The rainy season has continued in France since mid-October and the western and northern regions of the country have received record levels of rainfall. How can such heavy rain be explained? It is quite possible that the unusual warming of the waters in the Channel and the Atlantic markedly increased the intensity of the rain.

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In Pas-de-Calais, rainfall totals reached 250 to 350 mm.Is By November 10, the equivalent of 3 months of rain in 10 days. Several rivers flooded, causing historic floods in the department. But why does it rain so much? Situation weather reportweather report Yet it is classic for this time of year, with the recurring westerly flow spreading marine disturbances towards France. However, it is the extraordinary intensity of the rain that raises questions. If weather conditions can be explained with a set of atmospheric and oceanic parameters, one of them plays a fundamental role: water temperature.

The warmer the water, the greater the disturbance of rain

This is unusually high, both on the Channel coast (16 °C in recent days instead of the usual 12 °C at this time), but also higher than usual. The average surface temperature over the North Atlantic Ocean is 23 °C, a record range for November since records began (compared to the 1982–2011 average of 22 °C for early November).

However, the disturbances that dump all this rain on France come from the ocean, then cross the Channel. Circulating over these unusually warm waters, they are filled with rain: the warmer the water, the greater the rainfall disturbance because increased temperatures increase evaporation of surface water. presence ofAirAir Cold at high altitude in the north of France DifferenceDifference also with HeatHeat Coastal waters, which increase rainfall. Atmospheric rivers, these rainy streaks that extend through the atmosphere from the tropics to western Europe, are also more extreme.

In its latest report, ipccipcc States that for every additional degree of global warming, there is 7% more humidity in the atmosphere. The month of October was the warmest as well as rainiest ever recorded in the world, with several episodes of extreme rainfall occurring not only in France, but across the world.

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