Warming ocean waters are fueling hurricanes that can stay stronger for longer, according to a new study. As a direct result of climate change, hurricanes are taking substantially longer to weaken after they make landfall.
The researchers found that when hurricanes develop over warmer oceans, they are supplied with more moisture that extends the amount of time they will be remain powerful and destructive after making landfall. As global warming continues, hurricanes will impact more communities that are farther inland.
Study senior author Professor Pinaki Chakraborty is the head of the Fluid Mechanics Unit at the Okinawa Institute of Science and Technology Graduate University (OIST).
“The implications are very important, especially when considering policies that are put in place to cope with global warming,” said Professor Chakraborty. “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.”
Previous research has confirmed that climate change can intensify hurricanes, cyclones, and typhoons over the open ocean. However, the current study is the first to establish a clear link between global warming and North Atlantic hurricanes that have made landfall over the last five decades.
The researchers found that over the course of the first day after landfall, hurricanes are now weakening at a rate that is almost twice as slow compared to 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 study first author Lin Li.
The scientists used computer simulations to analyze the correlation between higher sea surface temperature and slower weakening past landfall. When a hypothetical hurricane reached category 4 strength, the experts simulated landfall by cutting off the supply of moisture from beneath.
“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,” explained Li.
“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 study revealed that even when simulated hurricanes 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 Professor Chakraborty.
Upon further analysis, the researchers tracked the additional intensity of slower weakening hurricanes to “stored moisture.” The study authors explained that when hurricanes make landfall, even though they can no longer access the ocean’s supply of moisture, they still carry moisture that is slowly depleted.
The increased level of stored moisture also drives “wetter” hurricanes that dump devastating amounts of rain during and after landfall.
The findings highlight the importance for climate models to carefully account for stored moisture to accurately forecast the impact of warmer oceans on hurricanes.
“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,” said Li. “Our work shows these models are incomplete, which is why this clear signature of climate change wasn’t previously captured.”
The researchers will expand upon their work to examine hurricane data from other regions of the world.
“Overall, the implications of this work are stark. If we don’t curb global warming, landfalling hurricanes will continue to weaken more slowly,” said Professor Chakraborty. “Their destruction will no longer be confined to coastal areas, causing higher levels of economic damage and costing more lives.”
The study is published in the journal Nature.
By Chrissy Sexton, Earth.com Staff Writer