Abstract
Abstract. The National Flood Insurance Program (NFIP) debt has accelerated research into private flood insurance options. Offering this coverage begins with the ability to transfer the risk to the reinsurance market. Within the industry, perils such as hurricanes and earthquakes have standard definitions, but no such definition exists for floods. An event definition must examine the spatial and temporal aspects of the flood as well as the complexities of individual events. In this paper we were able to apply a data-driven methodology to capture and aggregate flood peaks into independent events. To aggregate flood peaks into independent events we needed to define what constituted a basin as our area of aggregation. The USGS utilizes the hydrological unit code (HUC) a 2- to 12-digit code that follows the Pfafsetter Coding System. The HUC code is used to identify varying levels of basin sizes ranging from region (2 digits) to subwatershed (12 digits). We chose to analyze both the HUC8 and HUC6, and a total of 7932 HUC8 events and 8444 HUC6 events were recorded during the 15 water years used in our study. Each event was characterized by duration, magnitude and severity. Focusing on the HUC8, events were unevenly distributed nationally while severity was relatively evenly distributed. The goal for our study was to take a method and be able to apply it to basins of varying characteristics. This framework relied on the ability to analyze the individual processes related to each individual basin.
Highlights
Throughout the world, flood events are one of the most destructive natural disasters
A total of 7932 and 8444 events were calculated for basins defined by the HUC8 and HUC6 respectively
Comparing the frequency distribution of events between the two selected basins’ sizes suggests that frequencies within basins defined by the HUC6 are higher than frequencies defined by the HUC8 (Figs. 3 and 4)
Summary
Throughout the world, flood events are one of the most destructive natural disasters. Floods occur for a variety of reasons, and risk factors such as total rainfall, soil types and land use can contribute to the complexity of events, in particular impacted area and event duration (Uhlemann et al, 2010). Major and minor floods contribute to economic and insured losses (Joyce, 2014; FEMA, 2016). Since its inception in 1968, the NFIP premiums have largely covered the amount paid out in losses (NFIP Act of 1968). The 2005 hurricane season, including Hurricane Katrina, which was the costliest storm in the program’s history, costing more than USD 16 billion, pushed the NFIP into debt (Fig. C1) (Union of Concerned Scientists, 2016). The NFIP debt is estimated at USD 24 billion as of 2014 (Joyce, 2014)
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