Hot droughts in the Amazon provide a window to a future hypertropical climate
Summary
This Nature paper combines long-term field measurements, sapflow records and climate model projections to show how recent “hot droughts” in the central Amazon (notably 2015–16 and 2023) stress trees via elevated vapour pressure deficit (VPD) and canopy temperatures, reducing transpiration and increasing mortality. The study links plot-level demographic data (BIONTE) and micrometeorological observations with modelled future climate scenarios (CESM2/CMIP6) to project many more extreme VPD days by 2100, creating a warmer, drier “hypertropical” climate that intensifies hydraulic failure and carbon‑starvation risks for Amazon trees.
Key methods: integrated sensor networks (sapflow, canopy and air temperature, soil moisture), multilevel Bayesian mortality models, structural equation modelling and multi-model climate projections to estimate trends in extreme VPD days and likely biological outcomes.
Key Points
- Hot droughts combine higher temperatures with low soil moisture to raise vapour pressure deficit (VPD), intensifying tree water stress even when rainfall deficits are moderate.
- Field observations (2015–16 and 2023) show declines in sap flow and elevated tree mortality linked to high daytime canopy temperatures and prolonged low soil volumetric water content.
- Mortality mechanisms identified include hydraulic failure and carbon starvation, both reducing transpiration and altering forest functioning.
- Species- and trait-level differences matter: hydraulic strategy and wood-density-related traits influence vulnerability, so impacts will be heterogeneous across the basin.
- Multi-model projections (CESM2/CMIP6) indicate a sharp increase in “extreme VPD days” through the 21st century under standard SSP scenarios, effectively moving parts of the Amazon toward a hypertropical climate regime.
- The authors call for a network of instrumented sites across biogeographical gradients to monitor processes and improve predictions, noting existing NGEE-Tropics datasets and code are openly available.
Content summary
The paper synthesises observational and experimental data from central Amazon research sites (including BIONTE plots and K34 tower records) to quantify how heat and dryness interact to stress trees. Analyses show increased mortality in recent decades that aligns with more frequent hot drought conditions; model results project many more days with VPD exceeding thresholds observed during the 2015 drought. The combined evidence suggests physiological tipping points for some species and a future where hotter, drier extremes become the norm in parts of the Amazon.
The study emphasises mechanistic links (soil moisture thresholds, sap velocity shifts, canopy heating) and demonstrates how elevated VPD—rather than rainfall alone—can be the dominant stressor during hot droughts. Projections are ensemble-based and use a quantile approach to define extreme VPD thresholds comparable between observations and models.
Context and relevance
This work matters because the Amazon is a major global carbon sink and biodiversity store; shifts to more frequent hot droughts threaten forest carbon balance, species composition and feedbacks to the global climate system. It connects with broader findings on increased VPD, vegetation vulnerability and potential regional tipping points. For researchers, policymakers and conservation planners, the paper provides field‑validated thresholds and a clear forecast of increasing thermal‑hydric extremes that should inform monitoring, protection and restoration priorities.
Why should I read this?
Quick and blunt: if you care about whether the Amazon will still act like a carbon-sucking rainforest by mid‑century, read this. It packs field data, clear physiological mechanisms and model projections into a single picture showing that hotter droughts — not just less rain — could flip large patches of forest into an unfamiliar, stress-filled state. Short version: it’s where the rubber hits the road for climate impacts on tropical forests.
Author style
Punchy: the team combines rigorous fieldwork with robust modelling and makes a strong case that recent hot droughts are credible previews of a hypertropical future. The paper is essential for anyone tracking forest resilience, carbon budgets or climate tipping risks — it’s evidence you can act on, or be alarmed by.
Source
Article Date: 2025-12-10
Article URL: https://www.nature.com/articles/s41586-025-09728-y
Article Title: Hot droughts in the Amazon provide a window to a future hypertropical climate
Article Image: (none provided)