Abstract
Abstract. Landslides and floods, particularly flash floods, occurred recently in many Mediterranean catchments as a consequence of heavy rainfall events, causing damage and sometimes casualties. The high hazard is often associated with high vulnerability deriving from intense urbanization, in particular along the coastline where streams are habitually culverted. The necessary risk mitigation strategies should be applied at the catchment scale with a holistic approach, avoiding spot interventions. In the present work, a high-risk area, hit in the past by several floods and concurrent superficial landslides due to extremely localized and intense rain events, has been studied. A total of 21 small catchments have been identified: only some of them have been hit by extremely damaging past events, but all lie in the intense-rain high-hazard area and are strongly urbanized in the lower coastal zone. The question is what would happen if an intense rain event should strike one of the not previously hit catchments; some situations could be worse or not, so attention has been focused on the comparison among catchments. The aim of the research has been identifying a priority scale among catchments, pointing out the more critical ones and giving a quantitative comparison tool for decision makers to support strong scheduling of long-time planning interventions at the catchment scale. The past events' effects and the geomorphic process analysis together with the field survey allowed us to select three sets of parameters: one describing the morphometric–morphological features related to flood and landslide hazard, another describing the degree of urbanization and of anthropogenic modifications at the catchment scale and the last related to the elements that are exposed to risk. The realized geodatabase allowed us to apply the spatial multicriteria analysis technique (S-MCA) to the descriptive parameters and to obtain a priority scale among the analyzed catchments. The scale can be used to plan risk mitigation interventions starting from the more critical catchments, then focusing economic resources primarily on them and obtaining an effective prevention strategy. The methodology could be useful even to check how the priority scale is modified during the progress of the mitigation work realization. In addition, this approach could be applied in a similar context, even among sub-catchments, after identifying a suitable set of descriptive parameters depending on the active geomorphological processes and the kind of anthropogenic modification. The prioritization would allow to invest economic resources in risk mitigation interventions priory in the more critical catchments.
Highlights
Floods and landslides are very common in many areas of the Mediterranean basin, inducing a high geo-hydrological hazard (Canuti et al, 2001; Guzzetti and Tonelli, 2004; Luino, 2005; Luino and Turconi, 2017) and causing many casualties and significant damages every year
The question is what would happen if an intense rain event should strike one of the not previously hit catchments; some situations could be worse or not, so attention has been focused on the comparison among catchments
The past events’ effects and the geomorphic process analysis together with the field survey allowed us to select three sets of parameters: one describing the morphometric– morphological features related to flood and landslide hazard, another describing the degree of urbanization and of anthropogenic modifications at the catchment scale and the last related to the elements that are exposed to risk
Summary
Floods and landslides are very common in many areas of the Mediterranean basin, inducing a high geo-hydrological hazard (Canuti et al, 2001; Guzzetti and Tonelli, 2004; Luino, 2005; Luino and Turconi, 2017) and causing many casualties and significant damages every year. Many coastal Mediterranean areas are liable to this kind of hazard: the general climatic context, with the interface between cold air masses and the sea; the steep territory; and a complex geologic and geomorphologic context are the main natural factors In such a hazardous context the high vulnerability that characterizes most of the urbanization determines the elevated risk, while the intense anthropogenic modification of a large portion of catchments and of hydrographical networks tends to amplify the effects (Tropeano and Turconi, 2003; Nirupama et al, 2007; Audisio and Turconi, 2011; Petrea et al, 2011; Llasat et al, 2014; Faccini et al, 2018; Acquaotta et al, 2018b): impervious surfaces, induced by soil consumption and urban sprawl, increase the surface runoff and decrease the time of concentration (Shuster et al, 2007), while strictly constrained and often culverted riverbeds have frequently inadequate discharge capacity (Moramarco et al, 2005; Faccini et al, 2015b, 2016)
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