Hailstorms are becoming more and more disastrous

Hailstones are also changing with the climate crisis and becoming significantly more dangerous. Their stones continue to grow and in some cases reach the size of golf balls, with devastating effects on land, buildings, and people. It is estimated that hailstones larger than five centimeters in diameter can cause serious damage to crops, vehicles, and even buildings.

Europe, and Italy in particular, have become some of the world's most affected regions by the phenomenon of hailstorm growth, both in frequency and in the size of the stones. Everyone remembers well a hailstorm in July 2023 in Azzano Decimo, in the province of Pordenone, during which a hailstone measuring 19 centimeters in diameter was found, very close to the world record of 20,3 centimeters set in 2010 in South Dakota.

A study ofEuropean severe storms laboratory, attempts to reconstruct how the probability of intense hailstorms has changed from 1950 to 2023 using weather models and homogeneous atmospheric data over time. This is important because the number of reports is also growing due to smartphones, social media, and more efficient observatory networks. 

The study's main conclusion is that across much of Europe, the frequency of large hail (greater than 2 centimeters in diameter) and especially very large hail (greater than 5 centimeters in diameter) has increased since the 50s. The most marked increases are observed in northern Italy, southern France, and eastern Spain. The authors attribute much of this signal to increased moisture in the lower atmosphere, which provides more energy to thunderstorms. 

For Italy, the result is particularly notable: according to the ESSL reconstruction, the probability of very large hail in northern Italy is now approximately three times higher than in the 1950s. Furthermore, the hail season has lengthened, starting earlier in spring.

But why are these events becoming more frequent, more powerful, and more damaging in our region? Scientists have a clear answer: the primary cause lies in atmospheric warming, which has significantly increased the intensity of storms and thus the volume of hailstones. Essentially, the climate crisis and warming of land and sea surfaces are increasing atmospheric instability, creating ideal conditions for stronger and more violent storms, which form hail. And pollution can also indirectly affect hail: dust particles and other pollutants in the atmosphere can act as condensation nuclei, promoting the formation of denser clouds and the growth of hail.

About it, another study, published in May 2026 on Nature and carried out by Chinese and American researchers, led by Shiyi Zhang and John T. Allen, provides very complete answers. To verify their models, they analyzed over 14.000 historic hailstorms recorded worldwide, simulating the growth, fall and melting of hailstones under different weather conditions.

The most interesting finding is that global warming does not simply produce “more hail”, but tends to modify the size of the grains:

• in many regions the number of small and medium grains is decreasing;
• on the other hand, the larger and more destructive grains are increasing, capable of causing serious damage to crops, buildings and vehicles;
• These grains are projected to increase by 37,9-51,8 percent by 2100, while smaller grains will decrease by 4-12 percent. 

The physical reason is a sort of competition between two effects:

• the warmer atmosphere contains more moisture and fuels stronger updrafts, which allow the grains to grow more;
• At the same time, warmer air layers near the ground promote the melting of smaller grains before they reach the ground. 

This is why researchers speak of a “polarization” of hail size: fewer events with small hail and more events with very large hail.

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