Seasonal attribution disentangles physiological and available water-energy effects on hydrological changes under climate and CO2 changes in subtropical plantation catchment

Abstract Precipitation (P) partitioning, a critical process for local water management, exhibits complex responses to climate change and elevated atmospheric CO 2 (eCO 2 ) through plant physiological and available water-energy effects, yet disentangling these effects at the seasonal scale remains challenging. We proposed a seasonal attribution framework integrating the extended Budyko framework with the improved SWAT-C model to disentangle relative contributions of physiological and available water-energy effects under climate change and eCO 2 on hydrological change (1985–2023) in a subtropical plantation headwater catchment. Evapotranspiration (ET) changes were dominated by land-surface changes driven by physiological effects of climate change and eCO 2 , whereas runoff (R) changes were primarily controlled by climate-driven available water-energy effects. Warming and CO 2 fertilization raised leaf area index, increasing ET and reducing R in both seasons. Reduced P suppressed ET and R in the dry season, and increased P amplified them in the wet season. Climate–CO₂ interactions acted through plant water uptake, limited by reduced soil water storage in the dry season and by lower solar radiation in the wet season. Seasonal attribution therefore distinguishes the vegetation levers that govern ET from the climate and storage controls that govern runoff, informing adaptive forest and water management under climate change and eCO 2 .