NASA detects drop in global fires

Shifting livelihoods across the tropical forest frontiers of South America, the Eurasian Steppe, and the savannas of Africa are altering landscapes and leading to a significant decline in the amount of land burned by fire, a trend that NASA’s satellites have detected from space.

The global area of land burned each year declined by 24 percent between 1998 and 2015, according to analysis of satellite data by NASA scientists and their colleagues. The largest decline was seen across savannas in Africa, and due to changing livelihoods. CREDIT Credits: Joshua Stevens/NASA’s Earth Observatory

The ongoing transition from nomadic cultures to settled lifestyles and intensifying agriculture has led to a steep drop not only in the use of fire on local lands, but in the prevalence of fire worldwide, researchers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and colleagues found.

Globally, the total acreage burned by fires each year declined by 24 percent between 1998 and 2015, according to a new paper in Science that analyzes NASA’s satellite data, as well as population and socioeconomic information. The decline in burned lands was largest in savannas and grasslands, where fires are essential for maintaining healthy ecosystems and habitat conservation.

Across Africa, fires typically burn an area about half the size of the continental United States every year, said Niels Andela, a research scientist at Goddard and lead author on the paper. In traditional savanna cultures with common lands, people often set fires to keep grazing lands productive and free of shrubs. As many of these communities have shifted to cultivate more permanent fields and to build more houses, roads and villages, the use of fire declines. As economic development continues, the landscape becomes more fragmented, communities often enact legislation to control fires and the burned area declines even more.

By 2015, savanna fires in Africa had declined by 270,000 square miles (700,000 square kilometers) — an area the size of Texas.

“When land use intensifies on savannas, fire is used less and less as a tool,” Andela said. “As soon as people invest in houses, crops and livestock, they don’t want these fires close by anymore. The way of doing agriculture changes, the practices change, and fire slowly disappears from the grassland landscape.”

Andela and an international team of scientists analyzed the fire data, derived from the Moderate Resolution Imaging Spectrometer (MODIS) instruments on NASA’s Terra and Aqua satellites, as well as other sources. They compared these datasets with trends in population, agriculture, livestock density and gross domestic product.

The scientists found a different pattern in the rainforests and other humid regions close to the equator. Natural fires are rare in tropical forests, but as people settle an area they often burn to clear land for cropland and pastures. After the land is first cleared, as more people move into the area and increase the investments in agriculture, they set fewer fires and the burned area declines again.

The impact of human-caused changes in savannas, grasslands and tropical forests is so large that it offsets much of the increased risk of fire caused by warming global temperatures, said Doug Morton, a research scientist at Goddard and a co-author of the study. Still, the impact of a warming and drying climate is seen at higher latitudes, where fire has increased in parts of Canada and the American west. Regions of China, India, Brazil and southern Africa also show an increase in burned area. But the expansiveness of savannas and grasslands puts the global trend in decline.

“Climate change has increased fire risk in many regions, but satellite burned area data show that human activity has effectively counterbalanced that climate risk, especially across the global tropics,” Morton said. “We’ve seen a substantial global decline over the satellite record, and the loss of fire has some really important implications for the Earth…