Estimation of reference crop evapotranspiration (ET0) at synoptic stations of Tehran province

Evapotranspiration is one of the critical parameters in an interdisciplinary topic between agriculture and hydrology. Thus, the accurate estimate of evapotranspiration can reduce the casualties of water resources and cause proper management in planning. In this study, the standard FAO penman- monteith method is used to estimate the evapotranspiration of the refrence crop (ET0) in Tehran province for selected synoptic stations. Some studies show that in case of high temperature, the wind speed performs an important factor in increasing values of evapotranspiration. The lowest annual reference crop evapotranspiration in synoptic station north of Tehran with an average temperature of 15.6 degrees celsius high it is estimated the average 1160 mm. While Abali stations and Firouzkooh respectively 8.6 and 9 ° C mean annual temperature, 1180 and 1220 mm annual evapotranspiration values experience. The annual evapotranspiration reference plant in Doushan Tappeh station with average annual temperature of 18 °C, About1425 mm. The most important factor in reducing evaporation and transpiration synoptic station in northern Tehran and Doushan Tappeh with average annual temperature is much higher, Wind speed in this station. The maximum value of evapotranspiration estimated around 1700 and 1680 mm in geophysics station and then Mehrabad Airport stations respectively. Approximately, 75% of the annual reference crop evapotranspiration has been occurred from April to September. Also, the maximumvalue of evapotranspiration is observed between June and September, and the minimum is seen from November to Februaey in alla station.