France's flood score is a flag, not a depth gauge

Each commune carries a number from 0 to 7 on the natural-hazards layer. It is reasonable to read that as a flood severity scale — the layer was labelled flood risk until we measured what it actually counts. It is not one.

The score adds three things: the commune's seismic zone, two points if a flood-prevention plan is registered, and two more if a wildfire one is. Flood enters as a flag, not as a measurement. It is worth the same two points whether the hazard is a winter stream or the Rhône.

What the number is made of

Half of metropolitan France carries the flood flag — 17,599 communes of 34,832. At 6 and above, every commune has it. Below 2, none does. In between, the same number means different things in different places.

Two points is two points

343 communes score 4 or higher with no flood flag at all — they are earthquake and wildfire country. Another 5,117 sit at a score of 2 where that 2 is the flood flag, so a commune the map colours as mid-range is one the register has flagged for water.

Read the composite for what it is: a count of how many kinds of hazard have a prevention plan on file, weighted by seismic zone. Two communes sharing a 4 can have almost nothing in common.

What this figure cannot tell you

The score is municipal and flood zoning is drawn parcel by parcel. A commune at 0 can hold a plot on a flood plain, and one at 7 can be dry on the hill. Use the number to build a shortlist; it never clears an address.

It also records that a plan exists, not that your street floods. A commune with nothing on file is not proven safe — it may simply never have been assessed.

Before the notary, take the address to Géorisques itself. Use the layer here to decide which addresses are worth looking up: open natural hazards, add property price, and work down the list.