Sensitivity Analysis of Evapotranspiration to Change in Meteorological Parameters in North-West and West of Iran

Sensitivity analysis of reference crop evapotranspiration (ET0) is crucial for improving water management in the arid and semi-arid country as like Iran. However, it is important to analyze the sensitivity of ET0 to meteorological parameters, since the climate globally has been changed to some extent. In this study, sensitivity of ET0 by varying the climatic parameters at 36 selected stations in the West and Northwest of Iran was investigated. The priority and effect of the climatic parameters in different months at the selected stations were found by sensitivity analysis. The ET0 is calculated based on the most recommended form of the FAO-56 Penman-Monteith method. To analysis the sensitivity, variations of ET0 depends on the changes in minimum temperature (Tmin), maximum temperature (Tmax), wind speed (u2), minimum relative humidity (RHmin) and maximum relative humidity (RHmax), in the range of ±20% with the step of 5% was calculated. Finally, the parameter with higher importance for each station was obtained. Results showed that ET0 was more sensitive to the variation of Tmax at the 13 stations (36.11%) in annual time scale. The maximum change of ET0 by increasing of Tmax with+20% was found at Ardebil (15.54%) and the minimum change in the same situation was found to be 6.05 % at Meshkinshahr. The range of the changes by varying T min was between -47 % (in Sanandaj) to 0.91 % (in Khalkhal).