Sensitivity of the FAO-Penman MonteithReference Evapotranspiration Equation to Change in Climatic Variables in the North-Western Iran

Evapotranspiration is one of the most important components of hydrologic budget which commonly is calculated from records of climatic data and geographical attributes of a meteorological station. Many scholars have found that climate change can reveal different local effects on climatic variables. In order to handle any possible potential impact of such changes on evapotranspiration, current study attempts to analyze the sensitivity of FAO Penman-Monteith reference evapotranspiration equation to four climatic variables for four stations placed in north-western of Iran. In annual scale through all stations maximum temperature was the most sensitivity inducing variable and Ardabil had the greatest sensitivity so that by a ±30% change in maximum temperature, reference evapotranspiration varied from -32.03% to 38.19%. The second important variable was actual vapor pressure which, also, had the most impact in Ardabil. Wind speed and minimum temperature were in the distant priorities. The sensitivity induced by U2 didn’t change much from month to month. The results, although were not accomplished from real changes in the variables, provided good view for future water planners because wide range of climate change scenarios has been discussed in the paper.