2017 was the worst year on record for hurricane damage in Texas, Florida and the Caribbean from Harvey, Irma and Maria. We had hoped for a reprieve this year, but less than a month after Hurricane Florence devastated communities across the Carolinas, Hurricane Michael has struck Florida.
Coastlines are being developed rapidly and intensely in the United States and worldwide. The population of central and south Florida, for example, has grown by 6 million since 1990. Many of these cities and towns face the brunt of damage from hurricanes. In addition, rapid coastal development is destroying natural ecosystems like marshes, mangroves, oyster reefs and coral reefs – resources that help protect us from catastrophes.
In a unique partnership funded by Lloyd’s of London, we worked with colleagues in academia, environmental organizations and the insurance industry to calculate the financial benefits that coastal wetlands provide by reducing storm surge damages from hurricanes. Our study, published in 2017, found that this function is enormously valuable to local communities. It offers new evidence that protecting natural ecosystems is an effective way to reduce risks from coastal storms and flooding.
The economic value of flood protection from wetlands
Although there is broad understanding that wetlands can protect coastlines, researchers have not explicitly measured how and where these benefits translate into dollar values in terms of reduced risks to people and property. To answer this question, our group worked with experts who understand risk best: insurers and risk modelers.
Using the industry’s storm surge models, we compared the flooding and property damages that occurred with wetlands present during Hurricane Sandy to the damages that would have occurred if these wetlands were lost. First we compared the extent and severity of flooding during Sandy to the flooding that would have happened in a scenario where all coastal wetlands were lost. Then, using high-resolution data on assets in the flooded locations, we measured the property damages for both simulations. The difference in damages – with wetlands and without – gave us an estimate of damages avoided due to the presence of these ecosystems.
Our paper shows that during Hurricane Sandy in 2012, coastal wetlands prevented more than US$625 million in direct property damages by buffering coasts against its storm surge. Across 12 coastal states from Maine to North Carolina, wetlands and marshes reduced damages by an average of 11 percent.
These benefits varied widely by location at the local and state level. In Maryland, wetlands reduced damages by 30 percent. In highly urban areas like New York and New Jersey, they provided hundreds of millions of dollars in flood protection.
Wetlands reduced damages in most locations, but not everywhere. In some parts of North Carolina and the Chesapeake Bay, wetlands redirected the surge in ways that protected properties directly behind them, but caused greater flooding to other properties, mainly in front of the marshes. Just as we would not build in front of a seawall or a levee, it is important to be aware of the impacts of building near wetlands.
Wetlands reduce flood losses from storms every year, not just during single catastrophic events. We examined the effects of marshes across 2,000 storms in Barnegat Bay, New Jersey. These marshes reduced flood losses annually by an average of 16 percent, and up to 70 percent in some locations.
In related research, our team has also shown that coastal ecosystems can be highly cost-effective for risk reduction and adaptation along the U.S. Gulf Coast, particularly as part of a portfolio of green (natural) and gray (engineered) solutions.
Reducing risk through conservation
Our research shows that we can measure the reduction in flood risks that coastal ecosystems provide. This is a central concern for the risk and insurance industry and for coastal managers. We have shown that these risk reduction benefits are significant, and that there is a strong case for conserving and protecting our coastal ecosystems.
The next step is to use these benefits to create incentives for wetland conservation and restoration. Homeowners and municipalities could receive reductions on insurance premiums for managing wetlands. Post-storm spending should include more support for this natural infrastructure. And new financial tools such as resilience bonds, which provide incentives for investing in measures that reduce risk, could support wetland restoration efforts too.
Improving long-term resilience
Increasingly, communities are also beginning to consider ways to improve long-term resilience as they assess their recovery options.
There is often a strong desire to return to the status quo after a disaster. More often than not, this means rebuilding seawalls and concrete barriers. But these structures are expensive, will need constant upgrades as as sea levels rise, and can damage coastal ecosystems.
