Compound Continental Risk of Multiple Extreme Floods in the United States

Understanding spatially correlated floods and modeling joint hazard associated with threshold exceedances across multiple locations is crucial for accurate estimation of continental-scale portfolio risk. This work uses a non-parametric copula-based spatial simulator to analyze peak floods across the United States to derive the first-of-its-kind continental portfolio risk estimates at the 10- and 100-year return levels. We find significant interdependence in floods across the nation, revealing the recurring pattern of extreme events affecting the Northeast, Central, West, and Northwest United States in the same year. The stochastic simulator effectively manages high-dimensional data and offers reliable uncertainty estimates for both spatially dependent floods and the aggregated flood losses at the continental level. El Nino-Southern Oscillation and Atlantic Multidecadal Oscillation are identified as statistically significant tele-connectors of aggregate loss. This research aims to advance the understanding of compound continental flood hazard and the potential large-scale climate teleconnections that lead to such compound floods. It is important to know why past floods occurred in different parts of the United States in the same year and how they were connected to each other. This knowledge helps determine how likely it is for major annual floods to occur all across the country in the future. Consequently, an understanding of what drives such total annual flood losses each year and their relation to climate conditions is of strategic importance. Large-scale climate patterns can influence where, how much, and how often it floods in a given year. The coincidence of many such events in a year across the country is an example of a compound flood hazard, whose aggregate loss is of interest. This study uses a stochastic model for simulating multiple floods across the United States while preserving information as to their co-occurrence. The model also calculates the likelihood of combined flood losses, along with its uncertainty. The key patterns in the ocean and the atmosphere that lead to these widespread losses are then identified. The broader impact of this study is to establish a foundation that any country or region can use to evaluate potential consequences of compound risk from joint extreme events. A non-parametric copula-based stochastic framework is forwarded to assess the risk of multiple peak floods across a regionPeak floods in the US exhibit significant co-occurrence of extreme events, leading to compound flood hazard with high aggregate lossesThe joint occurrence of extreme flood events across the country is a signature of large-scale climate teleconnections