While Hurricane Harvey was a significant hurricane in terms of its size and wind speed, ultimately, the storm will be remembered for the extreme flooding it caused in Houston and surrounding areas.īetween August 25–30, unprecedented rainfall totals for a tropical cyclone (TC) in the contiguous United States were recorded. Harvey moved slowly inland, remaining nearly stationary about 100 km inland for four days before moving back into the Gulf and making a second landfall in Louisiana on August 30. It weakened to a tropical depression as it crossed the Yucatan Peninsula, but attained hurricane strength over the Gulf of Mexico on August 24, rapidly intensifying to reach Category 4 strength just before making landfall on the Texas coast 50 km east of Corpus Christi on August 25, causing severe wind damage in coastal towns. Hurricane Harvey formed as a tropical storm over the Atlantic Ocean on Augand crossed into the Caribbean Sea the next day. And while fortifying Houston to fully withstand the impact of an event as extreme as Hurricane Harvey may not be economically feasible, it is critical that information regarding the increasing risk of extreme rainfall events in general should be part of the discussion about future improvements to Houston's flood protection system. This analysis makes clear that extreme rainfall events along the Gulf Coast are on the rise. Extrapolating these results to the 2017 event, we conclude that global warming made the precipitation about 15% (8%–19%) more intense, or equivalently made such an event three (1.5–5) times more likely. The first also shows 2 × CC scaling, the second 1 × CC scaling and the third did not have a realistic representation of extreme rainfall on the Gulf Coast. We also analysed extreme rainfall in the Houston area in three ensembles of 25 km resolution models. This would indicate that the moisture flux was increased by both the moisture content and stronger winds or updrafts driven by the heat of condensation of the moisture. Observations since 1880 over the region show a clear positive trend in the intensity of extreme precipitation of between 12% and 22%, roughly two times the increase of the moisture holding capacity of the atmosphere expected for 1 ☌ warming according to the Clausius–Clapeyron (CC) relation. It was an extremely rare event: the return period of the highest observed three-day precipitation amount, 1043.4 mm 3dy −1 at Baytown, is more than 9000 years (97.5% one-sided confidence interval) and return periods exceeded 1000 yr (750 mm 3dy −1) over a large area in the current climate. This resulted in extensive flooding with over 80 fatalities and large economic costs. During August 25–30, 2017, Hurricane Harvey stalled over Texas and caused extreme precipitation, particularly over Houston and the surrounding area on August 26–28.
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