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Evapotranspiration as a component of water footprint: use of conventional and satellite data for better estimation of spatial and temporal pattern

One of the main scientific goals of the COST Action ES1106 (“Assessment of European Agriculture Water use and Trade under Climate Change” EURO-AGRIWAT) is the analysis of the global water footprint (WF) in agriculture and virtual water trade (VWT). The starting point for further activities is analyses and inventory of data and tools which could be helpful for WF and WFT assessments. Evaporation values (ET) are crucial for agriculture where estimates of water reserves available for crops are the basis for scheduling the time and intensity of irrigation, yield prognoses, etc. Detail evapotranspiration data are, therefore, of essential value. However, stations performing direct measurements of evapotranspiration are very scarcely distributed in Poland for which reason the interpolation of the data is necessarily biased. Hence, evapotranspiration values are calculated using indirect methods (usually empirical formulas). Data from geostationary meteorological satellites are used operationally for determination of evapotranspiration with good spatial and temporal resolution (e.g. Land-SAF product). Study of relation between evapotranspiration values determined with use of satellite data and calculated using Penman-Monteith formula was performed for the study area in Poland. Daily values and cumulated (i.e. decadal, monthly and yearly) values were analyzed to determine quality and possible added value of the satellite product. Relation between reference ET and actual ET in two consecutive years was discussed, both for whole test area and individual stations, taking into account land use and possible water deficit in the root region, represented by H-SAF soil wetness index product. The differences were presented and discussed.