Dynamic Changes in Both Summer Potential Evapotranspiration and Its Driving Factors in the Huai River Basin, China

Potential evapotranspiration (ETp) is an important component of the water and energy cycle. This study investigated the changing patterns of both summer ETp and its drivers in the Huai River Basin for the first time using the newly proposed anomaly contribution analysis method, as summer is usually the peak period of ETp but little has been done to study it specifically. The anomaly contribution analysis method is able to calculate the contribution rates of climate factors to summer ETp for every year, which helps to reveal the dynamic changes in the contribution of climate factors to summer ETp. The results show that the evaporation paradox is not accurate for the basin since summer ETp declines significantly while the trend of summer Tm is insignificant. Influenced by the abrupt changes in summer Sh and Ws, summer ETp underwent a mutation around the 1970s and 1980s. Sensitivity analysis and contribution analysis show that the most sensitive meteorological factors may not contribute the most to summer ETp. Contribution analysis at a multi–year scale and the results of the anomaly contribution analysis method demonstrate that dominant factors of ETp may be different at multi–year and seasonal scales in the same region. Moreover, the dominant meteorological factors of summer ETp are also different at station and basin scales due to scale effects. Further, dynamic changes in contribution rates show that contributions of summer climate factors have clear positive–negative alterations. Additionally, there are also differences in the spatial distribution of contribution rates between the north–south and east–west directions. These findings will not only provide valuable information for regional water resources management but also provide new insights into the evolution of ETp under climate change.