Satellite-derived estimates of evapotranspiration in the Gediz basin

Satellite-derived estimates of the regional evapotranspiration in the Gediz basin, Turkey, are presented. The remote sensing approach applied is based on a feedback relationship in which the surface temperature is used to obtain the vapour pressure deficit in the overlying air. The method has the advantage of allowing for the application of remotely sensed data in conjunction with conventional evapotranspiration models. It also represents a convenient approach for the application of satellite-derived estimates of regional evapotranspiration within hydrological models. The feedback relationship was applied in conjunction with NOAA-AVHRR and LANDSAT images of the region obtained for two selected dates in summer of 1998; the surface temperature, vapour pressure deficit and net radiation estimates derived from the satellite images were applied within a conventional evapotranspiration model to produce daily estimates. Data obtained from tower-mounted instrumentation in the agricultural region of the Gediz basin are used to verify the estimates of the input variables. The results from both remote sensing platforms showed evapotranspiration rates in the range of 2.5–4.5 mm/d for the basin.