Author(s): Silvia Santato; Jaroslav Mysiak; Mattia Amadio; Stefano Bagli; Paolo Mazzoli; Ricardo Tavares da Costa; Attilio Castellarin; Alessio Domeneghetti; Gunter Humer; Andreas Reithofer

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Keywords: Pluvial flooding; Urban hazard assessment; Nature-based solutions; Climate services; Flood risk mitigation

Abstract: Intense short-term precipitation events are projected to increase further across Europe. This work develops and tests services for a detailed, effective and fast-processing spatial pluvial-flooding hazard assessment, including incentives for risk reduction. Flood risk is accountable for the largest economic losses in Europe and in Italy and is expected to increase further due to warming of the earth and the intensification of the hydrological cycle. Global warming is projected to lead to higher intensity of precipitation as well as longer dry periods in Europe. Modelled projections of extreme precipitation events indicate an increase in the frequency, intensity and/or amount under future climate in Europe, and events currently considered extreme are expected to occur more frequently in the future. The floods caused by high river stages and storm surges are addressed by the Floods Directive (2007/60/EC) via the hazard mapping and assessment. However, the hazard arising from spontaneous overland runoff from extreme precipitation events in urban context have received little attention so far. The ensuing hazard maps have predominantly been designed for fluvial hazards and in a form (scale) that is unable to drive adaptation and risk mitigation in urban contexts. This is partly because hydraulic modelling in complex urban environments characterized by high degree of impermeable soil and presence of drainage/sewage network are associated with high costs. Furthermore, whereas nature-based solutions to climate risk are promoted, because of their co-benefits, evidence based and operational knowledge services designed for comprehensive assessments of these solutions are not yet fully developed. This study explores technical feasibility of cost effective hazard modelling based on a combination of state-of-the art hydraulic and hydrodynamic modelling capable of reducing the computational complexity, and delineation of hazard prone areas using downscaling modelling techniques, which exploit statistical relations between hazard characteristics and geomorphic indices (i.e., a combination of height, distance, area and slope data as well as hydrological characteristics) and hierarchical filling and spilling algorithm. This combination of small-scale efficient hydraulic modelling and innovative hazard delineation using proxies makes it possible to speed up the hazard assessment and substantially reduce the associated costs. The other part of the study tackles the understanding of i) how this innovative hazard and risk assessment tool can be deployed for the sake of design and evaluation of nature-based solutions in urban context, and ii) how to harness insurance and other financial instruments to protect or restore risk-mitigating ecosystem services. Nature-based solutions may mitigate natural hazard risks, by mediation of flows and nuisances; or through maintenance of physical, chemical, biological conditions in the face of pressures; through mass stabilisation, water flow regulation especially flood control, wind dissipation, and (micro- and regional) temperature regulation. Recognition of ecosystem services can motivate insurers and other stakeholders to protect or restore the ecosystems. The ultimate goal of our study is the design of a climate service that assesses the pluvial flood hazard in urban context, sheds light on how unsustainable land-use (soil sealing) and urban planning contributes to increased damage and loss, and explores incentives which insurers and public authorities may use to foster individual and collective risk reduction efforts.

DOI: https://doi.org/10.3850/978-981-11-2731-1_196-cd

Year: 2018