The use of nature-based solutions for hydrogeological risks mitigation in Italy: insights from ReNDiS, the monitoring database of the Italian Institute for Environmental Protection and Research (ISPRA)

Hydrogeological risk is a relevant issue in Italy, given its yearly and elevated socio-economic impacts in the country, including loss of lives in case of serious hazards. In the consistent case history of measures for hydrogeological risk mitigation ISPRA has developed the National Repository of hydrogeological risk mitigation measures (ReNDiS http://www.rendis.isprambiente.it/) which is a platform for monitoring measures funded by the Italian Ministry of the Environment and Energy Security (MASE) from 1999 onwards which also aims to managing the evaluation of funding requests coming from Regions.

The ReNDiS project aims at implementing a database, collecting updated information about mitigation measures such as engineering works as well as non- structural measures. Inside the ReNDiS DB, information is organized by single “mitigation works” meaning that for every measure each stage from the financing action to design, work and accounting data are collected and stored. In order to manage heterogeneous data collected for each intervention, the choice of essential information has been restricted to: governmental funding measure, funding amount, local beneficiary authority, affected municipality, title of intervention and location. Other important information regards: geological and hydraulic characterization of the phenomenon, risk mitigation measures adopted, economic accounting for design, works and management, as well as up to date information on the actual progress stage of the intervention.

Among this information, the typology of the works and of the natural hazard to be mitigated are indicated too. From the beginning of the monitoring, in 1999, around 12 thousand measures have been already recorded in the database, amounting to over EUR 29 billion of funds. Among these entries, the 60.8% are related to landslide risk mitigation and the 36.8% to hydraulic risk mitigation, while the remaining ones are related to other risks (Figure 1).

Considering each class of natural hazard, it was observed that measures implementing nature-based solutions are the 17%, the 11.8% and the 28.8% of the total number, within the landslide, hydraulic and other risks mitigation, respectively (Figure 2).

Within the measures on landslide risk mitigation, the NBS works adopted are represented in Figure 3. The highest number of these works mainly involve vegetation cutting, selective deforestation and planting, and structures made by biodegradable materials such as wood (edging, palisades, gutters), bio-mats, bio-nets and bio-felt. Among the measures on hydraulic risk mitigation (Figure 4), the most-used NBS implemented vegetation and the use of timber and stones in structures for water regulation measures. In both cases, a good variability of measure typologies was observed.

The analysis showed that measures implementing NBSs are a conspicuous number, compared to the total, also considering their use often as a complement to more 'traditional' engineering works. 

Within the hydraulic risk mitigation measures, the use of greened weirs and stone and timber materials was preferred. In this case, the erosive forces involved and the frequent need for water regulation implied the choice of more structural materials and measures.