Journal Article

Climate Change and Changes in Compound Coastal‐Riverine Flooding Hazard Along the U.S. Coasts

Kao, Shih‐Chieh, Arabi, Mazdak, Obeysekera, Jayantha, Ghanbari, Mahshid, Sweet, William

2021

Overview

The cooccurrence of coastal and riverine flooding leads to compound events with substantial impacts on people and property in low‐lying coastal areas. Climate change could increase the level of compound flood hazard through higher extreme sea levels and river flows. Here, a bivariate flood hazard assessment method is proposed to estimate compound coastal‐riverine frequency under current and future climate conditions. A copula‐based approach is used to estimate the joint return period (JRP) of compound floods by incorporating sea‐level rise (SLR) and changes in peak river flows into the marginal distributions of flood drivers. Specifically, the changes in JRP of compound major coastal‐riverine flooding defined based on simultaneous exceedances above major coastal and riverine thresholds, are explored by midcentury. Subsequently, the increase in the probability of occurrence of at least one compound major coastal‐riverine flooding for a given period of time is quantified. The proposed compound flood hazard assessment is conducted at 26 paired tidal‐riverine stations along the Contiguous United States coast with long‐term data and defined flood thresholds. We show that the northeast Atlantic and the western part of the Gulf coasts are experiencing the highest compound major coastal‐riverine flood probability under current conditions. However, future SLR scenarios show the highest frequency amplification along the southeast Atlantic coast. The impact of changes in peak river flows is found to be considerably less than that of SLR. Climate change impacts, especially SLR, may lead to more frequent compound events, which cannot be ignored for future adaptation responses in estuary regions. Plain Language Summary Compound coastal and inland flooding poses serious threats to many coastal cities around the world. Climate change could increase the level of compound flood hazard through sea level rise (SLR) and higher extreme precipitation and river flows. An example of recent compound flooding in the US is the cooccurrence of heavy precipitation and storm surge from Hurricane Harvey, which caused huge flooding along the Gulf coast of Texas. We propose a compound flood hazard assessment method to project compound coastal‐riverine flood frequency under climate change. Coastal and riverine flood impact thresholds are used to define compound major coastal‐riverine flooding. The application of the method along the Contiguous United States coast shows that SLR is the most prominent factor in increasing the frequency of future major compound flood events and the impact of changes in peak river flows is negligible in most of the locations. Under current climate conditions, the northeast Atlantic and the western part of the Gulf coasts are experiencing the highest compound major coastal‐riverine flood probability. However, future SLR scenarios show emerging high compound major flooding probability along the southeast Atlantic coast. Key Points A bivariate flood hazard assessment method is proposed to estimate compound coastal‐riverine frequency under climate change impacts Future sea level rise scenarios show emerging high compound major flooding probability along the southeast Atlantic coast The impact of changes in peak river flows is found to be significantly less than the impacts of sea level rise

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU),Wiley
• Subject: Bivariate analysis / Climate change / Climatic conditions / Coastal climates / Coastal flooding / Coastal zone / Coasts / compound flooding / copula / Environmental impact / ENVIRONMENTAL SCIENCES / Estuaries / Flood control / Flood hazards / Flood probability / Flooding / Floods / Future climates / generalized pareto distribution / Hazard assessment / Hydrology / Infrastructure / open climate campaign / Precipitation / River flow / Rivers / Sea level / Sea level rise / Stream flow / Thresholds / Tidal waves