Earlier on Friday (July 4th), a major storm dropped about a foot of water in Texas Hill Country in just a few hours. In 45 minutes, the water ran down the slopes of the area, towards the Guadalupe River, rising over 26 feet (8 meters) and beating the bank. In Kerr County, a flood of water wiped out people, homes and infrastructure, killing more than 100 people as of July 8th.
So, what is the cause of such a catastrophic flood?
Firstly, there is a flash flooding trend in the area. In fact, Texas is killing the United States due to floods. This is partly due to hilly areas and semi-arid soils, which do not absorb much moisture. Hatim Sharif, professor of civil and environmental engineering at San Antonio, writes for the conversation. “The water slabs can disappear quickly and shallow streams can rise rapidly.”
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What is flash flooding and why was it so bad in Texas?
Flash floods are a special type of flood, according to the National Weather Service. It can occur within minutes or within hours of excessive rainfall.
Texas is not a stranger to floods, and this particular area is known as the “all of flash floods,” UCLA climate scientist Daniel Swain told Live Science. “All the materials were in place due to potentially extreme rainfall,” he said.
The main drivers of these floods were enormous amounts of water, Swain said. “A very permanent, intense thunderstorm sat at the same fork for several hours and slowly propagated through the basin in the direction of a flood wave.”
Related: Climate change exacerbates April’s catastrophic floods, report discovery
The remains of Barry, a tropical storm that struck near Mexico last week, had already added moisture and instability to the atmosphere. The east wind then blew this saturated air inland, pushing warm atmospheric air up as it moved towards Texas. That air “surges into thunderstorms, creating heavy rainfall, with a very extreme rain rate of 2-3 inches per hour, which lasts for several hours,” Swain said.
In Texas, extreme flash floods localized to one river system have been created.
Can scientists predict flash floods?
Meteorologists can identify conditions that tend to fuel flash floods and areas that are prone to them, but it is very difficult to accurately predict when and where it may occur, an expert told Live Science.
“It’s extremely difficult to predict heavy rainfall and flash floods,” said Jess Neumann, a geographer specializing in flood risk management at the UK’s Reading University.
In this case, the National Weather Service issued a flash flood warning at 1:26am local time on Friday and posted a follow-up emergency flash flood warning to X at 4:06am
Some experts suggest that recent large-scale layoffs at the National Oceanic and Atmospheric Administration, which operates the National Weather Service, may be hampering surveillance efforts ahead of these events. For example, Kxan reported that a warning coordinated meteorologist at the National Weather Service Austin/San Antonio office had retired early following NOAA funding cuts. The office is the head of the area that has been most affected by flash floods.
However, Swain said the forecast from the office is as good as expected. “The real failure here was in the forecast and communications between local governments making plans of action and not setting it up to keep people safe,” he said.
Will flash floods worsen in the future?
As the climate warms, scientists warn that extreme rainfall events like those that led to flash floods in Texas become more common. A warm atmosphere can hold more water vapor and eventually falls to Earth as precipitation.
The fundamental law of thermodynamics, known as the Clavicle-Clapeylon equation, which describes the relationship between temperature and vapor pressure, predicts that the water vapor carrying capacity will increase by about 7%, to any degree atmospheric temperature rises.
But flash floods could be even worse, Swain said. “When we talk about very extreme rain events, especially the heavy rains of very extreme thunderstorms, they increase at a rate of multiplied rates.”
There are many locations in the US, and several locations in the southeastern states, increasing the risk of flash floods due to hill geography and proximity to the Gulf of Mexico.
“If you’re in immediate proximity to very warm waters, you can see these types of events when the air rises rapidly and the occasional storm system creates an unstable atmosphere that occurs,” Swain said. “At least the number of places where this is sometimes relevant is very widespread.”
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