Even after suffering years of damage, Florida’s mangrove wetlands and coral reefs play crucial roles in protecting the state from hurricane surges and waves. And yet, over the last six decades urban development has eliminated half of Florida’s historic mangrove habitat. Losses are still occurring across the state from the Keys to Tampa Bay and Miami.
Protecting and nurturing these natural first lines of defense could help Florida homeowners reduce property damage during future storms. In the past two years our team has worked with the private sector and government agencies to help translate these risk reduction benefits into action for rebuilding natural defenses.
Across the United States, the Caribbean and Southeast Asia, coastal communities face a crucial question: Can they rebuild in ways that make them better prepared for the next storm, while also conserving the natural resources that make these locations so valuable? Our work shows that the answer is yes.
This is an updated version of an article originally published on Sept. 25, 2017.
The risk of more severe storms and cyclones in the highly urbanised coastal areas of Newcastle, Sydney and Wollongong might not be acute, but it is a real future threat with the further warming of the southern Pacific Ocean. One day a major storm – whether an East Coast Low or even a cyclone – could hit Sydney.
With higher ocean temperatures killing and bleaching coral along the Great Barrier Reef to the north, we could also imagine where the right temperatures for a coral reef would be in a warmer climate. Most probably, this would be closer to the limits of the low latitudes, hence in front of the Sydney metro area.
We should then consider whether it is possible to help engineer a natural defence against storms, a barrier reef, should warming oceans make conditions suitable here.
Ocean warming trend is clear
The oceans are clearly warming at an alarming rate, with the unprecedented extent and intensity of coral bleaching events a marker of rising temperatures. After the 2016-2017 summer, coral bleaching affected two-thirds of the Great Barrier Reef.
On the other side of the Pacific, sea surface temperatures off Peru’s northern coast have risen 5-6℃ degrees above normal. Beneath the ocean surface, the warming trend is consistent too.
With the East Australian Current now extending further south, the warming of these south-eastern coastal waters might be enough in a couple of decades for Nemo to swim in reality under Sydney Harbour Bridge.
On top of this, when we plot a series of maps since 1997 of cyclone tracks across the Pacific, it shows a slight shift to more southern routes. These cyclones occur only in the Tasman Sea and way out from the coast, but, still, there is a tendency to move further south. The northern part of New Zealand recently experienced the impacts this could have.
Think big to prepare for a big storm
If we would like to prevent what Sandy did to New York, we need to think big.
If we don’t want a storm surge entering Parramatta River, flooding the low-lying areas along the peninsulas, if we don’t want flash-flooding events as result of river discharges, if we don’t want our beaches to be washed away, if we want to keep our property along the water, and if we want to save lives, we’d better prepare to counter these potential events through anticipating their occurrence.
The coast is the first point where a storm impacts the city. Building higher and stronger dams have proven to be counterproductive. Once the dam breaks or overflows the damage is huge. Instead we should use the self-regenerating defensive powers nature offers us.
Thinking big, we could design a “Sydney Barrier Reef”, which allows nature to regenerate and create a strong and valuable coast.
The first 30-40 kilometres of the Pacific plateau is shallow enough to establish an artificial reef. The foundations of this new Sydney Barrier Reef could consist of a series of concrete, iron or wooden structures, placed on the continental shelf, just beneath the water surface. Intelligently composed to allow the ocean to bring plants, fish and sand to attach to those structures, it would then start to grow as the base for new coral.
This idea has not been tested for the Sydney continental flat yet. But in other parts of the world experiments with artificial reefs seem promising. At various sites, ships, metro carriages and trains seem to be working as the basis for marine life to create a new underworld habitat
The Sydney Barrier Reef will have the following advantages:
Over decades a natural reef will grow. Coral will develop and a new ecosystem will emerge.
This reef will protect the coast and create new sandbanks, shallow areas and eventually barrier islands, as the Great Barrier Reef has done.
