By Mayara Subtil*
- Flying rivers account for more than 70% of rainfall in strategic areas of Peru and Bolivia, sustaining agriculture, water supply, and energy systems on a continental scale.
- The study integrated data on atmospheric circulation, land use categories, infrastructure, and deforestation risk to identify the territories most critical for the formation and maintenance of flying rivers. The results show that these routes cross Acre and the southwestern Amazon, near the corridors of highways BR-319 and BR-364 and extensive areas of FPNDs (Public Forests Not Designated for Specific Uses), making these regions strategic for South America’s water security.
- The study introduces the concept of Critical Moisture Territories, areas that play a central role in the recycling and transport of moisture in the Amazon. The results reinforce the need to incorporate these territories into land-use planning strategies, public forest allocation, and conservation policies.
- The study identifies that flying rivers depend heavily on the integrity of continuous forest corridors and maps three seasonal routes of the phenomenon. Among them, the dry-season route, located in the southwestern Amazon, is identified as the most vulnerable to deforestation and forest cover fragmentation.
- FPNDs cover approximately 50 million hectares in the Amazon and store roughly 5 billion tons of carbon, a volume equivalent to nearly half of annual global CO₂ emissions. While they remain unallocated, these areas are frequently targeted by irregular occupation and illegal deforestation, accounting for about 26% to 30% of the deforestation recorded in the Amazon.
- Among the study’s recommendations is the strengthening of existing forest conservation and restoration policies and programs, such as ARPA (Amazon Protected Areas Program) and Planaveg (National Plan for the Recovery of Native Vegetation), expanding their coordination with strategies aimed at protecting the flying rivers.
- Given that approximately 60% of the Amazon rainforest lies within Brazilian territory, the study also recommends strengthening cooperation among Amazonian countries. Cross-border agreements are identified as fundamental to ensuring water security, climate stability, and the reduction of risks associated with extreme events in Brazil and neighboring countries.
The Amazon produces enormous volumes of moisture that extend beyond the forest’s borders. Carried by the winds, this “invisible water” forms so-called flying rivers—streams of water vapor that travel thousands of kilometers and help sustain rainfall across virtually all of South America, including agricultural regions, cities, and energy generation systems in Brazil and neighboring countries. Globally, this natural phenomenon influences the planet’s climate balance.
FPNDs (Public Forests Not Yet Designated), areas of public forest that have not yet received an official designation, play a strategic role in maintaining the flying rivers. This is the conclusion of a study conducted by Amazon Conservation in partnership with IPAM (Amazon Environmental Research Institute), which mapped the main moisture transport routes between the Atlantic Ocean, the Amazon Basin, and the Andes Mountains.
To understand the role of these areas in the dynamics of flying rivers, researchers analyzed—using high-resolution atmospheric modeling and integrated geospatial data—how these moisture flows form, organize across seasons, and respond to changes in land use. The goal was to identify the critical moisture transport corridors between the tropical Atlantic, the Amazon Basin, and the foothills of the Andes, as well as the points where the loss of forest cover could compromise the efficiency of these rivers, particularly for the water security of countries such as Peru and Bolivia.
The study “Keeping the Flying Rivers Flowing: How Nature Loss in the Brazilian Amazon Threatens Rainfall in Peru and Bolivia” combines atmospheric reanalyses, moisture back-trajectories, deforestation maps, existing and planned infrastructure, as well as official surveys of protected areas, indigenous lands, and public forests.
Based on these assessments, the study identifies that the Amazon’s main moisture transport corridors traverse large expanses of FPNDs. These are approximately 50 million hectares of public forests that store roughly 5 billion tons of carbon and help regulate the climate and rainfall patterns in the Amazon and other regions of South America, functioning as critical territories for the transport of atmospheric moisture.
“Areas critical to the maintenance of the ‘flying rivers’ must be incorporated as a priority into policies on territorial governance, the allocation of public forests, and the fight against illegal deforestation. In this context, FPNDs play a strategic role. In addition to representing a legal commitment by the Brazilian government, their designation is fundamental for water security, the maintenance of rainfall patterns, and food production in Brazil and neighboring South American countries,” emphasized Rebecca Maranhão, a researcher at IPAM.
But while these forests await designation as protected areas, they have become the most vulnerable to deforestation and land grabbing, precisely in a context where their climate function is central to maintaining moisture flows. It is estimated that between 26% and 30% of Amazon deforestation occurs in these forests. In addition, about 60% of the total area of the FPNDs overlaps with records from the CAR (Rural Environmental Registry), a practice that fuels land speculation, illegal deforestation, and conflicts.
