Photo: Cham · CC BY-SA 4.0

–Not graded

Flood & hazards in Trets · Géorisques

Shrink-swell clay lies under the homes of 100% of Trets’ residents

What the state records for Trets: natural-disaster declarations since 1982, risk plans, mapped flood zones, clay ground, earthquake zone, radon and industrial sites. Hazard risk is not graded in France: there is no national flood map, so a town outside the mapped areas can’t be called safe from floods.

22natural disasters declared since 1982 0.3%of residents in a mapped flood zone Zone 2earthquake zone, low

By hazard

6 hazards in Trets at a glance

Bars show where the town sits among French towns of 2,500+; they are not a grade. Disaster declarations are shown, not compared.

Not on this page: wildfire maps and storm-surge levels: France publishes them only as plans.

Not graded

Why hazards aren’t graded in France

In the UK, the Hazard risk grade is the share of homes in a mapped flood zone; in the U.S., it is FEMA’s modelled yearly damage to buildings. Both rest on maps that cover the whole country. France maps flood zones in detail only in its 125 areas at highest risk (TRI), so most towns have no figure, and a blank would read as “dry”. The state’s disaster declarations don’t fill the gap: they depend on the mayor applying, and they don’t line up with the mapped zones. So Trets has no Hazard grade, and its overall grade uses the other six subjects.

Everything on this page is shown as published. We’ll grade it when France publishes a national flood map.

Flood map

Flood zones in Trets on the map

The state’s own layers from Géorisques, drawn over the street map. Tap a layer to switch it on or off.

Medium-probability flood zone (about 1 in 100 years)Mapped area (TRI)Clay: lowmediumhighTrets (commune boundary)

Flood zones are drawn only inside the state’s mapped areas (TRI, pink outline). Outside them, the map is blank because nobody has drawn it, not because the ground is dry.

Flood zones

0.3% of Trets’ residents live in a mapped flood zone

Residents in the state’s medium-probability flood zones, by where the water comes from. Mapped areas only.

Rivers0.3%of residents where a river can overflow

Runoff0%where heavy rain runs off

The sea0%where the sea can flood in

Where Trets sits among the 1,643 French towns of 2,500+ with a flood map

27%None

15%Under 1%Trets

22%1–5%

13%5–10%

11%10–20%

8%20–40%

2%40–60%

3%60%+

Share of residents in a medium-probability flood zone. Trets has more than 35% of mapped towns. The other 2,833 towns of 2,500+ have no detailed map.

Against the 40 mapped towns nearest its size: 14th of 41, from fewest to most residents in a flood zone

#	Town	People	In a flood zone
1	Saint-Saulve Nord	10,947	0%
2	Riorges Loire	11,139	0%
3	Chassieu Rhône	11,208	0%
…
12	Passy Haute-Savoie	10,856	0.2%
13	Le Pradet Var	10,933	0.3%
14	Trets Bouches-du-Rhône	10,946	0.3%
15	La Chapelle-Saint-Mesmin Loiret	11,017	0.6%
16	Brissac Loire Aubance Maine-et-Loire	10,878	0.6%
…
40	Pélissanne Bouches-du-Rhône	11,085	26%
41	La Riche Indre-et-Loire	10,487	98%

Mapped area: – (flood directive maps, 2nd cycle, 2020). Medium probability is roughly the 1-in-100-year flood. Residents placed by INSEE’s 200 m income grid (2021).

Disaster history

22 natural disasters declared in Trets since 1982, 7 for floods

The state’s register of natural-disaster orders, 1982 to January 2026.

2023Floods and mudflowsJune 13, 2023 · order published October 20, 2023
2023Drought: clay subsidenceApril 1, 2023 – June 30, 2023 · order published July 2, 2024
2022Floods and mudflowsNovember 1, 2022 · order published December 30, 2022
2022Drought: clay subsidenceApril 1, 2022 – September 30, 2022 · order published May 3, 2023
2021Drought: clay subsidenceApril 1, 2021 – September 30, 2021 · order published August 5, 2022
2019Floods and mudflowsOctober 22–23, 2019 · order published December 19, 2019

