Abstract: In order to predict the responses of reference crop evapotranspiration (ET0) to climate factors change,growing seasonal ET0 of 68 meteorological stations in the Loess Plateau from 1961 to 2010 was estimated by using of FAO-56 Penman-Monteith equation.Sensitivity coefficients of ET0 to average temperature,shortwave radiation,wind speed,and vapor pressure were calculated and their temporal-spatial distributions were analyzed.The results showed that vapor pressure was the most sensitive factor to ET0 in the region,followed by shortwave radiation and average temperature and wind speed.During growing season,the highest sensitive coefficient to average temperature was in July,while the absolute sensitive coefficient to vapor pressure was in September,the sensitive coefficient to shortwave radiation increased from April to October,the highest sensitive coefficient to wind speed was in April.The sensitive coefficients to all climate factors indicated large spatial variability.The sensitive coefficient to average temperature was higher in the eastern than in the western. The peak value of sensitive coefficient to shortwave radiation was in high elevation area,the peak value of sensitive coefficient to wind speed was in the western,while the peak value of sensitive coefficient to vapor pressure was in the relatively moist region.

Key words: Reference crop evapotranspiration, Penman-Monteith equation, Sensitivity coefficient, Loess Plateau