Detecting ecosystem water use efficiency responses to drought from long-term remote sensing data

• Systematically studied the cumulative and lag effects of drought on WUE across global ecosystems. • Revealed differences in WUE cumulative and lag effects across various vegetation types and climate zones. • Analyzed the cumulative and lagged effects of drought on global WUE along different hydrological balance gradients. • Explored the relationship between WUE and SPEI across multiple timescales. • Assessed the resilience of ecosystems in different vegetation types and climate zones to drought. Ecosystem water use efficiency (WUE) is a key indicator of the coupled water-carbon cycle. Understanding the cumulative and lagged effects of drought on global ecosystem WUE is crucial for assessing and responding to hydroclimatic disturbances. However, the spatial patterns and mechanisms of drought impacts on global WUE remain unclear. In particular, studies investigating the responses of different climate zones and biomes to drought under the framework of multi-scale standardized precipitation evapotranspiration index (SPEI) are still limited. Therefore, This study integrates global-scale WUE data with the multi-temporal SPEI to systematically quantify the lagged and cumulative effects of drought on WUE. The research consists of three main steps: First, pixel-level sliding − window correlation analysis is employed to identify the most significant correlations between WUE and SPEI, thereby quantitatively determining the duration of drought-induced lagged and cumulative effect. Second, both SPEI and its slope are incorporated to investigate how moisture gradients regulate the WUE response mechanism. Finally, the resilience index is used to classify and evaluate the recovery capacity of terrestrial ecosystems. The results indicated that both cumulative (48.44 %) and lagged (66.98 %) effects of drought on WUE were widespread, especially in grasslands (GRA), shrublands (CSH) and savannas (SAV), with cumulative effects ranging from 4.04 to 5.87 months and lagged effect concentrated between 5 and 7 months. In terms of climatic regions, the highest proportions of cumulative and lagged effect were observed in arid and semi-arid areas, with cumulative effect accounting for 40.67 % and 39.75 %, respectively, and lagged effect representing 74.70 % and 59.24 %, respectively. Further analysis revealed the different regulatory pathways of WUE response to SPEI and SPEI slope. The positive intensity of WUE was negatively correlated with SPEI and its slope, while the negative intensity exhibited the opposite pattern. The coupling characteristics of positive and negative effect along the moisture gradient revealed the spatiotemporal compensation mechanism of the ecosystem carbon–water cycle under drought conditions. This study provides critical insights into the long-term effect of drought on ecosystems, helps to predict dynamic changes in water availability under climate change.