Decadal variations in the driving factors of increasing water-use efficiency in China's terrestrial ecosystems from 2000 to 2022

Ecosystem water-use efficiency (WUE) is a crucial indicator for evaluating carbon and water cycles. Although greening and climate change have significantly altered the WUE in Chinese terrestrial ecosystems, the roles of physiological and ecological processes are not fully understood. To address this, WUE is broken down into two key ratios: gross primary productivity to transpiration (GPP/T), which mainly reflects the effect of plant physiological processes, and transpiration to evapotranspiration (T/ET), which primarily indicates the impact of vegetation changes. Both ratios are influenced by climate change. This study employed a newly developed satellite-based ecosystem service process model Carbon and Exchange between Vegetation, Soil, and Atmosphere-ecosystem service (CEVSA-ES) to examine the impact of GPP/T and T/ET on WUE in China's terrestrial ecosystems from 2000 to 2022, alongside an analysis of the environmental variables affecting these ratios. This study revealed a general increase in WUE during the study period with significant interdecadal differences. Between 2000 and 2010, WUE was relatively stable (slope = 0.0023 g C kg⁻¹ H₂O a⁻¹, p > 0.05), primarily because the decrease in GPP/T (p < 0.05) offset the increase in T/ET (p < 0.01). In contrast, from 2010 to 2022, a notable increase in WUE was observed (slope = 0.0145 g C kg⁻¹ H₂O a⁻¹, p < 0.01), driven primarily by an increase in GPP/T (p < 0.01), whereas T/ET remained relatively unchanged (p > 0.05). Factors affecting GPP/T and T/ET showed considerable variability. Precipitation had the main influence on GPP/T, accounting for 70 % of its variation. The initial decade of the 21st century experienced an overall precipitation deficiency, followed by a sustained surplus in the subsequent years, resulting in interdecadal fluctuations in GPP/T. In contrast, T/ET was affected by a combination of factors, including the leaf area index, temperature, and precipitation, contributing 39 %, 29 %, and 32 %, respectively. The present study advances our understanding of the interaction of terrestrial ecosystem with the atmosphere amid global changes, offering crucial insights for forecasting the future dynamics of carbon and water cycles.