Seasonal Routes
The research advances by mapping the flying rivers along three distinct seasonal routes, associated with the rainy, transitional, and dry seasons. Each of these routes exhibits different levels of vulnerability to deforestation and forest fragmentation. The dry season, for example, depends on moisture recycling by vegetation and traverses areas already under significant pressure due to forest loss in the southern Amazon. The transition season, in turn, acts as a critical period for the reorganization of atmospheric flow. During the rainy season, however, the flying rivers follow more stable trajectories, although all routes converge on strategic areas of the western Amazon before reaching the Andean barrier.
The study integrated data on atmospheric circulation, land use categories, infrastructure, and deforestation risk to identify the territories most important for the formation and maintenance of flying rivers. The results show that the routes of the flying rivers cross Acre, areas in the southwestern Amazon associated with infrastructure corridors, such as Federal Highways 319 and 364, as well as extensive areas of FPNDs, representing critical corridors for the transport of atmospheric moisture.
Acre receives special attention in the analysis because it is where the three seasonal routes of the flying rivers converge before the moisture moves toward Peru and Bolivia. According to the authors, the combination of advancing deforestation and infrastructure projects planned for the region may compromise the effectiveness of the flying rivers, which are responsible for sustaining rainfall in the southwestern Amazon.
Climate events and the agricultural sector
The study also links these findings to extreme weather events that have occurred in recent years. The drought that occurred between 2023 and 2024 in the Amazon, the most severe ever recorded, is used as a reference to illustrate the potential impacts of a prolonged reduction in the services provided by the flying rivers. Although the event had multiple climatic causes, it highlights the structural vulnerability of the Amazonian system to combined changes resulting from deforestation and shifts in atmospheric circulation.
These impacts have already manifested concretely in various sectors. In agriculture, there have been significant production losses, such as a reduction of up to 75% in soybean yields in Santa Cruz, Bolivia, as well as significant declines in Andean crops like potatoes in Puno, Peru, which are highly dependent on stable rainfall patterns.
In forest-based economies, supply chains such as the Brazil nut industry—which are vital to Peruvian and Bolivian communities—show high sensitivity to periods of drought, with direct effects on local community income and food security.
In ecosystems, the Tropical Andes host one of the highest levels of biodiversity on the planet, with a high rate of endemism and strong sensitivity to small variations in humidity, which can alter fire regimes, species composition, and carbon stocks. In hydrological systems, reduced rainfall affects interconnected basins such as the Madeira River basin, which depends on precipitation originating in the western Amazon and which, during the historic drought of 2024, recorded historically low levels, with impacts on navigation, energy, and riverside communities.
Recommendations
The report presents six recommendations to protect the “flying rivers” and reduce the risks of drought in the Amazon and neighboring countries. The main one is the creation of so-called Critical Moisture Territories, areas of forest at high risk of deforestation that play an essential role in moisture recycling and in maintaining the atmospheric flows that carry rain from the Amazon to other regions of the continent. Many of these territories coincide with the FPNDs of the Brazilian Amazon, which are considered strategic for conservation because they do not yet have formal legal protection.
According to the study, protecting these areas may represent one of the most effective measures for preserving the Amazonian hydrological cycle and reducing the risk of regional droughts.
The study also recommends:
- Considering the impacts on flying rivers in environmental assessments of major infrastructure projects in the Amazon, especially road projects with the potential to increase deforestation;
- Prioritizing the protection and management of FPNDs located in moisture transport corridors, directing resources to areas that contribute most to regional water security;
- Expand forest restoration in degraded regions of the Amazon, especially in key areas for atmospheric moisture circulation;
- Strengthen existing public programs and policies for forest conservation and restoration, such as ARPA (Amazon Protected Areas Program) and Planaveg (National Plan for the Restoration of Native Vegetation), reinforcing their coordination with strategies for protecting the flying rivers;
- Strengthen regional governance in the Amazon, recognizing Brazil’s strategic role in maintaining the flying rivers and promoting coordinated conservation actions among the basin’s countries regarding the flying rivers;
Develop climate adaptation strategies for regions most vulnerable to the impacts of reduced moisture transport; and - Invest in research, monitoring, and climate modeling to improve scientific understanding of the flying rivers and guide long-term public policies.
The document also argues that the transboundary impacts of deforestation should be more explicitly incorporated into territorial planning processes and environmental permitting for major projects in the Amazon. For the researchers, decisions made in areas of the biome can directly affect water availability, agricultural production, and the stability of ecosystems in neighboring countries, including Peru and Bolivia.
The research further reinforces the understanding that flying rivers constitute a natural climate infrastructure connecting the Atlantic to the heart of South America. Their disruption, caused by the loss of forest cover and the fragmentation of strategic corridors, does not only generate local impacts but also cascading effects on agriculture, energy, biodiversity, and water security on a continental scale, with repercussions that also return to Brazil through major hydrological systems such as the Madeira River basin.
*IPAM Communications Analyst. mayara.barbosa@ipam.org.br
