Global Warming is Affecting Present-Day Hurricanes

Rodiano Bonacci
Novembre 16, 2020

When Chakraborty and Li created virtual hurricanes that lacked stored moisture after hitting land, they found that the sea surface temperature no longer had any impact on the rate of decay.

Over the years, scientists have found lots of evidence that hurricanes are becoming more unsafe as the planet heats up.

Climate change means the air over the oceans can hold more of this moisture, intensifying the storms at sea.

This implies that in the days to come, as the globe continues to warm, hurricanes would probably reach communities that are residing further inland and cause more destruction.

Stormy futures " The implications are very important, especially when considering policies that are put in place to cope with global warming", said Professor Pinaki Chakraborty, senior author of the study and head of the Fluid Mechanics Unit at the Okinawa Institute of Science and Technology Graduate University (OIST).

While the reinsurance and ILS industry will also acutely remember the fact certain catastrophe risks models for hurricanes were adjusted for a slower degradation of tropical wind speeds overland, causing significant shifts in expected losses for covered portfolios of risk. "There's been a huge slowdown in the decay of hurricanes".

Researchers says that climate change gives the storms more energy, which continues to power them over land.

Although the study does seem to line up with other recent work showing an increased intensity from the largest hurricanes, outside researchers said more data for cyclones outside the Atlantic are needed to confirm this trend. But this is the first study to establish a clear link between a warming climate and the smaller subset of hurricanes that have made landfall. And they observed that during the duration of the first day following landfall, present-day hurricanes weakened nearly twice as slowly as they did half a century ago.

Chakraborty and his team analyzed North Atlantic hurricanes that made landfall over the past 50 years and found that over the first day the storms hit land, they weakened almost twice as slowly as they did five decades ago. Once these simulated hurricanes reached Category 4 strength, the team simulated their making landfall by turning off any upwelling moisture.

"This stored moisture constitutes a source of heat that is not considered in theoretical models of decay", the researchers explained, suggesting that any models not considering this may not be accurately forecasting hurricane damage potential over land. "Without fuel, the vehicle will decelerate, and without its moisture source, the hurricane will decay", Li further added.

In addition, they conclude that the slowdown in the decay of hurricanes over land over time, is "in direct proportion to a contemporaneous rise in the sea surface temperature".

Hurricanes that make landfall are taking more time to weaken - and climate change may be to blame. They only weaken by around 50 percent after landing, which means that hurricanes are twice as intense today and last twice as long.

The team used computer simulations to test the link between warmer sea surface temperature and slower weakening of hurricanes that reached land, which allowed them to set different temperatures during the study. All in all, they write that "warmer oceans significantly impact the rate that hurricanes decay, even when their connection with the ocean's surface is severed". Using additional simulations, they found that "stored moisture" was the missing link.

The researchers subsequently produced virtual hurricanes that did not contain this stored moisture after hitting land and observed that the temperature of the sea surface no longer had any effect on the decay rate.

The new study emphasizes the significance of climate models to cautiously consider the stored moisture when estimating the effect of warmer oceans on hurricanes.

When hurricanes make landfall, they carry a stock of moisture that slowly depletes. "Our work shows these models are incomplete, which is why this clear signature of climate change wasn't previously captured", said Li.

This study joins previous studies, many by Kossin, that show tropical systems are slowing down more, wetter, moving more toward the poles - and that the strongest hurricanes are getting stronger. "Their destruction will no longer be confined to coastal areas, causing higher levels of economic damage and costing more lives".

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