Enlarge image Large hailstones fall into a garden. (© picture alliance / dpa) Michael Kunz sometimes observes the powerful storms over the hilly region of Kraichgau near his office at the Institute for Meteorology and Climate Research at the Karlsruhe Institute for Technology (KIT). Yet, even when there are no dark clouds looming over the horizon, the researcher is nevertheless often occupied with strong weather and violent hailstorms. According to Kunz, the extreme weather events are the result of considerable climatic changes in recent years.

Hail and storms – there has been an unusual amount of both in recent weeks in Germany. Whether climate change is responsible for this is not a question that the 44 year-old meteorologists is trying to answer. It is clear, however, that during the past few decades the ground temperature and the air humidity have risen, particularly in low-lying areas in the southwest of Germany.

Michael Kunz and his team have used scientific models to determine that the conditions have become more favorable for the formation of powerful storms in Germany and other European countries. The meteorologist explained that violent storms occur especially frequently in the south of Germany because that region has higher temperatures and humidity than the rest of the country. These factors form low-pressure systems and raise the chance of storms, said Kunz.

Kunz emphasized that his research did not collect concrete statistics on storms themselves, but rather on the weather on days when the general conditions for strong storms and hail were present. The meteorologist justified the limitations of his research by pointing out that there are no reliable long-term measurements of the frequency of hail or storms. This is chiefly due to the dimensions of these weather phenomena: storms are typically only two to ten kilometers in diameter and hailstorms can be as little as a few hundred meters wide.

This is why storms and other similar phenomena often go undetected. “It is only in the last ten years that we have had reliable scientific observations of lightening in Germany,” explains Kunz. For this reason, there are no reliable empirical results of summer storms over the past few decades with which one can make comparisons with current storms.

The scientists have had to approach the phenomenon of hail in the form of a protracted puzzle. The instruments for the concrete weather analysis of hail are too imprecise. Radar units cannot, for example, distinguish between hailstones and water drops in the inside of a cloud. “Data on hailstorms are also difficult because this phenomenon takes place in small areas,” says Kunz.

The puzzle method that researchers have used in the case of hail is supposed to supplement the meteorological parameters with insurance data in order to determine a joint parameter that can describe the damage caused by hailstorms. In particular, the data on damage caused to buildings by hail has shown a strong increase in recent years.