Comprehensive response assessment of water use efficiency to climate change in ecologically fragile karst areas

Water use efficiency (WUE) is a crucial indicator for elucidating the carbon-water cycle processes within ecosystems. Unveiling its spatiotemporal trends and exploring the influences of climate change remain essential. To address unclearness in impacts of climate change, this study proposes a comprehensive assessment framework to quantify the response of WUE to climate change from two perspectives: individual climate factors and climate synergies. Furthermore, an improved ecosystem classification method for karst regions is introduced to explore differences in WUE caused by karst landform among ecosystems in South China Karst. The results showed that: (1) WUE exhibited a decreasing trend from 2001 to 2022, with a significant decrease observed in 39.85 % of the areas; however, 52.24 % of the areas are projected to shift from decreasing to increasing trends. Notably, in cropland and grassland, the annual mean WUE in karst areas exceeded that in non-karst areas, whereas forest exhibited the opposite pattern. (2) Regarding individual climate factors, the factors with the highest relative importance to WUE were solar radiation and precipitation in non-karst cropland and karst cropland respectively, precipitation in forest, temperature in grassland. The importance of temperature in karst grassland far outweighed other factors. (3) Regarding climate synergies, the spatial and global explanatory power of climate factors was significantly enhanced by climate synergies. The global explanatory power of climate synergies on WUE was 88.6 % in South China Karst, with values across ecosystems ranging from 36.7 % to 92.8 %. Our findings provide a beneficial supplement to carbon-water cycle research in ecologically vulnerable karst regions. • A comprehensive assessment framework is proposed to reveal the response of WUE to climate change. • Based on the karst landform, Southwest China Karst is finely divided into six different ecosystems. • Climate synergies significantly enhance the influence of climate factors on WUE. • WUE in Southwest China Karst is decreasing, but over 55% of the areas will shift to increase in the future.