Water stress assessment in rainfed crops and pastures by using remotely sensed evapotranspiration.

Agricultural drought is a natural and damaging phenomenon that is especially harmful to rainfed agriculture. It occurs when there is insufficient soil moisture in the root zone for plants to survive between two rainfall events. In the absence of soil moisture, a variety of losses, including soil evaporation and plant transpiration, cause an imbalance between water supply and water loss. An evapotranspiration-based index was used here to assess agricultural drought. We applied this framework to a less studied area near Fariman City in the northeast part of IRAN. Two time periods were selected for comparison including 2015 and 2016 spring season that are associated with dry and wet conditions, respectively. To calculate the drought index, actual and potential evapotranspiration were estimated by the Surface Energy Balance Algorithm for Land (SEBAL), the upgraded Priestley-Taylor method and remote sensing data. The Relative Water Deficit Index (RWDI) illustrated that lack of water in rainfed lands and pastures for the dry period was obtained from 80 to 100 percent, whereas this was between 50 and 70% for the wet period.