Study on Non-Stationary Characteristics and Driving Mechanisms of Potential Evapotranspiration in the East Asian Monsoon Region

To investigate the non-stationary characteristics of potential evapotranspiration (PET) and the driving mechanisms of the East Asian monsoon on basin-scale, this study takes the Huaihe River Basin as a representative study area. Based on daily meteorological data from 29 stations spanning 1960–2020, PET was calculated using the FAO56 Penman–Monteith method. An improved pre-whitening Mann–Kendall test, moving-window periodic analysis, cross-wavelet transform, and sensitivity analysis were jointly applied to reveal the non-stationarity of PET and its monsoon-driven mechanisms. The results show that: (1) Temporally, the East Asian monsoon exhibits a three-stage interdecadal transition pattern of “strong–weak–strong” at the interannual scale, while PET shows a trend of strengthening followed by weakening; the interdecadal turning points of them are highly synchronized in time. (2) Spatially, basin-wide PET displays an east–high to west–low distribution pattern, and spring PET exhibits a north–south gradient characterized by decreases in the north and increases in the south. In summer, PET at most stations shows a significant decreasing trend, with the rate of decrease increasing from east to west. In autumn and winter, PET changes are relatively gentle, and decreasing trends dominate across the basin except in the southeastern area and a few western stations. (3) The East Asian monsoon index and PET exhibit significant resonant periodicities at the interannual time scale, indicating a pronounced influence of the monsoon on PET. It demonstrates that the East Asian monsoon affects seasonal wind direction, thereby modulating basin-scale meteorological factors and ultimately driving the non-stationary behavior of PET. This forms a distinctive “East Asian monsoon–meteorological factors–PET” driving framework, which not only provides key support for understanding the response of the hydrological cycle to climate change in the East Asian monsoon region, but also offers insights for related studies in other monsoon regions worldwide.