Hyères: Clay Soil, Subsidence and Cracks – Official Data

Hyères, drought and clay: what the GASPAR record shows

Is your house more likely to crack in Hyères than elsewhere? Yes – and the figures confirm it: the GASPAR database records 6 drought prefectoral decrees (full list below) and 16 flood decrees, i.e. 22 natural disaster declarations (Cat Nat) for the commune. On the weather side, the trend matches: two dry years (2020, 2022), then a catch-up at 812 mm in 2024 (+30%) – exactly the kind of alternation that puts foundations under strain across the Hyères plain and on the Îles d’Or.

Cassini Expertise, an independent firm, handles cracks and drought-related damage in Hyères and throughout the Var. This page sets out the commune’s official figures, with no commercial slant – keep it to hand if you need to put an insurance file together or negotiate a sale.

Natural disaster declarations (Cat Nat) in Hyères: the official record

According to GASPAR (decrees published in the Journal officiel since 1982), Hyères totals 22 natural disaster declarations. If your cracks appeared during one of these periods, you have a case:

• 6 drought prefectoral decrees (differential ground movement through clay shrink-swell (RGA))
  • event of 01/07/2016 (prefectoral decree of 25/07/2017)
  • event of 01/04/2017 (prefectoral decree of 18/09/2018)
  • event of 01/04/2019 (prefectoral decree of 07/07/2020)
  • event of 01/01/2020 (prefectoral decree of 18/05/2021)
  • event of 01/04/2022 (prefectoral decree of 03/04/2023)
  • event of 01/04/2023 (prefectoral decree of 18/06/2024)
• 16 flood prefectoral decrees and storm

Each decree covers a precise window of time. The first thing to do: place the date your cracks appeared against these periods. If they match, two routes are open – natural disaster declaration (Cat Nat) compensation (provided you declared within 30 days), or failing that an action against the seller for hidden defect (vice caché) or fraud (dol).

Is my house in a clay zone in Hyères?

The GéoRisques platform (BRGM) classifies Hyères at high exposure to clay shrink-swell (RGA), with some sectors at medium exposure. To find out for your exact plot, check georisques.gouv.fr with your address – this is the benchmark level used by insurers and notaires. Another point to check on the same record sheet: the class 3 radon potential recorded across the commune (IRSN/GéoRisques data), a health-and-building watch point if you spend time in a basement or a closed ground floor.

This classification completes the decree history above: the hazard rating says what can happen, the decrees say what has already happened. If your area is rated “high exposure” and has seen one or more dry summers, the risk of damage is all the better documented – it is not fate, but it is a signal to monitor your property.

Why dry summers crack houses in Hyères

Annual rainfall recorded on the Hyères weather grid (Open-Meteo data):

• 2019: 789 mm · 2020: 434 mm · 2021: 639 mm · 2022: 493 mm · 2023: 597 mm · 2024: 812 mm
• Average over the period: 627 mm/year, driest year: 2020 (434 mm)
• Two years in deficit: 434 mm in 2020, 493 mm in 2022
• Then a rebound to 812 mm in 2024

Shrink-swell is a two-stage mechanism worth understanding properly before worrying unnecessarily: the drought dries out the clay at depth, it shrinks, and the first cracks appear; then the rain returns, the ground rehydrates at once and swells again, triggering differential movement. If you live in a 1970-2000 villa built on shallow foundations, watch your walls 12 to 24 months after each dry summer: that is the usual delay before cracks appear.

Forty years of decrees: the full chronology for Hyères

Each line = an event recognised by an interministerial decree published in the Journal officiel (GASPAR database):