Show all 21 events

2019Drought: clay subsidenceApril 1, 2019 – September 30, 2019 · order published September 3, 2020
2017Drought: clay subsidenceApril 1, 2017 – September 30, 2017 · order published July 27, 2018
2016Drought: clay subsidenceApril 1, 2016 – December 31, 2016 · order published September 1, 2017
2014Floods and mudflowsOctober 13, 2014 · order published February 19, 2015
2008Floods and mudflowsDecember 14–15, 2008 · order published April 22, 2009
2007Drought: clay subsidenceJuly 1, 2007 – September 30, 2007 · order published August 13, 2008
2007Drought: clay subsidenceJanuary 1, 2007 – March 31, 2007 · order published August 13, 2008
2002Drought: clay subsidenceJanuary 1, 2002 – June 30, 2002 · order published May 22, 2003
1998Floods and mudflowsSeptember 7, 1998 · order published January 13, 1999
1998Drought: clay subsidenceApril 1, 1998 – June 30, 1998 · order published December 29, 2000
1993Drought: clay subsidenceOctober 1, 1993 – March 31, 1998 · order published August 22, 1998
1992Drought: clay subsidenceJanuary 1, 1992 – September 30, 1993 · order published March 17, 1995
1989Drought: clay subsidenceMay 1, 1989 – December 31, 1991 · order published September 3, 1993
1984EarthquakeFebruary 19–20, 1984 · order published May 24, 1984
1982Floods and mudflows · StormNovember 6–10, 1982 · order published November 19, 1982

Declarations by hazard · 1982–2025

Drought (clay)13

Flood or mudflow7

Storm, hail, snow1

Earthquake1

Each line is a state order recognizing a natural disaster in the commune (“CatNat”), which lets insured owners claim. The latest flood began June 13, 2023; 6 flood declarations since 1995.

This count partly reflects how often a mayor applies for a declaration, so it isn’t compared between towns. It is a record of recognized claims, not a flood map. Source: GASPAR, Géorisques, file of 5 October 2026 (orders published to January 2026).

Plans and listings

The state lists 7 hazards for Trets

Risk plans in force or in preparation, and the prefecture’s list of major risks.

Risk plans in force

natural and industrial

Flood atlases

none covering the town

Area at high flood risk (TRI)

not designated

Mayor’s risk booklet (DICRIM)

On file

published 2010

Hazard	Risk plan (PPR)	Listed by the prefecture
River flooding and runoff	—	✓
Landslides and rockfalls	Approved 2009	✓
Clay shrink-swell	Approved 2007	✓
Earthquake	—	✓
Forest fire	Approved 2016	✓
Old mines	—	✓
Dangerous goods in transit	—	✓

A risk plan (plan de prévention des risques, PPR) is the state’s map of where building is banned or restricted because of a hazard; it is attached to the town’s planning rules, and a seller or landlord must tell you if the home is in one. The prefecture’s file of major risks (DDRM) lists the hazards it expects in each commune.

Clay and earthquakes

Earthquake zone 2 (low); 100% of residents on shrink-swell clay

What the ground under Trets does: national maps, the same for every town.

Clay shrink-swell

Residents on shrink-swell clay · share of residents

TretsMedian in Bouches-du-RhôneMedian French town

Medium or high100%

High100%

0%50%100%

Clay ground swells when wet and shrinks in drought, which cracks walls of houses on shallow foundations. Since 2020, a soil study is required before selling a building plot in a medium or high zone. 13 drought (clay) declarations here since 1982.

Earthquake zones: share of French towns of 2,500+

Zone 1 · very low33%

Zone 2 · low ← Trets36%

Zone 3 · moderate24%

Zone 4 · medium6%

Zone 5 · strong1%

Trets is in zone 2 (low). New buildings must follow the earthquake building code (Eurocode 8) for their type. The zone sets building rules; it isn’t a forecast.

Clay: BRGM shrink-swell exposure map 2025, residents placed by INSEE’s 200 m grid. Earthquakes: national seismic zoning, decree of 22 October 2010.

Radon

Radon potential in Trets: category 2 of 3 (low, with factors that can raise it)

Radon is a natural radioactive gas from granite and volcanic rock; it builds up indoors.

Share of French towns of 2,500+ in each category

Category 166%

Category 2 ← Trets12%

Category 322%

Trets is in category 2: low potential, but faults or old mines can let radon up into some buildings.

The category describes the rocks under the commune, not any home: a test is the only way to know.

Source: radon potential by commune, IRSN (now ASNR), 2019.

Industrial sites

No industrial risk plan reaches Trets

Hazardous sites whose danger zone reaches the town, and the technological risks the prefecture lists.

Listed by the prefecture

Dangerous goods in transit	road, rail, pipeline or waterway through the town
Old mines	old mine workings

Seveso sites

upper-tier Seveso sites in Trets

lower-tier Seveso sites in Trets

Seveso sites within 5 km of the center

7.2 km

to the nearest: STMICROELECTRONICS SAS (lower tier)

Seveso sites store or use large amounts of dangerous substances; upper-tier sites have a risk plan around them. Distances are from the town’s center.

