Analysis of variation in reference evapotranspiration and its driving factors in mainland China from 1960 to 2016

Abstract

Understanding the variation in reference evapotranspiration (ET_o) is vital for hydrological cycles, drought monitoring, and water resource management. With 1507 meteorological stations and 130 radiation-measured stations, the annual and seasonal ET_o were calculated at each site from 1960 to 2016 in mainland China. The phenomenon of coefficient ‘a’ being less than 0.25 and coefficient ‘b’ being greater than 0.50 in the Angstrom–Prescott model occurred in almost the whole country, except for a small area of western and northeastern China. Moreover, the Xiao’s method was more applicable to calculate the net longwave radiation (R _nl) and then improve the estimation accuracy of ET_o. The annual ET_o varied from 538.8 to 1559.8 mm and had a high-value center located in the plateau and desert of northwestern China and a low-value center located in Northeast China and near the Sichuan Basin. The spatial distribution of seasonal ET_o was roughly similar to that of annual ET_o, except for that in winter when ET_o was high in the south and low in the north. In mainland China, the annual ET_o decreased by 21.2 mm decade⁻¹ because of the declining sunshine duration before 1993 and increased by 21.1 mm decade⁻¹ due to the decreased relative humidity (RH) after 1993. Generally, the abrupt change of ET_o mainly occurred in the southern China rather than northern China (except for Qinghai Tibet Plateau). Basically, the dominant driving factors of annual and seasonal ET_o were RH and/or T _max after the abrupt change in most parts of China.