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“This event is unprecedented & all impacts are unknown & beyond anything experienced.” This was the extraordinary tweet from the US National Weather Service as the flooding from Hurricane Harvey began.
Harvey may have been unprecedented, but it certainly was not unexpected. Houston frequently experiences flooding and experts have repeatedly warned that worse could be to come as the world gets warmer.
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And yet Houston was shockingly unprepared, not least because its flood control directors think talk of climate change is a plot to prevent development, and its planning system fails to prevent building in the most at-risk areas.
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It is only a matter of time before more “unprecedented” flooding hits the US. Next in the firing line could be other major cities such as Miami, New York and Boston.
Yet relatively little is being done. On the contrary, just days before Harvey struck, Donald Trump rescinded rules that mean federal infrastructure projects must take into account flood risks related to climate change.
“The policy direction is to go backwards,” says Charles Iceland of the World Resources Institute in Washington DC. The US should be investing more in flood protection for its growing population and sprawling cities, he says. And climate change will only bring increasingly severe flooding events.
The climate link
Global warming may not have caused Hurricane Harvey to form, but it made the storm worse. Abnormally warm waters in the Gulf of Mexico fuelled the hurricane’s rapid intensification, enabling it to pump extraordinary amounts of moisture into the air over Texas.
Sea levels have risen 0.2 metres over the past century due to global warming. This also compounded the situation, slowing the drainage of flood waters and making the storm surge higher.
Finally, Harvey stalled for a long time after coming ashore, so huge amounts of rain fell in one area. This too might be linked to climate change. A growing number of studies suggest this makes weather systems increasingly likely to get “stuck”, which can lead to extreme rainfall – or extreme heat and drought.
All these factors will conspire to increase the number and severity of extreme flooding events as global surface temperatures soar past 2°C above pre-industrial in the next few decades.
As the air gets warmer, it will hold more moisture, causing more rain (or snow) to fall at certain times. Rising seas will massively increase the threat posed by storm surges, as well as directly causing flooding and erosion – and global sea level could rise more than 2 metres by 2100, according to some recent studies.
Swamped cities
So who is in the firing line?
Iceland runs the Aqueduct project, which assesses countries’ susceptibility to floods. In terms of the number of people at risk, populous countries like India, Bangladesh and China naturally top the project’s tables. Millions are already being affected by river flooding every year.
Indeed, this year, abnormally heavy monsoon rains have caused severe flooding across south-east Asia, killing at least 1200 people.
However, a different picture emerges when looking at the financial cost of flooding. American cities feature prominently in a list of the coastal cities facing the biggest losses from flooding by 2050, according to a 2013 study. The top five are Guangzhou, Miami, New York, New Orleans and Mumbai.
In general, rich cities such as Amsterdam have much better flood protection than poorer cities in developing countries, the study says. But many wealthy American cities have low protection levels.
Hold back the tide
It is clear the US needs to do far more to keep its people and cities safe.
The obvious course is to stop building homes – and chemical factories – in harm’s way. This is not just a problem in Houston: since the 1960s, the US has provided cheap, subsidised flood insurance that has encouraged development in high-risk areas. This scheme’s $24 billion debt is set to soar thanks to Harvey.
Big infrastructure projects have a part to play, too. Massive barrier schemes similar to the one protecting London have long been considered for protecting places such as New York City, but have yet to get the go-ahead.
But it is simply not feasible to protect many areas, such as the vast swathes of Florida set to disappear under the waves over the next century. “There is not much to do except to abandon those areas,” says Iceland.
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