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Context <p>Water use efficiency (WUE), the amount of carbon fixed per unit of water loss, reflects the coupling between ecosystem productivity and water consumption. Across tropical and subtropical Asia, ecological restoration and climate change may alter this carbon–water coupling, but stress thresholds of ecosystems in this process remain unclear.</p> Objectives <p>This study quantified long-term WUE trends across karst and non-karst landscapes in South China and Southeast Asia from 1992 to 2020, with a focus on identifying high-importance variables and nonlinear thresholds associated with WUE responses.</p> Methods <p>Satellite-derived data on gross primary production and evapotranspiration were used to estimate WUE. Trends were analyzed using Theil-Sen median trend analysis and the&#xa0;Mann–Kendall test, while the XGBoost model combined with SHAP analysis was employed to quantify the relative importance and contribution direction of candidate explanatory variables. Threshold regression models were then employed to assess nonlinear WUE responses to high-importance variables.</p> Results <p>WUE increased in 75% of the study area, with the highest growth observed in South China’s karst regions following the Grain for Green Program. NDVI showed the highest relative importance and positive SHAP contributions, while daily mean temperature and vapor pressure deficit (VPD) exhibited critical thresholds. WUE declined sharply beyond temperature thresholds of 19&#xa0;°C in South China and 26&#xa0;°C in Southeast Asia, and beyond&#xa0;VPD thresholds of&#xa0;around 1&#xa0;kPa. Mixed tree-shrub-grassland ecosystems showed the highest WUE.</p> Conclusions <p>Our findings reveal critical nonlinear thresholds in WUE, emphasizing the role of vegetation greening and climate adaptation in managing carbon-water dynamics. These results provide actionable insights for enhancing WUE through ecological restoration and species selection, particularly in regions such as Vietnam, Myanmar, and Indonesia.</p>

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Nonlinear thresholds of dominant controls on water use efficiency define management windows across South China and Southeast Asia

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月29日

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  • Shuhan Wang,
  • Yifan Lin,
  • Zihan Xu,
  • Jian Peng

摘要

Context

Water use efficiency (WUE), the amount of carbon fixed per unit of water loss, reflects the coupling between ecosystem productivity and water consumption. Across tropical and subtropical Asia, ecological restoration and climate change may alter this carbon–water coupling, but stress thresholds of ecosystems in this process remain unclear.

Objectives

This study quantified long-term WUE trends across karst and non-karst landscapes in South China and Southeast Asia from 1992 to 2020, with a focus on identifying high-importance variables and nonlinear thresholds associated with WUE responses.

Methods

Satellite-derived data on gross primary production and evapotranspiration were used to estimate WUE. Trends were analyzed using Theil-Sen median trend analysis and the Mann–Kendall test, while the XGBoost model combined with SHAP analysis was employed to quantify the relative importance and contribution direction of candidate explanatory variables. Threshold regression models were then employed to assess nonlinear WUE responses to high-importance variables.

Results

WUE increased in 75% of the study area, with the highest growth observed in South China’s karst regions following the Grain for Green Program. NDVI showed the highest relative importance and positive SHAP contributions, while daily mean temperature and vapor pressure deficit (VPD) exhibited critical thresholds. WUE declined sharply beyond temperature thresholds of 19 °C in South China and 26 °C in Southeast Asia, and beyond VPD thresholds of around 1 kPa. Mixed tree-shrub-grassland ecosystems showed the highest WUE.

Conclusions

Our findings reveal critical nonlinear thresholds in WUE, emphasizing the role of vegetation greening and climate adaptation in managing carbon-water dynamics. These results provide actionable insights for enhancing WUE through ecological restoration and species selection, particularly in regions such as Vietnam, Myanmar, and Indonesia.