Declining coupling between vegetation and drought over the past three decades

Abstract

Droughts have been implicated as the main driver behind recent vegetation die‐off and are projected to drive greater mortality under future climate change. Understanding the coupling relationship between vegetation and drought has been of great global interest. Currently, the coupling relationship between vegetation and drought is mainly evaluated by correlation coefficients or regression slopes. However, the optimal drought timescale of vegetation response to drought, as a key indicator reflecting vegetation sensitivity to drought, has largely been ignored. Here, we apply the optimal drought timescale identification method to examine the change in coupling between vegetation and drought over the past three decades (1982–2015) with long‐term satellite‐derived Normalized Difference Vegetation Index and Standardized Precipitation‐Evapotranspiration Index data. We find substantial increasing response of vegetation to drought timescales globally, and the correlation coefficient between vegetation and drought under optimal drought timescale overall declines between 1982 and 2015. This decrease in vegetation–drought coupling is mainly observed in regions with water deficit, although its initial correlation is relatively high. However, vegetation in water‐surplus regions, with low coupling in earlier stages, is prone to show an increasing trend. The observed changes may be driven by the increasing trend of atmospheric CO2. Our findings highlight more pressing drought risk in water‐surplus regions than in water‐deficit regions, which advances our understanding of the long‐term vegetation–drought relationship and provides essential insights for mapping future vegetation sensitivity to drought under changing climate conditions.

Large‐scale remote sensing analysis reveals an increasing coupling of grassland vitality to atmospheric water demand

“…Moreover, a consistently higher sensitivity level from 2010 to 2021 indicates that regional to national scale spatial patterns of grassland vitality are increasingly driven by atmospheric water demand. Our findings for grasslands underpin recent studies observing an increasing coupling of ecosystem productivity and drought across different ecosystems in humid regions (Gampe et al, 2021;Jiao et al, 2021;Li et al, 2024).…”

“…We included interactions of the predictor with the drought index to test whether drought sensitivities are different between grassland habitat groups and between habitat types. To further investigate the temporal variation of drought sensitivity, we built simple linear models based on data subsets from 5-year moving windows using the best performing drought index as a predictor for grassland vitality (following a similar approach as Jiao et al, 2021;Li et al, 2024). We used the Theil-Sen estimator to derive a trend estimate of drought sensitivity.…”

Declining precipitation frequency drivers earlier leaf senescence by intensifying drought stress and enhancing drought acclimation

“…In particular, we found a significant negative correlation between drought response lag and evapotranspiration (ET) (Extended Figure 2 A). Such results implies an enhanced water-use strategy of plants that further supports plant adaptation and acclimation, probably by strengthening the growth of root systems to extend downstream for deeper water sources under droughts 25 . This reason has been supported by our results showing increased root depth with lower drought response lag (Extended Figure 2 B).…”