Australia could see fewer cyclones, but more heat and fire risk in coming months


Jonathan Pollock, Australian Bureau of Meteorology; Andrew B. Watkins, Australian Bureau of Meteorology; Catherine Ganter, Australian Bureau of Meteorology, and Paul Gregory, Australian Bureau of Meteorology

Northern Australia is likely to see fewer cyclones than usual this season, but hot, dry weather will increase the risk of fire and heatwaves across eastern and southern Australia.

The Bureau of Meteorology today released its forecast for the tropical cyclone season, which officially runs from November 1 to April 30.




Read more:
It’s only October, so what’s with all these bushfires? New research explains it


Also published today is the October to April Severe Weather Outlook, which examines the risk of other weather extremes like flooding, heatwaves and bushfires.

Warmer oceans means more cyclones

On average, 11 tropical cyclones form each season in the Australian region. Around four of those cross the coast. The total number each season is roughly related to how much cooler or warmer than average the tropical oceans near Australia are during the cyclone season.

Map showing the average number of tropical cyclones through the Australian region and surrounding waters in ENSO-neutral years, using all years of data from the 1969-70 to 2017-18 tropical cyclone season.

One of the biggest drivers of change in ocean temperatures is the El Niño–Southern Oscillation, or ENSO. During La Niña phases of ENSO, the warmest waters in the equatorial Pacific build up in the western Pacific and to the north of Australia. That region then becomes the focus for more cloud, rainfall and tropical cyclones.

But during El Niño, the warmest water shifts towards the central Pacific and away from northern Australia. This decreases the likelihood of cyclones in our region.




Read more:
Explainer: El Niño and La Niña


And when ENSO is neutral, there is little push towards above or below average numbers of cyclones.

Temperatures in the tropical Pacific Ocean have been ENSO-neutral since April and are likely to stay neutral until at least February 2020. However, some tropical patterns are El Niño-like, including higher-than-average air pressure at Darwin. This may be related to the current record-strong positive Indian Ocean Dipole – another of Australia’s major climate drivers – and the cooler waters surrounding northern Australia.

The neutral ENSO phase alongside higher-than-average air pressure over northern Australia means we expect fewer-than-average tropical cyclones in the Australian region this season. The bureau’s Tropical Cyclone Season Outlook model predicts a 65% chance of fewer-than-average cyclones.

At least one tropical cyclone has crossed the Australian coast every season since reliable records began in the 1970s, so people across northern Australia need to be prepared every year. In ENSO-neutral cyclone seasons, this first cyclone crossing typically occurs in late December.




Read more:
El Niño has rapidly become stronger and stranger, according to coral records


Other severe weather

While cyclones are one of the key concerns during the coming months, the summer months also bring the threat of several other forms of severe weather, including bushfires, heatwaves and flooding rain.

With dry soils inland, and hence little moisture available to cool the air, and a forecast for clear skies and warmer days, there is an increased chance that heat will build up over central Australia during the spring and summer months. This increases the chance of heatwaves across eastern and southern Australia when that hot air is drawn towards the coast by passing weather systems.

Australian seasonal bushfire outlook, as of August 2019. Vast areas of Australia, particularly the east coast, have an above-normal fire potential this season.
Bushfire and Natural Hazards CRC/Australasian Fire and Emergency Service Authorities Council

Likewise, the dry landscape and the chance of extreme heat also raise the risk of more bushfires throughout similar parts of Australia, especially on windy days. And with fewer natural firebreaks such as full rivers and streams, even greater care is needed in some areas.

Widespread floods are less likely this season. This is because of forecast below-average rainfall and also because dry soils mean the first rains will soak into the ground rather than run across the landscape.

However, as we saw in northern Queensland in January and February this year, when up to 2 metres of rainfall fell in less than 10 days, localised flooding can occur in any wet season if a tropical low parks itself in one location for any length of time.




Read more:
Catastrophic Queensland floods killed 600,000 cattle and devastated native species


Most of all, it’s always important to follow advice from emergency services on what to do before, during and after severe weather. Know your weather, know your risk and be prepared. You can stay up to date with the latest forecast and warnings on the bureau’s website and subscribe to receive climate information emails.The Conversation

Jonathan Pollock, Climatologist, Australian Bureau of Meteorology; Andrew B. Watkins, Head of Long-range Forecasts, Australian Bureau of Meteorology; Catherine Ganter, Senior Climatologist, Australian Bureau of Meteorology, and Paul Gregory, BOM, Australian Bureau of Meteorology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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I’ve always wondered: who calls cyclones their names?


