarked on the Meteosat second generation (MSG) platform and other European satellite systems which have an imaging-re peat cycle of 15-30 minutes. For this research, the rainfall products were taken from EUMETSAT meteorological product extraction facility-multi sensor precipitation estimate (MPEF-MPE), but AET was estimated from remote sensing and ground- based data using surface energy balance system mode l (SEBS). Efforts were made in this research to estimate daily average EF, instantaneous FE at different solar times, EF from daily data, and daily AET for Castilla y Leon region in Spain using ground meteorological stations, and combined high temporal resolution geostationary satellite products and relatively high spatial resolution polar orbiting satellite products. In addition, the performance of SEBS model over different land cover classes was tested. The testing was only based on the comparison of daily averaged EF and instantaneous E F, and whether the results were reasonable or not over all land cover classes in the study area. The comparison of daily average EF with instantaneous EF and EF from daily averaged data was done over different land cover classes for 15th of March, 2009. In addition, SEBS estimated AET and Meteosat second generation evapotranspiration (MET) were compared with AET measured by an Eddy co variance system in sparse vegetation. The SEBS estimated AET was also compared with MET over different land cover classes. Finally, climatological water balance estimation “Precipitation minus evapotranspiration” was carried out over rainfed cropland during the study period (March, 15 – September, 15, 2009) using rainfall products from EUMETSAT and daily AET estimated by SEBS model . The results indicated that the average daily EF and instantaneous EF have shown strong relation over water bodies, irrigated croplands, rainfed croplands, shrubland, mosaic forest-shrubland and mosaic crop-vegetation respectively, but it shows poor agreement over sparse vegetation, broadleaved deciduous forest and needleleaved evergreen forest. There was no agreement between daily average EF and EF from daily averaged data in all land cover classes. It was observed that SEBS estimated AET is close to the measured AET but MET overestimate. Only MET and SEBS estimated AET have close values in irrigated croplands and water body, but MET overestimated in the remaining land cover classes. In addition, it was observed during water balance estimation that there were only few days in the months of May and June which have excess rainfall during the study period.

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