Using satellite observations, researchers show that the loss of vegetation leads to higher surface temperatures, reduced evapotranspiration, and a sharp decline in both total precipitation and the number of rainy days during the dry season.
The study, published in the journal Communications Earth and Environment, finds that highly deforested regions with less than 60 percent forest cover now exhibit climatic behavior similar to transition zones between rainforest and savanna.
In these degraded landscapes, average surface temperature during the dry season is about 3 degrees Celsius higher, while evapotranspiration and rainfall are 12 percent and 25 percent lower, respectively, than in nearby regions with dense forest.
On average, areas where forest cover has fallen below 60 percent also experience 11 fewer days of rainfall, meaning that deforestation alters not only how much rain falls but also how it is distributed through the season.
These hotter and drier conditions accelerate forest degradation, increase tree mortality, and heighten vulnerability to wildfires, threatening sensitive rainforest species and opening space for more opportunistic native and invasive species.
The researchers warn that this ecological shift compromises biodiversity and undermines the resilience of the Amazon, with direct consequences for economic sectors that depend on stable climate conditions, particularly agriculture.
They argue that tropical forests exert a powerful influence on climate, with implications for human well-being and economic activity, and call for policy debates on forests to extend beyond environmental protection to encompass national development strategies and coordinated action across society.
According to the team, the findings support strict compliance with Brazil's Forest Code, which requires rural properties in the Legal Amazon to maintain at least 80 percent native vegetation in forested areas, 35 percent in Cerrado regions, and 20 percent in open fields.
The Legal Amazon covers nine Brazilian states designated for socio-environmental development where the biome occurs, and the law defines how much native vegetation must be preserved in legal reserves on private lands.
Satellite-based land cover data indicate that the Brazilian Amazon lost about 13 percent of its native vegetation between 1985 and 2024, equivalent to roughly 520,000 square kilometers, an area larger than Spain.
Over the same period, pasture expanded from 123,000 square kilometers to 561,000 square kilometers, while cropland increased from 1,800 square kilometers to 79,000 square kilometers, and mining areas grew to 4,440 square kilometers by 2024.
Although deforestation rates have eased over the past three years, the biome continues to lose forest at an alarming pace, with more than 6,300 square kilometers of native vegetation cleared in the Legal Amazon in 2024 alone, according to Brazil's Amazon Forest Satellite Monitoring Program (PRODES).
Scientists stress that curbing deforestation is essential, but they also highlight the need to accelerate the global transition away from fossil fuels to tackle ongoing global warming, which is already amplifying climate risks in the region.
The year 2024 was the hottest on record and the first in which the global average temperature surpassed 1.5 degrees Celsius above pre-industrial levels, while the Global Carbon Budget report projects that fossil fuel carbon dioxide emissions will rise by about 1.1 percent in 2025, reaching a record 38.1 billion tons.
The authors note that forests deliver crucial ecosystem services, including cooling through evapotranspiration, enhanced water cycling, and carbon storage, all of which underpin water, food, and economic security.
They emphasize that restoring forest structure in degraded areas can help recover these services, lowering temperatures, boosting rainfall recycling, and strengthening resilience to climate extremes.
The study also aligns with a comprehensive review by the Food and Agriculture Organization of the United Nations, which concludes that forests are allies of agribusiness by supporting agricultural productivity and resilience through multiple climate-related benefits.
For their analysis, the scientists divided the Amazon into a regular grid of samples approximately 55 by 55 kilometers in size and grouped them into classes of remaining forest cover: up to 40 percent, 40 to 60 percent, and 60 to 80 percent.
They selected reference grids with more than 80 percent forest cover adjacent to deforested areas to represent climatic conditions with minimal direct influence from deforestation.
To isolate the role of native vegetation loss from other drivers, the team applied additional controls, including comparisons between neighboring reference regions, and evaluated 11 climate variables such as surface temperature, evapotranspiration, annual and seasonal rainfall, and the number of rainy days.
The strongest impacts emerged where remaining forest cover dropped to 40 percent or less, with surface temperatures during the dry season rising by up to 4 degrees Celsius relative to reference regions.
In these heavily deforested sites, average dry-season evapotranspiration was about 45 millimeters lower than in neighboring areas with intact forest cover, reflecting a sharp weakening of the land-atmosphere water flux.
The researchers explain that evapotranspiration, the combined flux of water vapor from plant transpiration and evaporation from soils and canopy surfaces, depends on vegetation type and structure, temperature, solar radiation, and wind.
When forests are cleared, evapotranspiration diminishes, promoting higher surface temperatures and reducing the recycling of atmospheric moisture into rainfall.
The work received support from the Sao Paulo Research Foundation (FAPESP) through graduate scholarships and funding for the Research Center for Greenhouse Gas Innovation, which investigates strategies to reduce emissions and enhance carbon management.
A related study led by scientists at the University of Sao Paulo and published in Nature Communications found that deforestation accounted for 74.5 percent of the reduction in rainfall and 16.5 percent of the temperature increase in the Amazon during dry months, highlighting the dominant role of land-use change over global climate forcing in shaping regional hydroclimate.
Together, these studies reinforce the message that protecting and restoring Amazonian forests is central to stabilizing regional climate, safeguarding biodiversity, and sustaining agricultural and economic activities that depend on reliable rainfall and moderated temperatures.
Research Report: Observed shifts in regional climate linked to Amazon deforestation
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