Basin-wide actual evapotranspiration estimation using NOAA/AVHRR satellite data

The present study elaborates on the estimation of actual evapotranspiration at watershed scale using mathematical models and remote sensing techniques. A water balance model was updated and used to simulate runoff from a watershed, based on input data of precipitation and potential evapotranspiration. The water balance simulation considers the loss and routing functions to estimate actual evapotranspiration. Two methods were used to estimate the areal precipitation, the precipitation gradient method and the Thiessen polygons method adjusted for the mean elevation of the watershed. Areal potential evapotranspiration was calculated using three empirical and semi-empirical methods based on temperature, precipitation, and solar radiation. The potential evapotranspiration methods used were the Thornthwaite, Blaney-Criddle, and the modified Penman-Monteith. The water balance model was calibrated with the observed monthly runoff. The actual basin-wide evapotranspiration was estimated using the water balance model. Monthly composites of the normalized difference vegetation index (NDVI), derived from the National Oceanic and Atmospheric Administration's (NOAA)/Advanced Very High Resolution Radiometer (AVHRR) data were correlated and linear relationships were developed with the water balance computed monthly actual evapotranspiration rates for four watersheds of Central Thessaly, Greece. The performance of the developed Actual evapotranspiration-NDVI relationships was examined using various statistical tests. The NDVI-derived actual evapotranspiration agrees well, in general, with the actual evapotranspiration calculated from the water balance method for both wet and water-limiting conditions. (C) 2004 Elsevier Ltd. All rights reserved.