Flood risk in Spain: reading the official flood maps before you buy

If you are looking at a house on Spain's Mediterranean coast, you probably remember the DANA of 29 October 2024. It left buyers with a practical question. Can water reach this plot? Spain answers it with an official map system, the Sistema Nacional de Cartografía de Zonas Inundables (SNCZI), run by the environment ministry MITECO and the river basin authorities (organismos de cuenca) so that citizens can see the flood hazard of a given area.

The maps are precise where they exist. Where they stop matters as much as what they show.

What do Spain's official flood maps show?

They show where rivers and the sea are expected to flood in three scenarios, how deep the water gets, and where public land along rivers begins.

MITECO set up the SNCZI following the principles of the EU Floods Directive 2007/60. The rules for the maps are in Real Decreto 903/2010, which transposes the directive and covers floods from rivers, mountain torrents and other watercourses as well as floods caused by the sea on the coast (Art. 2). Building rules come from the Reglamento del Dominio Público Hidráulico (RDPH, Real Decreto 849/1986). Both are quoted here in their consolidated texts in the BOE, the RDPH as updated on 03.06.2026 and RD 903/2010 as updated on 29.12.2016.

Open the viewer at your address and you see overlapping coloured areas. Each one means something different:

• High probability (alta probabilidad): the area flooded by an event the viewer links to a return period of 10 years (T=10).
• Medium probability (probabilidad media): Article 8 RD 903/2010 requires a scenario with a return period of 100 years or more.
• Low probability (baja probabilidad): the extreme scenario with a return period of 500 years. It also marks the legal flood zone (zona inundable), defined in Article 14 RDPH as the land that a 500-year flood can reach.
• Preferential flow zone (zona de flujo preferente): the channel where floodwater mainly runs, joined with the area where a 100-year flood could seriously harm people and property.
• Public water domain (dominio público hidráulico, DPH): the river bed itself, with a 5-metre easement strip for public use (zona de servidumbre) and a 100-metre control zone (zona de policía) beside it (Art. 6 RDPH).
• Coastal flooding (origen marino): separate hazard maps for flooding by the sea, shown in the viewer for T=100 and T=500.

For each scenario the hazard maps show the expected extent of the flood and the water depth (Art. 8 RD 903/2010). The RDPH puts hard numbers on "serious harm" in the preferential flow zone. Any one of three conditions is enough: water deeper than 1 m, a flow speed above 1 m/s, or a product of the two above 0.5 m²/s (Art. 9 RDPH).

The public water domain comes in two stages: first an estimated boundary drawn from a technical study, later possibly a formal demarcation (apeo y deslinde).

What does a "100-year flood" mean for a single year of ownership?

A 1 per cent chance in any given year. It does not mean one flood per century, and a flood last winter does not use up the next hundred years.

RD 903/2010 defines the return period (Art. 3 h) as the inverse of the probability that a flood above a given level occurs in one year. Turned round, each scenario gets a fixed yearly probability:

1. High probabilityT=10 years10 per cent in any single year (1/10), worked out from Art. 3 h RD 903/2010
2. Medium probabilityT=100 years1 per cent in any single year (1/100), worked out from Art. 3 h RD 903/2010
3. Low probabilityT=500 years0.2 per cent in any single year (1/500); also the edge of the zona inundable

No legal text spells these percentages out; they are the arithmetic of the definition. For the chance over several years, say the term of a mortgage, the official sources give no figure.

Where do you find the maps, and how current are they?

The SNCZI viewer is open to everyone on MITECO's website. Look for the date. MITECO's guide to the viewer says the last update of the hazard and risk maps for a zone is shown in the detailed information for that zone, inside the viewer itself.

Under Article 21 RD 903/2010, hazard and risk maps had to be reviewed by 22 December 2019 and every six years after that. Each new set goes out for public consultation for at least 3 months (Art. 10) and then feeds the flood risk management plan (Plan de Gestión del Riesgo de Inundación, PGRI) of its river basin district. So check two dates. One is the update date for your area. The other is whether a newer set of maps is in consultation, because consultation maps are drafts.

What does a blank spot on the map tell you?

Only that no flood zone has been drawn there.

Article 8 RD 903/2010 requires hazard maps for the areas that a preliminary assessment has picked out as having a potentially significant flood risk, the Áreas con Riesgo Potencial Significativo de Inundación (ARPSI), and MITECO adds that the maps can cover further areas beyond them. So the SNCZI is no full register of flood risk across Spain. An address outside every mapped area has not been assessed. That is a different finding from "no risk", and while no official text puts it in one sentence, it follows from the rule that mapping is limited to selected areas.

On the coast one more rule applies. Where a stretch of coast has an adequate level of protection, Article 8 RD 903/2010 allows the hazard map to show only the low-probability scenario. A missing 100-year layer on a beach can simply reflect that rule.

How often does an address fall into a blank spot? Claronda checks each property in its reports against the SNCZI river layers. On 30.09.2026 that covered 466 properties.

