Flash floods in Texas: Why do massive downpours impact Houston?

A spring storm unleashed up to 16 inches of rain in Houston and other parts of southeastern Texas on Sunday night, causing flooding from overflowing bayous.

David J. Phillip/AP
A resident looks out from the second floor as floodwaters surround his apartment complex Monday in Houston. A spring storm dumped up to 16 inches of rain on the city in only a few hours on Sunday.

Torrential downpours hit Houston and other parts of southeastern Texas on Sunday night, with some areas getting up to 16 inches of rainfall in only a few hours.

The National Weather Service issued flash flood warnings on Monday, with emergency officials making at least 74 high-water rescues overnight in the Houston area, ABC News reports. Schools in Houston were closed on Monday, along with local bus services and highways. The local Harris County Flood Control District also urged residents to stay in their homes, calling the flooding "life-threatening."

The heavy rain has forced seven of the city bayous out of their banks, leading to flooding in parts of the city that hadn't previously flooded for many years, Houston mayor Sylvester Turner told reporters on Monday. 

The problem is that despite efforts to reduce the impact of flooding by replacing bridges and adding detention ponds and other channels for rain runoff, officials have struggled to keep up with a population boom around Houston. New housing has gone up at a quick pace, laying down concrete and paved roads faster than workers can map the city's creeks and rivers. 

The rainfall is part of a large spring storm affecting much of the country's mid-section, CBS News reports. In the northern Rockies and central and northern high plains, it's producing a mixture of snow and rain. Severe thunderstorms that could create hail, heavy winds, and isolated tornadoes are forecast in south central Texas. Eastern Texas, southeast Oklahoma, southwest Arkansas, and western Louisiana are expected to experience heavy rain that could lead to flash flooding, say meteorologists.

But in Houston, the floods, which can often cause property damage and even the loss of life, aren't unusual. They come in spite of efforts by the Harris County Flood Control District to mitigate the impact of floods – a task it has been doing since 1937. 

Coupled with the addition of many more paved streets that make the city's topography essentially flat and a tradition of strong personal property and land use rights that leads to fewer regulations, that makes flood control a difficult task, the Associated Press reports. 

"Think about every time you put in a road, a mall and you add concrete, you've lost the ability of rain to get into the soil and you've lost that permeability," Walter Peacock, an urban planning professor at Texas A&M University, told the AP. "It's now impermeable. And therefore you get more runoff."

A massive storm last spring was thought to be attributed to the El Niño weather pattern, where warming sea surface temperatures in the Pacific Ocean impact wind and weather conditions, Popular Science reports. May 2015 was the rainiest month in Texas history.

In Texas' case, El Niño led the subtropical jet stream, a swiftly moving current in the atmosphere, to shift further south, where it met warm, moist air from the Gulf of Mexico and the Atlantic Ocean moving inland, causing a slew of intense thunderstorms.

No one is reported to have been injured in Sunday's downpour, though the flooding has left more than 100,000 homes and businesses in the Houston area without electricity.

More than 1,000 homes have flooded in Harris County, while three apartment buildings were evacuated, with residents sheltered at a nearby mall, Harris County Judge Ed Emmett said at a news conference Monday.

A CNN meteorologist said the storm is expected dumping heavy rainfall thorough Tuesday before the system begins to move toward the Northeast while it grows weaker.

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