Temperature and Humidity are influencing on the rate of evapotranspiration. High temperature increases evapotranspiration and humid weather decreases it. Wind speed is another important factor that extracts the accumulated vapor around the leaf surface and intensifies vapor pressure between leaf and air. In this study, we surveyed the relationship between changes of the most important meteorological parameters that have effect on reference evapotranspiration with reference evapotranspiration changes in Grand Karkheh basin at regional scale.
