Warming Oceans Help Hurricanes Stay Strong After Landfall

Category 3 Hurricane Delta is seen in a satellite image last month before it made landfall in Louisiana. (NASA via AP)

(CN) — A study of North Atlantic hurricanes over a 50-year period reveals that the warming ocean has supercharged hurricanes, leading to more destructive, longer-lasting storms.

“The implications are very important,” said Pinaki Chakraborty, lead author of the study and head of the fluid mechanics unit at the Okinawa Institute of Science and Technology Graduate University, in a statement. “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.”

Chakraborty and his OIST colleague Lin Li analyzed data on landfalling hurricanes recorded between 1967 and 2018. Their findings, published Wednesday in the journal Nature, reveal that while hurricanes that made landfall in the late 1960s tended to decay 75% within a day of reaching shores, contemporary hurricanes decay only 50% in the same timeframe.

In other words, hurricanes weaken almost half as quickly as they did half a century ago. What’s changed over those 50 years? The temperatures recorded at the water’s surface.

“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,” Li said in the statement.

Storms can gather more moisture from warmer seas, providing more fuel for their fire, so to speak. Hurricanes that have stocked more moisture not only release that extra wetness as rainfall once they’ve hit land, they also last longer, dissipating more slowly upon landfall.

“Hurricanes are heat engines, just like engines in cars. In car engines, fuel is combusted, and that heat energy is converted into mechanical work,” Li continued. “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.”

The storm begins to decay as it hits land because it has been separated from its source of moisture. Li and Chakraborty ran computer simulations to verify that hurricanes are able to store greater amounts of moisture when they form over oceans with higher surface temperatures.

“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,” Li said. “Our work shows these models are incomplete, which is why this clear signature of climate change wasn’t previously captured.”

Hurricanes will find more moisture in the North Atlantic over the coming decades. Humans are on track to warm the Earth by about 3 degrees Fahrenheit by 2100, and potentially 40 or more degrees by 2300. As things stand, the world’s oceans will get warmer before they cool.

“Overall, the implications of this work are stark. If we don’t curb global warming, landfalling hurricanes will continue to weaken more slowly,” Chakraborty said. “Their destruction will no longer be confined to coastal areas, causing higher levels of economic damage and costing more lives.”

The 2020 hurricane season has brought above-average storm activity to the U.S., pushing hurricane names into the Greek alphabet.
Other recent research suggests that the changing climate, especially the growing divide in the freshness of freshwater and the salinity of saltwater, have contributed to the extremity of hurricanes and other weather events.

Beside reducing greenhouse gas emissions, experts have suggested that wetland restoration projects can provide more effective storm protection at cheaper costs than sea walls, levees and other civil engineering projects.

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