These revisions are hugely consequential for Harris County. Their adoption will mean that thousands of acres of land will now be subject to more restrictive flood regulations. Thousands more will be subject to regulation for the first time.

The proposed FEMA maps can be found here (Click on Draft Database for Community Review and then zoom in to Harris County). The Houston Chronicle has also published an excellent map showing the changes in the flood map from the 2007 maps. Unfortunately, it is currently behind their paywall, so only subscribers can view it.

The changes primarily reflect updated rainfall projections for southeast Texas adopted by NOAA in 2018 – widely known as “Atlas 14.” These models predict about a 25%-30% increase in rainfall in our region.

The new maps also reflect changes to the physical watershed, such as additional runoff from paved areas and improvements such as detention facilities. One silver lining to the new maps is that some areas along Braes and Sims Bayous have been removed from the floodplains because of the massive drainage projects completed in those watersheds.

There are two immediate consequences of these changes. First, in nearly all cases, flood insurance will be required to obtain a mortgage on any property that has been moved into a 100-year flood plain. Second, any property moved into a 500-year floodplain will be subject to the regulations adopted by Harris County and the City of Houston after Hurricane Harvey. Generally speaking, these regulations require that any structure in a 500-year floodplain be raised to two feet above what is referred to as the “base flood elevation.” The base flood elevation must be calculated for each property.

While the new flood maps will mean that fewer homes and businesses will flood in future storms, they will also make it dramatically more expensive and difficult to build in Harris County. They will likely make it impractical to build in much of the County. That will, of course, encourage more development outside the County. In a perverse irony, much of the development will be shifted to Montgomery County, where the FEMA maps have not been updated. But of course, drainage from developments in Montgomery County mostly flows downstream into Harris County — once again making the case for a regional flood control authority.

The maps will also cause additional brand damage to the Houston region. They will once again remind individuals and companies considering relocating here of our region’s vulnerability to flooding.

The new maps also underscore the importance of the Harris County Flood Control Authority’s timely completion of the 2018 bond program.  The completion of those projects could serve as the basis for removing large tracts from the floodplains.

Building a giant metropolis on a flat coastal plain, subject to frequent hurricanes, reminds me of Robert Burns’ line in To a Mouse, “the best laid schemes of mice and men gang aft agley (often go astray).”

Yet perhaps we need to think about our excess rainfall differently and not purely as a liability. In a nation increasingly concerned about freshwater scarcity, Houston’s hydrologic surplus could be a long-term strategic asset. Each inch of rain across Harris County represents roughly 29 billion gallons of freshwater. The challenge is not how to make it disappear faster, but how to capture, store, and recharge more of it. With smarter regional detention, aquifer recharge strategies, and reservoir management, Houston could convert its principal liability into a strategic asset, indeed, perhaps an entirely new industry.

Because this issue is so hugely consequential for our region, I have decided to add a session on it at the Readers’ Conference. Commissioner Tom Ramsey and Jim Thompson will join me for a discussion on the implications of the change. Jim is a civil engineer who is currently the CEO of DCCM, a Houston engineering company. He was formerly the floodplain administrator for the City of Houston. Subject to working out his schedule, Dennis Paul, the State Representative and civil engineer from the Clear Lake area, will also be joining us. Dennis has introduced a bill in the last two legislatures to establish a regional flood authority.