Hail will become less common but larger and more damaging because of human-caused climate change — according to a new study published in the Nature journal Climate and Atmospheric Science.
“It’s like death by a thousand paper cuts when we’re talking about convective storms and hail,” Victor Gensini, a severe-storms researcher at Northern Illinois University and the study’s lead author, said in an interview. “Those aggregate losses begin to add up.”
His group simulated future hailstorms using weather models run on supercomputers and analyzed how such storms would change as greenhouse gas emissions from the burning of fossil fuels increase in the atmosphere.
The researchers found that while hailstorms should become less common because of warmer air and increased melting, the biggest hailstorms should become more frequent. More vigorous thunderstorm updrafts, which will feed off an increasingly warm and humid atmosphere, will suspend hailstones above the ground longer, allowing them to grow larger.
“There’s a pivot point, so to speak, right at about four centimeters,” Gensini said. Four centimeters is roughly the diameter of a golf ball. Hailstones smaller than four centimeters in diameter fall more slowly and will melt more readily, as the atmosphere warms.
“But when a hailstone reaches [four centimeters across], it has a higher terminal velocity, and … as it falls in that particular fall speed with those larger stones, it doesn’t melt,” Gensini said.
Matt Kumjian, a professor of atmospheric sciences at Penn State who was not involved in the research, concurred with the study’s findings and said that the predicted increase in maximum hail sizes could have costly consequences.
“Less frequent storms would tend to decrease the amount of damage, but the bigger sizes would increase the damage potential of storms,” he said in an email. “I could envision seeing more high-impact, high-dollar amounts to losses for less frequent storms hitting populated areas.”
Large hail is already a problem for insurers.
“Over the last 18 months, we’ve had over $100 billion in losses in the United States from [severe] storms, and a majority of that is hail,” Gensini said. “Hail does way more damage every year than tornadoes do. And you’re seeing it in your premiums. You’re seeing it in your policies.”
Kumjian said economic damage from hailstorms has been increasing for at least the past decade. “A big driver of this trend is more expensive infrastructure in more hail-prone regions,” he wrote.
More study needed
Researchers said a better understanding of how hail size will change in a warming climate and how to improve forecasting could help better characterize the threat and prepare for it. Large hail is a relatively poorly understood element of severe weather. While tornadoes generally require the same basic set of ingredients to form, hail can materialize under a much broader range of circumstances.
“How hailstorms, and specifically hail at the ground, may change as our climate changes is one of our biggest challenges as a community,” Ian Giammanco, who runs an ongoing hail study for the Insurance Institute for Business and Home Safety, said in an email. “But answering this question is imperative when we look at the amount of damage hailstorms cause each year, and that most of our building materials used today simply aren’t able to withstand large hail.”
Giammanco pointed to factors that could affect hail size that researchers haven’t begun to probe.
“There are still more pieces to the puzzle, like the vertical wind profile’s influence on updraft sizes and shapes, which changes how hailstones move and grow in a thunderstorm,” he wrote.
With the costs of hail rising, as well its potential size, Gensini’s next mission is to learn how to better forecast and track it.
“There is a proposed field campaign called ICECHIP that intends to be in the field studying hail in 2025,” he said. “It will … have mobile Doppler radars in the field, mobile mesonets, weather balloons … it’ll be the world’s largest field campaign to study hail.”
In addition to mesonets — dense networks of weather stations — Gensini’s team also plans to deploy sensors that can record hailstones’ impact.
For now, Gensini’s paper predicts that there won’t be any shortage of big hailstorms to study.
