Abstract
Duration is a key characteristic of floods influencing the design of protection infrastructures for prevention, deployment of rescue resources during the emergency, and repartition of damage costs in the aftermath. The latter financial aspect mainly relies on the insurance industry and allows the transfer of damage costs from the public sector to the private capital market. In this context, the cost of catastrophes affecting a large amount of insured properties is partly or totally transferred from insurance companies to reinsurance companies by contracts that define the portion of transferred costs according to the temporal extent of the flood events synthesized in the so-called hours clause. However, hours clauses imply standard flood event durations, such as 168 h (1 week), regardless of the hydrological properties characterizing different areas. In this study, we firstly perform a synoptic-scale exploratory analysis to investigate the duration and magnitude of large flood events that occurred around the world and in Europe between 1985 and 2016, and then we present a data-driven procedure devised to compute flood duration by tracking flood peaks along a river network. The exploratory analysis highlights the link of flood duration and magnitude with flood generation mechanism, thus allowing the identification of regions that are more or less prone to long-lasting events exceeding the standard hours clauses. The flood tracking procedure is applied to seven of the largest river basins in Central and Eastern Europe (Danube, Rhine, Elbe, Weser, Rhone, Loire, and Garonne). It correctly identifies major flood events and enables the definition of the probability distribution of the flood propagation time and its sampling uncertainty. Overall, we provide information and analysis tools readily applicable to improve reinsurance practices with respect to spatiotemporal extent of flooding hazard.
Highlights
Introduction and motivationNatural disasters such as hurricanes, earthquakes, and floods can cause large losses at regional and national scales and can affect financial markets because of their consequences on society, economy, and finance
We firstly perform a synoptic-scale exploratory analysis to investigate the duration and magnitude of large flood events that occurred around the world and in Europe between 1985 and 2016, and we present a data-driven procedure devised to compute flood duration by tracking flood peaks along a river network
Reinsurance contracts can be either proportional or non-proportional, where the former implies that the reinsurer accepts a fixed share of liabilities assumed by the primary insurer, whereas in the latter, which is known as excess of loss reinsurance, the reinsurer only becomes liable to pay if the losses incurred by the ceding company exceed some predetermined value (Carter 1983, p. 70)
Summary
Natural disasters such as hurricanes, earthquakes, and floods can cause large losses at regional and national scales and can affect financial markets because of their consequences on society, economy, and finance (insurance, catastrophe bonds, etc.). The 2011 Thailand floods were more problematic as they lasted 2–3 months and many reinsurance contracts did not have aggregate caps to limit the number of losses (Courbage et al 2012; Haraguchi and Lall 2015) In this case, intense rainfall events did not span few days, but affected the northern regions of Thailand early in the monsoon season (March and April). This situation was further exacerbated by heavy rainfall from four tropical storms, which doubled runoff (Komori et al 2012; Ziegler et al 2012; Gale and Saunders 2013; Takahashi et al 2015) These examples from heterogeneous regions are paradigmatic and indicate the importance of defining flood events and their duration or propagation time along a river network in order to set up more effective and efficient mitigation strategies along with clear and fair (re)insurance policies helping avoid legal controversies (England and Wales High Court 2013; Lees 2014).
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