Sensitivity of the Penman-Monteith Reference Evapotranspiration in Growing Season in the Northwest China

In order to predict responses of ET₀ to perturbation of climate variables, growing seasonal ET₀ for 132 meteorological stations in Northwest China from 1961 to 2005 was estimated with the FAO-56 Penman-Monteith equation. Sensitivity coefficients of ET₀ to air temperature, wind speed, relative humidity and shortwave radiation were calculated and their spatial-temporal characteristics were analyzed. The results show that shortwave radiation is the most sensitive variable to ET₀ in general for study area, followed by relative humidity, air temperature and wind speed. From April to October the highest sensitivity coefficients to air temperature and shortwave radiation is in July, while the lowest sensitivity coefficients to wind speed in July. The absolute sensitivity coefficients to relative humidity increases from April to October. The sensitivity coefficients to all climate variables indicate large spatial variability. The high value area of sensitivity coefficients to air temperature and wind speed is in the west study area, while the high value area of sensitivity coefficients to relative humidity and shortwave radiation is in the east study area.