• 🔵 09/1982 → 09/1982 – Floods (prefectoral decree of 24/12/1982)
• 🔵 01/1999 → 01/1999 – Floods (prefectoral decree of 23/02/1999)
• 🔵 11/2002 – Floods (prefectoral decree of 24/02/2003)
• 🔵 05/2005 – Floods (prefectoral decree of 23/09/2005)
• 🔵 12/2008 → 12/2008 – Floods (prefectoral decree of 16/10/2009)
• 🔵 09/2009 – Floods (prefectoral decree of 07/09/2010)
• 🔵 06/2010 → 06/2010 – Floods (prefectoral decree of 14/09/2010)
• 🔵 11/2011 → 11/2011 – Floods (prefectoral decree of 18/11/2011)
• 🔵 01/2014 → 01/2014 – Floods (prefectoral decree of 31/01/2014)
• 🔵 09/2014 – Floods (prefectoral decree of 04/12/2014)
• 🔵 10/2014 – Floods (prefectoral decree of 27/04/2015)
• 🔵 11/2014 → 11/2014 – Floods (prefectoral decree of 03/12/2014)
• 🔵 12/2014 → 12/2014 – Floods (prefectoral decree of 03/03/2015)
• 🔵 06/2015 – Floods (prefectoral decree of 23/07/2015)
• 🔴 07/2016 → 09/2016 – Drought – clay shrink-swell (RGA) (prefectoral decree of 25/07/2017)
• 🔴 04/2017 → 12/2017 – Drought – clay shrink-swell (RGA) (prefectoral decree of 18/09/2018)
• 🔴 04/2019 → 09/2019 – Drought – clay shrink-swell (RGA) (prefectoral decree of 07/07/2020)
• 🔵 11/2019 → 11/2019 – Floods (prefectoral decree of 12/12/2019)
• 🔴 01/2020 → 09/2020 – Drought – clay shrink-swell (RGA) (prefectoral decree of 18/05/2021)
• 🔴 04/2022 → 09/2022 – Drought – clay shrink-swell (RGA) (prefectoral decree of 03/04/2023)
• 🔵 08/2022 – Floods (prefectoral decree of 23/08/2022)
• 🔴 04/2023 → 09/2023 – Drought – clay shrink-swell (RGA) (prefectoral decree of 18/06/2024)

Expert reading: 6 droughts and 16 floods. Clusters (several decrees close together) flag up crisis periods – the summer of 2022-2023 is the best recent example. An owner whose damage dates from a covered period has a solid Cat Nat file; outside a covered period, the way forward is an action against the seller.

What the official clay mapping says

The GéoRisques platform (BRGM) classifies Hyères at high exposure to clay shrink-swell (RGA), with some sectors at medium exposure. This is the benchmark level used by insurers and notaires to assess the risk on a plot. Worth noting: radon potential class 3 across the commune (IRSN/GéoRisques data) – a health-and-building watch point in the affected zone.

This classification completes the decree history above: the hazard rating says what can happen, the decrees say what has already happened. A house rated “high exposure” that has come through one or more dry summers carries a risk of damage that is all the better documented.

The official exposure to clay shrink-swell (RGA)

The GéoRisques platform (BRGM) classifies Hyères at high exposure to clay shrink-swell (RGA), with some sectors at medium exposure. This is the benchmark level used by insurers and notaires to assess the risk on a plot. Worth noting: radon potential class 3 across the commune (IRSN/GéoRisques data) – a health-and-building watch point in the affected zone.

This classification completes the decree history above: the hazard rating says what can happen, the decrees say what has already happened. A house rated “high exposure” that has come through one or more dry summers carries a risk of damage that is all the better documented.

What 35 years of local rainfall tell us

The area’s weather archives cover 35 complete years (1991-2025). The driest ever recorded: 2007, with 382 mm over the year, against a local average of 691 mm. 2022 ranks as the 6th driest year out of 35 (493 mm against an average of 691 mm); 2023 follows in 15th place (597 mm).

This ranking gives the true measure of the recent sequence: when the years 2020-2023 sit high up the list of dry years, the clay has had no time to rehydrate between episodes – the textbook scenario for delayed cracking. The reverse is just as instructive: a very wet year following an exceptional drought triggers abrupt swelling of the ground.

Damp, water ingress and rising damp in Hyères

Damp in a wall can have four causes – rising damp, water ingress, condensation or a leak – and the treatments are completely different depending on the origin.

A reader in Hyères writes to me about damp marks at the foot of a wall. He has read online that he needs resin injections or mechanical ventilation. My message: not so fast. Each treatment matches one specific cause, and getting the diagnosis wrong means spending several thousand euros for nothing.

The 4 causes and how to recognise them

• Rising damp: water from the ground climbs into the masonry by capillary action. A halo that sits at the foot of the wall, often on older façades with no damp-proof course, with whitish salts (efflorescence) on the surface.
• Water ingress: water enters from outside (roof, gutter, crack, terrace). Localised stains, often high up or near an opening, that get worse after rain.
• Condensation: indoor water vapour trapped against a cold surface. Mould in wall corners, on roller-shutter boxes, in poorly ventilated rooms (bathroom, kitchen).
• Leak: a defective pipe or service. A stain that appears with no link to rainfall, sometimes alongside an unexplained spike in water consumption.

