How many flood events occur in the United States every year? Challenges in Defining Flood Events and Estimating their Frequency.
Abstract
Most natural catastrophic events are relatively short-lived, and spatially and temporally discreet, such as an earthquake or hurricane. However, when it comes to flood events, the definition is not straightforward due to the continuous, longer, and more varied nature of the hazard in space and time. Additional challenges to define flood events arise as a variety of stakeholder's objectives are considered (e.g., definition based on meteorology, hydrology, societal impacts, reinsurance treaties, etc.). The United States Geological Survey (USGS) streamflow data show that there are streamflow gauges at or above flood stage almost every day of the year in the conterminous United States. Given this characteristic of flow above flood stage, the important questions we ask are: (1) how can flood events be defined from USGS gauge data to organize rivers above flood stage into discreet events and (2) what is the frequency of flood events in the US according to this event definition? We used the location of gauges that exceed the 2-year return period as our minimum threshold for flooding as well as the timing of these peak flows into a clustering method to categorize all flooding instances into flood events. Clustering was applied in a multi-stage process (i.e., first time and then space) to study the sensitivity of parameters of interest to various stakeholders, such as flooding threshold, duration constraints (also called "Hours-Clause" in (re-)insurance parlance), etc. The event definition methodology based on the gauge data, which is sparse and spatially discontinuous, is then applied to the modeled peak flow results across the entire conterminous United States. Employing modeled flows allows us to determine the event characteristics on a much larger representation of rivers in the country and help explore the spatial and temporal signatures of the resulting flood events. The results from this study, providing insight on the distribution and frequency of flood events across the conterminous United States, will be presented.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H41N1904S
- Keywords:
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- 1803 Anthropogenic effects;
- HYDROLOGY;
- 1821 Floods;
- HYDROLOGY;
- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 4303 Hydrological;
- NATURAL HAZARDS