Amazon rainforest canopy.
Photo Credit: Dominick Spracklen
Scientific Frontline: "At a Glance" Summary
- Main Discovery: Tropical forests generate rainfall valued at billions of dollars annually for regional agriculture, with the Brazilian Amazon alone contributing roughly US$20 billion per year through evapotranspiration.
- Methodology: Researchers combined satellite observations with advanced climate model simulations to quantify forest-driven rainfall, then applied economic valuation methods to estimate its financial worth to the agricultural sector.
- Key Data: Each hectare of tropical forest generates approximately 2.4 million liters of rain annually, while recent deforestation in the Amazon has reduced these rainfall benefits by an estimated US$5 billion per year.
- Significance: This study quantifies the critical economic role of forests beyond carbon storage, demonstrating that forest loss directly threatens agricultural yields, hydropower generation, and water security through reduced precipitation.
- Future Application: These economic valuations provide a financial basis for forest conservation policies, potentially unlocking new investment streams and easing tensions between agricultural expansion and environmental protection.
- Branch of Science: Environmental Science and Ecological Economics.
- Additional Detail: The research indicates that water-intensive crops like cotton require moisture generated by a forest area twice the size of the cultivated land itself to sustain production.
Tropical forests help to generate vast amounts of rainfall each year, adding weight to arguments for protecting them as water and climate pressures increase, say researchers.
A new study led by the University of Leeds has put a monetary value on one of forests’ least recognized services as a source of rainfall to surrounding regions, finding that each hectare generates 2.4 million liters of rain each year - enough to fill an Olympic-sized swimming pool.
Satellite observations were combined with simulations from the latest generation of climate models, to reduce long‑standing uncertainty around the magnitude of forest‑driven rainfall. The researchers then applied a simplified economic valuation to estimate what that rain is worth to society and the economy.
Their conclusions are stark. Using this approach, they calculate that rainfall generation provided by forests in the Brazilian Amazon is valued at roughly US$20bn (£16bn) a year to regional agriculture. By comparison, current financial incentives aimed at protecting or restoring the Amazon amount to only a fraction of that figure.
Tropical deforestation is increasing, despite international efforts to halt forest loss. Demonstrating the financial benefits that tropical forests provide will unlock investment and strengthen arguments for forest protection.
Tropical forests help to sustain the regional and continental rainfall systems that underpin agriculture, water supplies and energy production via a process known as evapotranspiration where the sun’s energy is used to transfer moisture from the leaves into the atmosphere. The study estimates that, across the tropics, each square meter of forest contributes about 240 liters of rainfall annually, rising to around 300 liters in the Amazon.
“This is the most comprehensive and robust evidence to date of the value of tropical forests’ rainfall provision,” said lead author Dr Jess Baker, from the University of Leeds’ School of Earth, Environment and Sustainability.
“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.”
The study finds that producing enough rainfall to support some major crops requires moisture generated by more forest area than the crops themselves occupy. For instance, cotton uses 607 liters of moisture per square meter which is equal to the amount of water produced by two square meters of intact forest. Soybean crops need 501 liters of moisture – equal to 1.7 square meters of intact forest.
Forest loss has already imposed significant costs. The researchers estimate that deforestation over recent decades, which is around 80 million hectares in the Amazon, may have reduced rainfall‑generation benefits by almost US$5bn annually, with knock‑on effects for food production, hydropower and water security.
Brazil’s economy is particularly exposed. About 85% of the country’s agriculture is rain‑fed, and reduced rainfall and delayed wet seasons have already affected soy and maize yields in regions with high levels of deforestation.
Recognizing that crucial connection could ease tensions between agricultural and conservation interests whilst building broader support for protecting forests overall.
Beyond agriculture, declining rainfall linked to forest loss also threatens drinking water supplies, river transport in remote regions, hydropower generation, and even the carbon‑storage capacity of remaining tropical forests.
Despite repeated international pledges to halt deforestation by 2030, forest loss continues across much of the tropics. The authors of the study argue that failing to account for rainfall generation in economic and legal frameworks has obscured one of the strongest practical arguments for forest protection.
Published in journal: Communications Earth & Environment
Title: Quantifying tropical forest rainfall generation
Authors: Jessica C. A. Baker, Callum Smith, José A. P. Veiga, Harry Farnsworth, and Dominick V. Spracklen
Source/Credit: University of Leeds
Reference Number: env021726_01
.jpg)