Bedrock water storage regulates seasonal forest sensitivity to climatic water deficit in China's 'Central Water Tower'

Ecosystem sensitivity to hydroclimatic variability is central to forest resilience, but the modulating effect of bedrock water storage on seasonal drought sensitivity remains poorly clarified. Using four satellite vegetation metrics and meteorological reanalysis (2000–2023), we quantify seasonal sensitivity to climatic water deficit (CWD) across the hydro-lithological regions of the Qinling Mountains. Results show that functional-structural decoupling is pervasive and seasonal, with canopy function responding stronger to CWD than structural greenness. Warming generally reduced drought sensitivity in spring and summer, especially in regions with abundant soil and bedrock water, but increased it in autumn. By contrast, increased precipitation usually enhanced drought sensitivity in summer and autumn, although these effects varied across regions. Bedrock water buffered summer drought stress but increased spring sensitivity by advancing canopy development and subsequent water demand. Our findings demonstrate that drought assessment and forest management should account for hydro-lithological properties and bedrock water dynamics.