Daniel Bannister, Weather and Climate Risks Research Lead, Willis Research Network
As climate and landscapes change, the combination of fuel, weather and atmospheric conditions needed for the most extreme wildfires is becoming more favourable. This is creating a rapid fire intensification problem. As a result, wildfire losses could exceed historical experience and expose blind spots in current views of risk, says Daniel Bannister, weather and climate risks research lead, Willis Research Network.
Some of the largest catastrophe losses occur when the behaviour of natural hazards changes rapidly. In hurricanes, the phenomenon is known as rapid intensification, where a storm strengthens much faster than anticipated and materially alters its loss potential, as Hurricane Ian demonstrated when it intensified from a Category 3 storm to Category 5 intensity in around 12 hours before landfall in Florida. Wildfires can undergo a similar transition: rapid fire intensification.
The mechanism behind that change is pyroconvection, which occurs when a fire becomes so intense that it generates powerful convective updrafts and begins to interact with the atmosphere above it. Once this occurs, fire behaviour can become substantially more extreme, with accelerated growth, erratic spread patterns, long-range ember transport and, in severe cases, fire-generated thunderstorms known as pyrocumulonimbus clouds. These transitions can occur quickly and remain difficult to predict, turning a seemingly manageable fire into a much larger loss event. Extreme pyroconvective fires have been most closely associated with Australia and western North America, such as the Spokane Complex Fires. The 2026 Gironde fires in France, however, demonstrated that conditions capable of supporting unusually extreme fire behaviour can emerge outside traditional wildfire regions. Rapid fire intensification is often shaped by conditions that develop months before a fire starts, with researchers increasingly focused on hydroclimate whiplash, the rapid shift from unusually wet conditions to unusually dry conditions. Wet periods encourage vegetation growth and increase available fuel, while subsequent heat and drying can transform that vegetation into highly combustible material. This pattern preceded both the Palisades and Eaton fires in California and severe wildfire activity across parts of Europe in 2026.
The importance of these processes is likely to grow as warmer temperatures increase fuel dryness, amplify hydroclimate whiplash and create conditions that can support more extreme pyroconvective behaviour, particularly in Europe, the world’s fastest-warming continent. At the same time, landscape change is altering fuel characteristics in ways that can increase the energy available to a fire. Together, these changes increase the potential for rapid fire intensification and raise the ceiling for wildfire intensity beyond the historical record. For insurers and reinsurers, current views of wildfire risk may not fully capture the potential for rapid fire intensification, with implications for both portfolio loss potential and the performance of reinsurance programmes. This is because many approaches used by insurers and reinsurers do not fully capture changing fuel loads or explicitly represent pyroconvective processes. Given the role these factors can play in driving the most severe wildfire outcomes and creating a pathway into the upper tail of wildfire severity, wildfire losses could be materially larger than current modelled views suggest when conditions favour rapid fire intensification, potentially increasing the frequency of losses currently viewed as remote.
Within the Willis Research Network, we are exploring the implications of rapid fire intensification through physically plausible extreme wildfire scenarios. Early findings suggest relatively small changes in fuels, antecedent climate conditions or atmospheric environments can produce materially different wildfire outcomes, highlighting potential portfolio vulnerabilities and areas where loss potential may be underestimated. Scenario analysis provides one way of assessing whether portfolios and reinsurance programmes remain robust under more extreme, but still plausible, wildfire conditions.
The industry already recognises rapid intensification as a defining feature of hurricane risk. Wildfires have a rapid intensification problem too.
