Event-Specific Meteorological Drivers Shape Diverse Water-Use Efficiency Trajectories Under Drought Propagation

Drought propagation from meteorological to soil drought marks a critical phase in regulating vegetation water-carbon dynamics, yet the response trajectories of water-use efficiency (WUE) during these events remain poorly understood. Here, combining global flux tower observations with simulations from Earth System Models (ESMs), we quantified the spatiotemporal patterns of drought propagation characteristics, identified WUE response trajectories for characteristic-specific droughts, and investigated their dominant drivers. We found that 58% of soil droughts follow meteorological droughts. Most sites experience drought propagation events with increasing intensity, faster propagation, and shorter intervals. Among all identifiable trajectories, nonmonotonic patterns account for approximately 60%. WUE response trajectories generally follow continuous and nonmonotonic patterns, dominated by a rise-then-fall pattern. This pattern reflects a process in which vegetation functions regulated by stomatal behavior are initially stressed and then partially recover. Intra-site variability is extremely pronounced, mainly driven by event-specific thermal factors such as air temperature and net radiation. ESMs reproduce broad site-level prevalence of nonmonotonic patterns, but show discrepancies in the relative importance of drivers due to the coupling of different land surface models. These findings challenge the notion of fixed vegetation functional responses and highlight the dynamic variability of response trajectories in relation to event-specific characteristics, and provide concrete diagnostics to guide model improvements.