It will increase the beach area, because the conditions behind the reef will allow sediments to settle.
It creates new surfing conditions as a result of the sandbanks.
It will protect Sydney from the most severe storm surges as it breaks the surge.
It will present a new tourist attraction of international allure.
Let’s create a pilot project as a test. Let’s start to design and model the pilot to investigate what happens in this particular location. Let’s simulate the increase of temperature over time and model the impact of a cyclone.
Let’s create, so when Sandy hits Sydney, we will be better protected.
Certainly larger and more frequent storms are one of the consequences that the climate models and climate scientists predict from global warming. But you cannot attribute any particular storm to global warming, so let’s be quite clear about that. – Prime Minister Malcolm Turnbull, speaking to reporters in Tasmania on June 9, 2016.
In the aftermath of the deadly East Coast Low that swamped eastern Australia, dumping massive amounts of rain in early June, the prime minister toured flood-affected Launceston and announced emergency relief funding.
Turnbull told reporters that larger and more frequent storms were forecast by climate scientists but cautioned that no individual storm could be attributed to global warming.
Is he right?
Checking the source
The Conversation asked the prime minister’s office for sources to support his statement but did not hear back before publication deadline. Nevertheless, we can test his statement against recent published and peer-reviewed research on this question.
The science shows that, just like real estate, climate change is all about location. Different parts of Australia will be affected in different ways by climate change.
And global warming will have different effects on different types of weather systems.
Let’s break Turnbull’s statement into two parts: is it true that we can expect larger and more frequent storms as a consequence of global warming? And is it possible to attribute a specific storm to global warming?
Can we expect larger and more frequent storms as a result of global warming?
Yes – but not for all regions or types of storms.
There are many types of storms that affect different parts of Australia, among them East Coast Lows, mid-latitude cyclones (a category that includes cyclones that happen in the latitudes between Australia and Antarctica), tropical cyclones, and associated extreme rainfall events. Each will be affected in a different way by climate change, and the effect will vary by region and by season.
… East Coast Lows are expected to become less frequent during the cool months May-October, which is when they currently happen most often. But there is no clear picture of what will happen during the warm season. Some models even suggest East Coast Lows may become more frequent in the warmer months. And increases are most likely for lows right next to the east coast – just the ones that have the biggest impacts where people live.
For all low-pressure systems near the coast, “most of the models we looked at had no significant change projected in the intensity of the most severe East Coast Low each year,” Pepler wrote.
On mid-latitude cyclones: Another study predicted that the overall wind hazard from mid-latitude cyclones in Australia will decrease – except in winter over Tasmania.
On tropical cyclones: Northern Australia is expected to get fewer cyclones in future – but their maximum wind speeds are expected to become stronger.
On rainfall: Scientists tend to be quite confident that climate change will be accompanied by an increase in extreme rainfall for most storms in future. One of the main reasons for this is that increased temperatures will cause increased evaporation. While the total amount of water held in the atmosphere will also increase slightly in future, the total amount of rain has to go up too.
Is it true you can’t attribute any particular storm to global warming?
Turnbull is correct. We cannot say for sure that a particular flooding rainfall event was solely “caused” by climate change, any more than we can say for certain that a particular car accident was solely caused by speeding (even if excessive speed was a likely or even major contributing factor).
Evidence for the effects of global warming on extreme rainfall events that have already occurred is currently equivocal for most regions.
According to a collection of studies published in 2015:
A number of this year’s studies indicate that human-caused climate change greatly increased the likelihood and intensity for extreme heat waves in 2014 over various regions. For other types of extreme events, such as droughts, heavy rains, and winter storms, a climate change influence was found in some instances and not in others.
One recent study in that report found:
evidence for a human-induced increase in extreme winter rainfall in the United Kingdom.
Malcolm Turnbull was essentially correct on both points.
It’s true that scientists predict more frequent and intense storms for some parts of Australia as the climate changes. The evidence appears to be strong that extreme rainfall will increase. Some increases in extreme wind speeds are possible – but not in all regions or all seasons.
