State of emergency declared over Texas floods

Heavy rains moved through southeastern Texas on Monday (April 18), causing flash floods and damage across the region, prompting a state of emergency to be declared in nine counties.

A flash flood watch will remain in effect until Wednesday for most of the region, according to catastrophe modelling firm AIR Worldwide.

The Governor of Texas declared a state of emergency in nine counties on Monday afternoon due to flooding conditions. Forecasts alerting residents to the upcoming rains and potential for flooding were issued as early as Friday (April 15), and flash flood warnings have been issued throughout the event.

Although rainfall has ended, flood warnings for Colorado, Washington, Harris, Liberty, Walker, San Jacinto, Waller, Grimes, Montgomery, Austin, and Fort Bend Counties in southeastern Texas were in effect through midday Tuesday (April 19). A flash flood watch will remain in effect until Wednesday for most of the region.

Rainfall that began on Sunday night (April 17) and continued through Monday, producing 10–20 inches of rain in parts of southeastern Texas, reaching rates as high as 4 inches an hour.

A sizable mesoscale convective system―a collection of thunderstorms that act as one system and typically last more than 12 hours―moved through the region, caused by a large, upper-level low situated across the Rocky Mountains, according to AIR. The slow motion afforded by development in a weak upper-level flow allowed large amount of rain to fall across the Houston area.

A series of thunderstorms doused the suburbs with almost 18 inches of rain on Sunday night―the same amount of rainfall expected for this area in the five-month span of January 1–May 30―and delivered 6–8 inches of rain to central Houston on Monday.

An official from the Harris County Flood Control District said that 240 billion gallons of rainwater had fallen in the locality from Sunday–Monday. A new daily maximum rainfall record was set at the Houston Intercontinental Airport on Monday with a total of 9.92 inches recorded, breaking the previous record of 8.16 inches from 1976.

A second group of thunderstorms meandered through the region early Monday, worsening the situation.

The National Weather Service (NWS) issued a flash flood emergency for the hardest-hit Houston Metro area and flash flood watches for Austin, San Antonio, Dallas, Fort Worth, Tyler-Longview and Texarkana, and said that more than 110 subdivisions reported flooding.

According to the NNWS, several rivers were at major flood stage in five areas on Monday, including the Little River near Rockdale, White Oak Bayou at Houston, Peach Creek near Splendora, the West Fork of the San Jacinto River near Humble, and Cypress Creek near Hockley and Westfield―where some Harris County residents were forced from their homes on Tuesday morning due to high water levels. Cypress Creek at Cypress crested at 127.5 feet just below the 1994 record of 127.6 feet.

Evacuations are underway throughout southeastern Texas after more than 1,000 homes were flooded in Harris County alone, which includes the neighbourhoods of Braeswood Place, Rosslyn Road, and Cypresswood. Approximately 123,000 residents were reportedly without power in the Houston Metro area, and people were urged to shelter in place.

Some roadways collapsed while others were inundated, with local fire departments warning that exiting freeways could put motorists in 10–15 feet of water. Two dams along Interstate 10 and Texas 6 on Houston’s west side have been deemed “extremely high risk” by officials and are currently under investigation; expected to reach 50% capacity by mid-Tuesday, said AIR.

Houston County officials reported more than 1,200 water rescues by early Monday afternoon. Public schools and universities were forced to close. More than 500 flights scheduled for departure from Houston’s two major airports were cancelled. Bus and rail services were suspended.

The National Oceanic and Atmospheric Administration and the University of Oklahoma are reportedly calling the flood a 1-in-200 year event. Because flood damage and associated losses can result from time-related elements (e.g., length of exposure to flood water, how quickly mitigation is undertaken, and extent of business interruption), and can vary greatly by exposures (e.g., physical location of utilities in a structure, construction materials used, and occupancy), the impacts to the insurance industry will become more clear as flood waters recede and assessments can be conducted.

Additional heavy rain is expected in the Houston Metro area through at least Wednesday (April 20) that will also reach parts of Oklahoma, Kansas, and Louisiana. This could worsen conditions in areas already hardest hit by flooding, and cause new incidents of flash flooding in other locations, according to AIR.