Is the home you want to buy in Spain in a flood zone?

What T10, T100 and T500 mean

They are the three scenarios on MITECO's flood hazard maps: T10 is the flood with a 10-year return period (high probability), T100 the 100-year flood (medium) and T500 the 500-year flood (low probability or extreme events). Spain's Public Water Domain Regulation defines the flood zone as the area the 500-year flood would reach.

MITECO's hazard maps show how far the water would reach in 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 scenario they show the expected extent of the flood and how deep the water would be.

A return period is not a timetable. A T100 zone does not flood every hundred years on the dot: it is the flood that, on average, is reached or exceeded once in that span, and it can come two years running or not for decades. The lower the number, the more frequent the flood. In legal terms, Spain's Public Water Domain Regulation defines the flood zone as the land that 500-year floods would reach.

What are ARPSI areas and the preferential flow zone?

ARPSI areas are the stretches of river and coast where each river basin authority found a significant flood risk; that is where the detailed maps were drawn. The preferential flow zone is the strip where, in a 100-year flood, water could cause serious damage, and the Public Water Domain Regulation limits uses and new works there.

ARPSI (Áreas de Riesgo Potencial Significativo de Inundación) are the stretches of river and coast where each river basin's preliminary assessment found a significant flood risk. That is where the detailed maps were drawn, so a building outside every zone may simply stand next to a stretch that has not been studied.

The preferential flow zone (zona de flujo preferente) is the strip where water concentrates during a flood and where a 100-year flood could cause serious damage. The regulation restricts new uses and building work there, and for existing buildings in flood zones it asks the authorities to encourage measures that make them less vulnerable.

How to look it up in the SNCZI viewer

The SNCZI viewer is at gis.miteco.gob.es/web/snczi (in Spanish). Search for the address or zoom in to the building, switch on the flood zone layers by return period and see whether the building falls inside any of them. Start with the 500-year layer, the widest, then the 100 and 10-year ones. If the flat is near the sea, check the coastal flooding layers too.

Look at the distance as well. Being twenty metres from the 500-year zone is not the same as being a kilometre away, even if the building is outside it in both cases. And remember that these maps model rivers overflowing and the sea: they do not show every street or garage that floods in a heavy downpour.

What does PATRICOVA add in the Valencia region?

A second map for Alicante, Castellón and Valencia. PATRICOVA, the regional government's flood plan, whose maps the Institut Cartogràfic Valencià publishes, grades flood hazard into six levels by how often the flood comes (25, 100 or 500 years) and water depth, above or below 0.8 metres. It is worth checking both maps.

In the provinces of Alicante, Castellón and Valencia, the regional government has its own plan: the territorial action plan on flood risk prevention in the Valencian Community (PATRICOVA), approved by Decree 201/2015. Its maps are published by the Institut Cartogràfic Valencià and can be viewed online.

PATRICOVA grades flood hazard in six levels that combine how often the flood comes (25, 100 or 500 years) with its depth (more or less than 0.8 metres). Level 1 is high frequency and deep water; level 6, low frequency and shallow water. It adds a geomorphological hazard for land whose shape makes it floodable even where no flood has been modelled. A property can be outside the SNCZI zones and inside a PATRICOVA zone, or the other way round, so in those three provinces it is worth checking both.

What does buying in a flood zone involve?

Above all, checking the insurance and the works you may do. Spain's Consorcio de Compensación de Seguros pays for extraordinary flood damage only if a policy covering the home is in force, and a new policy does not cover floods for its first seven days. Flood zones and preferential flow zones also limit uses and works.

In Spain, damage to a home from an extraordinary flood is paid by the Consorcio de Compensación de Seguros, a public body, but only if there is a policy in force covering the property, such as a multi-risk home policy or a combined fire or theft policy. A newly taken-out policy does not cover floods during its first seven days, unless it replaces an earlier one without a gap. If you buy with a Spanish mortgage, the bank will require damage insurance on the property; ask for a quote with the exact address.

If you plan to renovate the ground floor, convert commercial premises into a home or extend, ask the town hall and the river basin authority first, because flood zones and the preferential flow zone come with limits on use and building work. Also ask the owners' association (comunidad de propietarios) whether water has ever got into garages, storerooms or ground-floor flats, and whether protection works have been approved.

How HOUSINGFAX checks it: check 10

Check 10 of the report answers “Is it in a flood zone?”. It crosses the building's location with the official SNCZI maps: the 10, 50, 100 and 500-year zones, the ARPSI areas and the preferential flow zone; if the building is outside, it tells you how far the nearest 500-year zone is. In Alicante, Castellón and Valencia it adds PATRICOVA hazard and risk with a second map. If a source does not respond on the day, the report says “no data today”, never that there is no risk.

Start with the free report: it shows the check with your building's real data and the key information blurred. To see it in full, the essential report costs €11 and the complete report, which adds the recorded building condition, €19. That is 22 checks on official sources, as a PDF in a few minutes, with a single payment and no account. The report does not replace a technical inspection of the building.