One Hectare of Tropical Forest Generates Rainfall Equal to an Olympic Swimming Pool

Tropical forests do more than store carbon and shelter wildlife. They actively generate rainfall on a scale large enough to fill an Olympic-sized swimming pool every year for every hectare of intact forest, according to new research published in Communications Earth & Environment, February 2026.

The study, led by scientists at the University of Leeds and released through EurekAlert!, provides one of the clearest quantifications to date of how much rainfall tropical forests help produce — and what that rainfall may be worth economically.

Researchers found that each square meter of intact tropical forest contributes approximately 240 liters of rainfall annually through a process known as evapotranspiration. Scaled up to one hectare — equivalent to 10,000 square meters — that amounts to roughly 2.4 million liters of rainfall per year.

For comparison, a standard Olympic swimming pool holds about 2.5 million liters of water. The near equivalence offers a striking way to visualize the hydrological power of tropical forests.

Forests as Rain-Making Systems

For decades, scientists have understood that forests influence local and regional climates. But this study strengthens the evidence that tropical forests function as active “rain-making” systems rather than passive recipients of precipitation.

Through evapotranspiration, trees draw water from the soil and release it into the atmosphere as water vapor. Solar energy drives this process, allowing moisture to accumulate in the air, form clouds and eventually fall as rain. Some of this recycled moisture precipitates locally, while some travels across regions, sustaining rainfall far from its source.

In the Amazon basin, the effect is even more pronounced. The study estimates that each square meter of Amazon forest may generate around 300 liters of rainfall per year, reflecting the region’s dense canopy and high moisture recycling rates.

Lead author Jess Baker of the University of Leeds said the findings offer empirical proof of forests’ role in sustaining rainfall. By combining satellite observations with advanced climate modeling, researchers were able to measure how rainfall declines when forests are removed — a method that allows scientists to calculate rainfall sensitivity to deforestation with greater precision than before.

The Economic Value of Rainfall

Beyond measuring rainfall volumes, the researchers also attempted to estimate its economic value. In Brazil’s Legal Amazon region, rainfall generated by forests is estimated to support agricultural production worth approximately $20 billion per year.

Brazil’s agricultural sector depends heavily on rain-fed systems. The majority of crops — including soybeans, maize and cotton — rely directly on natural rainfall rather than irrigation. If deforestation reduces rainfall, the economic consequences can ripple through food production, hydropower generation and freshwater supply.

According to the study, the loss of roughly 80 million hectares of Amazon forest in recent decades may have already reduced rainfall-related ecosystem services by nearly $5 billion annually. Such declines could intensify drought risk, disrupt planting cycles and increase water stress in both rural and urban areas.

Callum Smith, a co-author from the University of Leeds, noted that recognizing forests as critical infrastructure for rainfall could shift how policymakers evaluate land-use decisions. If the rainfall value of forests were fully accounted for, conserving forests might be seen not as a cost but as an economic investment.

The research comes at a time of continued global concern over tropical deforestation. While forests are widely recognized for their role in carbon storage and biodiversity protection, their contribution to regional rainfall patterns has received less attention in economic planning.

Reduced forest cover can lengthen dry seasons and make rainfall more erratic. Over time, this can create feedback loops in which less forest leads to less rainfall, which in turn stresses remaining forests and increases fire risk.

In some cases, the study notes, the amount of forest required to sustain rainfall for certain crops may exceed the size of the cropland itself. Converting forests to farmland could therefore undermine the long-term water supply needed to support agriculture.

Implications for Tropical Forests

Although the Amazon served as a key case study, the implications extend to tropical forests globally. Forests in Central Africa, Southeast Asia and other tropical regions likely play similar roles in sustaining regional rainfall systems.

In Southeast Asia, for example, tropical forests help regulate rainfall that supports rice cultivation and other staple crops. In the Congo Basin, forests sustain precipitation patterns critical to millions of smallholder farmers. If the rainfall-generation mechanism operates similarly across these regions, the cumulative economic value of tropical forests worldwide could reach into the hundreds of billions of dollars annually.

The findings suggest that tropical forests function as vast natural water infrastructures. Each hectare lost represents not only reduced biodiversity and carbon storage but also millions of liters of diminished rainfall each year.

By framing forest conservation in terms of tangible water and economic benefits, the study aims to inform climate policy, land-use planning and international conservation efforts. As global leaders continue to debate how to halt deforestation, the research underscores a simple but powerful message: protecting forests helps protect the rain that sustains economies, agriculture and human life across the tropics. (Sulung Prasetyo)