Estimating Crop Coefficient and Actual Evapotranspiration of Wheat By Remote Sensing: A Case Study, Gorgan Rood Command Area, Golestan, Iran.

Crop evapotranspiration (ETc) is one of the main factors essential for the assertion of water and energy balances at the earth surface. Although، the input parameters required for the estimation of ETc are spatially and temporally variables، ETc is usually estimated by reference evapotranspiration models that are locally calibrated and are site specific and then adjusted by implementing crop coefficient (Kc) to include the effects of a specific crop. The objective of this research was to investigate the feasibility of using time-series MODIS 250 m Normalized Difference Vegetation Index (NDVI) datasets in conjunction with ground data (climatic parameters) to calculate actual wheat crop coefficient in a large scale area (i. e.، Gorgan Rod watershed) during wheat growing season. The results indicated that the annual actual wheat evapotranspiration derived from remote sensing as compared with FAO-penman-monteith equation had RMSE، MAE، ME and E of 18 mm، 16 mm، -1. 1 mm and 1. 91 percent، respectively.