By Andrei Ionescu
Tropical forests help pull huge amounts of water into the atmosphere and turn it into rainfall, and a new analysis argues that this service is far more valuable than most policies currently acknowledge.
The researchers estimate that intact forests generate rainfall on a scale that directly supports farming, water supplies, and energy systems – and that losing forests means losing a steady, invisible source of water.
The findings come from a new study led by the University of Leeds.
Using satellite observations alongside the latest climate-model simulations, the team worked to pin down how much rainfall forests generate and then applied a simplified economic approach to estimate what that rain is “worth” in practical terms.
How forests generate rain
Forests help sustain regional rainfall through evapotranspiration. In simple terms, the sun’s energy pulls moisture from leaves into the air, where it can later fall as rain – sometimes nearby, sometimes farther downwind.
The study estimates that across the tropics, each square meter of forest contributes about 240 liters of rainfall per year. In the Amazon, the figure rises to around 300 liters.
Scaled up, the numbers become startling. The researchers estimate that each hectare of tropical forest generates about 2.4 million liters of rain every year – roughly enough to fill an Olympic-sized swimming pool.
One reason this study stands out is the way it tries to reduce long-running uncertainty.
The team combined satellite data with simulations from newer climate models to better estimate the size of the forest-rainfall effect, rather than relying on a single method that might over- or underestimate it.
Putting a price tag on rainfall
After estimating rainfall generation, the researchers used a simplified valuation method to connect that rainfall to benefits for society and the economy.
The headline result focuses on the Brazilian Amazon: they calculate that forest-driven rainfall is worth roughly US$20 billion a year to regional agriculture.
The experts also note a big mismatch between that value and the money currently flowing into protection and restoration. In short, the Amazon’s “rain service” appears to be worth far more than the incentives designed to keep forests standing.
“This is the most comprehensive and robust evidence to date of the value of tropical forests’ rainfall provision,” said study lead author Jess Baker from Leeds.
“Tropical deforestation is increasing, despite international efforts to halt forest loss. Our work highlights the vital role of tropical forests in producing rain. We estimate that the Amazon alone produces rainfall worth US$20 billion each year.”
“Demonstrating the financial benefits that tropical forests provide will unlock investment and strengthen arguments for forest protection.”
Crops depend on the forest
The study also makes the forest–farm connection feel more concrete by comparing crop water needs with the amount of rainfall forests help generate.
In some cases, producing enough moisture to support major crops requires evapotranspiration from a larger forest area than the cropland itself.
Cotton, for example, uses 607 liters of moisture per square meter – about the same amount produced by two square meters of intact forest.
Soybeans need 501 liters per square meter, equivalent to about 1.7 square meters of intact forest.
The point isn’t that every liter of water used by these crops comes directly from a nearby patch of forest. It’s that forest-driven moisture is a major input into the larger rainfall systems that agriculture relies on, and once forests shrink, that input weakens.
What deforestation may actually cost
The researchers estimate that deforestation in the Amazon over recent decades – around 80 million hectares – may already have reduced rainfall-generation benefits by almost US$5 billion per year.
And the impacts don’t stop at farms. The study links reduced rainfall to knock-on risks for food production, hydropower, and water security.
Brazil is highlighted as especially exposed because so much of its agriculture depends on rain rather than irrigation.
The study notes that roughly 85% of the country’s agriculture is rain-fed, and that reduced rainfall and delayed wet seasons have already affected soy and maize yields in regions with heavy deforestation.
Beyond farming, the study points to wider consequences: pressure on drinking water supplies, river transport in remote areas, hydropower generation, and even the ability of remaining forests to store carbon.
Less rain can stress forests, raising the risk of degradation. This means rainfall loss can make other climate and biodiversity problems worse.
A bridge for agriculture and conservation
The authors suggest one reason forest protection struggles politically is that rainfall generation isn’t properly counted in economic and legal frameworks.
If you ignore forests as a water source, you underestimate what is being lost – and you make it easier for short-term gains from land conversion to look “worth it.”
Despite repeated global pledges to halt deforestation by 2030, forest loss continues across much of the tropics.
The researchers argue that putting forest-generated rainfall on the balance sheet could change the conversation, because it connects conservation directly to everyday needs like water, food, and electricity.
Study co-author Callum Smith frames it as a way to lower the temperature in the long-running fight between farming and conservation.
“Tropical forests make it rain, supplying water that is essential for agriculture. Recognizing that crucial connection could ease tensions between agricultural and conservation interests whilst building broader support for protecting forests overall,” he said.
The study’s underlying message is pretty simple: forests are not just scenery or carbon storage. They are working infrastructure for rainfall. And as water pressures rise, treating that service as invisible is becoming harder and riskier to justify.
The study is published in the journal Communications Earth & Environment.
Source: Earth.com
