Hurricane Harvey: One-off event or climate catastrophe?

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With the influx of storms such as Ophelia and Brian affecting the British Isles in recent months, we may be reminded of the devastating effects that Hurricane Harvey caused in the US during the month of August. Yet while Brian was reported to have wind speeds of 60-70mph, Hurricane Harvey’s winds reached speeds of a huge 130mph, combined with intense rainfall and a storm surge which caused flooding around Texas, Louisiana and southern Arkansas. The effects of this hurricane have been devastating on these areas, with some estimates calling Harvey the most expensive natural disaster in the history of the US. As debates about climate change in the US are hotter than ever in light of President Trump’s sceptical views on the matter, discussions about just how much Harvey was influenced by climate change have been at the forefront of US meteorological research of late.

13 million people affected and 135,000 homes damaged or destroyed

Typically, hurricanes (also known as tropical revolving storms, cyclones and typhoons, depending on where they occur), are formed at the end of the summer or start of the autumn season over tropical oceans heated to at least twenty-six degrees Celsius over the summer months.

True to this description, Harvey formed over the Gulf of Mexico on August 17^th, gradually deepening into a tropical depression as the warm water of the Gulf allowed for uplift of moisture to feed the storm. After weakening slightly between August 18^th-19^th the storm rapidly intensified on the 23^rd, when it was named a Category 1 Hurricane, with wind-speeds of up to 80mph. Harvey reached peak strength on August 25^th as it passed over a particularly warm section of the Gulf known as an ‘eddy’, which increased its intensity to a Category 4 storm, and finally made landfall over San Jose Island and then South-central Texas.

It’s passage over Texas brought heavy flooding due to a deadly combination of heavy rainfall and a storm surge (caused by abnormally strong winds pushing seawater over the land), with an enormous 127cm of rainfall recorded in total over the Hurricane’s duration. What’s more, while usually hurricanes weaken inland away from their warm ocean energy-source, the rainfall that Harvey induced was so severe that the storm was then further fuelled by this floodwater, pulling it back up just like it would water from an ocean. This allowed for prolonged heavy rainfall and a more damaging passage inland.

So, with an estimated 13 million people affected and 135,000 homes damaged or destroyed, is climate change really to blame? Many experts seem to be suggesting the affirmative.

While climate change didn’t directly cause hurricane Harvey, scientists are pointing to increasingly warmer ocean temperatures to explain why tropical storms are growing in intensity and frequency. Oceans worldwide are only believed to have warmed by approximately 0.1 degrees Celsius over the past decade, but even this slight change is enough to exacerbate the effects of tropical storms by providing them with more energy, allowing for uplift of moisture to further drive the storms. What’s more, as water heats-up it expands, a cause of the well-known problem of sea-level rise. This of course allows for more damaging storm surges as water is pushed inland and backwards up river estuaries by the force of hurricanes.

In addition, warmer, wetter weather caused by rising global temperatures primes land for flooding as land already saturated with rainfall is unable to absorb water from intense storm-driven rainfall, resulting in flash flooding.

It is often difficult to pinpoint exactly how one weather event in particular was influenced by the global phenomenon of climate change, but looking at global trends over time can give a pretty clear indication that climate change is making weather worldwide more extreme, unpredictable and deadly.  So, while president Trump may remain convinced that the deadliest hurricanes affecting the US do not correlate with climate-change research, or even that climate change is a tenuous area of research altogether, it is difficult to ignore the global trends that show otherwise.

climate change is making weather worldwide more extreme, unpredictable and deadly

In conclusion, climate change is not the sole cause of Hurricane Harvey, rather an important factor among the numerous causes of this deadly hurricane. And while it cannot be proven exactly what the effects of climate change will be in the foreseeable future, it is certainly probable that tropical storms like Harvey will become more of a threat as global temperatures continue to rise.