Tropical Forests Generate Rainfall Worth US$20 Billion in the Amazon

Tropical forests draw vast volumes of water into the atmosphere, where it is transformed into rainfall, and a new analysis says this function is worth much more than current policies tend to recognise.

The researchers calculate that intact forests create rainfall at levels that underpin agriculture, water supplies and energy systems. When forests disappear, they argue, so does a dependable but unseen water source.

The conclusions are drawn from a new study headed by the University of Leeds.

Combining satellite measurements with the newest climate-model simulations, the researchers sought to establish how much rain forests produce. They then used a simplified economic method to assess the practical value of that rainfall.

How forests generate rain

Forests support rainfall across regions through evapotranspiration. Put simply, solar energy draws moisture from leaves into the atmosphere, from which it may later return as rain - either locally or farther downwind.

The study calculates that, throughout the tropics, every square metre of forest contributes roughly 240 litres of rain annually. In the Amazon, this rises to approximately 300 litres.

At a larger scale, those figures are striking. Each hectare of tropical forest produces an estimated 2.4 million litres of rain a year - about enough to fill an Olympic-sized swimming pool.

A key feature of the research is its attempt to narrow a long-standing area of uncertainty.

The team brought together satellite data and simulations from newer climate models to calculate the scale of the forest-rainfall effect more accurately, instead of depending on one approach that could either overstate or understate it.

Putting a price on forest rainfall

Once they had calculated rainfall generation, the researchers applied a simplified valuation approach to link this rain with social and economic benefits.

Their main finding concerns the Brazilian Amazon: forest-generated rainfall there is estimated to be worth about US$20 billion annually to agriculture in the region.

The experts also identify a major gap between this value and the funding currently directed towards protection and restoration. Put briefly, the Amazon’s “rain service” seems to be worth considerably more than the incentives intended to prevent forest loss.

“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 tropical forests

The study makes the relationship between forests and farms more tangible by setting crop water requirements against the rainfall that forests help to create.

For some crops, generating sufficient moisture requires evapotranspiration from a forested area larger than the area of cropland itself.

Cotton, for instance, requires 607 litres of moisture for every square metre - broadly the amount generated by two square metres of intact forest.

Soybeans require 501 litres per square metre, corresponding to around 1.7 square metres of intact forest.

This does not mean that every litre of water used by these crops comes straight from a nearby forest. Rather, forest-generated moisture is a significant contribution to the wider rainfall systems on which farming depends. As forests decline, that contribution is weakened.

The possible cost of deforestation

Deforestation in the Amazon during recent decades - about 80 million hectares - may already have cut rainfall-generation benefits by nearly US$5 billion each year, the researchers estimate.

The effects extend beyond agriculture. The study associates falling rainfall with subsequent risks to food production, hydropower and water security.

Brazil is identified as particularly vulnerable because such a large share of its farming relies on rainfall instead of irrigation.

About 85% of Brazilian agriculture is rain-fed, according to the study, while reduced rainfall and later wet seasons have already affected soy and maize yields in heavily deforested regions.

The research also highlights broader impacts beyond farming, including strain on drinking-water supplies, river transport in remote locations, hydropower production and even the capacity of surviving forests to store carbon.

Reduced rainfall can place forests under stress and increase the likelihood of degradation. As a result, rainfall losses can worsen other climate and biodiversity challenges.

A bridge between agriculture and conservation

The authors propose that one reason forest protection faces political difficulty is that rainfall generation is not adequately included in legal and economic frameworks.

When forests are overlooked as a source of water, the value of what is lost is underestimated - making the short-term benefits of converting land appear more “worth it.”

Although global commitments have repeatedly pledged to end deforestation by 2030, forest loss continues in much of the tropics.

The researchers contend that including forest-generated rainfall on the balance sheet could reshape the debate by directly linking conservation with everyday needs such as water, food and electricity.

Study co-author Callum Smith describes it as an opportunity to ease the enduring conflict between agriculture 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 central message of the study is straightforward: forests are more than scenery or carbon stores. They are functioning rainfall infrastructure. As pressure on water increases, it is becoming more difficult - and more risky - to treat this service as invisible.