Widespread increasing vegetation sensitivity to soil moisture

Abstract

Global vegetation and associated ecosystem services critically depend on soil moisture availability which has decreased in many regions during the last three decades. While spatial patterns of vegetation sensitivity to global soil water have been recently investigated, long-term changes in vegetation sensitivity to soil water availability are still unclear. Here we assess global vegetation sensitivity to soil moisture during 1982-2017 by applying explainable machine learning with observation-based leaf area index (LAI) and hydro-climate anomaly data. We show that LAI sensitivity to soil moisture significantly increases in many semi-arid and arid regions. LAI sensitivity trends are associated with multiple hydro-climate and ecological variables, and strongest increasing trends occur in the most water-sensitive regions which additionally experience declining precipitation. State-of-the-art land surface models do not reproduce this increasing sensitivity as they misrepresent water-sensitive regions and sensitivity strength. Our sensitivity results imply an increasing ecosystem vulnerability to water availability which can lead to exacerbated reductions in vegetation carbon uptake under future intensified drought, consequently amplifying climate change.

The global decline in the sensitivity of vegetation productivity to precipitation from 2001 to 2018

“…Grasslands indicate high S ppt , and their S ppt is still increasing in the past two decades (Table 2). This result is consistent with the elevated soil moisture sensitivity found by Li et al (2022) in the arid regions around the globe. This implies that climate change would introduce greater instability of vegetation productivity and carbon sink in grassland ecosystems, making them be more vulnerable.…”

“…Our results suggest that S ppt varied greatly across the globe, with high S ppt values in arid regions and low S ppt in mesic regions (Figure 1). This result is consistent with prior ground observations, which illustrate higher S ppt in more arid ecosystems (Huxman et al, 2004; Knapp et al, 2015), and is also consistent with a reported spatial pattern of global soil moisture sensitivity (Li et al, 2022). For example, a meta‐analysis by Liu et al (2021) for global grasslands suggests that ANPP has higher sensitivity to precipitation treatments at dry sites than at nonwater‐limited sites.…”

Earlier leaf senescence dates are constrained by soil moisture

“…A recent study suggests that low soil moisture is the dominant driver of dryness stress on vegetation, which weakens the capacity for carbon uptake in ecosystems (Liu et al, 2020). Furthermore, the sensitivity of vegetation to soil moisture has substantially increased since 1982 (Li, Migliavacca, et al, 2022). Previous studies found that not only temperature, but also plant‐available water affect autumn phenological processes (Fu et al, 2022; Luo et al, 2021; Tao et al, 2021; Wu et al, 2022).…”

Soil moisture-vegetation interaction from near-global in-situ soil moisture measurements

“…Under the continuous impact of climate change, the spatial distribution of climate and land cover classifications is assumed to be changed in the coming century (Beck et al 2018). It is also predicted that drying trend will continuously dominate and amplify climate change impact (Deng et al 2020, Li et al 2022. The pattern of the SM-LAI interaction in different regions is expected to change due to the shift in climate and land cover types.…”