Integrating FAO-56 and Remotely-Sensed Techniques for Estimating Actual Evapotranspiration in Semi-arid Region of Isfahan Province

Spatial mapping of evapotranspiration (ET) rates can indirectly be very important for rangeland management and rehabilitation. The map of evapotranspiration can be an indicator of plant water requirement. Mapping of ET from remote sensing data is more appropriate than field methods, because the spatial and temporal coverage of this method is very extend and time and cost are optimized. Among the evapotranspiration mapping methods using remote sensing data, the FAO-56 model is one of the usual ones. Therefore, this study aimed to spatially estimate the amount of ET in semi-arid region of Isfahan province using the integration of FAO-56 and remote sensing techniques. To calculate ET, Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) were obtained from geometrically corrected TM 2009 image and the standard crop evapotranspiration (ET0) was calculated using FAO-56 equation and then the crop coefficient (Kc), crop transpiration (Kcb) and soil evaporation (Ke) were extracted from NDVI data. Results showed that agricultural lands with 6/977 mm/day and bare ground with 0.012 mm/day had the highest and lowest ET in the study area. High relationships of ET map with well-known remote sensing maps such a NDVI (>99%) and LST (>92%) indicated that ET mapping in the region has been achieved with a high accuracy, therefore, it is a valuable supplementary technique to field methods in determining plant water requirements for rehabilitation purposes.