Richard Wardle, Australian Bureau of Meteorology

This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au


Who calls cyclones their names? – Guy Mullin, Mozambique.

In the Australian region, the Bureau of Meteorology gives tropical cyclones their name. You can write to the Bureau of Meteorology to suggest a cyclone name, but it is likely to be more than a 50-year wait.

Tropical cyclones are named so we can easily highlight them to the community, and to reduce confusion if more than one cyclone happens at the same time. The practice of naming tropical cyclones (or storms) began years ago to help in the quick identification of storms in warning messages. Humans find names far easier to remember than numbers and technical terms.

Aerial views of flooded areas following Cyclone Idai in March 2019.
EU Civil Protection and Humanitarian Aid Operations/flickr, CC BY-NC-ND



Read more:
Explainer: ‘bomb cyclones’ – the intense winter storms that hit the US (and Australia too)


Clement Wragge began naming cyclones in 1887

Tropical Cyclone Oma captured by NASA international space station.
NASA Johnson/flickr, CC BY-NC-ND

Now, people ask us all the time how we come up with the names for tropical cyclones. It started in 1887 when Queensland’s chief weather man Clement Wragge began naming tropical cyclones after the Greek alphabet, fabulous beasts, and politicians who annoyed him.

After Wragge retired in 1908, the naming of cyclones and storms occurred much less frequently, with only a handful of countries informally naming cyclones. It was almost 60 years later that the Bureau formalised the practice, with Western Australia’s Tropical Cyclone Bessie being the first Australian cyclone to be officially named on January 6, 1964.

Other countries quickly began using female names to identify the storms and cyclones that affected them.

Naming cyclones helps people quickly identify storms in warning messages. Cameras outside the NASAA international space station capture Hurricane Florence in 2018.
NASA Goddard Space Flight Center/flickr, CC BY-SA



Read more:
I’ve Always Wondered: How do we know what lies at the heart of Pluto?


How cyclone names are chosen

While the world was giving female names to cyclones and storms, International Women’s Year in 1975 saw Bill Morrison, the then Australian science minister, recognise that both sexes should bear the shame of the devastation caused by cyclones. He ordered cyclones to carry both male and female names, a world first.

These days the Bureau is responsible for naming tropical cyclones in the Australian region, with the names coming from an alphabetical list suggested by the Australian public. These names alternate between male and female. The Bureau of Meteorology receives many requests from the public to name tropical cyclones after themselves, friends, and even pets.

The Bureau cannot grant all these requests, as they far outnumber the tropical cyclones that occur in the Australian region.

Trees on the side of the road at Mission Beach, North Queensland, in the aftermath of Cyclone Yasi, 2011. Cyclone Yasi formed in Fiji and maintained the name from that region’s weather agency.
Michael Dawes/flickr, CC BY-NC



Read more:
Curious Kids: What causes windy weather?


Cyclone Oma was named in Fiji

Cyclone names are reused, but when a tropical cyclone severely impacts the coast, or is deadly, like Debbie in 2017 and Tracy in 1974, the name is permanently retired for reasons of sensitivity.

If a listed name comes up that matches the name of a well-known person, or someone in the news for a sensitive or controversial reason, the name is skipped to avoid any offence or confusion.

When a cyclone forms in another region, say near Fiji or in the Indian Ocean, and then travels into the Australian region, the original name given by that region’s weather agency is kept, such as 2019’s Cyclone Oma, which came from Fiji.

Tropical cyclone Bessie was the first Australian cyclone to be officially named by the Bureau of Meteorology.

A list of cyclone names around the world can be found here.The Conversation

Richard Wardle, Weather Services Manager, Queensland, Australian Bureau of Meteorology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Protecting wetlands helps communities reduce damage from hurricanes and storms



File 20181009 72133 1o1hr7u.jpg?ixlib=rb 1.1
Protecting coastal wetlands, like this slough in Florida’s Everglades National Park, is a cost-effective way to reduce flooding and storm damage.
NPS/C. Rivas

Siddharth Narayan, University of California, Santa Cruz and Michael Beck, University of California, Santa Cruz

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.

Coastal wetlands and flood damage reduction: A collaboration between academia, conservation and the risk industry.

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.

Wetland benefits for flood damage reduction during Sandy (redder areas benefited more from having wetlands).
Narayan et al., Nature Scientific Reports 7, 9463 (2017)., CC BY

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.

Reductions in annual flood losses to properties that have a marsh in front (blue) versus properties that have lost the marshes in front (orange).
Narayan et al., Nature Scientific Reports 7, 9463 (2017)., CC BY

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.

