What is flash flooding, and how weather impacted the Hill Country of Texas flooding disaster
Flash flooding can happen anywhere and at any time. The National Weather Service (NWS) says that flash flooding is any type of flooding that starts to occur after 3 to 6 hours of heavy rainfall, often from thunderstorms. Flash floods are so dangerous because they combine the power of a flood with incredible speed. The flash floods in Texas caused the Guadalupe River to rise from 2 feet to more than 24 feet in as little as 45 minutes.
Flash floods occur when the intensity of rainfall and the duration of the rain combined with environmental factors like topography, vegetation types and the soil water content level can determine how quickly flash flooding occurs.
According to the NWS flash flooding is the number one storm related killer in the United States. The national 30-year average for flood deaths is around 127 people per year.
The Associated Press stated that the Texas Hill Country is naturally prone to flash flooding events due to the dry dirt packed landscape that lets the rain 'skid along the surface of the landscape instead of soaking it up'. On top of that there was more moisture from the remnants of tropical storm Barry was over the area.
Forecasting flooding events is extremely challenging because it's so hard to pinpoint an exact location where the flooding will happen. On top of that forecast models struggle with the set up that was unfolding in Texas, slow moving mesoscale convective complexes, and determining where the heavier bands set up.
NWS offices had mentioned the flood risk in the forecast a day earlier and issued flood watches by Thursday, July 3rd. In a social media post NWS Austin/San Antonio said, 'local heavy rainfall could cause flash flooding.' Later that evening, the NWS upgraded the flood watch to a flood warning, and eventually a flash flood warning.
Remember that a flood watch is used when the conditions are favorable for flooding but does not mean that it will occur. While a flood warning means that flooding is imminent or already happening.
More than 3 trillion gallons of water had fallen across the region. Much of it surged into the Guadalupe River, officials state that the crest reached higher than the historic 1987 flood.
Let's put that in perspective, 3 trillion gallons of water is equivalent to the amount of water used in every home in the United States for a year. It is also about 1.5 million Olympic swimming pools worth of water and is about the same amount of water that flows at Niagara Falls in a month.
Can climate change be to blame for causing this flash flood in Texas? Well a warmer atmosphere can hold more water vapor which is how showers and storms are formed, the more water vapor present the heavier the rain can be. So while it is not the main cause it certainly can influence flooding impacts.
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