The 47 hits split by layer as follows: 8 properties in the 10-year area, 16 in the 100-year area and 29 in the 500-year area. Eighteen touched the estimated public water domain and 2 a formally demarcated one. A property can lie in several layers at once. The picture differs sharply from province to province:

• Murcia24of 78 checked, 23 not mapped
• Alicante9of 88 checked, 50 not mapped
• Valencia3of 42 checked, 25 not mapped
• Málaga3of 22 checked, 14 not mapped
• Girona3of 18 checked, 4 not mapped
• Barcelona2of 66 checked, 45 not mapped
• Almería1of 21 checked, 14 not mapped
• Tarragona0of 41 checked, 30 not mapped
• Illes Balears0of 49 checked, 43 not mapped

Read the zeros with care. In the Balearic Islands, 43 of the 49 properties lie outside any mapped river area, so the zero says little about where those houses stand in relation to water. Murcia is the opposite case: 24 of 78 properties had a hit, 6 of them in the 10-year area and 11 in the 100-year area.

The coast looks similar. In an earlier run on 29.09.2026 covering 435 properties, 6 lay in a mapped coastal flood layer, all 6 in the 500-year scenario and 5 also in the 100-year one, while 395 were outside any mapped coastal area. These figures describe the properties Claronda has checked, chosen by auctions and customer requests, and are no sample of Spain.

What did the 2024 DANA change for the maps?

Mostly the timetable, and with it the status of the new maps for the Júcar basin.

DANA stands for Depresión Aislada en Niveles Altos, an isolated low-pressure system at high altitude, according to the state weather service AEMET. Together with other factors it can bring very intense, locally torrential rain. Not every DANA does. AEMET notes that the heavy damage comes from intense storms or persistent rain, not from the DANA as such, and since October 2025 it names those DANAs expected to have a high impact, which requires orange or red warnings.

For a buyer, what counts is where water goes once it falls. Real Decreto 903/2010 names floods from rivers, torrents and other watercourses, and floods from the sea. MITECO's viewer guide sorts the hazard maps the same way, into floods of river origin and floods of marine origin. If a plot sits in a hollow or below street level, look at that on site as well.

According to MITECO, the effects of the DANA of October 2024 delayed the preparation of maps in many areas. The hazard maps of the third cycle for the Júcar river basin district (Demarcación del Júcar) are out for public consultation. They are not yet approved. After the DANA of 29 October 2024 a recovery and resilience plan was drawn up for the Comunitat Valenciana, as an advance on the revised Júcar flood risk management plan, which is due for approval in 2027. Separately, Real Decreto-ley 6/2024 set out urgent measures for damage caused by the DANA between 28 October and 4 November 2024 in the municipalities listed in its annex.

Which building rules follow from the lines on the map?

The rules bite when you build, extend or convert. Buying an existing house in a flood zone does not trigger them on its own.

The relevant articles are 9 bis, 9 ter and 14 bis RDPH, last amended by Real Decreto 665/2023 and in force in that version since 20.09.2023. They hinge on one question. Was the land rural (suelo rural) or already urbanised on 30 December 2016?

Preferential flow zone, rural land. Article 9 bis rules out, among other things, new buildings, extensions of the footprint or volume of existing buildings, basements and underground garages. Small agricultural buildings of at most 40 m² are allowed as an exception, under conditions.

Preferential flow zone, urbanised land. New residential use is allowed only at a height that a 500-year flood does not reach (Art. 9 ter). Before work starts, the developer needs a certificate from the land registry (Registro de la Propiedad) showing an entry that the building lies in the preferential flow zone.

Flood zone. On land that was rural on the cut-off date, new buildings should be placed outside the flood zone as far as possible, and new residential use must sit above the 500-year flood level (Art. 14 bis). The same land registry certificate is required before work starts.

In each case the developer signs a responsible declaration (declaración responsable) stating that they know and accept the flood risk; in the preferential flow zone it also commits them to pass that information on to anyone who may be affected. Outside a licence procedure, it goes to the water authority at least one month before work begins. Works in the 100-metre control zone need prior authorisation or a declaración responsable as well (Art. 9 RDPH). Classification as a flood zone changes neither the legal status of the land nor who owns it (Art. 14 RDPH). For existing buildings, the authorities are to promote measures that reduce vulnerability. The RDPH sets no duty for the seller of an existing house to tell the buyer about a flood zone, and since the registry entry is a duty for new works, an older house may carry none.

What should you check before you sign?

1. Pin down the exact location of the plot by its cadastral reference (referencia catastral) and find that point in the SNCZI viewer.
2. Check first whether the spot is mapped at all. If it lies outside every mapped area, note an open question, not an all-clear.
3. Switch the layers on one at a time, including the preferential flow zone, the public water domain and, near the sea, the coastal maps.
4. Read the update date for the area in the viewer's detailed information, and check whether newer maps are out for consultation.
5. On site, look at where the nearest river, stream or dry watercourse runs and whether the plot lies lower than its surroundings.
6. If you plan to extend or rebuild, ask the Confederación Hidrográfica and the ayuntamiento what Articles 9 bis, 9 ter and 14 bis RDPH allow on that plot.
7. Ask your insurer from which date the buildings or contents policy covers extraordinary floods through the Consorcio.

A Claronda property check runs the SNCZI river and coastal layers for one address and states plainly when a spot is not mapped. You can start a property check for the house you are considering.

In short

The SNCZI viewer shows river floods for 10, 100 and 500-year events and coastal floods for 100 and 500 years. A 100-year flood means a 1 per cent chance in any year. The maps cover selected risk areas only, so a blank spot is unassessed ground. After the 2024 DANA the new Júcar maps are still in consultation. For works on a specific plot, the river basin authority and the town hall decide.