The dense vegetation and shallow waters within wetlands can slow the advance of storm surge and dissipate wave energy.
USACE

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 Conversation

Siddharth Narayan, Postdoctoral Fellow, Coastal Flood Risk, University of California, Santa Cruz and Michael Beck, Research professor, University of California, Santa Cruz

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Predicting disaster: better hurricane forecasts buy vital time for residents


Jeffrey David Kepert, Australian Bureau of Meteorology and Andrew Dowdy, Australian Bureau of Meteorology

Hurricane Irma (now downgraded to a tropical storm) caused widespread devastation as it passed along the northern edge of the Caribbean island chain and then moved northwards through Florida. The storm’s long near-coastal track exposed a large number of people to its force.

At its peak, Hurricane Irma was one of the most intense ever observed in the North Atlantic. It stayed close to that peak for an unusually long period, maintaining almost 300km per hour winds for 37 hours.

Both of these factors were predicted a few days in advance by the forecasters of the US National Hurricane Center. These forecasts relied heavily on modern technology – a combination of computer models with satellite, aircraft and radar data.


Read more: Irma and Harvey: very different storms, but both affected by climate change


Forecasting is getting better

Although Irma was a very large and intense storm, and many communities were exposed to its force, our capacity to manage and deal with these extreme weather events has saved many lives.

There are many reasons for this, including significant construction improvements. But another important factor is much more accurate forecasts, with a longer lead time. When Tropical Cyclone Tracy devastated Darwin in 1974, the Bureau of Meteorology could only provide 12-hour forecasts of the storm’s track, giving residents little time to prepare.

These days, weather services provide three to five days’ advance warning of landfall, greatly improving our ability to prepare. What’s more, today’s longer-range forecasts are more accurate than the short-range forecasts of a few decades ago.

We have also become better at communicating the threat and the necessary actions, ensuring that an appropriate response is made.

The improvement in forecasting tropical cyclones (known as hurricanes in the North Atlantic region, and typhoons in the northwest Pacific) hasn’t just happened by good fortune. It represents the outcome of sustained investment over many years by many nations in weather satellites, faster computers, and the science needed to get the best out of these tools.

Tropical cyclone movement and intensity is affected by the surrounding weather systems, as well as by the ocean surface temperature. For instance, when winds vary significantly with height (called wind shear), the top of the storm attempts to move in a different direction from the bottom, and the storm can begin to tilt. This tilt makes the storm less symmetrical and usually weakens it. Irma experienced such conditions as it moved northwards from Cuba and onto Florida. But earlier, as it passed through the Caribbean, a low-shear environment and warm sea surface contributed to the high, sustained intensity.

In Irma’s case, forecasters used satellite, radar and aircraft reconnaissance data to monitor its position, intensity and size. The future track and intensity forecast relies heavily on computer model predictions from weather services around the world. But the forecasters don’t just use this computer data blindly – it is checked against, and synthesised with, the other data sources.

In Australia, government and industry investment in supercomputing and research is enabling the development of new tropical cyclone forecast systems that are more accurate. They provide earlier warning of tropical cyclone track and intensity, and even advance warning of their formation.

Still hard to predict destruction

Better forecasting helps us prepare for the different hazards presented by tropical cyclones.

The deadliest aspects of tropical cyclones are storm surges (when the sea rises and flows inland under the force of the wind and waves) and flooding from extreme rainfall, both of which pose a risk of drowning. Worldwide, all of the deadliest tropical cyclones on record featured several metres’ depth of storm surge, widespread freshwater flooding, or both.

Wind can severely damage buildings, but experience shows that even if the roof is torn off, well-constructed buildings still provide enough shelter for their occupants to have an excellent chance of surviving without major injury.

By and large, it is the water that kills. A good rule of thumb is to shelter from the wind, but flee from the water.

https://embed.windy.com/embed2.html?lat=-28.845&lon=135.439&zoom=4&level=surface&overlay=wind&menu=&message=&marker=&forecast=12&calendar=now&location=coordinates&type=map&actualGrid=&metricWind=kt&metricTemp=%C2%B0C

Windy.com combines weather data from the Global Forecast System, North American Mesoscale and the European Centre for Medium-Range Weather Forecasts to create a live global weather map.

This means that predicting the damage and loss caused by a tropical cyclone is hard, because it depends on both the severity of the storm and the vulnerability of the area it hits.

