No continent burns like Africa: roughly 70 percent of the land scorched worldwide each year lies in the savannas and grasslands north and south of the equator. That makes what satellites have recorded there over two decades all the more striking – the burned area is not growing, it is steadily shrinking. A research team at the Chinese Academy of Sciences has now offered an explanation that has less to do with the thermometer than with the calendar.
For the study, published in the journal Geophysical Research Letters, the researchers around Xiyan Xu, with PhD candidate Sharafaldin Mohammed as lead author, combined daily rainfall measurements from three mutually independent datasets covering 1990 to 2023 with satellite records of burned area and fire counts from 2003 to 2022. Earlier work mostly asked how much rain falls in a year. The decisive quantity, the analysis shows, is when it falls.
The dry season across the continent has grown shorter, mainly because it starts later: by about 1.75 days per decade north of the equator and around 0.4 days per decade to the south. The cause is extra rain in precisely the transitional phase when soils and grasses would otherwise dry out. They stay moist for longer, and the window in which fires can spread across large areas narrows. The declines are sharpest in the peak fire months – December in the north, August in the south. According to the American Geophysical Union, millions of acres less land burns each year as a result, several thousand square kilometres.
Other forces are at work in the south
The effect is not uniform. In northern Africa the link between a shorter dry season and a smaller burned area is clear-cut; in southern Africa it is markedly weaker. Other developments are likely at play there: farmland, roads and settlements cut through the once continuous vegetation that let fires travel far, and organised fire management adds to that.
The authors also name the limits of their analysis. Small fires escape the satellites, so actual fire activity is probably underestimated, and the data do not distinguish between naturally ignited and deliberately set fires. Globally, meanwhile, heatwaves and droughts continue to create better conditions for fire in many regions.
The finding is useful all the same. Many forecasting systems still rely on annual rainfall, temperature and drought indices. Watching the rhythm of the rain instead allows fire seasons to be estimated earlier and more accurately – and crews, equipment and warnings to be readied where they will be needed in the months ahead.