Panel 1
Carla Iadanza, Alessandro Trigila
The indicator provides information on the landslide-prone areas of the Hydrogeological Management Plans (PAI) on the national territory. The total surface area, in Italy, of the PAI landslide hazard areas and the areas of attention is equal to 69,530 km 2 (23% of the national territory), of which 28,801 km 2 (9.5%) are areas of high P3 and very high P4 danger, subject to the most restrictive land use constraints.
The indicator provides information on the areas at risk from landslides delimited in the Hydrogeological Management Plans (PAI), drawn up by the District Basin Authorities (formerly Basin Authorities) and, for the territories of respective competence, by the Autonomous Provinces of Trento and Bolzano. The areas at risk from landslides include, in addition to landslides that have already occurred, also the areas of possible evolution of the phenomena and the areas potentially susceptible to new landslide phenomena.
ISPRA has developed the new national mosaic (v. 5.0 - 2024) of the dangerous areas of the Hydrogeological Management Plans - PAI, according to the legend harmonized in 5 classes for the entire national territory: very high danger P4, high P3, medium P2, moderate P1 and AA attention areas. The legend was defined by ISPRA in 2015, in line with the Guidance and Coordination Act (Prime Ministerial Decree of 29 September 1998), and used for previous versions of the mosaic.
Provide a framework on the landslide hazard areas of the PAI on a national, regional, provincial and municipal basis.
Collection, processing, archiving and dissemination of data regarding soil protection and hydrogeological instability referring to the entire national territory (art. 55 of Legislative Decree 152/2006 “Regulations on environmental matters”); D. L. 180/98 “Sarno Decree” converted into Law 267/1998, Prime Ministerial Decree of 09/29/98 (Guidance and coordination act), L. 365/00.
Panel 2
Trigila A., Lastoria B., Iadanza C., Bussettini M., Mariani S., D'Ascola F., Salmeri A., Cassese M. L., Pesarino V., Di Paola G., Romeo S., Rischia I., Dessì B., Spizzichino D., Licata V., Gallozzi P. L. (2025) Hydrogeological instability in Italy: hazards and risk indicators - 2024 Edition. ISPRA, Reports 415/2025
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Data quality assessment
National mosaicing: https://idrogeo. isprambiente. it/
Cartography of Hydrogeological Management Plans: sites of the District Basin Authorities and the Autonomous Provinces of Trento and Bolzano.
National, Regional, Provincial, Municipal
2024
Indicator assessment
The mosaicking of the areas at risk from landslides was carried out through the analysis and harmonisation, according to a legend in 5 classes for the entire national territory (very high danger P4, high P3, medium P2, moderate P1 and AA attention areas), of the data provided by the District Basin Authorities and the Autonomous Provinces of Trento and Bolzano.
the surface area of the landslide-prone areas of the PAI was then calculated on a regional, provincial and municipal basis.
The total surface area, in Italy, of the PAI landslide hazard areas and the areas of attention is equal to 69,530 km 2 (23% of the national territory), of which 28,801 km 2 (9.5%) are areas of high P3 and very high P4 danger, subject to the most restrictive land use constraints.
At present, a trend for the indicator cannot be defined due to the limitations of the historical series available (2015, 2017, 2021, 2024).
Data
Table 1: Landslide hazard areas PAI at regional level – Mosaic 2024
ISPRA
* ISTAT administrative boundaries 2024
** The Autonomous Region of Valle d’Aosta has adopted, for areas classified as high and medium hazard, constraints comparable respectively to P4 and P3; therefore, in the national reclassification it was considered appropriate to give priority to land protection measures rather than to the adopted nomenclature.
*** It should be noted that the landslides, largely newly formed, triggered following the hydrometeorological events of May 2023 in Emilia-Romagna and mapped in the framework of the drafting of the Preliminary Special Plan of interventions on hydrogeological instability situations (Decree Law 1 June 2023, no. 61 converted, with amendments, by Law 31 July 2023, no. 100), at the date of the Mosaic (v. 5.0 – 2024) were not included in the PAI perimeters. The Po District Basin Authority has initiated the updating procedures.
