Temporal and Spatial Variations of ET₀ and Sensitivity Coefficients in Spring-summer in Eastern Agricultural Areas of Qinghai, China

Reference crop evapotranspiration (ET₀) is a key parameter to calculate crop water requirements. In the paper, ET₀ during 1960-2005 was calculated with FAO-56 PM in eastern agricultural areas of Qinghai, China. Then the sensitivity coefficients of ET₀ to meteorological variables were estimated through the nondimensional partial derivative in FAO-56 PM. Results show that the mean annual ET₀ of the whole area is 904 mm, and ET₀ portrays a very significant decrease during the 46 years. In spatial, ET₀ decreases from southeast to northwest, firstly increases then decreases from southwest to northeast. Through sensitivity analysis, in spring the most sensitive variable is relative humidity, while in summer is temperature. The temperature, sunshine duration and wind speed sensitivity coefficients (S(TA), S(n), S(u)) are higher in middle areas as opposed to surrounding areas, while the relative humidity sensitivity coefficient (S(RH)) has an opposite distribution rule.