WTW-sponsored research by Columbia University, A Stochastic Statistical Model for U.S. Outbreak-Level Tornado Occurrence Based on the Large-Scale Environment, has been highly commended in the climate risk research paper of the year category.
This research uncovers important new trends in tornado outbreaks across the US providing insurers with vital insights into the risks posed by severe convective storms (SCS).
In 2023 alone, SCS events — including straight-line winds, hail, and tornadoes — caused over $50bn in claims in the US, representing more than half of all global insured losses.
While it is expected that a warmer world will lead to stormier conditions, the Intergovernmental Panel on Climate Change (IPCC) has expressed low confidence in past trends of tornado, hail, and wind activity. This makes it essential for insurers and their clients to quantify how climate change is impacting SCS activity.
The research identified previously unrecognised trends in tornado outbreaks — instances where multiple tornadoes occur within one or two days — and provides a fresh perspective on present-day risks.
This updated understanding has been integrated into WTW's Global Peril Diagnostic, enabling clients to more accurately gauge their exposure to tornado risk using the latest scientific insights.
The study focuses on key environmental factors, including convective precipitation (which measures the strength of rising motion), storm relative helicity (which reflects the potential for rotation within storms) and convective available potential energy (a proxy for atmospheric instability).
Using these factors, the research highlights geographic regions, such as Alabama, Georgia, Missouri, and Mississippi, where tornado outbreaks have more than doubled in frequency since the early 1980s.
The research also reveals complexities in Tornado Alley, where environmental conditions have become more favourable for tornado outbreaks, but there has not been a corresponding increase in on-the-ground reports.
Overall, this research represents a major step forward in understanding how climate change may be impacting tornado risk, offering valuable data for insurers managing their exposure to these devastating events.
