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Harvey sets rainfall, damage records in Texas and Louisiana

Cambridge will experience a brief cooldown on Friday as a cold front pushes through the northeast. Temperatures Friday night could approach 50 °F (10 °C) before Hurricane Harvey’s remnants pass near the region over the weekend. Harvey, the eighth storm, third hurricane, and first major hurricane of the 2017 Atlantic hurricane season, is finally moving away from the gulf coast regions of Texas and Louisiana it battered so badly over the past week. Harvey made landfall late Friday evening near Rockport, Texas (approximately 160 miles SW of Houston) as a category 4 hurricane with 130 mph winds (about 210 km/h). It was the first major hurricane to make landfall in the United States since Wilma did so in Florida in 2005, and the first hurricane to hit Texas since Ike did so in 2008.

However, it was not Harvey’s winds and storm surge that caused the greatest impact. The storm took an extremely unusual path following landfall first slowing, then reversing its motion and moving back offshore over the course of several days. It eventually reversed course again and made landfall once again in southwest Louisiana early Wednesday morning. It was Harvey’s unyielding, torrential rains along this bizarre path that caused the greatest destruction. Harvey is expected to still be located over northern Louisiana Thursday afternoon, a week after its rains first started to impact the gulf coast.

The incredible longevity of Harvey’s impacts led to unfathomable rainfall amounts; a rainfall maximum of 51.88” (131.78 cm) was recorded in the Houston metro area according to the National Weather Service. The amount would represent a single-storm rainfall record for the continental US and fall just short of the 52.00” (132.08 cm) overall record from 1950 Hurricane Hiki in Hawaii. Over six million people, mostly in the Houston area, experienced over 30” (76.20 cm) of rainfall. Harvey unleashed over 25 trillion gallons of water on Texas and Louisiana; to understand just how much water this is, consider that if this volume was placed on MIT’s campus, it would extend about 140 kilometers into the sky. Spread over Massachusetts, this water would form a layer 3.4 meters deep; over the entire US (including Alaska and Hawaii), it would still form a layer almost 1 centimeter deep.

This incredible volume of water created the incredible, long-lasting flooding seen in news reports and social-media, and the human and economic impacts of the damage caused will last for months. Harvey is one of the costliest natural disasters in US history; it remains unclear whether it will exceed Hurricane Katrina to become the costliest. 

In the face of a warming climate, links between Harvey and climate change may be prematurely drawn. Climate change is expected to increase the likelihood and frequency of heavy rain events and to potentially increase the intensity of hurricanes and their impacts. However, it is too soon to attribute any responsibility for Harvey’s devastation to this change - little analysis has been done to understand what factors contributed to this particular disaster.

While it is possible increased moisture, higher sea surface temperatures, and other factors derived from a warmed climate aided Harvey's rains, the storm also took a very slow and unusual, but not at all unreasonable path that placed it over the same locations for many days. Quantifying climate change’s impact on Harvey will undoubtedly be the subject of much future analysis in the atmospheric sciences.

Dr. Kerry Emanuel, Cecil & Ida Green Professor of Atmospheric Science and Co-Director of the Lorenz Center at MIT, conducted some preliminary statistical climate analysis on Harvey-like rainfall events in Texas that suggests that these sorts of events were in fact more likely over the past 3 years than they were before 2014, but increases in temperature and moisture are not enough to explain the increase in likelihood. Rather, he implicates weaker steering currents over that time period as a likely driving factor, and points out that these changes in steering currents are not of sufficient longevity to link to climate change.

Future research remains necessary to continue to understand how natural disasters will evolve in the future; right now, the long road to recovery begins for those affected by the storm.