Hurricane Katrina in 2005 provides a good illustration. Katrina was a Category 3 storm when it made landfall over New Orleans, about as intense at landfall as Australian tropical cyclones Vance, Larry and Yasi. Yet Katrina caused at least 1,200 deaths and more than $US100 billion in damage, making it the third deadliest and by far the most expensive storm in US history. One reason was Katrina’s relatively large area, which produced a very large storm surge. But the other factor was the extraordinary vulnerability of New Orleans, with much of the city below normal sea level and protected by levées that were buried or destroyed by the storm surge, leading to extensive deep flooding.

We have already seen with Hurricane Irma that higher sea levels have exacerbated the sea surge. Whatever happens in the remainder of Irma’s path, it will already be remembered as a spectacularly intense storm, and for its very significant impacts in the Caribbean and Florida. One can only imagine how much worse those impacts would have been had the populations not been forewarned.

The ConversationBut increased population and infrastructure in coastal areas and the effects of climate change means we in the weather forecast business must continue to improve. Forewarned is forearmed.

Jeffrey David Kepert, Head of High Impact Weather Research, Australian Bureau of Meteorology and Andrew Dowdy, Senior Research Scientist, Australian Bureau of Meteorology

This article was originally published on The Conversation. Read the original article.

Explainer: how does the sea ‘disappear’ when a hurricane passes by?


Darrell Strauss, Griffith University

You may have seen the media images of bays and coastlines along Hurricane Irma’s track, in which the ocean has eerily “disappeared”, leaving locals amazed and wildlife stranded. What exactly was happening?

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These coastlines were experiencing a “negative storm surge” – one in which the storm pushes water away from the land, rather than towards it.


Read more: Irma and Harvey: very different storms, but both affected by climate change


Most people are familiar with the idea that the sea is not at the same level everywhere at the same time. It is an uneven surface, pulled around by gravity, such as the tidal effects of the Moon and Sun. This is why we see tides rise and fall at any given location.

At the same time, Earth’s atmosphere has regions where the air pressure is higher or lower than average, in ever-shifting patterns as weather systems move around. Areas of high atmospheric pressure actually push down on the ocean surface, lowering sea level, while low pressure allows the sea to rise slightly.

This is known as the “inverse barometer effect”. Roughly speaking, a 1 hectopascal change in atmospheric pressure (the global average pressure is 1,010hPa) causes the sea level to move by 1cm.

When a low-pressure system forms over warm tropical oceans under the right conditions, it can intensify to become a tropical depression, then a tropical storm, and ultimately a tropical cyclone – known as a hurricane in the North Atlantic or a typhoon in the northwest Pacific.

As this process unfolds, the atmospheric pressure drops ever lower and wind strength increases, because the pressure difference with surrounding areas causes more air to flow towards the storm.

In the northern hemisphere tropical cyclones rotate anticlockwise and officially become hurricanes once they reach a maximum sustained wind speed of around 120km per hour. If sustained wind speeds reach 178km per hour the storm is classed as a major hurricane.

Surging waters

A “normal” storm surge happens when a tropical cyclone reaches shallow coastal waters. In places where the wind is blowing onshore, water is pushed up against the land. At the same time the cyclone’s incredibly low air pressure allows the water to rise higher than normal. On top of all this, the high waves whipped up by the wind mean that even more water inundates the coast.

The anticlockwise rotation of Atlantic hurricanes means that the storm’s northern side produces winds blowing from the east, and its southern side brings westerly winds. In the case of Hurricane Irma, which tracked almost directly up the Florida panhandle, this meant that as it approached, the east coast of the Florida peninsula experienced easterly onshore winds and suffered a storm surge that caused severe inundation and flooding in areas such as Miami.

The negative surge

In contrast, these same easterly winds had the opposite effect on Florida’s west coast (the Gulf Coast), where water was pushed offshore, leading to a negative storm surge. This was most pronounced in areas such as Fort Myers and Tampa Bay, which normally has a relatively low tide range of less than 1m.

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The negative surge developed over a period of about 12 hours and resulted in a water level up to 1.5m below the predicted low tide level. Combined with the fact that the sea is shallow in these areas anyway, it looked as if the sea had simply disappeared.


Read more: Predicting disaster: better hurricane forecasts buy vital time for residents.


As tropical cyclones rapidly lose energy when moving over land, the unusually low water level was expected to rapidly rise, which prompted authorities to issue a flash flood warning to alert onlookers to the potential danger. The negative surge was replaced by a storm surge of a similar magnitude within about 6 hours at Fort Myers and 12 hours later at Tampa Bay.

