“We are living, from today, we must no longer speak in the future, of events that are becoming more and more extreme“, indicates Saturday June 4 on franceinfo Alix Roumagnac, president of Predict Services, the “risks” subsidiary of Météo France.
>> Follow the progress of thunderstorms in France live on franceinfo
65 departments are on orange alert for violent storms.
franceinfo: We are talking on Saturday evening of an exceptional alert in terms of its magnitude. Is this the case in your opinion?
Alix Roumagnac: Absolutely. Several factors explain this exceptional character. Our colleagues from Météo France have placed more than 65 departments on orange alert. It is a great cross-section of France. The thunderstorms started in the west of France, they hit the west of the Paris basin at the end of the afternoon and a second salvo is expected at the start of the evening. It will start from the south-west of France, cross the Massif Central and touch Burgundy and the Grand Est during the night and in the early morning. Météo France is expecting particularly intense, extreme storms with potentially significant gales, possible hail and intense rains which can cause intense rains in urban areas. Therefore, we can only encourage the greatest caution.
There could be hailstones the size of tennis balls. How are they formed? How can we have such big hailstones?
It’s really the temperature difference between the ground and the top of the clouds. The greater this gradient, the greater the risk of seeing very large hailstones. This is the case this weekend, with very high clouds, with very cold temperatures on the top of the clouds. Some studies tend to show that climate change can have an influence on increasingly large hail events due to temperature differentials. These are studies that are in the process of being validated, but which confirm what we experience on a daily basis. We live, from today, we must no longer speak in the future, of events that are becoming more and more extreme.
The land is very dry in places, since many regions are currently affected by droughts. It means that the earth is impermeable or practically impermeable. Should we fear land runoff?
You are quite right. Many farmers are waiting for water. So, we hope that these rains which are coming will be good for agriculture. But indeed, there are several elements: if it arrives too intensely with soils that can be closed, if it arrives in the form of hail in urban areas even more where the soils are sealed, these rains can cause rapid runoff. This is what happened Friday around Rennes. This obliges, and we support for this, the mayors to implement plans for communal safeguards, security measures, and which obliges everyone to take precautionary actions when these events occur.