More people in Southeast Asia are dying from heat worsened by deforestation than in the Congo or Amazon rainforests, despite losing a smaller total area of forest than in the Americas, a recent study has found.

Every year in Southeast Asia, around 15,680 rural residents die of heat-related complications worsened by deforestation, compared with 9,890 for the tropical regions of Africa and 2,520 for the Americas.

Between 2001 and 2020, Southeast Asia lost about 490,000 square kilometers of vegetation, while tropical Central and South America lost about 760,000 sq km of forest.

"Southeast Asia has lost a smaller total area of tropical forest, but has higher population density, leading to higher heat-related mortality," said Carly Reddington from the University of Leeds, who is the lead author of the study.

She added that Latin America has seen the greatest forest loss, but the death toll is lower because fewer people live in the deforested areas.

The study, published in the scientific journal Nature Climate Change in late August, found that over 20 years, climate change and deforestation increased Southeast Asia's temperature by 0.72 degrees.

Forests not only sustain life and absorb planet-warming carbon dioxide, but also have a cooling effect on people.

While the canopies provide shade, the leaves release water vapor into the air and remove some heat, much like humans sweating to cool their bodies.

When trees are cut down, this cooling effect is reduced. When shade is gone, more sunlight hits the ground directly and the land can become drier and darker, absorbing more heat, Reddington explained.

"This combination leads to significant local warming, sometimes even hotter than the warming caused by global climate change over the same period," she added.

Reddington and her team used satellite data to calculate the changes in temperatures in tropical forest areas between 2001 and 2020, comparing deforested areas to intact areas.

The satellite findings were then combined with existing health data on how sensitive a population is to heat-related deaths.

Alongside over-exertion, exposure to high temperatures can lead to heatstroke and organ damage for outdoor workers.

The regions they work in could also have limited access to cooling and healthcare, Reddington said.

The paper noted that vulnerable populations, including indigenous communities, often reside near deforested areas and have limited access to resources and infrastructure needed to cope with rising temperatures and environmental changes.

A separate 2021 study found that deforestation in the Berau Regency of Indonesia between 2002 and 2018 accounted for more than 100 additional heat-related deaths each year. Unsafe work duration also increased by 20 minutes each day.

Over the 16 years studied, more than 4,300 sq km of land was cleared in Berau, East Kalimantan — about six times larger than the total land area of Singapore. The study was led by environmental nonprofit The Nature Conservancy.

Other studies have shown that the productivity and cognitive performance of rural workers in East Kalimantan were substantially lower in deforested areas than in forested ones, Reddington noted.

"Tropical deforestation doesn't just affect the environment — it could directly harm human health, especially in communities least equipped to cope. Protecting tropical forests is not only vital for the planet, but also for safeguarding lives," she said.

Reddington urged governments of tropical nations to strengthen forest protection laws, invest in reforestation and improve heat management solutions — such as providing shaded workspaces, cooling centers and better access to healthcare in high-risk areas.

"Climate finance should prioritize forest conservation and health resilience in the tropics, where the risks are greatest and resources are often limited," she added.

Commenting on the recent study, Kimberly Fornace, associate professor from the National University of Singapore Saw Swee Hock School of Public Health, said: "We need to consider land cover when developing early warning (for extreme heat). We have seen this with urban heat in cities, and there is a need to consider effects on rural populations as well."

Winston Chow, Singapore Management University's professor of urban climate, said that members of the public — including city dwellers, like in Singapore — need to be better informed about heat risks so they can cope with rising temperatures.

He said environmental and socioeconomic conditions within Southeast Asia vary drastically, and country-specific data would be more beneficial in estimating heat mortality.

Fornace said that further on-the-ground studies are needed to augment the paper's findings. For one thing, the impacts of rising heat on individuals are not always clearly captured by secondary health data, because the effects can vary significantly in different populations.

"While the authors have done a nice job of highlighting the scale of deforestation-related heat health impacts, there is still a need for more local population-based health studies," she said.

The Straits Times, Singapore