A semi-quantitative methodology at a local scale is presented, aimed at increasing the efficacy of Land Use Planning related to the Management of risks, in particular for multiple risks impinging on the same territory (Multi-risks). At the moment, each risk is managed through a dedicated sectorial plan, having its proper procedures and scale, and the only meeting point for these plans - at least in Italy - are the Municipal city plans. The Municipalities have to implement the contents related to the various risks and directly intervene on the territory, but the lack of linkage and coordination between the plans and the authorities in charge often makes the emergency management and LUP less effective towards the achievement of a real safety of territories. A semi-quantitative approach, based on an index scale from 0 to 3 onwards was developed for a direct use from Municipal technicians; the proposed scale is applied to measure both the impact of the risks and risk interaction. The methodology is composed by 4 steps: 1) characterization of the risks; 2) assignation of the ratings to the risks; 3) assessment of binary risk interactions; 4) assessment of the compatibility and planning phase. Each step is accompanied by GIS mapping. The methodology was tested on two Italian case-studies, two Municipalities affected by multiple types of risks which could interact; the proposed approach demonstrated to be able in identifying and bring multi-risks aspects to the attention of the decision makers, constituting a guide to risk that can be integrated with the existing planning instruments to improve the quality of decisions related to risks.
The paper presents a further step in the research related to the methodology, investigating the influence on the interaction values provoked by the discretion in the assignation of the rating operated by the users. A sensitivity test was developed on one of the case studies analysed with the methodology; the interaction values demonstrated to be sensitive to the variations of the ratings, in particular in the zones near the change of scale intervals.