Characteristics and trend of the wildfire activity in the Southern Hemisphere (2003-2022)

Global wildfire activity has a major impact on regional climates because of the large amount of particulate matter injected into the atmosphere during and after the biomass burning. If its evolution has been extensively studied in specific regions of the globe, very few studies have been presented for the Southern Hemisphere, at a continental scale. This study aims to evaluate wildfire activity across three continents: Southern Africa (SAF), South America (SAM), and Oceania (OCE), and quantify its trend over the last two decades (2004-2024), using Active Fire MODIS satellite data. The first key outcome of this work is the heterogeneity of the wildfire seasonality among the three continents. The Oceanian continent, in particular, showed no clear seasonality during the studied time period, suggesting that different fire regimes co-exist in this area. The SAF and SAM continents exhibited clear seasonal patterns with a 20-week fire activity duration from May to October, characterised by low inter-annual variability for SAF, and a 14-week duration from July to October, marked by high inter-annual variability for SAM. Trend-changing points were determined using the robust Piecewise Linear Functions method, leading to different time slicing for each continent's trends. In terms of fire number (and summed FRP) tendencies, the results show a decrease of -13 (-21)% per decade for SAF (2010-2022), and an increase of +22 (+42)% per decade for SAM (2013-2022). The number (and summed FRP) of the most severe fires follows a slightly stronger decreasing trend for SAF, while their trend triples (almost doubles) for SAM compared to all fires. This may be attributed to an increase in fire activity driven by the sensitivity of wildfires in the SAM region to climatic conditions and their recent changes, as well as to regional land-use practices and fire management strategies.