Houston, the fifth most populated city in the United States, and the surrounding areas of southeast Texas are currently facing down a historic storm known as Hurricane Harvey. The National Weather Service has warned of “catastrophic flooding” and tweeted that the storm “is unprecedented and all impacts are unknown and beyond anything experienced.” More than 250 highways have been closed due to flooding and more than 2,000 calls for rescue have been made since the storm began. An estimated 76,000 people remain without power.
When asked if his relief agency was prepared to be in Houston dealing with the aftermath for months, Brock Long, the head of the Federal Emergency Management Agency (FEMA) responded, “FEMA is going to be there for years.”
What makes Hurricane Harvey so uniquely strong? Does the storm represent a new norm in extreme weather?
How are hurricanes classified?
Hurricane Harvey was classified as a Category 4 storm when it first made landfall just south of Corpus Christi, Texas. According to the National Hurricane Center, a branch of the National Oceanic and Atmospheric Administration, these categories rank the hurricane’s sustained wind speed on the Saffir-Simpson Hurricane Wind Scale. The scale of 1 to 5 also accounts for potential property damage and loss of life.
In a Category 4 storm, winds clock in at 130 to 156 miles per hour. Power outages are predicted to last weeks and “most of the area will be uninhabitable for weeks or months”. Even well-built houses are expected to sustain severe damage including the potential for the loss of its roof and exterior walls.
But the extreme nature of Hurricane Harvey, and the potential threat brought on by other intense storms like it, is due to more than wind speed. Storm surge – how much ocean levels rise due to onshore winds - and total rainfall also contribute to a hurricane’s intensity. Harvey offers up a particularly destructive combination: an already problematic, but not unheard of, storm surge of a few feet, extremely high levels of rainfall, and a stalling of the storm over a single area for several days.
How much is 50 inches of rain?
Houston and surrounding cities recorded between 25-27 inches of rain in just 24 hours and 15-20 inches more are expected throughout the week. For comparison, Houston ordinarily sees around 50 inches of rain in a year. That means half of a year’s worth of rain fell in a single day, with potential for an entire year’s worth of rain over the course of just one week.
To look at this level of rainfall another way, an estimated 9 trillion gallons of water has fallen over the greater Houston area. As calculated by the Washington Post, this is enough water to cover the entirety of the contiguous 48 states in 0.17 inches of rain or to fill the Great Salt Lake twice.
The level of flooding is thus severe and photos have already shown cars and entire highways submerged, as well as residents navigating city streets in boats. Adding to the problem, Galveston Bay can no longer serve as a source of drainage for the excess water since it too was elevated by Harvey’s storm surge.
Along with the high levels of rainfall and the significant storm surge associated with Hurricane Harvey, the longevity of the storm over the Houston area is even further contributing to the extreme levels of flooding. There is a lack of winds to force the hurricane inland, but rather multiple areas of high-pressure winds in the upper atmosphere that have essentially left the storm trapped above the Texan coastline for several more days. 5-10 trillion more gallons of rain are expected before the storm is done.
Modeling hurricane patterns is incredibly complicated.
Is climate change to blame for the intensity of Hurricane Harvey?
Modeling hurricane patterns is incredibly complicated, but of course predictions based on climate change models are even more complex. Thus, it’s not as simple as drawing a clear connection between a single storm event and the complex web of activity that results from climate change.
However, we do know that an increase in the intensity and frequency of weather events is one of the main predictions of climate change models. In particular, hurricanes are fed by warm, moist air at the ocean’s surface. This can lead to hurricanes losing intensity before making landfall if they churn up enough deeper – and thus cooler – ocean water leading to a decrease in surface air temperature. Harvey, however, was fed by water in the Gulf of Mexico that has been reported as unusually warm, perhaps due to record high temperatures associated to global warming.
For more information on Hurricane Harvey, newspapers like the New York Times and the Washington Post have lifted their paywalls for news relating to Hurricane Harvey. The United States Geological Survey is tracking the changes made to the coastline by Hurricane Harvey through dune erosion, overwash (the inland movement of sand over the tops of coastal dunes), and inundation (the submersion of shoreline).
Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.
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