Hurricane Harvey made landfall late August and devastated southeast Texas, leaving in its wake 77 fatalities, unprecedented flooding, more than one million displaced individuals, 200,000 homes in a path of destruction stretching for more than 300 miles, and estimated damages between $150-$180 billion. Harvey was the most powerful hurricane to hit Texas in 50 years. Now a recent analysis by the National Oceanic and Atmospheric Administration (NOAA), which looked at rainfall data in Texas in past decades, up to and including Harvey, suggests the standards used to develop floodplain regulations, map flood zones and design flood control projects routinely underestimate the severity of the Houston area’s downpours.
According to an article in the Houston Chronicle, NOAA’s analysis shows that the amount of rain that defines a “100-year storm"” – one that has a one percent chance of occurring in any given year – has risen by three to five inches in Harris County (the most populous county in Texas and the third-most populous county in the U.S.) since the last estimates were put in place in 2002. Therefore, in lieu of anticipating 12 to 14 inches in a day during a 100-year storm, the data shows the county should expect 15 to 18 inches.
What does this all mean? In anticipation of an increase in rainfall during a 100-year storm, developers need to look at designing subdivisions and commercial retail space, such as strip malls, to compensate for higher runoff. In addition, more existing residential and business properties would be included in new floodplain maps, which will affect flood insurance costs and development regulations.
"We design our infrastructure and our society and homes to be resilient to a certain level of risk," said John Nielsen-Gammon, the Texas state climatologist and professor of atmospheric science at Texas A&M University in the Houston Chronicle article. “Having updated, more accurate numbers means that we’re better able to do that, and the risk we’re undertaking matches the risk we're designing for.”
NOAA’s final data is set to be published in May 2018, the first statewide update to the federal agency's rainfall estimates in nearly 50 years. The preliminary data will be available for comment until Jan. 19, 2018.
Hurricane Harvey, in addition to the Tax Day 2016 floods and the Memorial Day 2015 floods, in fact, have prompted local officials to consider a series of ideas to revamp the flood-control strategy around Houston. Just this month, for example, the county proposed a set of vastly expanded regulations for new development in floodplains, including a requirement that developers build new homes up to eight feet higher than previously required in some areas, as well as regulating, for the first time, in 500-year floodplains instead of 100-year floodplains, broader geographic areas around bayous and creeks.
There are also 15 proposed measures on the table to improve flood control efforts, including the construction of a third dam and reservoir system in the northwest part of Harris county, widespread buyouts of flood-prone homes, and an effort to push the state to give the County the authority to levy a sales tax to pay for costly flood-control measures, according to the Houston Chronicle.