Sources: GASPAR (PPRT, DDRM), Géorisques, 5 October 2026; Seveso sites from Géorisques’ register of classified installations.

Neighbors

Hazards in Trets’ neighbors

Towns of 2,500+ within 30 km. Tap one to open its hazards page.

PeynierRoussetSaint-ZachariePourrièresLa BouilladisseAuriolTrets

Town	Flood zone*	Seismic zone	Radon
Trets	0.3%	2	2
Peynier 3,739 · 4 km	under 0.1%	2	2
Rousset 5,425 · 6 km	0.3%	2	2
Saint-Zacharie 5,879 · 7 km	—	2	2
Pourrières 5,642 · 8 km	0.2%	2	2
La Bouilladisse 6,547 · 9 km	—	2	2
Auriol 13,037 · 9 km	under 0.1%	2	2

* Share of residents in a mapped medium-probability flood zone; a dash means no detailed map, not no risk. Radon: category 1 to 3.

Be ready

Being ready in Trets

Where France publishes warnings, and what to ask before you buy or rent.

Get warnings

Météo-France’s vigilance map gives the day’s warnings by département, from yellow to red.
Vigicrues shows river levels and flood warnings for the main rivers, updated twice a day.
FR-Alert sends emergency alerts to every phone in the area; no sign-up needed.

Météo-France vigilance · Vigicrues

Buying or renting

The seller or landlord must give you a risk statement (état des risques) for the address, listing the plans it is in.
They must also tell you about any natural-disaster claim paid on the home.
Géorisques gives the same statement for any address, free.

Check an address

If water rises

Don’t drive or walk through floodwater.
Go upstairs, not to the cellar or car park.
Call 112 if you’re in danger.

Before you move to Trets

Ask for the risk statement and read which plans the address is in.
Ask the town hall for its risk booklet (DICRIM) and safety plan (PCS).
For a house, look for cracks and ask about the foundations: much of the town is on shrink-swell clay.
Check that home insurance includes natural-disaster cover (it comes with fire cover).

How to read these numbers

What this data can and can’t tell you

Not graded. France has no national flood map, so we don’t grade hazard risk. Comparisons on this page are with other French towns of 2,500+, shown for context.
Mapped areas only. Flood shares exist only where the state has mapped flooding in detail (the TRI areas). A town without a figure has no map, not no risk.
Disaster declarations. A CatNat order recognizes a disaster so that insurers pay; it follows the commune’s application. The count partly reflects how often a mayor applies, so we show it but don’t compare towns on it.
Plans. A risk plan maps where building is limited; it doesn’t say any one home will flood.
Clay, earthquakes, radon. National maps of the ground: they describe susceptibility and set building rules, not damage or forecasts.

Check any address on Géorisques

Questions about hazards in Trets

Does Trets flood?

The state has declared 7 flood disasters in Trets since 1982, the last starting June 13, 2023. On the state’s detailed map, 0.3% of residents live in a medium-probability flood zone.

Is Trets at risk of earthquakes?

Trets is in seismic zone 2 of 5 (low). The zone sets building rules for new construction; it isn’t a forecast.

Is there radon in Trets?

Radon potential is category 2 of 3 (low, with factors that can raise it). It describes the ground under the commune; only a test tells you a home’s level.

Are there dangerous industrial sites near Trets?

No industrial risk plan reaches Trets; 0 Seveso sites lie within 5 km.

Why doesn’t Trets have a Hazard grade?

France maps flood zones in detail only in its areas at highest risk, so most towns would have no figure, and a blank would look like no risk. We show the data instead, and will grade it if France publishes a national flood map.

Sources: Géorisques (Ministry of Ecological Transition), GASPAR file of 5 October 2026: CatNat orders, risk plans (PPRN, PPRT, PPRM), flood atlases, DDRM, DICRIM · flood directive maps, 2020 (TRI 2nd cycle) and 2024 outlines · BRGM clay shrink-swell map 2025 · seismic zoning, decree of 22 October 2010 · ASNR (formerly IRSN) radon potential 2019 · INSEE 200 m income grid 2021 (where residents live) · map: Géorisques layers over © OpenStreetMap contributors · Seveso sites: Géorisques register of classified installations. Licence Ouverte / Open Licence (Etalab). Not graded.

Contains public sector information under the Licence Ouverte / Open Licence 2.0 (Etalab): INSEE, DGFiP, the Interior Ministry’s statistics service (SSMSI), the Ministry of Education (DEPP), the Health Ministry’s statistics service (DREES) and the Housing Ministry (Carte des loyers). Commune boundaries: IGN Admin Express.