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Hurricane Harvey and Climate Change

Many people want to know if Hurricane Harvey was caused by a warming climate. The quick answer to the question is “Good Question”. Frankly we are in no position to tell categorically as land-falling hurricanes are rare events and we do not have the data of atmospheric circulation, ocean heat content and other parameters all together.

We do know that from June 7th to August 7th the upper ocean heat content did increase by 2°c along Harvey’s path off Texas. The rapid intensification was unusual and this thick warm pool could have had something to do with this.

Also the Clausius-Clapeyron equation suggests that a hotter atmosphere contains more water vapor so with every 1°c of warming in the atmosphere it can hold 7% more water vapor thus when it rains it can lead to monsoonal-like downpours. In the case of the stalled Harvey it dumped 44 trillion liters of rain over southeast Texas causing terrible flooding. Basically this type of rainfall – perhaps not as extreme would be expected in a warming world.

It had been suggested that the stalling of Harvey could be due to a general slow down of the atmospheric circulation is mid-latitudes and coupled with a very warm Gulf of Mexico sea surface temperature just turned into a water producing machine producing about 125 cm over the length of the storm and in some locations a rain rate of 15 cm per hour. The drainage systems in the US are just not equipped to deal with this rain rate. The previous rain record was about 100cm in the region with tropical storm Alison in June 2001 in Houston so not too far different.

So why such an effect?

There are some schools of thought that these storms are not necessarily disasters in their own right but are natural triggers that challenge societies requirements to build in flood plains, below dams and even below sea-level like Holland and New Orleans relying on engineering to beat nature. Certainly building on barrier islands is going to always be a bad idea with rising sea-level and subsidence. It is just going the wrong way.

In Houston, subsidence from the extraction of water for irrigation is one large issue. The subsidence in some parts of Houston have been 10 feet ( Figure 1) and in many neighborhoods where there were dam releases the flooding was about 6 feet. If there had been no subsidence many of these homes would have been not in harms way.

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Figure 1: Subsidence around the Houston area from 1906 to 2000
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Figure 2: Observed Precipitation during Hurricane Harvey

The rains in Texas were incredible and unprecedented for one event. Hurricane Harvey was responsible for a terrible loss of life, injury and property damage, and brought the 4th largest city in the US to its knees for a period. Although it has been many years for a major land falling storm to hit the US is clear that they can happen any hurricane season and as a society we will have to prepare the best we can.