Hurricane Irma has left a trail of devastation across the Caribbean, like Harvey in Texas just days before it. The final cost won鈥檛 be clear for months but it will run into billions of dollars.
In the immediate aftermath of聽these record-smashing storms, there is an urge to rebuild as quickly as possible. But there is聽also a brief window of opportunity to better prepare for聽future events, say disaster planners聽鈥� to pause and think about what should be done differently.
So what can be done to protect these regions in the future? And perhaps just as importantly, what pitfalls should we avoid?
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Thanks to better forecasting and preparedness, the death toll from most hurricanes these days is much lower than a century ago. But the damage they cause, and its financial cost, is soaring. The main reason for this is that more people are living in areas at risk, and as a result more valuable infrastructure is being built there.
In the US, for instance, the strip of land within 50 kilometres of the vulnerable Gulf and Atlantic coasts has the greatest density of housing in the country. There are now 27 million housing units in this area, up from 4 million in the聽1940s, according to a 产测听 of Northern Illinois University. This rapid growth is projected to continue over the next century, particularly around Miami.
Even if the climate weren鈥檛 changing, repeats of past storms like the Great Miami Hurricane of聽1926 would cause far more damage, as there is more real estate. A similar event today could cost an .
Warming seas
But the climate is changing. For starters, global warming has already raised sea levels by around 20 centimetres, making all storm surges聽鈥� coastal floods caused by storms pushing more seawater towards shores聽鈥� that bit higher. Even this small increase can lead to hundreds or thousands more homes flooding, says Hal Needham of Marine Weather & Climate in Texas. Given the seas could rise 2 or 3 metres by 2100 as the planet warms further, there is no doubt that storm surges will get even higher.
Rising seas can also make inland flooding much worse. Even聽a few centimetres of sea level聽rise can really increase the time it takes water to drain, says Needham.
Climate change is making tropical storms more destructive in several ways, such as by increasing top wind speeds. 鈥淭he聽speed limit will go up as the climate warms,鈥� says hurricane researcher Kerry Emanuel of the Massachusetts Institute of Technology. Beside the direct damage they do, stronger winds will pile up bigger storm surges on聽top of the rising seas. And as the atmosphere gets moister, storms will produce even more聽rainfall and flooding.
The rational response would be to halt development in the areas most at risk and start a gradual process of moving people and critical infrastructure to safer regions. But people want to live near sunny beaches and warm seas, businesses make money developing such regions and local聽governments rake in taxes from the building boom. The prosperity of Florida and many Caribbean islands depends heavily on their beach-front real聽estate.
That doesn鈥檛 mean nothing can聽be done. The US federal government could stop funding this unsustainable growth, for example. 鈥淔ederal tax聽dollars should not be subsidising development and growth in our聽most vulnerable areas,鈥� says聽Ashley.
This happens in all kinds of聽ways, from support for infrastructure projects such as roads and bridges聽in risky areas, to聽a deep-in-debt federal scheme that provides cheap flood insurance, to direct aid to help rebuilding after disasters.
鈥淭he US has many policies that聽essentially subsidise people living in dangerous places,鈥� says Emanuel. With many leaders in the US still denying that climate change is an issue, this is unlikely to change anytime soon.
Local plans
This makes it even more vital that local planning regulations ban development in the places most at聽risk from storm surges and flooding. 鈥淲e need to plan for an evolving and growing risk under climate change,鈥� says Ashley.
It is the lack of such planning laws that made Houston so woefully vulnerable to Hurricane Harvey. But more is being done in聽Florida: its most vulnerable counties have formed the to work together on mitigation and adaptation to both hurricanes and climate change.
After Hurricane Andrew in 1992, Florida also tightened its building regulations. Structures in Miami-Dade and Broward counties have to be able to withstand winds of at least 210聽kilometres per hour. But Irma聽had top winds of 295 kph.
Future storms could have even faster winds. The limiting factor is聽the temperature difference between the ocean and the atmosphere, and this is expected to increase further as the planet warms, says Emanuel. 鈥淲e are going to be breaking records.鈥�
This is even scarier than it sounds because the destructive power of winds rises exponentially with speed. Winds of 200 kph can do twice as much damage as those of 160 kph.
Relaxed rules
But making buildings more storm-resistant is costly. In poorer regions such as Haiti most people can鈥檛 begin to afford to pay for it, and even in rich Florida, the rules were recently relaxed to reduce costs. 鈥淢aybe weakening Florida鈥檚 Building Code wasn鈥檛 such a smart聽idea. Thank you Florida Homebuilders & Developers,鈥� the former head of the Federal Emergency Management Agency, Craig Fugate, as Irma hit.
Even if we implement tougher regulations on where and how buildings are built, that won鈥檛 help those existing structures in聽high risk areas.
Instead, cities like Miami are turning to engineering fixes like sea walls, but these are costly to build and maintain. And with seas set to rise, such defences will have to be made ever higher. So low-lying areas could get locked into spending bigger and bigger sums to try to hold back the seas.
鈥淲e need to have some humility around our ability to聽conquer nature,鈥� says Mark Stevens, a hazards mitigation planner at the聽University of British Columbia in Canada.
For instance, sea walls alone aren鈥檛 enough in Florida, as water can flow up through the porous limestone bedrock. So Miami is also having to raise the level of roads and new developments. This process could end up turning the city into an island聽鈥� assuming it doesn鈥檛 run out of money first as people realise the risks and the real estate market collapses.
Future disaster
Going down the engineering approach could even make future disasters worse. The problem is that building flood defences encourages more development in聽the area, as people assume the defences make it safe. If those defences aren鈥檛 maintained, or if a聽storm comes along that exceeds the design specifications, the result is a much bigger disaster than if those defences hadn鈥檛 been built in the first place.
鈥淲e saw that with Katrina,鈥� says Stevens. Or as Raymond Burby at the University of North Carolina wrote in a : 鈥淗urricane Katrina and the flooding of New Orleans could be viewed as an expected consequence of federal policy rather than an aberration that is unlikely to be repeated.鈥�
This 鈥渟afe development paradox鈥�, as it is known, would be聽a problem even in a constant climate. Defences built against so-called 1-in-100 year events don鈥檛 stop 1-in-500 year events.
But now global warming is changing the odds in ways we can鈥檛 predict with much certainty, greatly increasing the chances of聽storms that could breach the defences. This is why the safest option is managed retreat as the seas rise and storms grow stronger.
But that鈥檚 not a message most people are ready to hear. 鈥淚t鈥檚 going to take large events to convince people that retreat is the right thing to do,鈥� says Stevens.
This article appears in print under the headline 鈥淟ife after the storm鈥�
