When Forests Disappear, Rivers React: Climate Change and Deforestation Threaten the Jari River's Blue Waters

Redacción HC
15/06/2025

As the Amazon continues to face the compounded threats of deforestation and climate change, one of its lesser-known tributaries—the Jari River—is becoming a focal point in understanding how these forces are reshaping the hydrological balance of the region. A recent study published in Water (2025) dives deep into the "blue water" resources of the Jari Basin, examining how surface and groundwater flows may evolve under different future scenarios.

Using advanced hydrological modeling, the researchers unveil a concerning forecast: more surface runoff, less groundwater recharge, and greater extremes in flooding and drought. The study not only quantifies these changes but also connects them to forest loss and shifting rainfall patterns. These findings carry urgent implications for environmental governance, rural livelihoods, and the long-term resilience of the Amazon's water systems.

Blue Water in a Green Forest: What's at Stake?

Blue water refers to surface and underground water that feeds rivers, lakes, and aquifers—essential for agriculture, ecosystems, and human consumption. In forested tropical basins like the Amazon, this water is regulated by dense vegetation that acts like a natural sponge, absorbing rainfall and slowly releasing it into aquifers and streams.

However, deforestation weakens this buffering capacity, and climate change brings additional variability in rainfall, compounding the risks of water scarcity and extreme events. In the Jari River Basin, located in northern Brazil, these two pressures are already converging.

"How do climate change and deforestation interact to affect surface runoff and aquifer recharge in the Jari River Basin through 2050?" This is the central question the authors, led by Paulo Ricardo Rufino of UFZ (Germany/Brazil), set out to answer.

The Science Behind the Forecast: Using SWAT to Simulate Future Water Scenarios

The researchers employed the SWAT (Soil and Water Assessment Tool) hydrological model, which integrates climate data, land-use patterns, and soil properties to simulate water flows. The model was calibrated and validated using historical streamflow data from the basin, achieving high accuracy:

• Nash-Sutcliffe Efficiency: 0.85 (calibration), 0.89 (validation)
• PBIAS: -9.5% and -0.6%
• RSR: 0.39 and 0.33

They then tested four contrasting scenarios combining climate change projections with varying levels of deforestation through 2050.

Key variables analyzed included:

• Annual surface runoff
• Groundwater recharge
• Seasonal flow variability

Limitations included inherent uncertainties in climate projections, assumptions in land-use models, and the absence of more recent field validation.

What the Data Reveals: A Watershed Under Pressure

1. Runoff Is Rising

In combined scenarios of climate change and deforestation, surface runoff increased by an average of 18 mm per year. This is driven by reduced soil permeability due to vegetation loss and erratic rainfall patterns.

2. Groundwater Recharge Becomes Highly Variable

Groundwater recharge showed swings between a loss of 20 mm (in drier, deforested scenarios) and a gain of up to 120 mm when rainfall increased—but with degraded soils that still limited infiltration. This dual trend shows that "more rain doesn't always mean more available water."

3. Hydrological Extremes Intensify

The basin exhibited greater seasonal flow variability, with intensified floods during wet seasons and deeper droughts in dry periods. This reflects both rainfall irregularity and reduced underground water storage due to forest loss.

4. High Risk of Floods and Water Scarcity

The interplay of these dynamics increases the risk of hydrological extremes, threatening the water security of local communities and ecosystems.

"Forests play a crucial role in dampening hydrological variability. Their removal amplifies both floods and droughts." — Rufino et al., 2025

5. Confirms a Regional Pattern

The findings align with other studies in nearby basins such as Tocantins-Araguaia, where deforestation has led to declining water availability and growing uncertainty in water planning.

Beyond the Model: Real-World Implications

A. Policy and Land Management

Protecting native forests is essential not just for biodiversity but for sustaining blue water. The study supports regulations that limit intensive land use in critical recharge areas and encourages the adoption of agroforestry systems.

B. Water Planning and Adaptation

Forecasts of increased runoff and reduced groundwater call for new flood mitigation infrastructure, decentralized water storage, and adaptive water governance in Amazonian territories.

C. Conservation and Community Resilience

Integrating riparian forests and aquifer zones into conservation strategies is key to ensuring year-round water availability. Forest cover acts not just as a biodiversity haven, but also as hydrological insurance.

D. Practical Recommendations

• Prioritize conservation policies in key recharge zones
• Promote sustainable land-use practices
• Enhance real-time water monitoring and adaptive management frameworks

A Regional Warning with Global Lessons

The Jari River Basin may be a small part of the Amazon, but it represents a broader truth: climate change and deforestation do not act in isolation. Together, they reshape the entire water cycle—often in unpredictable and damaging ways.

For the Amazon—and other tropical basins around the world—this means that protecting forests isn't just about carbon. It's about water, too.

Topics of interest

Climate