Landslides, avalanches, floods and earthquakes: what the maps say, hamlet by hamlet

To find out whether a piece of land is exposed to a landslide, an avalanche or a flood, you do not look at the view: you look at four maps.

• The PAI, the hydrogeological plan for the basins of the Isonzo, the Tagliamento, the Piave and the Brenta-Bacchiglione, approved by decree on 21 November 2013. For Sappada, which lies in the Piave basin, it maps landslide hazard and avalanche hazard.²³
• The flood risk management plan of the Eastern Alps district, approved on 1 December 2022: since 2023 it has been the sole reference for water, while the PAI still applies to landslides and avalanches.⁷
• The municipal land-use plan, with its F2 zones for unstable ground and avalanche sites.¹⁰
• The regional avalanche register, which records how far the known avalanches have reached.⁵

The PAI classes run from P1, moderate hazard, to P4, very high. They do not pass judgement on a house: they say what may be built there and what may not. Classes P3 and P4 carry the strictest restrictions.²⁴

Within the municipality the regional landslide hazard map counts 26 areas, covering about 68 ha. Almost all of that surface is in the two upper classes: 18 areas in P3 covering about 33 ha, and 5 in P4 covering about 33 ha. The lower classes account for 3 areas, about 2 ha.¹

The largest areas are on the mountainsides, far from the hamlets. Near the hamlets there are small ones, between 0.09 and 0.93 hectares, on the slope above the built-up area. The table gives, for each hamlet, the distance from its centre to the nearest P3 or P4 area.

Then we counted the buildings. In all, 3 buildings have their centre in a P3 or P4 area: two at the upper edge of Bach, one on its own. Around the hamlet centres 30 buildings stand less than fifty metres from a P3 or P4 area, and 19 of them are in Granvilla. In Cretta 11 buildings fall within the P1 area, the lowest class.¹¹³

The rules are set out in the PAI regulations, and they tighten as the class rises.²

In short: in P3 a house can be lived in, maintained, restored and renovated, but it cannot be split into more dwellings and can be extended only a little; in P4 it can be maintained without adding dwelling units. Every project in these classes must come with a technical report on the hazard.²

The land-use plan adds a step. Work inside the unstable zones or “in the immediate surroundings” calls for further investigation, and any project, public or private, that does not concern existing buildings must be preceded by geological and geotechnical checks.¹⁰

The Region's register records 164 avalanche sites that touch the municipality, surveyed in the field or known from historical records: 124 are dated 1988, 19 are dated 2025. They cover about 1,281 ha, 20.6% of the municipality; adding the areas identified from aerial photographs brings the total to about 1,784 ha, 28.7%.⁵

The PAI map for Sappada, drawn up in February 2012, uses the same two families of perimeters, those surveyed on the ground and those from photo interpretation: class P2 where there is only one, P3 where they overlap. Applying its criterion to today's layers, P3 would cover about 902 ha, 14.5% of the municipality. This is our own reconstruction: the official map is what counts.⁶⁵

For houses the picture is clear. None of the 1,341 buildings around the hamlet centres falls within a site; those inside number 17, all far from the hamlets, in the gullies and high up. The hamlet centre closest to a site is that of Cima Sappada, at about 381 m; on its edge 10 buildings stand less than a hundred metres from two small sites, whose avalanches start just above the village.⁵¹³

Flood hazard is covered by the flood plan. Outside the river areas it divides the land into three classes, from P1 to P3, and marks as attention zones the land where there are reports of possible instability but no class yet.⁸

In the municipality the river areas, that is the riverbeds, cover about 54 ha; the attention zones about 649 ha; the classified areas about 14 ha. There are 9 buildings inside an attention zone and 2 in class P1; none in P2 or P3.⁹¹³

Cretta is the valley-floor hamlet: its centre is about 7 m from the river area of the Piave. For a new development beside the river in Cretta, the land-use plan set the levels of the buildings one metre above the level of the Piave's hundred-year flood, as required by the Genio Civile, the public works engineering office.⁹¹⁰

A practical rule: in the river areas and in those of high or medium hazard, no basements or semi-basements may be built; in those of moderate hazard, only with means of getting out safely. In an attention zone, until the plan classifies it, the rules for high hazard apply.⁸

In the classification of the Dipartimento della Protezione Civile, Italy's civil protection department, updated to 31 May 2025, Sappada is in zone 2: “in this zone strong earthquakes are possible”. For this zone the reference value of ground acceleration lies between 0.15 and 0.25 g, with a ten per cent probability of being exceeded in fifty years.¹¹

Ravascletto is in zone 2, like Sappada; Tarvisio and Forni Avoltri are in zone 3.¹¹

For a buyer one question matters: when the house was built, and under which rules. Before any work on the structure, the answer comes from an engineer, not from the listing.

The Italian building standards, the Norme tecniche per le costruzioni, set for each altitude the ground snow load that structures are designed for. The provinces of Udine and Belluno are in zone I – Alpine, where the value grows with the square of the altitude.¹²

At the altitude of the town hall it comes to 5.44 kilonewtons per square metre, about 554 kilos; at Cima Sappada 5.8, about 592 kilos. At the altitude of Tarvisio the value is 2.9, about 296 kilos.¹²

It is not a forecast of how much snow will fall: it is a statutory minimum, tied to a fifty-year return period, for those designing new structures. The roof of an existing house was calculated under the rules of its time: to find out, ask for the design, or have it checked.¹²

• The plot on the PAI map sheets for the municipality of Sappada: one for avalanches, four for landslides, published by the basin authority.⁶²
• The same plot on the flood plan, which the district publishes on its map portal.⁹
• The land-use plan zone, and whether the plot falls in an F2 zone or next to one.¹⁰
• For an old house, the year of construction, the structural filings and the work done after a heavy winter.
• For land or an isolated hay barn, the avalanche register too, which has more recent surveys than the PAI map.⁵

The overlay is done by a surveyor, an architect or a geologist, before signing and not after.

For the homes we handle, before the listing goes up, we overlay the plot on the PAI, flood plan and land-use plan maps, and write in the property details what comes out. We do not say “no risk”: we say what the maps say, with the date. When a geological report is needed, a geologist signs it.

If you own a home in Sappada and are thinking of selling, this is where we start: our written valuation also sets out what the maps say about your plot, so the buyer reads it from us rather than discovering it at the notary's.