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

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.