**** With regard to the territory of Calabria, the data was calculated on the basis of the Hydrogeological Setting Plan – Landslide Risk – PAI 2001 of the territories of the former Regional Basin Authority of Calabria (approved by the Institutional Committee with Resolution no. 13 of 29/10/2001, by the Regional Council with Resolution no. 115 of 28/12/2001; subsequent Resolutions of the Institutional Committee of the Regional Basin Authority of Calabria no. 26 of 02/08/2011 PAI FR and FI Updating Procedures and no. 27 of 02/08/2011 Updated Text of the Implementation Rules and Safeguard Measures – NdA).
In the previous ISPRA Report on hydrogeological instability in Italy – 2018 Edition, the data had instead been calculated on the basis of the Update Project of the Hydrogeological Setting Basin Plan – PAI 2016 (Note from the Secretary General of the Regional Basin Authority of Calabria of 24/06/2016 Prot. no. 0203855), initiated with the approval of the “Procedures for updating the Landslide Risk of the Calabria PAI – New Hazard and Landslide Risk Maps” (Resolution of the Institutional Committee no. 3 of 11/04/2016), for which the former Regional Basin Authority of Calabria had started the consultation phase with local authorities.
This Draft Plan did not complete the adoption process. The Southern Apennines District Basin Authority is currently carrying out the review and updating of all thematic layers related to the physical system, landslide phenomena and landslide hazard.
The data are affected by mapping and classification inconsistencies, mainly due to the different methodologies used by the District Basin Authorities and the Autonomous Provinces for the assessment of landslide hazard.
Table 2: Landslide hazard areas PAI at provincial level – Mosaic 2024
ISPRA
*ISTAT administrative boundaries 2024
The data are affected by mapping and classification inconsistencies, mainly due to the different methodologies used by the District Basin Authorities and the Autonomous Provinces for the assessment of landslide hazard.
Figure 1: Landslide hazard areas PAI on the national territory – Mosaic 2024
ISPRA
Figure 2: Percentage of territory with high hazard P3 and very high hazard P4 landslide areas at municipal level – Mosaic 2024
ISPRA
Figure 3: Mosaic of PAI landslide hazard areas on the ISPRA IdroGEO Platform
ISPRA
The total surface area, in Italy, of the PAI landslide hazard areas and the areas of attention is equal to 69,530 km 2 (23% of the national territory) (Figure 1). The surface area of the areas with very high landslide danger is equal to 10,598 km 2 (3.5%), the highly dangerous one is equal to 18,203 km 2 (6%), with medium danger at 18,074 km 2 (6%), moderately dangerous at 15,489 km 2 (5.1%) and the areas of attention are equal to 7,165 km 2 (2.4%). Considering the most dangerous classes (high P3 and very high P4), subject to the most restrictive land use constraints, the areas amount to 28,801 km 2, equal to 9.5% of the national territory.
From the Mosaic analysis of landslide hazards on the national territory (Figure 1), local inhomogeneities in mapping and classification emerge.
Tuscany, Emilia-Romagna, Valle d'Aosta, Campania, Sardinia, Piedmont, Abruzzo, Lombardy and the Autonomous Province of Trento present the largest surfaces (in km 2) at high risk P3 and very high risk P4 (Table 1).
From the comparison between the 2024 ISPRA national Mosaicing and that of 2020-2021, a 15% increase in the overall surface classified by the PAI (classes P4, P3, P2, P1 and AA) and 9.2% in the most dangerous classes (high P3 and very high P4) emerges. Between the 2020-2021 ISPRA national mosaicing and the 2017 one, the percentage increase was 0.8% of the total surface classified by the PAI and 3.8% of the most dangerous classes; between Mosaicing 2017 and 2015, it was 2.9% of the overall surface and 6.2% in P3-P4. These changes are mainly linked to the integration/revision of the perimeters by the District Basin Authorities and the Autonomous Provinces, also with more detailed studies or in areas not previously covered and to the mapping of new landslide phenomena. The most significant increases in the high and very high risk surface area between the 2024 and 2021 national mosaics concerned the Autonomous Province of Bolzano, the regions of Sardinia, Sicily and Tuscany.
The national mosaic (Figure 3) can be consulted on the IdroGEO national platform ( https://idrogeo. isprambiente. it/).