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Nat. Hazards Earth Syst. Sci., 19, 2855–2877, 2019 https://doi.org/10.5194/nhess-19-2855-2019 © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. Changes in flood damage with global warming on the eastern coast of Spain Maria Cortès1,2, Marco Turco3,*, Philip Ward5, Josep A. Sánchez-Espigares6, Lorenzo Alfieri7, and Maria Carmen Llasat1,2 1Department of Applied Physics, University of Barcelona, 08028 Barcelona, Spain 2Water Research Institute (IdRA), University of Barcelona, 08001 Barcelona, Spain 3Barcelona Supercomputing Center (BSC), 08034 Barcelona, Spain *Now at: Regional Atmospheric Modeling (MAR) Group, Department of Physics, University of Murcia, 30100 Murcia, Spain 5Institute for Environmental Studies (IVM), Vrije Universiteit Amsterdam, 1081 HV Amsterdam, the Netherlands 6Department of Statistics and Operations Research, Polytechnic University of Catalonia, 08028 Barcelona, Spain 7European Commission, Joint Research Centre (JRC), Ispra, Italy Correspondence: Maria Cortès ([email protected]) Received: 30 July 2019 – Discussion started: 1 August 2019 Revised: 21 November 2019 – Accepted: 25 November 2019 – Published: 18 December 2019 Abstract. Flooding is one of the main natural hazards in are included. When population is considered, all the periods the world and causes huge economic and human impacts. and models show a clearly higher increase in the probability Assessing the flood damage in the Mediterranean region is of damaging events, which is statistically significant for most of great importance, especially because of its large vulner- of the cases. ability to climate change. Most past floods affecting the re- Our findings highlight the need for limiting global warm- gion were caused by intense precipitation events; thus the ing as much as possible as well as the importance of includ- analysis of the links between precipitation and flood dam- ing variables that consider change in both climate and so- age is crucial. The main objective of this paper is to esti- cioeconomic conditions in the analysis of flood damage. mate changes in the probability of damaging flood events with global warming of 1.5, 2 and 3 ◦C above pre-industrial levels and taking into account different socioeconomic scenarios in two western Mediterranean regions, namely Cat- alonia and the Valencian Community. To do this, we anal- 1 Introduction yse the relationship between heavy precipitation and flood- damage estimates from insurance datasets in those two re- In the Mediterranean region, intense precipitation events gions. We consider an ensemble of seven regional climate constitute a real danger to the population. Heavy precipi- model (RCM) simulations spanning the period 1976–2100 to tation, sometimes associated with strong winds, can cause evaluate precipitation changes and to drive a logistic model floods, with dire consequences for people and the environ- that links precipitation and flood-damage estimates, thus de- ment (Fourrie et al., 2016) particularly during the autumn riving statistics under present and future climates. Further- season. Most of these events are a consequence of short and more, we incorporate population projections based on five local heavy rains in small catchments, often near the coast different socioeconomic scenarios. The results show a gen- in densely populated areas (Thiébault, 2018). The relief sur- eral increase in the probability of a damaging event for most rounding the Mediterranean Sea forces the convergence of of the cases and in both regions of study, with larger incre- low-level atmospheric flows and the uplift of warm wet air ments when higher warming is considered. Moreover, this masses that drift from the Mediterranean Sea to the coasts, increase is higher when both climate and population change thereby creating active convection. In addition, population growth is particularly high along the Mediterranean coasts, Published by Copernicus Publications on behalf of the European Geosciences Union. 2856 M. Cortès et al.: Future flood damage leading to a rapid increase in urban settlements and popula- in future risk projections, which clearly contribute substan- tions exposed to flooding (Gaume et al., 2016). tially to changing risks. In the last few years, much research has focused on the Insurance data may provide a good proxy for describing study of climate change in the Mediterranean region, an area flood damage (Barredo et al., 2012), and several studies note that is identified as highly vulnerable to climate change ac- their potential for describing economic damage caused by cording to the “Fifth Assessment Report” of the Intergovern- surface water and urban floods (Spekkers et al., 2013; Torg- mental Panel on Climate Change (IPCC, 2014). Some studies ersen et al., 2015; Cortès et al., 2018). However, there are have found an increase in precipitation extremes with global still few studies that relate flooding to insurance data, since warming projections in the Mediterranean region (Colmet- these companies are reluctant to provide their databases, and Daage et al., 2018; Drobinski et al., 2018), although a general some of them are not even available due to confidentiality re- decrease in the annual precipitation is projected (Jacob et al., strictions (André et al., 2013; Leal et al., 2019). Nevertheless, 2014; Cramer et al., 2018; Sillmann et al., 2013; Rajczak and in the Mediterranean region, 20 years of flood-related insur- Schär, 2017). Cramer et al.