Estimation of Actual Evapotranspiration at Regional Scale using Remote sensing data in Shahrekord Plain (II) Comparing SEBAL and METRIC to Some Mathematical Models of Evapotranspiration

This study was designed to investigate the possibility of using the surface energy balance algorithm for land (SEBAL) and mapping evapotranspiration at high resolution with internalized calibration (METRIC) models to estimate evapotranspiration (ET) in Shahrekord plain (Chaharmahal va Bakhtiari province, Iran). Two sets of Landsat ETM data dated June 30th and August 21st, 1999 were provided to estimate and compare reference evapotranspiration (alfalfa) at regional scale using Landsat ETM data to ET estimations by five mathematical methods (experimental and combined) known as standardized Penman-Monteith by American Society of Civil Engineers (ASCE-stPM), Penman-Monteith (F56PM), Blaney-Cridle (F24BC), Hargreaves-Samani (HS) and evaporation pan (F24P). Results showed that ET at cold anchor pixel for SEBAL were 6.97 and 6.77 millimeters per day and for METRIC were 10.27 and 9.31 millimeters per day, on days when the satellite passed over. Hargreaves-Samani ET values, as the suitable mathematical model for the studied area, were 8.0 and 7.5 millimeters per day, respectively, on two satellite passes. Results showed that, in the first pass all statistical indices for SEBAL were less than the second pass, maybe due to higher air temperature and wind speed. On the other way, statistical indices in METRIC on the alternate pass, however, showed higher values over the corresponding values in SEBAL. ET values on two satellite passes for anchor pixels were 5.65 and 5.93 mm/day in SEBAL, and 5.22 and 6.65 mm/day in METRIC, respectively. ET values on the same days of satellite overpass for Hargreaves – Samani (HS) were 8.0 and 7.5 mm/day. Consequently, based on the results, both RS-ET models were comparable to empirical models such as (HS). Generally, the results showed that SEBAL had higher accuracy than METRIC, presumably due to lack of accurate weather data (hourly data), so SEBAL is recommended in similar conditions. Generally, the results showed that SEBAL had higher accuracy in comparison to HS and lysimeters data than METRIC, so SEBAL is recommended in similar conditions.