Changes of Pan Evaporation in the West of Iran

摘要: Evaporation is an important component of the hydrological cycle and its change would be great significance for water resources planning, irrigation control agricultural production. The main purpose this study was to investigate temporal variations in pan evaporation (Epan) associated changes maximum (Tmax), mean (Tmean) minimum (Tmin) air temperatures precipitation (P) 12 stations Hamedan province western Iran period 1982–2003. Significant trends were identified using Mann–Kendall test, Sen’s slope estimator linear regression. Analysis Epan data revealed a significant increasing trend 67% at 95% 99% confidence levels. To put perspective, averaged over all (+)160 mm per decade. Trend analysis meteorological variables examination causal mechanisms showed warming Tmax, Tmean Tmin series almost stations, which half total stations. On contrary, no found approximately Furthermore, moderate positive correlation observed between Tmin, while inverse P data. results indicated that area has become warmer drier last 22 years, hence evaporative demands atmosphere thereby crop requirements have increased.