The Regulatory Role of Lagged and Cumulative Climatic Drivers in Global Terrestrial Ecosystem Water Use Efficiency

Water use efficiency (WUE) links carbon uptake to water loss and is central to diagnosing carbon–water coupling in terrestrial ecosystems. Yet the extent to which WUE responds to climate through lagged and cumulative pathways remains unclear at the global scale. In this study, we used long-term satellite-derived datasets of GPP and ET, vegetation indices, and reanalysis-based climate variables to assess the spatiotemporal variations in WUE from 2000 to 2019,and quantified concurrent driver hierarchies with random forests and structural equation modeling; Finally,we assessed lagged and cumulative effects of four representative drivers: land surface temperature (T-skin), precipitation (P), net surface shortwave radiation (NSSR), and volumetric soil water (VSW). Our results show that vegetation and climate jointly explained 75% of the spatial variation in WUE, with vegetation playing a dominant role globally and across climate zones. WUE increased in 47% of vegetated areas, primarily driven by enhanced GPP. Notably, 72.2% of the land showed lagged responses of WUE to T-skin with a mean lag of 5.4 months and with the longest delays in tropic regions. P and VSW regulated WUE mainly via short-term or medium-term lags, with cumulative effects varying across biomes. Positive WUE-VSW coupling prevailed at short and long lags intervals, while negative correlations at 6–8 months reflected vegetation suppression under prolonged drought. These findings demonstrate temporal memory in WUE–climate coupling and provide biome-specific constraints for benchmarking model representations of delayed and accumulated climate effects on carbon–water interactions.