Turnbull was right to say you cannot attribute any particular storm to global warming. –Kevin Walsh
This is a good FactCheck that summarises the broad conclusions from a range of studies examining the nature of current and likely future storms across Australia.
As the author points out, Australian storms range from tropical cyclones in the northern tropical regions to temperate east coast lows and mid-latitude cyclones.
The consensus regarding tropical cyclones is that they will generally decrease in frequency in the Australian region. In northeast Australia, they are forecast to experience the most dramatic decrease in frequency of any ocean basin globally. Some northern hemisphere ocean basins will see an increase in their frequency.
The intensity of these types of storms is expected to increase. This will not only involve higher wind speeds but also higher storm surges and floods. That will mean greater coastal impacts and damage to coastal developments and infrastructure.
So the prime minister’s statement about more frequent storms resulting from climate change does not apply to tropical cyclones – however, he was right to say that larger and more frequent storms are one of the predicted consequences of climate change. This consequence is predicted to apply to other storm categories, but not tropical cyclones.
And yes, climate scientists are hesitant to attribute the occurrence of any single storm to global warming. – Jonathan Nott
Australia’s east coast is recovering from a weekend of wild winds, waves and flooding, caused by a weather pattern known as an East Coast Low. Tragically, several people have died in flooding.
Parts of New South Wales have received more than 400mm of rain since Friday morning. Some places such as Canberra and Forster recorded their wettest June day on record. Waves have also caused severe coastal erosion and damaged property.
East Coast Lows are a type of low-pressure system or cyclone that occur on the Australian east coast. They are not uncommon, with about seven to eight lows a year causing widespread rainfall along the east coast, particularly during late autumn and winter. An East Coast Low in April last year caused similar damage.
But whenever they happen they raise the question: did climate change play a role?
Climate models suggest that the cyclones that move through the global mid-latitudes, around 30° to 50°S, are moving south. This is contributing to long-term declines in winter rainfall in southwestern Australia and parts of southeast Australia.
These models also suggest that the atmospheric conditions that help East Coast Lows form could decline by between 25% and 40% by the end of the century.
In recent work, my colleagues and I looked even more closely at how climate change will affect individual East Coast Lows.
Our results also found East Coast Lows are expected to become less frequent during the cool months May-October, which is when they currently happen most often.
But there is no clear picture of what will happen during the warm season. Some models even suggest East Coast Lows may become more frequent in the warmer months.
And increases are most likely for lows right next to the east coast – just the ones that have the biggest impacts where people live.
What about the big ones?
The results in the studies I talked about above are for all low-pressure systems near the coast – about 22 per year, on average.
But it’s the really severe ones that people want to know about, like the current event, or the storm that grounded tanker Pasha Bulker in Newcastle in June 2007.
These storms are much rarer, which makes it harder to figure out what will happen in the future. Most of the models we looked at had no significant change projected in the intensity of the most severe East Coast Low each year.
Warming oceans provide more moisture, so intense rainfall is expected to increase by about 7% for each degree of global warming. East Coast Lows are no different – even during the winter, when East Coast Lows are expected to become less frequent, the frequency of East Coast Lows with heavy rain is likely to increase.
Finally, even though there may be fewer East Coast Lows, they are occurring in an environment with higher sea levels. This means that many more properties are vulnerable to storm surges and the impact of a given storm surge is that much worse.
Was it climate change?
While the frequency of cool-season East Coast Lows looks likely to decrease in the future, changes in the big ones are a lot less certain.
However, East Coast Lows are very variable in frequency and hard to predict. So far, there hasn’t been any clear trend in the last 50 years, although East Coast Lows may have been more frequent in the past.
As for extreme rainfall, studies have found little influence of climate change on Australian extreme rainfall so far. Climate variability, such as El Niño, currently plays a much larger role. This doesn’t mean climate change is having no effect; it just means it’s hard to tell what impact a warming world is having at this stage.
