With global warming, will the Cevennes rains intensify?

Studies carried out by climatologists over the last ten to fifteen years show that the increase in temperatures has an effect on extreme rainfall. If summers are getting hotter, heavy rainfall is likely to intensify.

Heat, the only factor of heavy rains?

However, the heat is not the only factor in the heavy rains. You also need a significant source of humidity, such as the Mediterranean. We also speak of Mediterranean rains or Cévennes rains, in reference to the Cévennes, a mountainous relief close to the Mediterranean and « homeland » of extreme rains which occur mainly at the end of summer and at the beginning of autumn, after hot weather.

With solar energy, heat and rising sea temperature, the water will evaporate and form a mass of moist air. The winds push this mass of air towards the mountainous barriers of the Cévennes or the Mediterranean foothills, which can be found in particular in the Hérault or the Gard, which forces the water vapor to rise. It is then that it cools, condenses and turns into precipitation. If temperatures increase in the years to come with global warming, the evaporation of water from the Mediterranean will be greater, and therefore the rains more intense. In addition, warmer air can hold more water vapour.

In terms of timing, there are two possibilities. Either the longer duration of summer and high temperatures will lead to a shift towards winter of these periods of rain in the Cévennes, or these periods will be longer due to temperatures that will remain high for longer.

More frequent rains

From a geographical point of view, it is not known whether these precipitations will extend to other areas in addition to the reliefs close to the Mediterranean. Extreme phenomena occur exceptionally outside these usual areas, as in May 2016 in the Paris Basin (Paris had then experienced its rainiest month since 1960, and floods caused by a major flood of the Seine, Editor’s note)and the Cévennes rains sometimes overflow the Cévennes ridge.

It is therefore possible, but the mountainous reliefs still have an extremely important role and do not move. Except in exceptional cases, moving rains will therefore not have the same intensity elsewhere than in these places.

On the other hand, the intensification of the Cevennes rains and the floods they can cause will not cause more damage, but they will be more frequent. A major flood that normally occurs every twenty years may occur every fifteen years.