Rapid tree loss in the Amazon region, driven mainly by unsustainable farming, mining and logging, undermines the rainforest's ability to absorb planet-warming carbon dioxide.
It has also affected weather patterns regionally, with previous research showing that the reduction in vegetation reduced water being taken up into the atmosphere and led to generally drier conditions.
The new study, published in the journal Nature, sought to get a more fine-grained picture by using regional climate simulations and satellite forest data from 2000 to 2020.
The researchers, based in China and Thailand, found that impacts in the Amazon change with the seasons.
More rain fell over areas where trees were felled in the wet season (December to February), they found, with the exposed land becoming warmer and causing an upward airflow that acts to draw in moisture.
In the dry season (June to August), when plants need water the most, the deforested area saw a reduction in evaporation from vegetation causing less rain to fall over a wider region.
"Owing to their pivotal roles in regulating regional and global climate, sustained efforts are needed to protect the remaining forest in the Amazon, as well as rehabilitate degraded lands," the authors concluded.
The authors stressed that tree loss in the Amazon, which is frequently caused by the illegal expansion of farmland, is a particular threat to crops.
Increased rainfall "could exacerbate the wet season flooding in certain deforested regions, harming regional agriculture and the social economy", they said.
Overall, they found that continued deforestation in the Amazon "could lead to declines in total rainfall", which would threaten wildlife, intensify drought and worsen wildfire, as well as reducing CO2 absorption capacity.
Reduced regional rainfall may also result in "substantial economic losses in agriculture".
- 'Tipping point' -
In a linked commentary published in Nature, Wim Thiery, associate professor at the Vrije Universiteit in Brussels, said the study was "pioneering" and that research of this kind was important to understand the complex interactions between deforestation, climate change and plant health.
That could help researchers assess if the rainforest is nearing a so-called "tipping point", which would pitch the crucial ecosystem towards becoming a savanna, said Thiery, who was not involved in the research.
In a study last year, published in Nature, an international group of scientists estimated that between 10 and 47 percent of the Amazon will be exposed to the combined stresses of warming and forest loss by 2050, which could lead to widespread ecosystem change.
That could cause the critical ecosystem to release the carbon it stores, further driving global warming and intensifying its effects.
Drought parched the Amazon region from mid-2023 through 2024, driven by human-caused climate change and the El Nino warming phenomenon, helping to create conditions for record wildfires.
Globally, the trend towards the destruction of rainforests is continuing despite pledges to end the practice by 2030, according to last year's "Forest Declaration Assessment" report by research organisations, NGOs and advocacy groups.
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