Abstract
Abstract. The north-west (NW) Mediterranean coastal zone is a populous and well-developed area in which the impact of natural hazards like flash floods and coastal storms can result in frequent and significant damages. Although the occurrence and impacts of such hazards have been widely covered, few studies have considered their combined impact on the region, which would result in more damage. Within this context, this study analyses the occurrence and characteristics of compound extreme events of heavy rainfall episodes (as a proxy for flash floods) and coastal storms (using the maximum significant wave height) along the Catalan coast as a paradigm of the NW Mediterranean. Two different types of events are considered: multivariate, in which the two hazards occur at the same location, and spatially compounding, in which they occur within the same limited time window, and their impacts accumulate at distinct and separate locations. The analysis is regionally performed along a coastline extension of about 600 km by considering seven coastal sectors and their corresponding river catchment basins. Once the compound events are analysed, the synoptic atmospheric pressure fields are analysed to determine the prevailing weather conditions that generated them. Finally, a Bayesian network is used to fully characterize these events over the territory. The obtained results show that the NW Mediterranean, represented by the Catalan coast, has a high probability of experiencing compound extreme events. Despite the relatively small size of the study area, there are significant variations in the event characteristics along the territory, with the most frequent type being spatially compound, except in the northernmost sectors where multivariate events dominate. These northern sectors also present the highest correlation in the intensity of both hazards. Three representative synoptic situations have been identified as dominant for the occurrence of these events, with different relative importance levels of the compounding drivers (rainfall and waves) and different distributions of impacts across coastal basins. Overall, results obtained from specific events indicated that heavy rainfall is related to the most significant impacts despite having a larger spatial reach.
Highlights
Coastal zones are one of the highest risk areas in the world given the concentration of natural hazards, people, and buildings along coastlines (e.g. Kron, 2013)
(i) we quantify the occurrence frequency of the different types of compound events; (ii) we analyse the spatial variability of the different types of compound hazards and the dependence between extreme variables; and (iii) we examine the prevailing synoptic meteorological patterns during the compound events to identify whether the meteorological drivers can be distinguished in terms of event type and the intensity of the drivers
140 episodes can be classified as compound events in which wave storms are accompanied by heavy rainfall in any area along the coast
Summary
Coastal zones are one of the highest risk areas in the world given the concentration of natural hazards, people, and buildings along coastlines (e.g. Kron, 2013). Among the different hazards, flooding is currently the most frequent, dangerous, and costly (IPCC, 2012; Blöschl et al, 2020), and it is very likely to significantly increase under climate change One of the intrinsic characteristics of flooding in coastal areas is that it can be induced by different climatic drivers such as storm surge, run-up, rainfall, and/or river flow, each of which may act individually but are often interconnected (Berghuijs et al, 2019). When flooding is induced by marine drivers, such as storm surge and/or waves, impacting sedimentary coastlines, erosion occurs simultaneously. Risk assessments in coastal zones usually consider the impact of sea hazards and climate drivers individually Sanuy et al.: Classifying compound coastal storm and heavy rainfall events
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