R code for intensified water constraints on global tree growth

Recent warming has intensified the frequency, severity, and duration of droughts, increasing the risk of reduced forest productivity and tree growth. However, the temporal dynamics of global tree growth responses to water stress remain poorly understood. Here, using long-term tree-ring width data from 3757 sites worldwide, we demonstrate a significant increase in both the overall sensitivity of tree growth to water availability (β) and the proportion of sites exhibiting significant water constraints on tree growth from 1961 to 2010. This indicates a global intensification of water constraints on tree growth through time. Temperature emerged as the dominant factor explaining the temporal trend of tree growth sensitivity to water availability (β trend). Sites with warmer baseline temperatures exhibited stronger increasing trends in β, likely through their effects on soil organic carbon content (SOC) and root depth. This suggests a stronger temporal intensification of water constraints on tree growth in warmer regions. Our findings thus reveal that global tree growth is likely to become more constrained by water shortage and drought stress under warming climates.