How do you read Spain's official flood map without speaking Spanish?

Is this Spanish flat in a flood zone?

Open the SNCZI viewer of the Spanish Ministry for the Ecological Transition (gis.miteco.gob.es/web/snczi), find the building and switch on the flood zone layers for the 10, 100 and 500-year return periods. If the building falls inside the 500-year area, it is in a flood zone in the legal sense of Spanish water law.

The viewer is free and needs no account, but its menus, legends and help are in Spanish. This guide is a reading companion for people who do not read Spanish comfortably: what each layer means, which words you will see and how to note the result. What a flood zone means for the purchase itself, and how the HOUSINGFAX report checks it, is on our flood-zone page.

What do T10, T100 and T500 mean on the map?

They are return periods. MITECO maps three scenarios: high probability, linked to a 10-year return period (T10); medium probability, 100 years (T100); and low probability or extreme events, 500 years (T500). For each one the maps show how far the water would spread and how deep it would be.

A return period is an average, not a timetable. A T100 flood is the one reached or exceeded, on average, once in a hundred years; it can happen two years running or not for decades. The lower the number, the more often that area floods. In Spanish law, the flood zone (zona inundable) is the land that 500-year floods would reach (Royal Decree 849/1986, article 14), so T500 is the widest layer and the one to switch on first.

How do you read the SNCZI viewer, step by step?

Search for the municipality or zoom in to the street, switch on the flood zone layers from widest to narrowest (500, 100, then 10 years), and look at where the building sits. Then add the preferential flow zone and note the distance to the nearest coloured area.

Words you will meet in the viewer and in its documents: «zona inundable» is flood zone; «periodo de retorno» is return period, written T=10, T=100 or T=500 años (years); «probabilidad alta, media, baja» is high, medium, low probability; «calado» or «profundidad» is water depth; «zona de flujo preferente» is the preferential flow zone; «Dominio Público Hidráulico (DPH)» is the public water domain, the river beds that belong to the State; «ARPSI» is an area with significant potential flood risk; «inundación fluvial» is river flooding and «inundación costera», coastal flooding.

Write down three things: whether the building is inside any layer and which one, whether it is inside the preferential flow zone, and roughly how far it is from the edge of the 500-year area. A screenshot with the date helps when you later ask your lawyer, the owners' association or an insurer. The national hazard maps are drawn at a working scale of 1:25,000, so at street level treat the edge of a layer as an approximation, not a line on the pavement.

What is the preferential flow zone and why does it matter?

It is the strip where floodwater concentrates. Spanish law defines it as the main floodway plus the area where, in a 100-year flood, water would be more than 1 metre deep, flow faster than 1 metre per second, or where depth times speed exceeds 0.5 m²/s. It is the most restrictive layer on the map.

For a buyer it matters for two reasons. Serious damage is most likely there, and the authorities restrict new uses and building works in it. Article 14 bis of the regulation also asks the authorities to promote measures that make existing buildings in flood zones less vulnerable. If the flat is in that strip, ask the town hall and the river basin authority (confederación hidrográfica) before planning works on a ground floor or a change of use.

What if the building is outside every zone?

It means no official map marks it; it does not mean there is no risk. Under Royal Decree 903/2010, detailed hazard maps are drawn for the areas that each river basin's preliminary assessment found to have a significant potential risk, the ARPSI. A street next to an unstudied stream can show nothing at all.

The maps are also reviewed on a six-year cycle (article 21 of the same decree), and MITECO's current national river hazard layers carry an update date of 20 December 2024. Look at the distance to the nearest mapped zone, the ARPSI stretches nearby and the terrain: a flat twenty metres from the 500-year edge is not in the same position as one a kilometre away. Ask the owners' association whether water has ever got into garages, storerooms or ground floors.

On the coast there is one more nuance. Article 8 of Royal Decree 903/2010 says that, in coastal areas with an adequate level of protection, the hazard map is limited to the low-probability scenario. So on a seafront you may see only the 500-year layer: the absence of the 10 and 100-year layers does not mean water cannot arrive sooner, only that the stretch was mapped that way. If the flat is by the sea, look at coastal flooding too and ask about past storms.

What does a flood zone mean for insurance, a mortgage and works?

In Spain, flood damage from an extraordinary event is paid by the Consorcio de Compensación de Seguros, a public body, but only if the home has a policy in force covering at least one usual risk, such as fire, theft or window breakage, typically a multi-risk home policy with payments up to date.

If you buy with a Spanish mortgage, the bank will normally ask for damage insurance on the property, so ask for a quote with the exact address before signing the arras. If you plan to renovate a ground floor, convert commercial premises into a home or extend, check first with the town hall, because flood zones and the preferential flow zone come with limits on uses and works.

What does check 10 of the HOUSINGFAX report tell you?

Check 10 answers «Is it in a flood zone?». It crosses the building's location with the official SNCZI layers (10, 50, 100 and 500-year zones, ARPSI areas and the preferential flow zone) and, when the building is outside, gives the distance to the nearest 500-year zone. In the Valencian Community it adds the regional PATRICOVA plan.

You get it in English, with a map on an aerial photo and the building marked, and the source and date of each lookup. If an official source does not answer on the day, the report says there is no data today, never that there is no risk. Start with the free report; the Essential report costs €11 and the Complete report, with the recorded building condition, €19: 22 checks on official sources, as a PDF within minutes, one-off payment, no account.

What are the limits of the flood map?

The SNCZI maps model river and coastal flooding in the studied stretches. They do not record every street that floods in a downpour, nor say when a flood will come or whether water will get into a given flat. A report built on these records does not replace an on-site technical inspection of the building.

Treat the map as the first question, not the last answer. With the layer, the distance and the owners' association's history of water in the building, you can decide whether to ask for an insurance quote, a specialist's opinion or a condition in the arras contract.