Each hectare of tropical forest generates $2,400 worth of rainfall for regional agriculture

Tropical forests are already recognized as carbon sinks and biodiversity reservoirs. A study published in Communications Earth and Environment argues they deserve equal recognition for something more immediately practical: generating rain. The University of Leeds-led research puts concrete numbers on how much water tropical forests pump into the atmosphere each year and what that water is worth to the agriculture that depends on it.

The central finding is that each hectare of tropical forest generates approximately 2.4 million litres of rainfall annually - enough to fill an Olympic-sized swimming pool. Across the Brazilian Amazon, this produces rainfall estimated to be worth roughly US$20 billion per year in agricultural water value. By comparison, current financial incentives for protecting or restoring the Amazon amount to a fraction of that figure.

The mechanism: evapotranspiration at scale

Tropical forests draw water from the soil through their roots and release it from their leaves as water vapor in a process called evapotranspiration. This vapor rises into the atmosphere and condenses to form clouds and rain - often hundreds or thousands of kilometers downwind of the forest itself. The forests, in effect, create their own rainfall and export it to surrounding agricultural regions.

The study combined satellite observations of actual evapotranspiration rates with simulations from the latest generation of climate models to pin down how much rainfall tropical forests generate and where it falls. Previous estimates had ranged widely; the combination of observational data and model output reduced that uncertainty substantially. Lead author Dr Jess Baker, from the University of Leeds' School of Earth, Environment and Sustainability, described it as "the most comprehensive and robust evidence to date of the value of tropical forests' rainfall provision."

What crops need and what forests provide

The research also mapped the forest area required to sustain specific crops' water needs. Cotton, which requires 607 litres of moisture per square metre, needs water equivalent to the output of roughly two square metres of intact forest. Soybean crops require 501 litres per square metre - the equivalent of water generated by 1.7 square metres of forest. Brazil's soy industry, one of the world's largest, sits in a region where forest cover and rainfall generation are directly linked.

About 85% of Brazil's agriculture is rain-fed rather than irrigated. The country's exposure to forest loss is therefore direct and economically concrete. Reduced rainfall and delayed wet seasons linked to deforestation have already affected soy and maize yields in regions with high forest loss rates, and these losses compound as deforestation continues.

The cost of what has already been lost

The researchers estimate that deforestation of approximately 80 million hectares in the Amazon over recent decades may have reduced rainfall-generation benefits by almost US$5 billion annually. This figure does not include knock-on effects for hydropower generation, which depends on river flows fed by forest rainfall, or for drinking water security in downstream communities.

Beyond agriculture, forest loss affects carbon storage capacity: drier forests are more vulnerable to fire, and fire releases the stored carbon that made the forests valuable as climate mitigation tools in the first place.

Why this valuation matters for policy

The study's authors argue that failing to include rainfall generation in economic and legal frameworks has obscured one of the strongest practical arguments for forest protection. Current conservation finance mechanisms - REDD+, voluntary carbon markets, biodiversity credits - do not yet systematically price water generation. Adding it to the accounting changes the cost-benefit calculation for deforestation dramatically.

"Recognising that crucial connection could ease tensions between agricultural and conservation interests whilst building broader support for protecting forests overall," said co-author Dr Callum Smith of Leeds.

The study's economic calculations involve simplifying assumptions about how rainfall translates to agricultural production and how that production is valued - the authors apply a single crop price estimate across a complex, variable agricultural landscape. The US$20 billion figure should be treated as an indicative estimate rather than a precise accounting, but the order of magnitude helps frame how large the unpriced benefit of tropical forests actually is.