The storms will not leave us this summer. For several weeks, the majority of French territory has been affected by heavy showers. But if the latter should moderate, this is not the case with thunderstorms. Indeed, the dry storm phenomenon will make a comeback this summer. But what does it correspond to? What is the difference with a classic thunderstorm, and what are the consequences?
“It’s a bit of what we fear”, explains Patrick Marlière, meteorologist and director of Agate Météo, when asked if this phenomenon will be back this summer. Indeed, in September 2022, a dry storm broke out in Alençon, in the Orne. The latter had caused minor damage. Quite rare, this phenomenon had been the subject of numerous publications on social networks. But what are its specificities? “It is a stormy degradation which is not accompanied by precipitation, hence its qualification as dry”, continues Patrick Marlière. Nevertheless, “it takes place almost every summer, but represents a very small part of all the storms that occur”, specifies Guillaume Jauseau, meteorologist in charge of the scientific pole of Météo
If the dry storm is not accompanied by rain, the latter forms in the same way as a classic storm. Indeed, “it’s about the same storm base”, explains Guillaume Jauseau. According to Météo-France, the cumulonimbus is the characteristic cloud of thunderstorm phenomena. It also causes hailstorms and can reach up to 15 kilometers wide. During the creation of a dry storm, this cloud is therefore present, but certain climatic conditions prevent the rain droplets from reaching the ground.
According to Guillaume Jauseau, three factors can explain the lack of precipitation during these summer storms:
But why are meteorologists so worried about their return?
“These dry storms cause significant electrical activity and increase the risk of fire”, specifies Patrick Marlière. “When they arrive during a drought, that is to say when there has been a lack of rain for several weeks, lightning on the ground will strike trees and cause fires”. This phenomenon is therefore particularly feared for the violent forest fires it can cause.
“This is one of the main types of storms that cause forest fires,” says Guillaume Jauseau. Indeed, meteorologists consider that between 10 and 15% of these fires are caused by natural phenomena such as dry storms. As fires cannot be extinguished by rain, dry storms can cause greater damage. But “there is not only the risk of forest fires”, specifies Patrick Marlière.
When specialists predict the arrival of dry storms, they consider that electrical activity is guaranteed. However, this situation has other consequences, particularly in homes. “If it falls in your home or near your home, it can generally cause damage to homes because this type of impact can even cause explosions”, specifies Patrick Marlière. “For example, during the last electrical activity, that of the lightning is much more important around the weather phenomenon than in the center of the storm”.
In other words, lightning can strike above you, even if the thunderstorm has not started in your area of residence. This phenomenon can therefore be the cause of many disasters. Nevertheless, the latter should not be more numerous in the coming years. “They will be much more powerful because they will have much more capacity to develop, to acquire energy, especially with global warming which will provide them with additional energy to pour more rain in a very short period of time”, announces Guillaume Jauseau. But what precautions should be taken during these storms? Can we really protect ourselves from it?
“Storms are very complicated systems to predict”, specifies Guillaume Jauseau. Therefore, it is difficult to predict where lightning will strike. “During the presence of these dry storms, obviously we must be vigilant, but it is after the passage of these storms that there should be a control system which can see if the lightning has not fallen in areas forests and did not cause fires”, says Patrick Marlière.
Guillaume Jauseau, for his part, specifies that it is necessary “to clear brush to avoid that there are small vegetations that are too dry which will participate in a more intense forest fire”. In addition, for several years, techniques have been put in place to try to control them. “There are several scientific studies that have tried to come up with a plan to place iron spikes to drive thunderstorms to these facilities instead of them reaching the forest or homes.” Nevertheless, these techniques remain “undeveloped and very hypothetical”.
“We will have to be very vigilant with regard to the next dry storm zone which will fall on regions where drought is very present”, concludes Patrick Marlière.