Globally, the total acreage burned by fires declined 24 per cent between 1998 and 2015, according to the study published in the journal Science.

Scientists determined that the decline in burned area was greatest in savannas and grasslands, where fires are essential for maintaining healthy ecosystems and habitat conservation.

The research team, led by Niels Andela of NASA's Goddard Space Flight Center, analysed fire data derived from the Moderate Resolution Imaging Spectrometer (MODIS) instruments on NASA's Terra and Aqua satellites.

They then compared these data sets with regional and global trends in agriculture and socio-economic development.

Across Africa, fires collectively burned an area about half the size of the continental US every year.
In traditional savanna cultures, people often set fires to keep grazing lands productive and free of shrubs and trees.

However, as many of these communities have shifted to cultivating permanent fields and building more houses, roads, and villages, the use of fire has declined.

By 2015, savanna fires in Africa had declined by 700,000 square kilometers.

A slightly different pattern occurs in tropical forests and other humid regions near the equator. Fire rarely occurs naturally in these forests; but as humans settle an area, they often use fire to clear land for cropland and pastures.

As more people move into these areas and increase the investments in agriculture, they set fewer fires and the burned area declines again.

The changes in savanna, grassland, and tropical forest fire patterns are so large that they have so far offset some of the increased risk of fire caused by global warming, said Doug Morton, a forest scientist at NASA Goddard.

The impact of a warming and drying climate is more obvious at higher latitudes, where fire has increased in Canada and the American West.

Regions of China, India, Brazil, and southern Africa also showed increases in burned area.

Fewer and smaller fires on the savanna mean that there are more trees and shrubs instead of open grasslands. This is a significant change in habitat for the region's iconic mammals like elephants, rhinoceroses, and lions.

"Humans are interrupting the ancient, natural cycle of burning and regrowth in these areas," said Jim Randerson of the University of California, Irvine in the US.

"Fire had been instrumental for millennia in maintaining healthy savannas, keeping shrubs and trees at bay and eliminating dead vegetation," said Randerson.

There are benefits to fewer fires as well. Regions with less fire saw a decrease in carbon monoxide emissions and an improvement in air quality during fire season.