Description

Extreme wildfires have substantial economic, social and environmental impacts, but there is uncertainty whether such events are inevitable features of the Earth’s fire ecology or a legacy of poor management and planning. We identify 478 extreme wildfire events defined as the daily clusters of fire radiative power from MODIS, within a global 10 × 10 km lattice, between 2002 and 2013, which exceeded the 99.997th percentile of over 23 million cases of the ΣFRP 100 km−2 in the MODIS record. These events are globally distributed across all flammable biomes, and are strongly associated with extreme fire weather conditions. Extreme wildfire events reported as being economically or socially disastrous (n = 144) were concentrated in suburban areas in flammable-forested biomes of the western United States and southeastern Australia, noting potential biases in reporting and the absence of globally comprehensive data of fire disasters. Climate change projections suggest an increase in days conducive to extreme wildfire events by 20 to 50% in these disaster-prone landscapes, with sharper increases in the subtropical Southern Hemisphere and European Mediterranean Basin. Extreme wildfires have substantial economic, social and environmental impacts, with concern that climate change is increasing their occurrence 1,2 . We show that such events are globally distributed and are associated with highly anomalous fire weather conditions. Our validated global database of extreme wildfires shows that those reported as being economically or socially disastrous are concentrated in suburban areas intermixed with flammable forest in the developed world. The lower occurrence of fire disasters in the Mediterranean compared to the climatically analogous regions in the western United States and southeastern Australia suggest regional land use can substantially reduce the occurrence of fire disasters. Extreme wildfire events are inevitable features of flammable biomes, and climate change is likely to increase their frequency and global occurrence, particularly in subtropical regions of the Southern Hemisphere, and the European Mediterranean Basin and Levant. Climate change is causing fire seasons to start earlier and finish later 2,3 , with an associated trend towards more extreme wildfire events in terms of their geographic extent and duration, intensity, severity, associated suppression costs, and loss of life and property 4 . Determining the relative role of biome, climate change, and past fire management practices in influencing these extreme fire events is essential for effective wildfire policy, and to do this demands using consistent terminology regarding how fires impact the environment 5,6 . The term ‘megafire’ is widely used to describe such extreme fire events 7,8 , but there is currently no agreed-upon operational definition of this concept — which, combined with fragmentary records of fire events and their economic and environmental costs, frustrates global and historical analyses of extreme fire events. Here, we use energetically extreme landscape fire events as a robust index of the ‘extreme wildfire event’. We base our analysis on energy release from the fire radiative power (FRP) MODIS product using daily ΣFRP within a global 10 × 10 km lattice for 4,382 days between 2002 and 2013. We identified over 23 million events and selected the top 500 representing the 99.997th percentile of all the ΣFRP 100 km−2 in the MODIS record. We used a systematic verification process to validate that the events were wildfires (Fig. 1), although this approach was unable to differentiate if the cause of the event was multiple individual fires in the same geographic location, or a single fire with multiple high-intensity fire fronts. Accordingly, we describe our unit of analysis as an ‘event’ rather than as an individual fire. Our approach enables robust analyses given these events are precisely quantified in terms of their energy release, location and timing.