Tropical forests are home to much of the world’s biodiversity and are a major store of carbon making them a key ally in tackling global climate change. Less widely appreciated, however, is their role in regulating local and regional climate. Tropical forests pump vast quantities of water into the atmosphere through evapotranspiration. Evaporation of moisture consumes energy, leading to strong local cooling. It also recycles moisture back into the atmosphere altering where, when, and how much rain falls.
Deforestation disrupts these processes. Clearing tropical forests reduces evapotranspiration and alters the amount of sunlight reflected back to space. Recent studies have shown that tropical deforestation leads to local warming, increasing dangerous heat stress for nearby communities (Reddington et al., 2025). Other work has demonstrated that deforestation also drives changes in observed local and regional rainfall patterns (Smith et al., 2023).
Despite their importance, these climate benefits are not always fully recognised by key stakeholders. People living in or near tropical forests often value forests for the cooler temperatures and reliable rainfall they provide (Sodhi et al., 2010; Wolff et al., 2018). However, while these benefits are widely acknowledged, local communities frequently lack access to clear, quantitative information that could support discussions around the management of forest resources.
Environmental NGOs typically emphasise biodiversity conservation and global climate mitigation, but local climate impacts are less consistently incorporated into their messaging and decision-making. To better understand these knowledge gaps, we organised sessions at a workshop run by the World Land Trust, which brought together more than 50 environmental organisations working across the tropics. Knowledge of the local climate impacts of tropical forests varied widely, but there was a strong and shared desire for better information, particularly of downwind rainfall provision.
Financial institutions, meanwhile, are increasingly interested in reducing deforestation within their portfolios. In Brazil, insurance companies are increasingly facing larger payouts due to crop failures, caused by drought that in some cases could be linked to deforestation. Through discussions with bankers and financers we realised many institutions struggle to access clear, credible evidence of the local climate consequences of forest loss. This lack of clear information was a major stumbling block in designing financial instruments that could support better forest governance.
Across all these groups, one theme stood out repeatedly: rain matters and information on the rainfall benefits of forests is lacking.
Assessing the rainfall generation of tropical forests
To address this clear need, we set out to build a more detailed and robust picture of how tropical deforestation affects rainfall. We synthesised evidence from satellite observations with results from climate model experiments designed to isolate the impacts of forest loss. Bringing these complementary approaches together allowed us to derive a more comprehensive and consistent estimate than any single study could provide.
By combining the available evidence, our analysis shows that tropical deforestation reduces annual rainfall by an average of around 240 mm. We used this to calculate that each hectare of intact tropical forest supplies 2.4 million litres of rainfall per year to the surrounding region. Put another way, that means each hectare of forest provides enough rainfall to fill an Olympic-sized swimming pool every year.
Tropical forests of the Amazon had an even stronger rainfall-creating ability, with each hectare of tropical forest supplying 3 million litres of rainfall per year.
This framing helps illustrate the tangible role that forests play in supplying water to nearby ecosystems, agricultural systems, and communities.
We then translated this biophysical effect into an approximate economic value. Focusing on the Brazilian Amazon, we used estimates of the agricultural value of water to calculate the monetary worth of this rainfall generation service. Our analysis suggests that each hectare of tropical forest contributes rainfall worth about US$59.40 per year.
While modest at the scale of a single hectare, the cumulative value is striking: across the Brazilian Amazon, tropical forests generate rainfall with an annual value of around US$20 billion. Deforestation in Brazil to date has already reduced the rainfall generating services of Brazil’s forests by almost US$5 billion, representing a quantifiable loss to Brazil’s economy.
Implications for tropical forest conservation
Our work provides a solid evidence base for new efforts to value the services provided by standing tropical forests. The Tropical Forests Forever Facility a Brazil-led mechanism proposing to reward countries for conserving tropical forests through annual payments of $4 per hectare of standing forest. Our work supports these payments, showing that forests deliver more than this value through rainfall generation alone.
HIFOR, a new nature finance initiative for intact tropical forests, aims to reward the multiple benefits forests provide including ongoing removal of CO2, local and regional cooling, protection of high levels of biodiversity and regulation of regional rainfall. Our work quantifies these rainfall benefits and helps provide a solid evidence base for such initiatives.
Tropical forests make it rain. Our work aims to make this largely invisible, rainfall-generating service visible. By providing robust evidence of how tropical forests influence rainfall, and by clearly communicating this evidence to stakeholders, we seek to support better decisions for tropical forest governance and for the communities that depend on tropical forests and the rainfall they generate.