Climate change causes landfalling hurricanes to stay stronger for longer
Warming oceans means hurricanes weaken more slowly and inflict more destruction farther inland, new study shows

Date:
November 11, 2020
Source:
Okinawa Institute of Science and Technology (OIST) Graduate
University
Summary:
Climate change is causing hurricanes that make landfall to take
more time to weaken, reports a new study. Researchers showed that
hurricanes that develop over warmer oceans carry more moisture and
therefore stay stronger for longer after hitting land. This means
that in the future, as the world continues to warm, hurricanes
are more likely to reach communities farther inland and be more
destructive.



FULL STORY ========================================================================== [Hurricane photo | Credit: (c) EvgeniyQW / stock.adobe.com] Hurricane
photo illustration (stock image; elements furnished by NASA).

Credit: (c) EvgeniyQW / stock.adobe.com [Hurricane photo | Credit: (c) EvgeniyQW / stock.adobe.com] Hurricane photo illustration (stock image; elements furnished by NASA).

Credit: (c) EvgeniyQW / stock.adobe.com Close Climate change is causing hurricanes that make landfall to take more time to weaken, reports a
study published 11th November 2020 in the journal Nature.


==========================================================================
The researchers showed that hurricanes that develop over warmer oceans
carry more moisture and therefore stay stronger for longer after hitting
land. This means that in the future, as the world continues to warm,
hurricanes are more likely to reach communities farther inland and be
more destructive.

"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). "We know that coastal areas need to ready themselves for more intense hurricanes, but inland communities, who may
not have the know-how or infrastructure to cope with such intense winds
or heavy rainfall, also need to be prepared." Many studies have shown
that climate change can intensify hurricanes -- known as cyclones or
typhoons in other regions of the world -- over the open ocean.

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.

The scientists analyzed North Atlantic hurricanes that made landfall
over the past half a century. They found that during the course of the
first day after landfall, hurricanes weakened almost twice as slowly
now than they did 50 years ago.

"When we plotted the data, we could clearly see that the amount of time
it took for a hurricane to weaken was increasing with the years. But
it wasn't a straight line -- it was undulating -- and we found that
these ups and downs matched the same ups and downs seen in sea surface temperature," said Lin Li, first author and PhD student in the OIST
Fluid Mechanics Unit.



==========================================================================
The scientists tested the link between warmer sea surface temperature
and slower weakening past landfall by creating computer simulations of
four different hurricanes and setting different temperatures for the
surface of the sea.

Once each virtual hurricane reached category 4 strength, the scientists simulated landfall by cutting off the supply of moisture from beneath.

Li explained: "Hurricanes are heat engines, just like engines in cars. In
car engines, fuel is combusted, and that heat energy is converted into mechanical work. For hurricanes, the moisture taken up from the surface
of the ocean is the "fuel" that intensifies and sustains a hurricane's destructive power, with heat energy from the moisture converted into
powerful winds.

"Making landfall is equivalent to stopping the fuel supply to the engine
of a car. Without fuel, the car will decelerate, and without its moisture source, the hurricane will decay." The researchers found that even
though each simulated hurricane made landfall at the same intensity,
the ones that developed over warmer waters took more time to weaken.



========================================================================== "These simulations proved what our analysis of past hurricanes had
suggested: warmer oceans significantly impact the rate that hurricanes
decay, even when their connection with the ocean's surface is severed. The question is -- why?" said Prof. Chakraborty.

Using additional simulations, the scientists found that "stored moisture"
was the missing link.

The researchers explained that when hurricanes make landfall, even
though they can no longer access the ocean's supply of moisture, they
still carry a stock of moisture that slowly depletes.

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

"This shows that stored moisture is the key factor that gives each
hurricane in the simulation its own unique identity," said Li. "Hurricanes
that develop over warmer oceans can take up and store more moisture, which sustains them for longer and prevents them from weakening as quickly."
The increased level of stored moisture also makes hurricanes "wetter"
-- an outcome already being felt as recent hurricanes have unleashed devastatingly high volumes of rainfall on coastal and inland communities.

This research highlights the importance for climate models to carefully
account for stored moisture when predicting the impact of warmer oceans
on hurricanes.

The study also pinpoints issues with the simple theoretical models widely
used to understand how hurricanes decay.

"Current models of hurricane decay don't consider moisture -- they just
view hurricanes that have made landfall as a dry vortex that rubs against
the land and is slowed down by friction. Our work shows these models are incomplete, which is why this clear signature of climate change wasn't previously captured," said Li.

The researchers now plan to study hurricane data from other regions
of the world to determine whether the impact of a warming climate on
hurricane decay is occurring across the globe.

Prof. Chakraborty concluded: "Overall, the implications of this work
are stark.

If we don't curb global warming, landfalling hurricanes will continue
to weaken more slowly. Their destruction will no longer be confined
to coastal areas, causing higher levels of economic damage and costing
more lives."

========================================================================== Story Source: Materials provided by Okinawa_Institute_of_Science_and_Technology_(OIST)
Graduate_University. Original written by Dani Ellenby. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Lin Li, Pinaki Chakraborty. Slower decay of landfalling hurricanes
in a
warming world. Nature, 2020; 587 (7833): 230 DOI:
10.1038/s41586-020- 2867-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/11/201111122826.htm

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