Assessing the Effects of Climate Change on Compound Flooding in Coastal River Areas

Abstract

Globally, floods are the most common natural hazard and have major economic, social, and ecological impacts on communities (CRED & UNISDR, 2015). Coastal river areas concentrate population, infrastructure, and economic activity, all of these highly vulnerable to floods (Koks et al., 2015). The effects of global warming in such already flood-prone areas raise concerns about future flood conditions, making imperative the need for reliable methods for their analysis (Seneviratne et al., 2012) and innovative approaches to their planning and management. These challenges, however, have been insufficiently addressed by regulations and policies. In the European Union (EU), the EU Floods Directive (2007/60/CE) and the Water Framework Directive (2000/60/ EC) establish the framework for assessing and managing flood risks. It defines a cycle that includes a preliminary assessment to identify areas at risk of flooding, the creation of flood hazard and risk maps, and the establishment of flood risk management plans focused on prevention, protection, and preparedness. It also establishes that these steps need to be reviewed every 6 years, and acknowledges the need to take into account the likely impact of climate change on the magnitude and frequency of floods. The European Water Framework Directive does not go beyond these procedural obligations, leaving open the question as to which methodological approaches are most appropriate for such flood risk assessments.The prediction of flooding in coastal river areas is not an easy task due to the complexity and interaction of the underlying physical processes. Elevated water levels in coastal reaches originate from the interaction of several coastal and inland drivers, such as storm surge and river discharge. These flood drivers are often not independent since they share a common meteorological forcing. For example, the combined effects of low atmospheric pressure and strong winds associated with synoptic-scale storms can induce storm surges along the coast. Concurrently, or in close succession, heavy precipitation increases freshwater runoff, and as a result leads to high river discharge. Elevated sea levels can block or slow down river drainage into the sea, leading to increased upstream water levels. Compared to flood events caused by a single driver, compound floods can usually be expected to yield higher impacts, as evidenced, for example, in the recent floods in Ravenna (Italy) (Bevacqua et al., 2017) or in the Hurricane Harvey Flood in Houston Area (Valle-Levinson

Quantitative Stress Test of Compound Coastal‐Fluvial Floods in China's Pearl River Delta

“…Second, the quantitative stress test framework applied in this study can be viewed as a simplified and targeted climatological-hydrodynamic approach, which is originally proposed by Lin et al (2012). To our best knowledge, this climatological-hydrodynamic methodology tends to be a standard workflow to quantify how global warming affects the compound flood hazards caused by storm surge, sea-level rise, and extreme rainfall in coastal cities (Bermúdez et al, 2021;Ganguli et al, 2020;Garner et al, 2017;Gori et al, 2022;Lin & Emanuel, 2016;Marsooli et al, 2019;Marsooli & Lin, 2020;Rezaie et al, 2021). Instead of driving the hydrodynamic model by large ensembles of synthetic TCs, which are statistically generated from reanalysis or GCM-projected future climate, our framework is based on the physically consistent storylines depicting several worst-case scenarios, making it possible to achieve the same goal but at the minimal computational cost.…”

“…Bermúdez et al. (2021) employ a continuous simulation approach that considers seasonality and correlation between different flood drivers to assess compound flood hazards in Mandeo Delta under historical and future climates. The climatological‐hydrodynamic methodology used in these studies tend to be a standard framework to explore the impact of global warming on compound flood hazards in river deltas.…”

“…Statistical methods are routinely used to investigate possible compound mechanisms by examining statistical dependence between proxy variables of different flood types regionally or globally, such as rainfall and storm surge (Lai et al., 2021; Sanuy et al., 2021; Zellou & Rahali, 2019; Zheng et al., 2014), river flow and storm surge (Couasnon et al., 2020; Nasr et al., 2021b), and river flow and sea level (Ghanbari et al., 2021; Piecuch et al., 2018; Ward et al., 2018). Numerical models are widely applied to simulate tide, storm surge, river flow, and their nonlinear interactions on coastal inundation dynamics locally, for example, in Mississippi Delta (Bunya et al., 2010), Ganges‐Brahmaputra‐Meghna Delta (Ikeuchi et al., 2017), Lee River Delta (Olbert et al., 2017), Shoalhaven Delta (Kumbier et al., 2018), Pearl River Delta (PRD) (De Dominicis et al., 2020), Humber and Dyfi Delta (Harrison et al., 2021), Breede Delta (Kupfer et al., 2021), and Betanzos Delta (Bermúdez et al., 2021). To perform a robust and integrated assessment, intrinsic characteristics of statistical and numerical methods are suggested to be linked for representative compound flood hazard assessments (Moftakhari et al., 2019).…”

Future Changes in High and Low Flows under the Impacts of Climate and Land Use Changes in the Jiulong River Basin of Southeast China

“…These extreme events may have a negative impact on biodiversity [6], crop yields [7], human health [2] and on various other socioeconomic factors [8]. Coastal areas typically have dense populations, concentrated urban construction and developed economies that are highly vulnerable to extreme floods [9,10]. Thus, it is imperative to explore the potential changes in future flow regimes by considering both climate change and human activities under global warming and socioeconomic development to formulate adaptation and mitigation strategies, especially for coastal basins [11].…”

Sea Level Rise Impact on Compound Coastal River Flood Risk in Klaipėda City (Baltic Coast, Lithuania)

“…To develop an accurate future flood risk assessment, it is necessary to assess all factors related to flood hazards in the context of climate change. The vulnerability of coastal river reaches is growing due to the increasing number of extreme hydrometeorological events caused by climate change [1][2][3][4][5]. Thus, the assessment of compound flooding with respect to climate change scenarios in coastal river reaches has become more relevant.…”