Recent Water Constraints Mediate the Dominance of Climate and Atmospheric CO2 on Vegetation Growth Across China.

Multiple lines of evidence confirm a widespread increase in vegetation growth across China over the past few decades. The relationship between vegetation growth and water availability is thought to be becoming stronger under climate change, that is, water constraints on vegetation growth have been increasing. However, our understanding of how water constraints have influenced these vegetation greening trends, especially those climate change‐driven ones, remains limited. Here, we conduct a comprehensive evaluation of recent water constraints and their implications for vegetation growth in China between 1982 and 2015. By analyzing the spatiotemporal patterns of the relationship between vegetation growth and water availability, we reveal recent water constraints and their changes hidden within an overall greening trend in China. Further analysis demonstrates that two climate change‐related categories, defined broadly as "climate" (e.g., air temperature, precipitation, and so on) and "CO2" (i.e., atmospheric carbon dioxide), have exerted varying levels of importance in regulating vegetation growth across different water constraints. With increasing water constraints, the proportion of the climate‐dominated area has significantly risen, while that of the CO2‐dominated area has sharply declined. Our findings highlight that water constraints can mediate the dominance of climate and atmospheric CO2 on vegetation growth. This has the great potential to exacerbate the uncertainty surrounding current and future sustainable vegetation greening trends. Plain Language Summary: China's vegetation growth has shown a broad increase under climate change and human activities over the past few decades. At the same time, changes in vegetation water demand, terrestrial water availability, and climatic factors are expected to lead to increasing water constraints on vegetation growth. However, whether water constraints have influenced climate change‐driven vegetation greening trends remains unclear. In this study, we provide a comprehensive assessment of recent water constraints and their implications for vegetation growth in China between 1982 and 2015. To do this, we analyze the spatiotemporal patterns of the relationship between vegetation growth and water availability to reveal recent water constraints hidden within China's vegetation greening. Further analysis shows that climate and atmospheric CO2 have exerted varying levels of importance in regulating vegetation growth across different water constraints. With increasing water constraints, more regions become climate‐dominated and fewer become CO2‐dominated. Overall, our findings highlight that water constraints can mediate the dominance of climate and atmospheric CO2 on vegetation growth. This will help decision‐makers recognize the uncertainty of sustainable vegetation greening trends. Key Points: We reveal recent water constraints and their changes hidden within China's widespread vegetation greeningClimate and atmospheric CO2 have exerted varying levels of importance in regulating vegetation growth across different water constraintsWith increasing water constraints, more of China's vegetated regions become climate‐dominated and fewer become CO2‐dominated [ABSTRACT FROM AUTHOR]

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