News Blip:
Are You In A Flood Risk Area?
Lower 48 Residents May Unknowingly Be At Risk From River Flooding Until The Waters Start To Rise, Due To An Incomplete Flood Map Assessment That Is Too Expensive And Time-Consuming Otherwise.
Editor's Note: This news item was retrieved through Cool Green Science's website via The Nature Conservancy and credited to Cara Byington.
A new study from Environmental Research Letters has some sobering news for people living in the Lower 48 states: They may be at risk from river flooding and not even know it until the waters start to rise! In fact, the study, "Estimates of present and future flood risk in the conterminous United States," found that 41 million U.S. resid-ents – about 13 percent of the entire population of the study area – are at risk from flooding along rivers. That’s about three times more than current estimates based on the regulatory flood zone maps produced by the Federal Emergency Man-agement Agency (FEMA), which primarily map the areas at risk for 1-in-100-year floods in populous river basins.
Cool Green Science writer Cara Byington relays in her article: "In general, FEMA prioritizes risk-assessment areas based on their population: reserving expensive, field-work intensive methodologies for the more populous river basins, adopting more approximate methodologies in others, and many rivers have not yet been mapped at all." The sheer size of the U.S. means that flood maps generated in this way are incomplete – it would be too expensive and time-consuming to survey and model every river basin in the country. The national-scale flood zone maps produced by FEMA therefore constitute a patchy mosaic of local assessments that leave a large portion – about 40 percent – of the country and its flood risk unaccounted for. For this research, scientists from The Nature Conservancy and other partners, including the University of Bristol in the U.K., adopted a pioneering methodology that avoids the pitfalls of the FEMA approach – where individual catchments are studied – by making use of big data and fast computers. The study used a new high-resolution model, produced by the flood-mapping organization Fathom, that simulates floods on all rivers across the entire continental United States.
Using streamflow data from the US Geological Survey the research team was able to produce flood risk maps across the country, with a level of accuracy along specific rivers that compares well with the FEMA flood maps that presently serve as the primary source of flood hazard data in the U.S. The increase in numbers of people at risk shown in the study is a result of the expanded coverage of the map combined with the model’s ability to estimate flooding on small streams and flooding directly from rainfall – what hydrologists call “pluvial flooding.”
For the complete article and link to the study, click here.