The ConversationRising waters are the deadliest aspect of hurricanes – even more than the ferocious winds. So while it may be tempting to explore the uncovered seabed, it’s certainly not wise to be there when the sea comes rushing back.

Darrell Strauss, Senior Research Fellow, Griffith University

This article was originally published on The Conversation. Read the original article.

Irma and Harvey: very different storms, but both affected by climate change


Andrew King, University of Melbourne

There has been no let up since Hurricane Harvey dumped record-breaking rains on the Houston area of Texas. Hurricane Irma lashed parts of the Caribbean and Cuba and is now heading onto the US mainland, having devastated the Florida Keys and the state’s west coast.

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We also have Hurricane Jose following Irma through the Caribbean, and Hurricane Katia, now downgraded after tracking through parts of eastern Mexico.


Read more: Are catastrophic disasters striking more often?


This very active season comes after a “hurricane drought” with very few major storms making landfall on the US coast over the previous decade.

So why are we seeing so many hurricanes now? Is climate change to blame?

How to make a hurricane

There are several vital ingredients needed for hurricanes to form. These include an initial disturbance in the atmosphere for the storm to form around, very warm sea surface temperatures to sustain the storm, and a lack of vertical wind shear so the storm is not torn apart during its formation.

In the Atlantic Ocean, hurricanes often form near Cape Verde off the coast of West Africa. They then track westward towards the Caribbean and the US.

Lots of factors can affect how strong these storms ultimately become, including how much time they spend gathering strength over the ocean, and the background weather patterns through which they travel.

Sea surface temperatures are well above normal over the tropical Atlantic. The effects of Hurricane Harvey mixing up cooler waters off the Texan coast can be seen.
NOAA Office of Satellite and Product Operations

This storm season we have seen sea temperatures persistently 1-2℃ above normal over the tropical Atlantic Ocean, which has allowed stronger storms to form and develop.

Atlantic sea temperatures have warmed over the past century, thus enhancing one of the key ingredients for hurricane formation. The climate change influence is clear for the sea temperatures, but not so much for the other ingredients required in forming hurricanes.

Harvey and Irma

While we have low confidence in the effect of human-caused climate change on hurricane formation, it is clear that climate change is enhancing some of the impacts of these storms.

Hurricane Harvey hit southern Texas hard by stalling over the Houston area and dumping huge amounts of rain. Climate change might have contributed to the stalling effect, but what’s clearer is that climate change is making intense extreme rainfall events like we saw over Houston more likely. By warming the atmosphere we’re also increasing its capacity to carry moisture.

When we have the trigger for heavy rainfall, climate change makes it rain harder.

Hurricane Irma is a very different beast to Harvey. It devastated several Caribbean islands including Anguilla and the Virgin Islands when it was a Category 5 system. It then struck Cuba before re-intensifying and moving north across the Florida Keys and onto the US mainland.

Irma’s main impacts have been through the storm surge, the strong winds and the heavy rains.

Climate change has likely worsened the effects of Irma. As described above, we know that climate change is intensifying extreme rain events. We also know that climate change is worsening storm surges by raising the background sea level on which these events occur.

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Sea levels are projected to rise further over the coming century, by 50-100cm under a high greenhouse gas emissions scenario, and 20-50cm if we greatly reduce our emissions.

So while it’s likely that climate change is contributing to more extreme hurricanes, we have even more confidence that climate change is worsening the impacts of these storms, and will continue to do so over the coming decades.

Paving over the Gulf Coast

Besides the climate change influence, the widespread urban development on the US Gulf Coast is exacerbating the impacts of hurricanes.

Much like the Houston area, Florida also has a growing population. This means that not only are there more people in harm’s way when a major hurricane strikes, but there is also more concrete and other impervious surfaces that allow the water to pool in low-lying areas.

Is there any good news?

While climate change and development in hurricane-prone areas are worsening the impacts of these hurricanes, there are some glimmers of good news.

Scientists’ ability to track and forecast these major systems has improved greatly. Better forecasting of hurricanes allows for earlier planning for their impacts and should improve evacuation processes.

In theory, with the right plans in place, better hurricane forecasting should reduce death tolls from events like Irma. But it doesn’t necessarily reduce the economic costs of these storms, and for both Harvey and Irma the clean-up and recovery bills will be more than A$100 billion each.

The ConversationIt’s clear that climate has worsened the impacts of Atlantic hurricanes and will continue to do so. Improved forecasting provides a glimmer of hope that the death tolls from future events can be reduced, even as the economic impacts increase.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

This article was originally published on The Conversation. Read the original article.