So did climate change cause this weekend’s storms? No: these events, including intense ones, often occur at this time of year.
But it is harder to rule out climate change having any influence at all. For instance, what is the impact of higher sea levels on storm surges? And how much have record-warm sea temperatures contributed to rainfall and storm intensity?
We know that these factors will become more important as the climate system warms further – so as the clean-up begins, we should keep an eye on the future.
As the climate changes, we can expect more frequent and more extreme weather events, which will put pressure on our current infrastructure. It has been suggested that increasing temperatures will intensify rainfall, indicating that we are likely to endure bigger storms and more dangerous flooding in a future warmer climate.
Our study, published today in the journal Nature Geoscience, shows that this intensification in flooding may be even greater than expected. This is because of changes to the distribution of rainfall within storms – something known as the “temporal pattern”.
This study is the first to show that temperature changes are disrupting temporal rainfall patterns within storms themselves. When it comes to flash flooding, this is just as important, if not more so, than the total volume of rainfall that a given storm delivers.
If this trend continues with future climate warming, more destructive flooding across Australia’s major urban centres is likely. Because our findings were true across every Australian climate zone, ranging from tropical and arid to temperate, we can expect similar risks throughout the country, and conceivably elsewhere in the world too.
Looking to the past
Whether it is in politics, science or engineering, the past can be a good indicator of the future. Historical records of rainfall have long been examined for patterns to help us make sense of how the climate might change in the future.
By linking existing observations of rainfall intensity and temperature it has been found, in general, that we can expect more rainfall when temperatures are higher. This observation is founded in thermodynamics and underwritten by the Clausius-Clapeyron relationship, which states that for each degree Centigrade increase in temperature, 7% more moisture will accumulate in the atmosphere. It is not a large step to surmise from this that rainfall volumes will be 7% greater.
However, historical observations do not necessarily confirm this rate of increase – at least, not in a uniform way. Some places have experienced rainfall increases of more than 7%, while others have seen less than 7%.
This discrepancy is important. It suggests that changes in overall storm intensity are not the only change in rainfall a warmer climate may bring. There are other, more subtle disruptions we need to look for.
Finding the unexpected
In our study, we used historical data from 79 different locations around Australia, collected by the Bureau of Meteorology. This includes sites at each of the major capital cities, as well as regional areas in all states and territories. At each location we isolated storm events and then split each storm event into five segments, to determine the percentage of rain that fell in each. So, for example, a one-hour storm would be divided into five 12-minute segments.
By comparing the amounts of rainfall in each of these fractions to the average daily temperature at that location, we were able to check if there was any systematic relationship between the rainfall fractions within the storm and the ambient temperature.
Our results were unexpected. At every location, we saw that higher temperatures were linked to an increase in the largest fraction and a corresponding decrease in the smallest fraction. In other words, the storm pattern was less uniform and more erratic when the temperature was higher. Moreover, we found that these changes would increase flood peaks even if the storm volume remained unchanged, because more of the rainfall was concentrated into intense bursts.
Factor in the changes in overall storm volumes, which are also likely to increase with warming, and this is a recipe for more flood danger in areas including Australia’s urban centres.
Informing flood guidelines
So why is this important? Engineers Australia is in the process of rewriting the Australian Rainfall and Runoff guidelines, which dictate how we estimate potential flooding when designing infrastructure. Every structure, whether it be a roadside gutter, a bridge, or an office block, is built to withstand a flood of a given size and risk of occurrence. But if rainfall is changing, we need to plan for how we will design and build these structures to withstand the possibility of more destructive floods.
Although history doesn’t necessarily have to repeat itself, the increase in non-uniformity linked to higher temperatures suggests that if temperatures increase we may see more increases in the destructive force of floods in the future. Planners need to consider whether the existing infrastructure that we take for granted every day needs added fortification to withstand the impacts of climate change.