Sensitivity Analysis of Reference Evapotranspiration to Meteorological Parameters (Case Study: Synoptic Stations of Yazd Province)

Due to quantity and quality water crises in Yazd province and the necessity of precise determination of crop water need, sensitivity analysis of reference evapotranspiration to meteorological parameters is essential. For this purpose in this study, the effects of variations of each meteorological parameter on reference evapotranspiration (estimated by FAO Penman-Mantith 56) were analyzed in different weather stations of Yazd province. Meteorological parameters during 2001 to 2020 including temperature, humidity, wind speed, and sunshine hours were changed in the range of ±20%. Based on the results of this study wind speed, maximum temperature and sunshine hours were the most important parameters that affect reference evapotranspiration in three yearly, seasonal, and monthly scales. 20 percent changing of each parameter including wind speed, maximum temperature, and sunshine hours caused sensitivity coefficients of yearly evapotranspiration to be (0.32-0.46), (0.27-0.34), and (0.12-0.2) respectively. In general, on a seasonal scale, the most impact of wind speed parameter on reference evapotranspiration was in summer and the most important impact of maximum temperature parameter on reference evapotranspiration was in spring and autumn. From November until April the most sensitivity of reference evapotranspiration was observed for maximum temperature, wind speed, and sunshine hours. From April until October the most sensitivity of reference evapotranspiration was observed for wind speed, maximum temperature, and sunshine hours. According to the results of this study, for monthly scale the sensitivity of reference evapotranspiration to the wind speed is higher for the station with lower altitude. Also, the altitude variation of meteorological stations has been effective in the sensitivity of reference evapotranspiration to the wind speed for annual and seasonal scales.