Extreme Harvey-Like Rains in Texas 6x More Likely Today Than 25 Years Ago
https://www.wunderground.com/cat6/extreme-harvey-rains-texas-6x-more-likely-today-25-years-ago
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Texas rainfall events as intense as that produced by Hurricane Harvey, which had about a 1 percent annual likelihood in the 1990s, had already increased in likelihood to about 6 percent annually in 2017, and by 2090 could be about 18 percent. That’s according to the paper "Assessing the present and future probability of Hurricane Harvey’s rainfall", published on Monday in Proceedings of the National Academy of Sciences by Dr. Kerry Emanuel of MIT, who is widely regarded as the world’s leading hurricane expert.
Dr. Emanuel used a very high-resolution, specialized computational hurricane model embedded within six different state-of-the-art climate models to make his assessment. The model generated 3,700 predictions of hurricane tracks and rainfall amounts for the projected climate in at the end of the century, in the years 2081 - 2100. These predicted rainfall amounts were then compared to the rainfall amounts generated by the model for hurricanes simulated during the historical period 1979 – 2015. Using a storm-total amount of 20+ inches as his benchmark, Dr. Emanuel determined that in the old climate of the 1990s, some location in Texas could expect to see a hurricane dump that amount of rain once every 100 years (a 1% chance of occurrence in any particular year.) Looking specifically at Houston (not the entirety of Texas), he wrote: “Harvey’s rainfall in Houston was “biblical” in the sense that it likely occurred around once since the Old Testament was written”—meaning that Harvey’s rains were a 1-in-2000 year event at that specific location in Texas (a 0.05% chance of occurring in Houston in any particular year.)
His model showed that these odds had already shifted in the year 2017 to a 1-in-17 year event for Texas (and 1-in-325 year event for Houston.) By the end of the century (the years 2081 – 2100), the model showed the odds of a Harvey-like rainfall event continuing to increase, to a 1-in-6 year event for Texas and 1-in-100 year event for Houston. Dr. Emanuel did not attempt to ascertain the dominant reason why climate change could be causing this increase in odds of Harvey-like rains, but cited greater water vapor concentration, stronger upward motion in storms, longer duration of events, and greater frequency of events as possible contributors. Dr. Emanuel gives an interesting summary of the research in a 70-minute lecture presented at MIT in September 2017 (video here).
Harvey’s rains were the greatest ever recorded for any U.S. tropical cyclone
Hurricane Harvey was the second most expensive weather-related disaster in world history behind Hurricane Katrina (2005), with damages of $90 billion, said insurance broker Aon Benfield last week. Other insurance groups put the damages at $70 billion - $200 billion. Remarkably, the usual culprits in extreme hurricane damage—storm surge and destructive winds—were only of secondary importance for Harvey. The majority of the great hurricane’s damage occurred because the storm stalled in place and dumped truly prodigious rains in excess of fifty inches over one of the world’s largest metropolitan areas—Houston, Texas. The nearby Port-Arthur/Beaumont, Texas area received even more extreme rains—up to 60 inches. These rains washed away many all-time meteorological and hydrological records, not only for Texas, but for the entire United States. More than 6.7 million people in a 29,000 square mile area (the size of West Virginia) received at least 20 inches of rain in seven days, said NOAA’s Tom Di Liberto in an article at climate.gov, and an area larger than the state of Massachusetts received 30+ inches of rain. Several locations received more than 25 inches of rain in one day, including 26.03 inches on August 29 at the Beaumont-Port Arthur Airport; rainfall rates over 5 inches per hour were reported in some places.
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