Flood zones P1, P2 and P3 in Italy: what they mean

Italian flood maps use three codes: P3, P2 and P1. They show the flood hazard (pericolosità idraulica), that is how likely an area is to be flooded. For anyone buying a house this is one of the most useful pieces of information, and one of the most often misunderstood.

The three scenarios

The levels come from the EU Floods Directive of 2007, adopted into Italian law in 2010. Each level corresponds to a scenario:

"One every 100 years" is a statistical average, not a calendar: a P2 area can flood twice in a few years and then stay dry for a long time.

The areas sit one inside the other: a P3 area is normally also P2 and P1, because a rare flood covers more land than a frequent one. A house "only in P1" is therefore outside the P2 and P3 areas.

Hazard and risk are not the same thing

Hazard is about how likely the event is. Risk (levels R1 to R4) combines the hazard with what is in the area: homes, roads, businesses, people. For a buyer, the starting point is the hazard at the location; the risk to your own home then depends on how it is built.

Which maps are binding

There are several maps and they may not match:

• PGRA, the flood risk management plan (Piano di gestione del rischio di alluvioni) for each river basin district, updated every six years;
• PAI, the hydrogeological plans of the river basin authorities, which contain the rules on what can be built;
• ISPRA's national map (mosaicatura), which combines the river basin authorities' maps into a single layer you can view on IdroGEO. The latest national version for floods dates from 2020.

The national map is handy for a first check, but it has no legal value and does not include later updates. For an official check you need the plan of the river basin district authority and the planning documents of the Comune (the local council), which may add further restrictions.

What to ask if the house is in a P2 or P3 area

A house in a flood-prone area is not necessarily one to rule out. Many historic centres and lowland neighbourhoods are in P2 areas. But the questions change:

1. Are there basement or semi-basement rooms? Cellars, garages and basement rooms are the first to flood. A bedroom or kitchen below street level is a very different situation from a second-floor flat.
2. How high is the ground floor? A few steps above the street make a difference.
3. Has the building ever flooded? Ask the seller, the building manager and the neighbours; look for news of recent events in the area.
4. Are there flood defences? Sump pumps, non-return valves on drains, flood barriers for entrances.
5. What do the planning rules say? In some areas basement rooms cannot be made habitable and extensions are not allowed.
6. How much does insurance cost? For private homes flood insurance is not compulsory in Italy, but in a P3 area the premium can be high: it is better to get a quote before buying.

How to check an address

On IdroGEO you can search for the address and turn on the flood hazard layer. Our report does the same check on the building's cadastral parcel: it tells you whether the parcel is in a P3, P2 or P1 area, how much of it is covered and what lies within 100 metres, with the version of the map used.

The other checks on the area, from landslides to earthquakes, are gathered in What to check before buying a house in Italy.