Abstract
Abstract. Floods are one of the most frequent and damaging natural threats worldwide. Whereas the assessment of direct impacts is well advanced, the evaluation of indirect impacts is less frequently achieved. Indirect impacts are not due to the physical contact with flood water but result, for example, from the reduced performance of infrastructures. Linear critical infrastructures (such as roads and pipes) have an interconnected nature that may lead to failure propagation, so that impacts extend far beyond the inundated areas and/or period. This work presents the risk analysis of two linear infrastructure systems, i.e. the water distribution system (WSS) and the road network system. The evaluation of indirect flood impacts on the two networks is carried out for four flooding scenarios, obtained by a coupled 1D–quasi-2D hydraulic model. Two methods are used for assessing the impacts on the WSS and on the road network: a pressure-driven demand network model and a transport network disruption model respectively. The analysis is focused on the identification of (i) common impact metrics, (ii) vulnerable elements exposed to the flood, (iii) similarities and differences of the methodological aspects for the two networks, and (iv) risks due to systemic interdependency. The study presents an application to the metropolitan area of Florence (Italy). When interdependencies are accounted for, results showed that the risk to the WSS in terms of population equivalent (PE/year) can be reduced by 71.5 % and 41.8 %, if timely repairs to the WSS stations are accomplished by 60 and 120 min respectively; the risk to WSS in terms of pipe length (km yr−1) reduces by 53.1 % and 15.6 %. The study highlights that resilience is enhanced by systemic risk-informed planning, which ensures timely interventions on critical infrastructures; however, for indirect impacts and cascade effects, temporal and spatial scales are difficult to define. Perspective research could further improve this work by applying a system-risk analysis to multiple urban infrastructures.
Highlights
Linear infrastructure systems such as the water supply system (WSS), electricity and transportation are considered critical infrastructures (CIs) because their failure would jeopardize public health and economic security, with repercussions on the whole society (Fekete, 2019; Tarani et al, 2019; Lhomme et al, 2013)
The impact to water distribution system (WSS) is classified as “high” when the municipality is affected by a loss of functionality of the unique source of water supply, “medium” is when a municipality might rely upon an alternative water source but still will experience some loss of service and “low” is when the municipality does not experience loss of service
Downstream neighbourhoods are served by local water tanks; they are favoured by lower terrain elevations; their nodes are affected later than those in the city centre (Fig. 5a, green dots)
Summary
Linear infrastructure systems such as the water supply system (WSS), electricity and transportation are considered critical infrastructures (CIs) because their failure would jeopardize public health and economic security, with repercussions on the whole society (Fekete, 2019; Tarani et al, 2019; Lhomme et al, 2013). CIs are exposed to natural hazards, such as flooding; in particular, ∼ 7.5 % of road and rail infrastructures are exposed to a 1-in-100-year flood event worldwide (Koks et al, 2019). Flooding can damage CIs directly (when impacts are due to the physical contact with floodwaters, i.e. direct impacts) and indirectly (when impacts are not due to the physical contact and/or occur outside the inundated area in space or time, i.e. indirect or cascade impacts). Changes in socio-economic and climatic conditions, as well as infrastructure interdependencies, could aggravate both direct and indirect impacts in the future (Pregnolato et al, 2017a; Evans et al, 2020). Lyu et al, 2018) and direct flood impacts (Winter et al, 2016; Kellermann et al, 2016).
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