Divergent Controls on Sustained Increases and Decreases in Global Water Use Efficiency over the Past Four Decades

Global water use efficiency (WUE) is a key indicator characterizing the carbon–water coupling relationship in terrestrial ecosystems. Elucidating its spatiotemporal evolution characteristics and driving mechanisms is of great significance for evaluating ecosystem carbon sink functions and formulating water resource management strategies under global change. Based on multi-source datasets integrating satellite remote sensing products and land surface model-derived evapotranspiration (ET) from 1982 to 2018, this study systematically analyzed the spatiotemporal evolution patterns of global WUE and identified the strongest statistical association factors and their spatial distributions, clarifying the key driving factors and spatial distribution characteristics of sustained increases and decreases in global WUE. The results were as follows: (1) From 1982 to 2018, WUE showed an increasing trend in approximately 62.24% of vegetated areas globally, with a significant increase in area accounting for 14.95% (slope ≥ 0.01). By trend type, monotonically increasing and monotonically decreasing areas accounted for 20.96% and 9.36% of global vegetated areas, respectively. (2) Under the combined influence of biotic and climatic factors, leaf area index (LAI) had the strongest correlation with areas of sustained WUE increase, covering the highest proportion (78.55%). When considering only climatic factors, temperature exerted the most significant influence on sustained WUE increase, covering an area of approximately 75.69%. (3) For areas of sustained WUE decrease, climatic factors exhibited the strongest correlation under the combined effects of biotic and climatic factors, accounting for approximately 55.28%, among which temperature contributed the most (approximately 54.09%). When considering only climatic factors, the impact of temperature on sustained WUE decrease rose to 92.42%. This study deepens the understanding of global vegetation carbon–water coupling mechanisms and provides a key scientific basis for identifying regionalized water resource management strategies that enhance ecosystem carbon sink capacity under climate change.