Evapotranspiration (ET) is one of the most important factors in irrigation systems designing. The different methods estimate ET which FAO-Penman-Monteith (F-P-M) method is one of the validest of methods which it estimates ET. Thus aim of this research was investigation of ET changes in synoptical stations on Golestan region/Iran (stations: Gorgan, Gonbad and Maraveh- Tappeh) in duration(1981-2005). Results shown that for yearly scale: ET values in Gorgan and Gonbad were increasing procedure exept 1992-2000 duration, and in Maraveh- Tappeh station ET was decreasing procedure until 2000 year. But the later years were increasing procedure. In this manner for seasonly scale: ET maximum for autumn, winter and spring seasons, was happen in 1985. The maximum value of ET in Gorgan, Gonbad and Maraveh- Tappeh station were 1000, 1260 and 2000 mm/yr respectively and 510, 530 and 1000 mm/season respectively.

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