On the attribution of changing water surface evaporation across China

Abstract

Study regionChina Study focusWater evaporation represents a pivotal indicator of the terrestrial ecosystem and hydrological cycle, influencing regional water and energy balance to some extent. In this study, the long-term data series of water surface evaporation (Ep) were assimilated across China, with the observations from 552 national benchmark weather stations. The trends of Ep and the influential climate variables were well detected. The analytical derivation method was built up to quantitatively attribute the effects from 5 key climate fields to Ep variations, including wind speed (u2), sunshine duration (n), relative humidity (RH), daily maximum (Tmax), and minimum (Tmin) air temperature. New hydrological insights for the regionThe attribution results were more accurate and reasonable than those from two commonly used statistically based climate elasticity methods, which tended to overestimated the Ep variations. Most weather stations had experienced the decreasing trends of Ep during the entire research period of 1961–2018, which were mainly attributed to the decreasing in u2, n and RH, while the effects of regional warming (rising air temperature) were less influential on Ep variations at the long-term scale. The variations of Ep attributed to the three main influential climate variables (u2, n and RH) across China had also shown different temporal and spatial tendency patterns during different historical research periods. For example, the changing n and RH had shown increasing power on Ep variations in the western China climate zones. Comparatively, the u2 has been losing its power in decreasing Ep in most regions of China due to the slowdown in the declining rates of wind speed. This dynamic Ep attribution process is worthy of continuous focus and systematic research.