Uncovering Trends In U.S. Tornado Outbreaks

Are severe convective storms becoming more common? WTW-sponsored research picks out those U.S. regions where tornado outbreaks have trended upwards in recent decades.

Severe convective storms (SCS) made a sizable impact on the (re)insurance industry in 2023. This category of peril, which includes straight-line winds, hail, and tornadoes, caused more than $50 billion in claims for the U.S. alone and accounted for more than half of all global insured losses ¹. During the past few decades, SCS-related losses have steadily increased largely due to exposure growth. But how have the frequency and severity of SCS themselves changed during that period? Until now, has been difficult to answer these questions because of the intrinsic nature of SCS hazards and the way we have recorded their occurrence. But new research from our group at Columbia University has leveraged what we know about broad-scale atmospheric conditions to uncover previously unknown trends in one of the