When the Amazon Turns to Savanna: Climate Simulations Warn of a Hotter, Drier Brazil

Redacción HC
02/03/2024

As the Amazon rainforest teeters on the edge of ecological transformation, new climate simulations from Brazilian researchers offer a stark warning: if deforestation continues and global warming accelerates, Brazil could face drastically longer dry seasons, extreme heatwaves, and widespread hydrological disruption. Published in Scientific Reports (Nature), the study led by Marcus Jorge Bottino and colleagues from INPE and other institutions explores how Amazon “savannization” and climate change could reshape the region’s climate by the end of the century.

The findings are sobering: up to 14 °C of additional heat, 44% less rainfall, and a 69% increase in dry season length under the worst-case scenario. These projections aren't just numbers—they signal cascading consequences for agriculture, water security, energy generation, and public health across Brazil and neighboring countries.

Understanding the Risk: What Is Amazon Savannization?

Savannization refers to the conversion of rainforest into dry, open landscapes similar to savannas, driven primarily by deforestation, fire, and climate stress. In the Amazon, this shift would radically alter the hydrological cycle—turning a self-sustaining “green pump” of continental rainfall into a fragmented system unable to support its own humidity.

The study asks a crucial question:

How do savannization and climate change, individually and combined, affect rainfall, soil moisture, heat extremes, and water flow across Brazil?

The Simulation Model: Probing Brazil’s Climate Future

Using the BESM v2.5, Brazil’s national coupled ocean-atmosphere-land-ice climate model, researchers simulated four future scenarios between 1983–2010 and 2073–2100:

• HiFo: Historical climate with forest cover
• HiSa: Historical climate with savanna
• R8Fo: Future emissions (RCP8.5) with forest
• R8Sa: Future emissions with full savannization

Each scenario was run over 28 years after calibration, focusing on variables like rainfall, temperature extremes, soil moisture, and river runoff. Although the savannization scenario assumes a total forest-to-savanna shift (a worst-case projection), the model offers a powerful tool to anticipate trends and vulnerabilities.

What the Simulations Reveal: A Drier, Hotter, Riskier Future

️ Rainfall Collapse and Longer Dry Seasons

In the R8Sa scenario, which combines high emissions with Amazon savannization:

• Annual rainfall in the Amazon decreases by up to 44% compared to current levels.
• The dry season lengthens by nearly two months, a 69% increase.

These changes would make vast regions of Brazil more arid, threatening agriculture, biodiversity, and water supplies.

Record-Breaking Temperatures

• Local daily maximum temperatures rise by as much as 14 °C in the Amazon.
• Average warming reaches 5.4 °C in R8Sa—well beyond the 3.3 °C rise under emissions alone.

Such heat extremes would significantly increase heat stress, fire risk, and public health emergencies.

Soil Moisture and Water Flow in Decline

• Soil moisture drops by up to 15%, impacting crop resilience and forest recovery.
• River runoff declines sharply in the Amazon and Brazil’s central-west, threatening hydroelectric power generation.

This loss of hydrological stability could devastate rural livelihoods and the country’s energy infrastructure.

Broader Implications: From Energy to Equity

⚠️ Threat to Hydropower and Agriculture

Brazil depends heavily on hydropower, much of which relies on rainfall-fed river basins. A 15% drop in runoff could undermine energy security and force a shift to more carbon-intensive sources.

Agriculture—the backbone of Brazil’s economy—also stands to lose. Prolonged dry seasons and less predictable rainfall will reduce yields, increase irrigation demands, and escalate food insecurity.

Deforestation as a Climate Multiplier

The research confirms what other studies have long warned: deforestation acts as a climate amplifier. Not only does it reduce rainfall and evapotranspiration, it disrupts atmospheric moisture transport from the Amazon to other parts of South America.

“Without the forest acting as a climate buffer, Brazil becomes significantly more vulnerable to warming and hydrological collapse.” — Bottino et al., 2024

Social and Public Health Consequences

• Indigenous and riverine communities will face water scarcity, reduced food availability, and health risks from heatwaves and wildfires.
• Urban centers will suffer from increased heat island effects, straining public health systems.

Policy Recommendations: Urgency in Action

To avoid this dire future, the authors call for:

1. Preserving and restoring Amazonian forest cover as a continental climate stabilizer.
2. Reducing global greenhouse gas emissions to mitigate temperature rise.
3. Integrating these projections into national planning—including energy, agriculture, and urban policy.
4. Supporting regional cooperation across Amazonian countries to safeguard shared resources and resilience.

Global and Regional Resonance

The study has profound implications beyond Brazil. Countries like Peru, Bolivia, and Colombia—which also share the Amazon basin—could face similar disruptions. Lower rainfall means drier rivers, loss of fish stocks, and weakened river transport systems, critical for food and medicine delivery in remote areas.

In Peru, for instance, rivers like the Ucayali and Madre de Dios could shrink, affecting both indigenous subsistence and national hydropower systems.

Conclusion: Climate Tipping Points Within Reach

The Amazon is not just a forest—it’s a climate engine for all of South America. The study’s worst-case scenarios remind us that climate tipping points are no longer hypothetical—they are measurable, modelable, and fast approaching.

This isn’t just a Brazilian issue—it’s a continental emergency. If we fail to act, we risk turning one of the world’s most vital ecosystems into a source of crisis rather than stability.

“The Amazon could become the very driver of the droughts and heatwaves it once helped prevent.”

Now is the time to shift course: protect the forest, curb emissions, and build resilience from the ground up.

Topics of interest

Climate Biodiversity