Changes in the relationship between climate variables and vegetation carbon uptake in East Asia

To understand the carbon cycle in East Asia in the context of rising CO 2 , we analyzed a land carbon cycle dataset (TRENDY) from 1982 to 2020, examining the relationship between vegetation carbon uptake and two climate variables (i.e. precipitation and surface temperature) during the vegetation growing season (March to September). Our results show that, since the early 2000s, the relationship between gross primary production (GPP) and surface temperature has strengthened, while the relationship between GPP and precipitation has weakened in East Asia. Further analyses suggest that this strengthening of the GPP-surface temperature relationship is primarily due to a combination of CO 2 fertilization effects and significant increases in surface temperature, which lead to reduced soil moisture and increased water use efficiency in vegetation. This appears to result in an increase in GPP in the long term along with the absence of significant changes in precipitation. As a result, vegetation carbon uptake is less dependent on precipitation and more correlated with surface temperature in the recent decades. This result indicates that the relationship between vegetation carbon uptake and climate variables is non-stationary, and therefore requires careful attention to properly develop carbon mitigation plans through afforestation. When looking at climate effects alone, the S3 minus S1 scenarios show observable trends in land surface temperature, precipitation, soil moisture, and water use efficiency from the late 1990s to the mid-2000s. While precipitation has remained relatively stable, land surface temperature has been increasing since the late 1990s and soil moisture has been decreasing in a staggered manner. These conditions temporarily impede and delay the increase in GPP due to the CO 2 fertilization effect, but consequently increase the water use efficiency of plants, leading to an increase in total GPP. The increase in water use efficiency has resulted in a weaker dependence of carbon sequestration by vegetation on precipitation and a stronger dependence on surface temperature in recent decades. • The relationship of gross primary production-precipitation (temperature) has become weaker (stronger) in East Asia. • Warming in East Asia, driven by climate and land use, reducing the dependency of gross primary production on soil moisture. • Warming and CO 2 effect increase water use efficiency, enhancing the sensitivity of gross primary production to temperature.