(2018) state that future warming ance damage claims are available from the Spanish public in the Mediterranean region is expected to exceed the global reinsurer, the Insurance Compensation Consortium (Consor- mean rates by 25 %, with peaks of 40 % in summer. As a re- cio de Compensación de Seguros – CCS), for the Spanish sult, flood risk associated with extreme precipitation events regions of Catalonia and the Valencian Community. CCS is a is expected to increase due to climate change in this area but public institution that compensates homeowners for damage also due to non-climatic factors such as increasingly sealed caused by floods, playing a role similar to that of a reinsur- surfaces in urban areas and ill-conceived storm-water man- ance company (Barredo et al., 2012). Therefore, in this study, agement systems (Cramer et al., 2018). insurance data are used as a proxy for flood damage. A large number of floods affecting the western Mediter- The main objective of this paper is to estimate changes in ranean region are surface water floods (Llasat et al., 2014; the probability of damaging flood events with global warm- Cortès et al., 2018). This type of flood can be regarded as ing of 1.5, 2 and 3 ◦C above the pre-industrial levels, tak- coming under the most general definition of rainfall-related ing into account different socioeconomic scenarios. To do floods (Bernet et al., 2017; Cortès et al., 2018). For this rea- this, we analyse the relationship between heavy precipitation son, precipitation is the main hazard driver of the damage and flood-damage estimates from insurance datasets in two caused by these events. western Mediterranean regions, namely the Valencian Com- Nevertheless, flood disasters are the result of both soci- munity and Catalonia regions of Spain. We use an ensemble etal and climatological factors; hence several other drivers of seven regional climate model (RCM) simulations and five other than climate must be considered for the assessment of different socioeconomic scenarios to study future changes in flood-damage trends (Barredo, 2009). Bouwer(2011) anal- these relationships. yses 22 disaster loss studies around the globe, showing that This article is organized as follows. After an Introduction, economic losses from various weather-related natural haz- the Methods section describes the study region, the data used ards have increased. However, most of these studies have and the methodology describing the model developed for the not found a trend in disaster losses after normalization for present climate, and the treatment applied for the future pre- changes in population and wealth, pointing towards increas- cipitation and population projections. Then, the Results and ing concentrations and values of assets as the principle cause discussion section presents the statistical models developed, of the increasing damage and losses from natural disasters. the analysis of the future data, and the probability of flood In Spain, the findings of Barredo et al.(2012) align with damage with global warming, comparing our results with these results; they find no significant trend in adjusted in- those obtained in other studies. Finally, a section describing sured flood losses between 1971 and 2008. Other studies the limitations of the study and possible future research is such as López-Martínez et al.(2017) and Pérez-Morales presented, followed by the Conclusions, which summarize et al.(2018) also mention the vulnerability and exposure the main findings of this study. components as possible drivers responsible for the increasing flood risk in Mediterranean regions of Spain. Specif- ically, these studies mention the institutional vulnerability 2 Methods (Raschky, 2008), which represents the sensitivity of public administrations to dealing with hazards as one of the main Figure1 describes the overall methodology followed in this causes. Also, Pérez-Morales et al.(2018) demonstrated that study and the data used. After selecting the flood events that the exposure in flood-prone areas in the south-east of Spain have affected the region of study, we collected information (part of the region of study) has increased in the last decades on damage (insurance payments), hazard (precipitation) and due to poor management of these areas by government in- exposure (population) for each basin affected by these events stitutions and the regulation adopted by them. These studies (panel 1). These data have been used to develop general- show the need to include exposure and vulnerability changes ized linear mixed models in order to assess the probability of damaging events for the present climate (panel 2). Pre- Nat. Hazards Earth Syst. Sci., 19, 2855–2877, 2019 www.nat-hazards-earth-syst-sci.net/19/2855/2019/ M.

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