Vapor pressure deficit dominated actual evapotranspiration changes in the Southeast River Basin of China from 1981 to 2021: A PML-based attribution analysis

Study area The Southeast River Basin is one of China's nine major river basins. As a typical monsoon humid region, it has exhibited significant actual evapotranspiration（ET a ） growth in recent years. Study focus Existing studies in this basin predominantly rely on publicly available global datasets, lacking process-based mechanism analyses. This study employs Penman-Monteith-Leuning (PML) model to simulate daily-scale ET a from 1981 to 2021. Owing to insufficient observed ET a data, the three-cornered hat method was employed to assess simulation accuracy,then use detrending experiment to systematically analyse the spatiotemporal evolution and component variations of ET a , identifying the dominant factors. New hydrological insights for the region The PML model demonstrated the highest stability in cross-validation across three datasets. Since 1981, ET a in this basin has exhibited significant growth (4.39 mm year −1 , p < 0.05), with the fastest increase occurring in spring (1.45 mm year −1 ). Spatially, trends are most pronounced in the northwestern and central regions, while northeastern and coastal areas exhibit weaker trends or even declines. Component-wise, transpiration accounts for 71.20 % of ET a . Trend analysis indicates that vapour pressure deficit (VPD) is the primary driver (contributing 38.70 %), followed by leaf area index (LAI, 18.41 %). These findings mark a shift from trend description to mechanistically driven quantitative understanding, providing robust data support and theoretical foundations for comprehending ET a dynamics and ecohydrological processes in the southeastern of China.