The Big and Small of Fire in Africa

Each red dot on this map from NASA’s Fire Information for Resource Management System (FIRMS) shows fires across Africa detected from space using Earth-observing satellites. With so many red dots blotted across the map, it would be easy to think a large swath of Africa is on fire. Fires of that magnitude would be big news and send massive smoke plumes billowing around the world. Yet, on January 31, 2022, when the map was made, there was no such event raging across the continent.

“It certainly looks like a huge swath of Africa is on fire, but that really isn’t the case,” said Diane Davies, the operations manager for NASA’s Land Atmosphere Near-real-time Capability for EOS (LANCE), which houses FIRMS. “The reason it looks that way is that no matter how big or small a fire is, we have to make the pixel plot size big enough to show up on a map. The result is when there are numerous fires in Africa and you’re looking at them zoomed out on a map, it can look like the whole place is on fire, but if you zoom in far enough, you can see the individual fire pixels.”

Another factor in how fires appear on the FIRMS Fire Map is the mix of data sources used to plot them.

FIRMS data come from sensors aboard multiple satellites. These sensors have different spatial resolutions and use different processing algorithms. For example, NASA’s Terra and Aqua satellites carry the Moderate Resolution Imaging Spectroradiometer (MODIS), which has a resolution of one kilometer square per pixel. If a fire occupies an area smaller than a kilometer, it will be plotted as being one kilometer square in size because that is the smallest area the sensor can measure. Also, if the borders of the fire happen to spread into four neighboring pixels, then the fire will be plotted in four pixels and will appear to extend over a much larger area. Similarly, the resolution of the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites is 375 meters square per pixel, which means fires that take up four pixels may not actually be as large as they appear. Overall, the result is that plots based on MODIS and VIIRS data can only be used to assess the approximate location of a fire.

Agricultural Fires in the Sahel

Still, big or small, there can be a lot of fires burning in Africa—especially across the continent’s Sahel and the adjoining subhumid region during seasonal dry months where most of the red dots in the FIRMS Fire Map image above are concentrated.

The Sahel is a semiarid belt spanning Africa along the southern border of the Sahara Desert. Millions of people live in the region, including nomadic groups that follow their livestock as the animals graze across the land. When the animals finish feeding in an area, the nomads burn the land to clear and prepare it for the next growing and grazing season. At their peak, there may be many of these small fires only tens to hundreds of meters wide, and those fires are often detected by sensors aboard Earth observing satellites.

“It’s important to understand that not all fires are bad. In fact, some seeds will only germinate in areas that have been burned,” said Davies.

The practice of burning farmland, of course, precedes modern concerns about conservation and climate change, and was born out of simple necessity that still exists today. The method clears leftover crop stubble from the land and returns vital nutrients to the soil.

“Most of the farmers living in the Sahel and other parts of Africa do not have machinery with which to practice mechanized agriculture,” said Dr. Charles Ichoku, a professor of Earth and atmospheric sciences at Howard University and a former research physical scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “So, fire is the easiest way to clear the land they use.”

Ichoku is an expert in using remote sensing technologies, such as satellites, and is studying how the burning of land may be changing the weather across Africa. Ichoku’s research includes data from Aqua and Terra’s MODIS and Suomi NPP’s VIIRS sensors.

According to Ichoku, historically, the rainfall amount gradient south of the Sahara increases quickly toward the equator, making the savannah and subhumid regions south of the Sahel good for farming because it’s not as dry as the desert but also not as wet as the tropical forests further south.

But that may be changing.

Research by Ichoku shows that as farmland burning increases during the October to May dry season, there is a drop in soil moisture, evaporation, and vegetation during the following wet season.

“Crop land is increasing and that means that there is more burning because fire is the main tool to clear land,” said Ichoku. “But, when you clear the land, the water that falls during the rainy season does not get retained by the vegetation. Instead, the water evaporates or flows away by enhanced surface runoff because of diminishing vegetation cover.”

Ichoku and other scientists say the effect requires more study, but if there is a proven link, it could be of great concern to Africans as they try to feed their increasing population.

Protecting Park Land in Madagascar

More than 3,000 miles to the southeast of the Sahel is the island-nation of Madagascar. The country is home to world-renowned national parks that feature extraordinary biodiversity and are on the list of the United Nations Educational, Scientific and Cultural Organization’s (UNESCSO) World Heritage Sites. In 2008, national park officials in Madagascar began partnering with the non-governmental organization Conservation International (CI) to use the group’s Firecast fire monitoring system to protect valuable lands.

Firecast uses MODIS and VIIRS data to provide alerts and produce forecasts. The system was co-developed for CI by remote sensing specialist and consultant Andriambolantsoa Rasolohery.

“NASA’s fire products have been an important tool for protected areas managers and the government to use, and for demonstrating the efficiencies of fire management already in place,” said Rasolohery.

In more specific terms, NASA fire products have aided managers in taking actions that have resulted in protected land now having fewer fires compared with non-protected outside areas. The data have also been used to create a map of burn frequencies—depicting areas that burn frequently or areas that do not burn at all—in order to better understand fire dynamics and inform Madagascar officials how to allocate resources for the future.

Today, Rasolohery is using FIRMS data to create historical databases of fire points and areas for the entire country. Rasolohery is also working on a project to validate VIIRS and MODIS fire data to determine the proper level of confidence to assign to them when assessing the existence of a detected fire.

The NASA data that Davies, Ichoku, Rasolohery, and many others use to track and study wildfire provide critical information they need to determine what blazes mean for African communities. Understanding the data can certainly be complex and nuanced at times, such as when viewing hundreds of tiny fire points on a world map. But the knowledge the data provides is invaluable because it might produce the first alert of a dangerous new fire or underpin important research discoveries, helping the world understand the big importance of even the smallest fires in Africa.

Explore NASA Fire Data

For more information on NASA fire data and tools for working with these data, see the Earthdata Wildfires data pathfinder. Additional NASA fire-related resources include:

• NASA Near Real-time Data for Fires
• “Satellite Detections of Fire” (NASA Worldview)
• Wildfires Program Area (NASA Applied Sciences)