Using S-SEBI and Remote Sensing To Estimate Evapotranspiration over Vegetated Areas (Case Study: Isfahan)

Evapotranspiration (ET) is one of the key elements in both energy and water balance studies. The satellite-assisted data acquisition method is instrumental in collecting the temporal and spatial ET variations at the regional scale. Evaporative fraction (EF) has been used by Roerink to simplify a procedure of ET derivation, S-SEBI, from the satellite acquired data. The EF data in this study were obtained using the reflectance and temperature colleted by the MODIS satellite over the Province of Isfahan in an 8-day time steps during the 2000-01 (dry year) and 2004-05 (wet year) periods based on the application of a triangle space concept between the land surface temperature and the surface albedo data. A simplified procedure to obtain the surface albedo has been mentioned. Spatial distribution of the EF has shown that during the 2004-05 period the EF values of the province, particularly in the western and central parts were significantly higher (at the 0.01 level) than those of the dry period. Furthermore, a linear relationship (r2=90%) was obtained the EF and soil water index, which may be considered as a water stress indicator.