Compounding effects of sea level rise and fluvial flooding

Abstract

Sea level rise (SLR), a well-documented and urgent aspect of anthropogenic global warming, threatens population and assets located in low-lying coastal regions all around the world. Common flood hazard assessment practices typically account for one driver at a time (e.g., either fluvial flooding only or ocean flooding only), whereas coastal cities vulnerable to SLR are at risk for flooding from multiple drivers (e.g., extreme coastal high tide, storm surge, and river flow). Here, we propose a bivariate flood hazard assessment approach that accounts for compound flooding from river flow and coastal water level, and we show that a univariate approach may not appropriately characterize the flood hazard if there are compounding effects. Using copulas and bivariate dependence analysis, we also quantify the increases in failure probabilities for 2030 and 2050 caused by SLR under representative concentration pathways 4.5 and 8.5. Additionally, the increase in failure probability is shown to be strongly affected by compounding effects. The proposed failure probability method offers an innovative tool for assessing compounding flood hazards in a warming climate.sea level rise | coastal flooding | compound extremes | copula | failure probability F looding hazard, characterized by the intensity/frequency of flood events (1), is an important consideration in local level planning and adaptation (2). Coastal cities are especially demanding sites for flood hazard assessment because of exposure to multiple flood drivers such as coastal water level (WL), river discharge, and precipitation (3, 4). Furthermore, dependence among the flood drivers [e.g., coastal surge/tide, sea level rise (SLR), and river flow] can lead to compound events (5) in which the simultaneous or sequential occurrence of extreme or nonextreme events may lead to an extreme event or impact (6). For example, in estuarine systems, the interplay between coastal WL and freshwater inflow determines the surface WL (and hence the flood probability) at subtidal (7) and tidal (8-11) frequencies.In the United States, flood hazard assessment practices are typically based on univariate methods. For example, procedures for rivers often treat oceanic contributions (e.g., tides and storm surges) using static base flood levels (e.g., ref. 12), and do not consider the dynamic effects of coastal WL (e.g., ref. 13). Similarly, flood hazard procedures for coastal WLs (e.g., ref. 14) do not account for terrestrial factors such as river discharge or direct precipitation into urban areas. Previous studies indicate that univariate extreme event analysis may not correctly estimate the probability of a given hydrologic event (15,16). This points to the potential importance of multivariate analysis of extreme events in coastal/estuarine systems and consideration of compounding effects between flood drivers (6). Bivariate extreme event analysis has been explored in a coastal context with different variables and in different areas (5, 17-33) (see SI Appendix, Table S2 for more details). B...

Storm surge and extreme river discharge: a compound event analysis using ensemble impact modelling

“…Poulin et al (2007), who used families of copulas to study the joint behavior of river flood peaks and flood volumes, demonstrated that 25 resulting joint return periods are significantly sensitive to the choice of the copula model and inclusion of tail dependence in the analysis. Recent studies, such as Bevacqua et al (2017) and Moftakhari et al (2017) for the US coast and Italy respectively, further explored the importance of multivariate (copula) analysis of compound events related to coastal flooding including sea water level and river discharge. Also, these studies confirmed a substantial decrease in return periods if the compound occurrence probability of related events was considered.…”

Climate‐Induced Changes in the Risk of Hydrological Failure of Major Dams in California

“…The failure probability concept, which quantifies the likelihood of experiencing a flood with a given magnitude at least once within a given design lifetime of a structure, is of interest to the engineering design of hydrological infrastructures (Moftakhari et al, 2017;Read & Vogel, 2015). The failure probability concept, which quantifies the likelihood of experiencing a flood with a given magnitude at least once within a given design lifetime of a structure, is of interest to the engineering design of hydrological infrastructures (Moftakhari et al, 2017;Read & Vogel, 2015).…”

“…Response of streamflow to precipitation depends on different factors, such as spatial distribution of precipitation event, temperature, catchment size, and land use land cover change (Li et al, 2018;Sharma et al, 2018;Wasko & Sharma, 2017). However, potential changes in the intensity and frequency of precipitation events will change flooding hazard (Moftakhari et al, 2017;Sadegh et al, 2018a). Different studies have projected an increasing trend in river flood hazard under a warmer climate condition (Arnell & Gosling, 2016;Dankers et al, 2014;Hirabayashi et al, 2013;Kundzewicz et al, 2014;Slater & Wilby, 2017;Winsemius et al, 2016), which is anticipated to change failure risks of water infrastructure systems.…”

Multihazard Scenarios for Analysis of Compound Extreme Events

“…The interdependence between two or more hazard drivers, which may not necessarily be extreme events individually, may trigger significant extreme impacts—a phenomenon known as a compound event (Leonard et al, ; Mehran et al, ; Vahedifard et al, ; Wahl et al, ). Compound events (or impacts) may occur as a result of one of the following situations (Field, ): (1) two or more simultaneous or successive extreme events (e.g., simultaneous extreme precipitation and storm surge, Moftakhari et al ()), (2) combinations of extreme events with underlying conditions that amplify the impact (e.g., droughts and heat waves, Mazdiyasni & AghaKouchak, ), or (3) combinations of events that are not themselves extreme but collectively lead to an extreme event or impact (e.g., a moderate coastal flood occurring during above average tide, Moftakhari et al, ).…”