Temporal analysis of reference evapotranspiration to detect variation factors

Abstract

There are many factors that can change reference evapotranspiration (ET0). In this study, after comparison of six reference evapotranspiration equations, variations of each model have been investigated to detect main factor(s) of temporal changes of ET0 from 1981 to 2010 in Goragn, Iran. Although Priestley-Taylor (PT) estimates ET0 is more identical to FPM than the other equations during 30-year period, the results show that accuracy of PT is reduced after 2000. The study of variations of temperature, relative humidity, wind speed, and sunshine, underlines that there is a considerable difference between the averages of the weather variables before and after 2000. Compared to 1981–1999, the average of wind speed has been increased more than three times after 2000 that it introduces the wind speed as the most important variable for changes of ET0 and alarms a climatic change in Gorgan, Iran.