Sensitivity Analysis of the Penman-Monteith reference Crop Evapotranspiration to Climatic Variables in Iran

<Para ID="Par1">Sensitivity analysis of reference crop evapotranspiration (ET<Subscript>0</Subscript>) in Iran is an important necessity due to better management of water in such an arid and semi-arid country. It is important to analyze the sensitivity of ET<Subscript>0</Subscript> to weather parameters as climate seems to be changed to some degree everywhere. In this study, sensitivity of ET<Subscript>0</Subscript> to climatic variables at the eight selected stations of Iran was investigated. To estimate the ET<Subscript>0</Subscript>, the most recommended form of the FAO-56 Penman-Monteith method was used. Sensitivity of ET<Subscript>0</Subscript> was analyzed in terms of change in mean air temperature (T<Subscript>mean</Subscript>), actual vapor pressure (e<Subscript>a</Subscript>), wind speed (u<Subscript>2</Subscript>) and net solar radiation (R<Subscript>n</Subscript>) within a range of ±20 %, in 5 % steps, from their corresponding normal long-term values (1965–2005). Results showed that ET<Subscript>0</Subscript> was most sensitive to T<Subscript>mean</Subscript> at the six of the stations in annual time scale. Increase in T<Subscript>mean</Subscript> by +20 %, caused the most increase in ET<Subscript>0</Subscript> at Chabahar. In contrast ET<Subscript>0</Subscript> was least sensitive to e<Subscript>a</Subscript> in most selected stations. In this study, we investigated the interaction parameters in different scenarios on ET<Subscript>0</Subscript> at all stations in monthly and annual time scale. Results showed in annual time scale increasing T<Subscript>mean</Subscript> and WS by 20 % and decreasing e<Subscript>a</Subscript> by 20 % yielded ET<Subscript>0</Subscript> increasing 36.4 % at Chabahar. But, in monthly time scale 10 % increase in T<Subscript>mean</Subscript> and WS as well as 10 % decrease in R<Subscript>n</Subscript> yielded ET<Subscript>0</Subscript> to be increase to about 30.5 % in December at Bandar Anzali. Copyright Springer Science+Business Media Dordrecht 2014