HOUSTON, Sept. 11 (Xinhua) -- Experts from two universities in the State of Texas found that there are serious errors in the Federal Emergency Management Agency (FEMA)'s 100-year flood plain maps.
According to a news release by the Rice University, Texas on Monday, an analysis of flood claims in several southeast Houston suburbs from 1999 to 2009 found that the FEMA's maps - the tool that U.S. officials use to determine both flood risk and insurance premiums - failed to capture 75 percent of flood damages from five serious floods, none of which reached the threshold of a 100-year event.
The research by hydrologists and land-use experts at Rice University and Texas A&M University at Galveston was published in the journal Natural Hazards Review just days before Hurricane/Tropical Storm Harvey inundated the Houston region and caused some of the most catastrophic flooding in U.S. history.
"The takeaway from this study, which was borne out in Harvey, is that many losses occur in areas outside FEMA's 100-year flood plain," said study co-author Antonia Sebastian, a research associate at Rice's Severe Storm Prediction, Education and Evacuation from Disasters (SSPEED) Center and a postdoctoral researcher at Delft University of Technology in the Netherlands.
"What we've tried to show, both with this study and several others, is that it is possible to do better," said lead author Russell Blessing, a Texas A&M-Galveston graduate student with joint appointments at the SSPEED Center and Texas A&M-Galveston's Center for Texas Beaches and Shores, adding "there are innovative computational and hydrological tools available to build more predictive maps."
In the new study, Blessing, Sebastian and co-author Sam Brody, a professor of marine sciences at Texas A&M-Galveston, director of the Center for Texas Beaches and Shores and a SSPEED Center investigator, examined the Armand Bayou watershed in southeast Harris County, a county where Houston is located.
Brody said one problem with FEMA's 100-year flood plain maps is that they assume that flooding will only take place in one dimension, that is, either downstream or upstream, and not perpendicular to the channel.
Another issue with FEMA's maps is their lack of granularity. Brody and Blessing said the type of soil (such as clay versus sand) and the way land is used (such as a concrete parking lot or a school playground) have significant impacts on flooding, and FEMA's models often use a single classification for entire neighborhoods or groups of neighborhoods. In so doing, they miss out on small-scale features that can significantly affect flooding.
Sebastian said focusing on 100-year events is also problematic because short, intense rainfall events that don't meet the 100-year threshold can still cause serious flooding.
Harvey blew ashore on Aug. 25 as the most powerful hurricane to hit Texas in more than 50 years, displacing more than 1 million and damaged some 200,000 houses in a path of destruction that stretches for more than 480 km. The Houston area was hit by severe flooding, after receiving about 1.4 meters of rain.
