Is Houston America's Flood Capital?
According to NOAA's National Centers for Environmental Information, there were 96 days with at least one report of flooding or flash flooding in Harris County from 1996 through 2015. This equates to an average of four to five days of flooding each year over that time period.
Of course, not all of these flood events are as severe as April 2016, Memorial Day 2015, or Allison in 2001. The fact that flooding happens with such regularity most years in an area just slightly larger than the state of Rhode Island is quite impressive.
There have been at least 26 events that flooded homes in the Houston metro area since the mid-1970s, according to Houston-based Weather Research Center (WRC) and National Weather Service records. WRC documented area floods, some related to tropical cyclones, back to 1837, the year after the city was founded.
These events have happened every time of the year, even in late fall and winter.
Apart from the prodigious rainfall from tropical cyclones and their remnants, thunderstorms and thunderstorm clusters tend to slow and stall near the Gulf Coast, especially from late spring through early fall.
There's also Houston's geography and method of flood control.
"We now force rainwater into streets, and then into bayous, which flush out to Galveston Bay and the Gulf (of Mexico)," said Matt Lanza, an operational meteorologist in energy based in Houston.
Lanza says the streets, therefore, are part of the flood control system. "It's a good idea in theory because you'd rather flood roads and cars than houses. But I'm not sure any method of flood protection can prevent what unfolded over us in April 2016."
Then, there's Houston's notorious urban sprawl.
"The population has exploded here in the last 10 years, much of it settling north and west of the city," said Lanza.
"What was once farm or wetlands is now pavement and suburbia. Thus, there is less barren land to suck up the rain now, and that further exacerbates flooding."
Houston also sits only about 43 feet above sea level, so the flat system of bayous drains very slowly.
As severe as recent flood events were, imagine what happens when a tropical storm moves inland, its remnants stall, then move back over the Houston metro area.
TROPICAL STORM ALLISON (2001)
U.S. Highway 59 in Houston, Texas, remained flooded on June 10, 2001, due to rain from Tropical
Such was the case with Tropical Storm Allison in 2001.
An initial soaking as Allison moved ashore on June 5-6 was followed by a second epic deluge after Allison's remnant moved off the Texas coast on June 8-9.
By the time the rains ended, parts of the Houston metro area had picked up more than 35 inches of rainfall over the five-day period, much of which fell during that second round. This is roughly three-quarters of the average annual rainfall in just five days.
Furthermore, Allison's torrential rain – 10 inches or more – was much more widespread over the Houston metro, not to mention east Texas and the northern Gulf Coast (map), than the Memorial Day event of 2015.
More than 14,000 homes were destroyed or heavily damaged, with an additional 34,000 homes suffering at least minor damage, according to the National Hurricane Center's recap.
Total damage from Allison was estimated at $9 billion, easily the costliest tropical cyclone that never became a hurricane in U.S. history. Allison claimed 23 lives in Texas and became the first non-hurricane to have its name retired by the World Meteorological Organization.
Here are a few bayou crests in Harris County from the Memorial Day event, compared to Allison and other events.
Buffalo Bayou at Shepherd Drive (west of downtown Houston; flood stage is 28 feet):
Brays Bayou at Beltway 8 (southwest Harris County; top of bank is 64.2 feet):
Memorial Day 2015 crest: 65.91 feet
Hurricane Ike 2008 crest: 58.7 feet
This Memorial Day event was near the September 1983 flood of record along middle and upper Brays Bayou, per the Harris County Flood Control District.
Greens Bayou at Shepherd Drive (outside Interstate 610 loop northeast of downtown Houston; flood stage is 30 feet):
Memorial Day 2015 crest: 34.02 feet
Hurricane Ike 2008 crest: 36.24 feet
Allison 2001 crest: 44.01 feet (the record crest)
More within the article
Todays events in Huston
