Much larger area in Africa subject to fires than previously thought
New satellite data show that the land area that burns annually in Africa is more than 2 million square kilometres larger than previously assumed. This discovery was made by a team of Spanish and Dutch researchers, including VU Amsterdam scientists Dave van Wees and Guido van der Werf.
02/25/2021 | 12:39 PM
The additional area is equivalent to about four times the size of Spain, and this has implications for greenhouse gas emissions released by fires in African savannahs and forests. The study was published today in the journal Proceedings of the National Academy of Sciences (PNAS).
Fires are nothing unusual in savannahs
Forest fires regularly make the news, especially when they rage close to towns and cities. Tropical savannah makes up by far the largest share of the world’s land area that burns. Yet these fires do not readily make the news since fires are nothing unusual in savannahs, which in extreme cases burn down every year. However, scientists are mapping these burnt areas. Until now, they used data from satellites with a relatively coarse resolution: pixels of 500 by 500 metres. With this resolution, a fire can only be detected if an entire pixel indicates a fire.
New satellite data
Based on new satellite data from the mission with the European Sentinel-2 satellites, the research team, including VU scientists Dave van Wees and Guido van der Werf, has recalculated the burnt surface. The resolution of these earth observation satellites is much higher: one pixel is 20 by 20 metres. To their surprise, the researchers found a large number of relatively small fires that were impossible to distinguish using the old satellite data.
Increase of 80 percent
This data resulted in the burnt area increasing by 80 percent. In addition, the researchers observed that the fire season lasts longer than previously assumed, given that more of these small fires are detected during the transitions between wet and dry seasons.
These new data prompted a new measurement of greenhouse gas emissions, based on the area burned and biomass data. The emissions also turned out to be much higher, in the most extreme case twice as high as earlier measurements had indicated. This new insight has no consequences for the increase of CO2 in the atmosphere; the CO2 that is released during the burning of savannah grasses in particular is again absorbed during the wet season when vegetation grows again. However, it does mean that the contribution of fires to the emission of other greenhouse gases, such as methane, needs to be adjusted upwards.
Fire in the Mozambique savannah. These relatively small fires were previously undetected but nevertheless account for almost half of the total area that goes up in flames in Africa. Photo by Tom Eames.