Reference evapotranspiration change and its sensitivity to climate variables in southwest China

Abstract

Reference evapotranspiration (ET 0 ) is the key factor for hydrologic water balance, irrigation scheduling, and water resources planning. Based on Food and Agriculture Organization (FAO) Penman–Monteith method and the climate variables of 57 meteorological stations from 1960 to 2010 in southwest China, the spatial and temporal distributions of ET 0 were analyzed by using Mann–Kendall test and Sen’s slope estimator. Sensitivity coefficient was used to analyze the sensitivities of ET 0 to four climate variables, and the key climate variables attributed to ET 0 change were determined. Result showed that there was a slight downward trend of ET 0 from 1960 to 2010 and spatially increasing trend from northeast to southwest in annual time scale. Results also showed that ET 0 had relatively higher sensitivity to wind speed and mean air temperature, and wind speed was the dominant variable for change of ET 0 in southwest China. The inverse relationship between increasing air temperature and decreasing evaporation, “evaporation paradox,” existed in southwest China, and the negative contribution of wind speed to the changes of ET 0 offset the positive contribution of air temperature.