“As much rain fell in 15 hours as in a month, unheard of! »

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Administrator of the Météo 77 Facebook page and volunteer firefighter asweather expert with the Departmental Fire and Rescue Service of Seine-et-Marne (Sdis77), Lucas Bouhier brings his analysis on the series of floods which hit the north of the department THE October 9 and 10, 2024.

The inhabitants of the Grand Morin region have just suffered their fourth episode of flooding in a year, including two in the last fortnight. How can we explain that this sector of the department is so deeply affected?

There are several elements to take into account. THE Grand Morin sector East hillyand therefore subject to changes during heavy rains, especially when they are sudden and heavy, like this summer or this week.

Then you have right now waterlogged soils because of the humid summer we experienced. Finally, the Grand Morin crosses a relatively urbanized areaconcreted, which promotes water flow and not absorption.

It is unfortunately an aggravating cocktail against which we cannot do much, particularly for homes built before the establishment of flood zones. Hence the strong weariness of the affected residents.

Why was the south of the department rather spared from flooding during Storm Kirk?

In the souththe risk of flooding is essentially based on the floods of the Seine and the Loingas we have seen in the past, such as in 2016. Apart from these dramatic episodesbut occasional, it is most of the time fields and roads which are flooded, because the sector is also more rural.

During Storm Kirk, wetlands of the sector thus seem to have played their role of tampon naturel. Streets and roads were affected, but few homes, because fewer of them were located just a few meters from a watercourse. The Grand Morin, on the contrary, passes two or three meters from certain houses.

Like what we observe throughout the world, climatic phenomena are intensifying in Seine-et-Marne. Should we get used to these events?

Global warming effectively increases the intensity of phenomena, regardless of their nature. In Seine-et-Marne, the measurements taken on October 9, 2024 during storm Kirk prove it: on average, it fell that day more than 50 mm of water in less than 15 hoursthat is to say as much as the usual average recorded for the month of October (58 mm, editor’s note). This is unheard of in the department!

In light of all these elements, are we heading towards a rainy end to the year?

In the coming days, the trend is calm and to drier weather. But in the long term, it is impossible to predict. For example, last June, we were expecting a dry and hot summer, when we ended up having the opposite.

On the other hand, it will be necessary be vigilant this winterbecause the level of groundwaterrivers or even retention basins, is already very high. In the event of heavy rainfall, the risk of further flooding could therefore be high.

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