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Keywords:

  • climate change;
  • Iran;
  • reference crop evapotranspiration;
  • trend

Abstract

Evapotranspiration is one of the most important factors in agriculture and the hydrological cycle that can be influenced by global warming and climatic changes. In this study, the trend of reference crop evapotranspiration (ET0) computed by penman Penman-Monteith equation and surveyed in 42 synoptic weather stations during last 3 decades (1975–2005). Nonparametric statistical test, Kendall's rank correlation (or τ test) was used to determine ET0 trends. Although, downward and upward trends were observed, increasing trends had more frequency. Spatial analysis of results indicated upward trends especially in the boundary parts of the country while, no significant trends were distributed in central parts. In addition, correlation analysis between ET0 trend and other climatic parameters trend (the trend of mean temperature, mean of minimum temperature, and mean of maximum temperature, mean of relative humidity, mean of wind speed and mean of sunshine duration) showed that wind is the most effective parameter on ET0. Iran losses more than 70% of annual precipitation by ET0. It is obvious that in this country where there are many limitations for water resources management, increase in ET0 could lead to more problems. Copyright © 2011 Royal Meteorological Society