The trap of the diagnosis sold by the treatment contractor

In Hyères as elsewhere on the coast, many damp-treatment companies offer a “free quote”. The problem: that diagnosis is carried out by the firm that then sells the solution, and it almost always concludes rising damp – the cause that justifies the most expensive works (injections, drainage). An independent expert, with no commercial interest in the works, identifies the true cause before any money is spent.

Before commissioning works in Hyères, request an independent diagnosis. You can also read my damp guide for 06, 83 and 13 to understand the right reflexes before signing a quote.

What characterises Hyères in building surveys

In Hyères, the contrasting relief between the foothills of the Massif des Maures, the hills of Fenouillet and Costebelle, and the alluvial plain sloping down to the Giens peninsula creates highly heterogeneous ground conditions within a single neighbourhood. The built fabric is varied: Provençal villas from the 60s-70s built on shallow foundations with no prior soil survey, more recent estates won over from backfilled clay ground, and a few modern constructions on the outskirts towards l’Ayguade or la Bayorre. The subsoil, rich in the swelling clays typical of the Var fringes, reacts sharply to the alternation of damp and summer drought, intensified by the dense presence of pines and oaks whose root systems draw water from depth and locally dry out the clays around foundations. In this area we regularly see marked differential settlement on individual houses built at the edge of a slope or close to large trees, where the ground shrinks unevenly beneath the dwelling. Sloping-site villas, common on the heights of Hyères, are particularly exposed because their foundations often rest at varying depths, which encourages façade cracking, especially at the corners of openings and along the joints between extensions and the original building.

Cracks in Hyères: when to worry and who to call

• A stair-step crack, passing through the wall, open by more than 2 mm
• A crack that evolves (fit a tell-tale – a patch of plaster or a marker pen line – and check it over several months)
• associated signs: doors and windows sticking, tiles splitting diagonally, render coming away
• Aggravating factors: a house built on clay, nearby trees, failed drainage

With 6 drought prefectoral decrees already recognised for the commune, as soon as you build up several of these signs, call in an expert before any repair – and before any signature, whether buying or selling. Repairing too quickly without a diagnosis can mask damage that will keep developing.

Buying or selling a cracked house in Hyères: what the law says

With the recent drought decrees and the volume of transactions underway, quite a few properties are changing hands with damage kept quiet. If you are buying and discover cracks after signing, you have two levers:

• Hidden defect (article 1641 of the Code civil): serious cracks, not detectable at the viewing, that predate the sale → price reduction or cancellation of the sale, to be claimed within 2 years of discovery
• Fraud (dol) (article 1137): the seller knew and said nothing → cancellation plus damages, 5-year deadline; the commune’s GASPAR decree then helps underpin the file

In both cases, keep every photo, invoice or written exchange predating the sale: this is what will allow an expert to date the damage. For the legal side, appoint a property-law solicitor (avocat).

How a drought/clay survey unfolds in Hyères

• Site visit: crack survey and classification, crack-width measurement, functional damage recorded
• Context analysis: clay zone, the commune’s natural disaster declaration (Cat Nat) history (6 drought decrees), local drought episodes
• Works estimate: underpinning, injections, drainage – several costed scenarios
• A written report usable by the insurer or the solicitor

For an on-site visit: building expert in Hyères.

Independent expert, with no ties whatsoever to any building contractor. Request a visit in Hyères – also worth reading, our complete RGA and Cat Nat guide for 06, 83 and 13.

Soil surveys on clay ground: what the regulations say

The requirement for a prior geotechnical survey has applied since 1 October 2020 (ELAN law, art. 68); the new exposure map of 1 July 2026 widens its scope. This obligation, stemming from ELAN law no. 2018-1021, article 68 (decree no. 2019-495 of 22 May 2019), applies particularly to Hyères (high exposure in the BRGM classification).

