2024-04-04 16:56:27
The exceptional floods which hit Burgundy and the Center Val de Loire took place just a few weeks after the deadly floods in the south of France.
It’s the turn of Burgundy and the Center Val-de-Loire to have their feet in the water. The departments of Yonne and Aube were still on high orange alert on April 4, while a new wave of rain crossed the northern half of the country from west to east. Despite a slight decline that began very slowly during the night from Wednesday to Thursday, the situation remains critical in the Yonne, flooded by floods from the Armançon and Serein rivers.
“Numerous and damaging excesses will still be observed this Thursday morning”warns the Météo-France Vigicrues organization, which affirms that it is a “exceptional flood” since the levels have exceeded those of April 1998 upstream and are of the same order as May 2013, or even a little higher downstream. In Chablis, one of the towns most exposed to flooding in the Yonne, the peak was reached during the night from Tuesday to Wednesday: the level of the Serein exceeded 2.50 meters, or 35 centimeters higher than the record flood of 2013.
Also read: “It’s urgent!” : hell continues for victims of the Pas-de-Calais floods
Barely three weeks earlier, the devastating floods in Gard and Ardèche following the passage of storm Monica had left five dead and caused significant damage, just a few months after the exceptional floods due to their intensity in the Nord Pas de Calais. Are flood episodes destined to increase in number in France?
Rainfall excess of 85%
“The flooding phenomenon depends on several factors”would like to clarify Françoise Vimeux, climatologist and research director at the Research Institute for Development. “The first criterion is the rain: its intensity, its volume, its duration”. However, the month of March 2024 was particularly rainy, announces Météo France. “Nationally, excess rainfall reached around 85%” compared to the 1991-2020 average, notes the organization. This is the fifth wettest March since weather measurements began in 1958.
These intense precipitations partly originate from air masses very laden with humidity coming from the Mediterranean Sea and the Atlantic Ocean, whose temperatures are gradually increasing with global warming and are particularly high at the moment. This humid air is pushed by westerly winds to France, and ends up “pour into it in the form of precipitation”describes Françoise Vimont. “The combination of heavy rains lastingly blocked by the reliefs [en France] is one of the parameters involved in the flooding this year.completes Régis Crépet, meteorologist at The Weather Channel*.
“When global warming causes ocean and atmospheric temperatures to rise, the rain pattern changes”, Françoise Vimeux further advances. The frequency and intensity of these torrential rains are thus exacerbated and the floods that these episodes cause can be more frequent. “Nevertheless, projections of changes in winter rainfall still contain a lot of uncertainty: we do not see reliable trends for the coming years”continues the climatologist.
One in 4 French people lives in a flood zone
Furthermore, the future frequency of floods will not only depend on precipitation, insists Alexandre Isgro, meteorologist and forecaster, but also on the nature of the soil and their impermeability. Concretely, if they are concreted, or saturated because they have been subjected to heavy rainfall for several weeks, they can no longer absorb the water which will then run off towards areas more «basses» continues the researcher, and towards the waterways which swell and overflow. On flat ground, water will stagnate and cause local flooding.
Currently, one in four French people live in flood zones, and this proportion could increase, partly due to the installation of human activities in these exposed areas, which are poorly suited to resist flooding. “As a result, the cost of flooding is increasing, but this is not just due to increased flooding. On the other hand, we must seek to adapt to extreme rain events which will increase.warns Françoise Vimeux.
No more marine submersion
Global warming also plays a role in the vulnerability to flooding of certain coastal areas, points out the climatologist. “Average sea levels are rising and causing more marine flooding than before”, she explains, or temporary flooding of the coastal area. The combination of intense rains and rising ocean levels complicates the flow of rivers towards the sea, which can overflow and cause flooding.
For the two experts, it is therefore difficult to establish trends on the frequency of floods in the years to come given the multifactorial nature of these phenomena. Especially since the projections of changes in winter rainfall for the near future are not very reliable. However, we need to remain vigilant about our “vulnerability” to flooding, given the land use planning in flood-prone areas, underlines Françoise Vimeux. Without knowing whether there will be more floods in the future, it is however more certain that we are already more vulnerable to floods.
*The weather channel is owned by the Figaro group.
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