Hailstones may get bigger as the climate warms — bringing higher insurance costs

The sudden, percussive crackle came as Barb Berlin was standing in the garage of her farmhouse near Inman, Nebraska.

“I thought it was a gun,” she said.

Then came a streak of white. She realized the sound wasn’t gunfire but hail.

A fist-sized hailstone had pounded the tin roof on Berlin’s garage. Soon, others were leaving softball-shaped craters in the hood of her Ford Mustang, which was parked outside.

“It was so loud and it was scary. I did a lot of praying,” Berlin said, adding that she worried for her livestock. “I’ve never been in hail like that before.” 

Hail is a sneaky hazard. This year, amid a spring and summer of extreme weather, hail — not hurricanes, floods or tornadoes — has caused the highest damage costs in the U.S., according to Gallagher Re, a global reinsurance firm that tracks such data. 

And research suggests that large hailstones like the ones Berlin saw Monday will become more common as Earth warms. That was the finding of a study published last month, which suggested that the likelihood of smaller, less-damaging hailstones will decrease. 

The study by Northern Illinois University researchers projects that the frequency of hailstones roughly 1½ inches or larger will rise by 15% to 75%, depending on how much greenhouse gas pollution humans emit.

Hail is generated when thunderstorms circulate rain drops into the upper layers of the atmosphere. It typically forms where temperatures are between minus 22 degrees and 14 degrees Fahrenheit. The reason climate change affects hail is that higher temperatures provide more energy to create upward pushes of air within thunderstorms. 

“We see stronger updrafts in the future because we have more atmospheric instability,” said Victor Gensini, a lead author of the study and professor of meteorology at Northern Illinois University. 

These powerful updrafts allow hailstones to remain longer in sections of a storm that are favorable for hail formation, the research says. That, in turn, will lead them to accumulate more ice before they get too heavy and fall to the ground. 

“Imagine taking a hair dryer and turning it on end and pointing it up at the sky and trying to balance a ping pong ball,” Gensini said, explaining how an updraft lifts a hailstone. “Now try to balance a baseball or a grapefruit. You’re gonna need a much stronger updraft to balance the downward force of that.” 

The prospect of bigger hail, which is already one of the costliest weather hazards in the U.S. and a key factor driving up insurance premiums, will only intensify those issues.

“Thunderstorm losses are a really, really big piece of why premiums continue to go up and why there’s this massive reassessment of risk by not just the insurance industry, but banks and the federal government,” said Steve Bowen, chief science officer for Gallagher Re.

He added that hail “accounts for roughly 50 to 80% of insured claims filed from thunderstorm-related losses.” 

So far this year in the U.S., thunderstorms have been responsible for about $61 billion in economic losses, according to Bowen. Hail was likely responsible for between $31 billion and $49 billion of that total. In the same period, tropical storms and flooding together have accounted for $14 billion in losses. 

The atmospheric dynamics involved in hailstorms are complicated and can be difficult to study, but advances in climate and weather modeling now allow scientists to create complex simulations that model thunderstorms and their microphysics, including hail size. 

For their study, Gensini and his fellow researchers took future climate projections and plugged them into a weather model, not unlike what television forecasters use. 

The study predicts fewer days where hail falls in the Plains states, but more severe hail overall, and in other regions. 

Although a warmer atmosphere allows for more melting as hail falls to the ground, that dynamic mostly affects smaller hailstones, which descend more slowly. 

The terminal velocity of a baseball-sized piece of hail is roughly 100 mph, according to Harold Brooks, a senior research scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory, who was not involved in the recent study. By contrast, a 1-inch piece of hail falls at 20 to 30 mph.  

He said the study’s findings track with previous work. A 2017 study used a different modeling approach and predicted larger average hail size but fewer days of hail. Researchers in Italy, meanwhile, evaluated more than a million dents from hail from 1988 to 2016 and suggested that storms were producing fewer and larger hailstones.

“It makes sense. We’ve had some hints from observations,” Brooks said. “The basic physical mechanisms they’re talking about, I don’t think are particularly surprising at all.” 

Even though hail causes more monetary damage annually than tornadoes, on average, research on the former had stalled until recent advances in radar and weather modeling.

“It just doesn’t seem as sexy as tornadoes,” Brooks said.

He added that key questions about hail remain: “Can we learn enough about how hail forms, and about what the distribution of hail sizes during a storm are to make actionable forecasts several hours in advance?”

Next year, Gensini and scientists from several other institutions are planning the first U.S. field study of hail done since the 1970s. The researchers will chase hailstorms the way some do tornadoes and try to deploy mobile Doppler radars and other instruments to capture the storms’ inner physics.

After the Monday storm in Nebraska, Berlin said she spotted plenty of roofing company trucks rolling through town. An insurance adjuster has already assessed her roof for damage. Her Mustang suffered about $3,500 in damage. 

With more notice, she said, she would have shepherded her animals to safety and put her car into the garage — she did not get a hail warning in the forecast, and only received a weather app alert after the storm passed. 

Luckily, Berlin said, “none of the livestock was hurt, but it was big enough that it could have done some major damage.”