FACT CHECK: Has Hurricane Harvey Caused Once-In-500-Year Flooding?

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David Sivak Fact Check Editor
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As Texas experiences record-setting rainfall from Hurricane Harvey, President Donald Trump tweeted Sunday about the magnitude of the flooding, calling it a “once in 500 year” flood.

Verdict: True

Weather experts confirmed to The Daily Caller News Foundation that parts of Texas have experienced once-in-500-year flooding due to the hurricane. Such a flood has a one-in-500 annual chance of occurring and can happen more than once every 500 years.

Fact Check:

As major rescue operations were underway in Texas due to hurricane flooding, Trump tweeted about the severity of the rainfall, calling it a once-in-500-year flood event.

Hurricane Harvey has brought record-setting rainfall to Harris County, a part of Southeast Texas that includes the city of Houston. The Harris County Flood Control District, which has been monitoring the flooding, confirmed to TheDCNF that parts of the county have witnessed rainfall intense enough to qualify as once-in-500-year flooding.

Such flooding has a one-in-500 chance of occurring in a given year. To qualify, an area must experience a certain amount of rainfall over a given interval of time. In Harris County, for example, there must be around 18.5 inches of rain over a 24-hour window.

This sort of flooding, while statistically rare, can happen more than once every 500 years. Texas experienced a once-in-500-year flood event in 2001 with Tropical Storm Allison, and such extreme flooding has occurred repeatedly across the U.S. in the last decade.

Although flooding from a hurricane is not unusual, Hurricane Harvey is particularly severe. “It’s behaving like a hurricane behaves, but the unfortunate circumstance of it is the very, very slow track,” Patrick Burke, senior forecaster for the National Weather Service, told TheDCNF. “Normally, we would expect very heavy rain, but it would get more evenly distributed.”

Hurricane Harvey is projected to surpass the U.S. record for the most rainfall from a tropical cyclone, a record set by Tropical Storm Amelia in 1978. Amelia produced 48 inches of rainfall, which is more than what Harris County receives on average across an entire year.

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