• What it changes for building: the soil survey is no longer an option – the ELAN law makes it compulsory in an exposed zone for every sale of building land and every construction contract. Adapted foundations, ground treatment, drainage arrangements: the specifications flow directly from the survey.
• What it changes when buying a recent property: ask whether the survey was carried out and which specifications were applied. A house built without following the geotechnical recommendations on clay soil is a medium-term cracking risk.
• What it changes when selling: the absence of a survey on a property built before the obligation is not a defect in itself – but if damage appears, a seller who knew about it and concealed it exposes themselves to an action for fraud (dol).
• The link with the data above: Hyères combines high exposure with a well-documented history of drought decrees. Building or buying here without checking the nature of the ground means building on a known and measured risk.

Cassini Expertise handles these files: compliance checks between geotechnical specifications and execution, damage surveys on clay ground, second-opinion expert assessments. Request a consultation.

Frequently asked questions

Is Hyères among the at-risk clay zones?

Yes. The Alpes-Maritimes and the Var are largely covered by the clay shrink-swell (RGA) hazard (BRGM map, viewable on georisques.gouv.fr). In Hyères, the 6 drought decrees recognised by GASPAR show that the risk is not theoretical: it has already materialised six times since 2016.

Is my cracked house in Hyères eligible for natural disaster compensation?

Only if your damage falls within a period covered by a decree (the latest recognised drought periods: 2017, 2018, 2020, 2021, 2023, 2024) and if you declared the loss within 30 days of the decree. Failing that, the action against the seller remains – and there, precisely dating the damage through a survey becomes the decisive element.

Can the figures on this page be checked independently?

Yes: the decrees come from the GASPAR database (Journal officiel, open data, 2025 update), the rainfall from Open-Meteo archives for the Hyères grid. Cassini Expertise does not adjust these figures – you can cross-check them yourself before making a decision.

Drought right now (as at 04/10/2026)

In the commune: recent rain (3 days ago). Rainfall over the last 30 days: 34 mm, against roughly 51 mm expected at this time of year – a 33% deficit.

A sustained deficit over this window, especially in the growing season, often precedes by a few weeks the drop in the water table shown above: it is the first signal owners can track themselves, before any cracks appear.

This week’s drought watch (as at 05/10/2026)

In the commune: recent rain (4 days ago). Rainfall over the last 30 days: 34 mm, against roughly 52 mm expected at this time of year – a 35% deficit.

A sustained deficit over this window, especially in the growing season, often precedes by a few weeks the drop in the water table shown above: it is the first signal owners can track themselves, before any cracks appear.

Where does rainfall stand today? (as at 12/10/2026)

In the commune: recent rain (4 days ago). Rainfall over the last 30 days: 154 mm, against roughly 61 mm expected at this time of year – a 152% surplus.

A sustained deficit over this window, especially in the growing season, often precedes by a few weeks the drop in the water table shown above: it is the first signal owners can track themselves, before any cracks appear.

This week’s drought watch (as at 19/10/2026)

In the commune: recent rain (1 day ago). Rainfall over the last 30 days: 190 mm, against roughly 70 mm expected at this time of year – a 171% surplus.

A sustained deficit over this window, especially in the growing season, often precedes by a few weeks the drop in the water table shown above: it is the first signal owners can track themselves, before any cracks appear.

The aquifer against its historic record: what do 26 years of measurements say?

The reference piezometric station for the area (002LDFT) has been monitoring the aquifer since 2000 – 26 years of records. As at 02/10/2026, the average level over the last thirty days is 141.35 m NGF (French ordnance datum). Across the whole record, the aquifer has spent only 7.2% of its time below this level: a very low level, rarely reached in the station’s history.

• Last equivalent episode: 04/01/2024 – 2.7 years ago
• Frequency: 26 similar episodes recorded since 2000, i.e. an annual return on average – in hydrologists’ language, a rare event
• Historic minimum: 141.1 m NGF, reached on 01/10/2000

This long memory changes how the risk is read: a low level is not just a weather episode, it is an event whose frequency is known. For a house on clay, it is this frequency that tells you the probability of fresh settlement – and therefore how urgent the precautions are.

Find out more: Article 1641 of the Civil Code and the hidden defects warranty (garantie des vices cachés), explained.

Survey carried out by Frédéric Faucouneau, independent building expert – Antibes, Alpes-Maritimes (06), Var (83), Bouches-du-Rhône (13). Find out more

📅 Last updated 06/11/2026 - Cassini Expertise, independent building expert – departments 06, 83 and 13.