John Bogna
New data shows the parameters used to map out Houston’s 100-year floodplain routinely underestimated how much rain the Bayou City gets every year.
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A recent study conducted by the National Oceanic and Atmospheric Administration (NOAA) shows the amount of rainfall qualifying as a 100-year storm – a storm with a one percent chance of occurrence in any given year – rose several inches since 2002.
In Harris County, the estimate increased by 3-5 inches, according to the study.
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It’s authors claim this means, instead of planning for 12-15 inches of rain per day during a 100-year event, Harris County should be planning for 15-18 inches per day, according to the Houston Chronicle.
While this may not seem to be a significant difference to some, analysts agree it could affect everything from floodplain maps to construction requirements, to who must buy flood insurance to protect their homes under law.
In turn, then, they say it could change insurance costs and the regulations placed on builders who want to develop in or near the floodplain.
Climatologist and Professor John Nielsen-Gammon said the following on the subject in an interview:
“We design our infrastructure and our society and homes to be resilient to a certain level of risk. 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 is reportedly making its preliminary findings available for public comment until January 19, and the final estimates will be published in May 2018.
Many described Harvey as a 1000-year flood event, but it reportedly came at least as the third 500-year storm to hit Houston in a year.
Before the NOAA study announcement, weather experts agreed the hurricane marked a clear need to recalibrate the estimates we use to prepare for flood events.
Once completed, they believe the latest study could be another step down this path.
Should it effectuate a change, floodplain maps could need to be redrawn, and developers may see new restrictions:
“Detention basins would have to be larger. Bridges and culverts would have to be larger. Land plans for new development would change…,” Matt Zeve, director of operations for the Harris County Flood Control District, said in an interview. “It’s a big deal, it’s going to affect people that don’t even know that they will be affected.”
Officials, like Houston’s Judge Ed Emmet, said they are already considering flood control plans for Harris County and surrounding areas, especially those hardest hit by the hurricane.
The city also proposed new development regulations this month, some requiring homes to be built eight-feet higher than before, according to the Chronicle.
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Stay tuned, Houston.
