Sensitivity analysis of reference evapotranspiration in humid climate of the southern shore of Caspian Sea

Changes in climatic variables that affecting access to water can play a key role in the sustainable development of agriculture and the environment. Since ET0 is the most important variable affecting access to water resources after rainfall. Therefore, the present study examines temporal and spatial variations of ET0, temporal analysis of trend, sensitivity and relative contribution rate of climatic variables including Sun Duration (SD), Relative Humidity (RH), Wind Speed (WS), air pressure (P), maximum Temperature (Tmax) and minimum Temperature (Tmin) for a period of 30 years (1988-2017) at 7 synoptic stations on the southern shore of the Caspian Sea at different time scales. The spatial distribution of ET0 in the Caspian Sea basin showed that ET0 increases from west to east. The results showed that on the annual and monthly time scale including March, May, June, July, August and September, all stations had upward trend at 5% probability level of Significance. While the results of sensitivity analysis showed that ET0 has the highest sensitivity to variables of RH, Tmax and WS respectively, but results of relative contribution rate showed that variables of RH, WS and Tmin are the main actors on ET0, in the southern shore of the Caspian Sea during the last 30 years, respectively.