Recurrent droughts increase risk of cascading tipping events by outpacing adaptive capacities in the Amazon rainforest

Abstract

Tipping elements are nonlinear subsystems of the Earth system that have the potential to abruptly shift to another state if environmental change occurs close to a critical threshold with large consequences for human societies and ecosystems. Among these tipping elements may be the Amazon rainforest, which has been undergoing intensive anthropogenic activities and increasingly frequent droughts. Here, we assess how extreme deviations from climatological rainfall regimes may cause local forest collapse that cascades through the coupled forest–climate system. We develop a conceptual dynamic network model to isolate and uncover the role of atmospheric moisture recycling in such tipping cascades. We account for heterogeneity in critical thresholds of the forest caused by adaptation to local climatic conditions. Our results reveal that, despite this adaptation, a future climate characterized by permanent drought conditions could trigger a transition to an open canopy state particularly in the southern Amazon. The loss of atmospheric moisture recycling contributes to one-third of the tipping events. Thus, by exceeding local thresholds in forest adaptive capacity, local climate change impacts may propagate to other regions of the Amazon basin, causing a risk of forest shifts even in regions where critical thresholds have not been crossed locally.

Early warnings for multi-stage transitions in dynamics on networks

“…We used cubic polynomials to drive the node’s dynamics (and hence a potential in the form of quartic polynomials) and unipartite networks to test our ideas. These modelling assumptions are reasonable for investigating, for example, climate and vegetation cover transitions [38,39]. By contrast, various ecological systems are better modelled by bipartite networks, in which the two layers of nodes typically represent pollinators (or seed dispersers) and plants [12,40].…”

Network motifs shape distinct functioning of Earth’s moisture recycling hubs

“…Considering that particularly FFLs have been shown to increase the possibility of cascading tipping in networks of tipping elements 19 , we here present an additional argument for assessing the robustness of Earth’s major moisture recycling hubs. It is feared that parts of the Amazon rainforest may tip as a result of deforestation and climate change 24 , 41 , 42 . The weakening of links in the network may heavily affect moisture flows down the network.…”

“…Previous work found that parts of networks with many FFLs are more likely to spread perturbations and lead to cascading transitions 19 . To examine and compare the spread of such perturbations globally among the (tropical) ecosystems, the notion of motifs could be linked to dynamical-systems studies that include simplified vegetation dynamics of ecosystems 41 , 43 . Furthermore, as the atmosphere warms, it can contain more water vapor.…”

Multi-fold increase in rainforests tipping risk beyond 1.5-2⁰C warming

“…10 under future climate can also attract ITCZ northwards in Africa 75,82,83 . Since these shifts in ITCZ can potentially both counteract and aggravate (especially critical for highly water-stressed forests) the impact of water-deficit, including those impacted by the localised deforestation [84][85][86][87] . It warrants the need to include changes in atmospheric circulation for studies analysing the impact of future climate on the resilience of natural and human-influenced systems 43,44 .…”