Wednesday, August 30, 2017

Hurricane Harvey Questions

A rescue during Hurricane Harvey. Click for photo credit.
A friend of mine sent me an interesting piece from Scientific American on the science of Hurricane Harvey. As everyone knows by now, the storm is proving to be one of the most significant natural disasters in the history of the country.

Each hurricane is different, but Harvey is rather unusual in recent history. What makes it so unique is its extreme rainfall and subsequent flooding. The damage was not from a major storm surge like we saw with Superstorm Sandy in my region or from wind as was the case in Hurricane Andrew. Instead, it was from days and days of rain in the Houston area. There was no where for the rain to go.

There are two interesting questions that I found particularly interesting in the Scientific American article: Why did the storm stay in place so long? and Why was there so much rain?

It turns out that the storm stayed in place due to distinct high pressure systems that kept the low pressure hurricane from moving. As to why there was so much rain, there are many reasons, two which I will highlight. First, the Gulf of Mexico was unusually warm. Certainly climate change plays a part here, but the Gulf here can get rather warm naturally without the addition of anthropogenic oceanic warming. Second, due to all the flooding across southeast Texas, there was a plentiful supply of water that could reenter the atmosphere as evaporation occurred. The flooding essentially created an extension of the ocean which normally feeds hurricanes their moisture.

Many people have asked me if climate change was responsible for the storm. That is a simple question with a complex answer. Climate and individual weather phenomena like hurricanes are complex and have multiple inputs. Certainly warmer temperatures in air and oceans add more energy to earth systems. But there is no direct line where one can say global climate change is responsible for Hurricane Harvey. Yet it would also be incorrect to say that global climate change did not influence the storm. 

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