Climate experts from Newcastle University, the Met Office, and the University of Bristol used European-wide km-scale simulations to model future changes to hail with global warming. The study, published in the journal Nature Communications, shows that under a high-emissions scenario (RCP8.5), severe hail is likely to become less common – except potentially for very large hail.
Severe hail has a diameter of 2 cm, while a diameter of 5 cm or more is considered very large. Bigger hailstones cause more damage than smaller ones, and even a small increase in their size could outweigh any benefits from having fewer hailstorms overall.
The researchers attribute this decrease to more than one factor. Hail forms higher in the atmosphere as it warms, where storm updrafts could be weaker, and this gives hail more time to melt before reaching the ground. Another factor is the weakening large scale circulation, affecting the vertical profile of winds and leading to environments not beneficial for thunderstorm organization.
Importantly, the authors found that future warm seasons feature a warmer thunderstorm type similar to hail-producing storms found in the tropics, where the largest hailstones can still reach the surface. The findings suggest that, in the future, these storms will become most frequent over southern Europe, leading to regional increases in severe hail frequency.
Study lead author, Dr Abdullah Kahraman, Senior Researcher in Severe Weather and Climate Change, School of Engineering, Newcastle University and long-term Visiting Scientist at Climate Processes and Projections (CPP), Met Office Hadley Centre, said: “Our findings indicate that the effects of climate change on severe thunderstorms are more complex than previously thought, and high-resolution models can produce results that differ significantly from earlier research. Society may need to prepare for less frequent, yet more damaging hail events locally, in a 5-degree warmer future.”
Professor Lizzie Kendon, Head of Climate Projections at the UK Met Office and Professor of Climate Science at the University of Bristol, added: “These results are very concerning. They imply we need to be prepared for tropical-type hailstorms impacting Europe in the future, associated with very large hailstones that can cause severe impacts. This possibility also extends to the UK, although the risk of hail here remains low into the future.”
Study co-author, Professor Hayley Fowler, Professor of Climate Change Impacts, Newcastle University School of Engineering, said: “As a society we need to be better prepared for unprecedented extreme events and this study shows that future storms in the Mediterranean could bring giant hail, with devastating impacts. Recent hailstorms have caused significant direct damage to properties and infrastructure, crops, and even aircraft.”
The team’s analysis shows that the possibility for very large hailstones decreases around Central Europe, and that it remains low over the British Isles and Northern Europe land areas. In contrast, it increases in Southern Europe in autumn and winter, balancing decreases in summer and spring.
The occurrence of warm-type thunderstorms in Southern Europe in a future warmer climate could amplify the impact of hailstorms in Italy and surrounding areas, with overall more frequent significant severe hail.
The authors acknowledge the uncertainty regarding the effect of enhanced melting associated with higher freezing levels on the largest hailstones. They recommend further studies of these warm thunderstorms to improve the understanding of their potential to produce very large and damaging hail at the surface.
Paper
‘Future changes in severe hail across Europe, including regional emergence of warm-type thunderstorms’ by Abdullah Kahraman et al. in Nature Communications