Climate change fueled the 2020 hurricane season’s rainfall, study shows

Over the course of six months, hurricane exercise in 2020 churned like by no means noticed earlier than in the Atlantic. The season marked the most named storms on file, the most storms to make landfall in the continental United States, and chalked up greater than $40 billion {dollars} in injury. It additionally spawned two class 4 storms to hit the identical area in Central America inside weeks of each other.

A brand new study quantifies how human-caused local weather change fueled the historic season.

In 2020, local weather change elevated hourly rainfall charges from tropical storms by as much as 10 %, whereas hourly rainfall charges from hurricanes had been as a lot as 11 % larger than preindustrial situations, in line with a study launched in the present day in Nature Communications.

“One of the clearest signals of climate change is appearing within our extreme weather events, particularly with cyclones,” mentioned Kevin Reed, lead writer of the study. He mentioned he expects to see such elevated rainfall charges and accumulation in a study of 2021 and in the upcoming season “because the climate change signal is only increasing in time.”

Human-induced local weather change has elevated the world common floor temperature by greater than 1.8 levels Fahrenheit (1 diploma Celsius) since preindustrial instances. As the environment warms, analysis has proven how the elevated temperatures improve threats by hurricanes.

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For one, oceans take up greater than 90 % of Earth’s extra warmth, primarily attributed to greenhouse gases. Warmer ocean waters present extra vitality for hurricanes to type and intensify extra rapidly.

Reed and his colleagues estimated sea floor temperatures in 2020 rose by 0.72 levels to 1.6 levels Fahrenheit to (0.4 to 0.9 levels Celsius) throughout the Atlantic. With temperatures approaching file ranges, September 2020 turned the most energetic storm month on file for the Atlantic basin.

A hotter environment may maintain extra water vapor — round 7 % extra water per 1.8 diploma (1 diploma C) of warming. As a end result, extra tropical storms — particularly intense, slower-moving storms — are dropping exceptional quantities of rain.

In 2017, Hurricane Harvey dropped 50 inches of rain in Houston, which was thrice extra prone to happen due to local weather change. Researchers attributed extreme rainfall by hurricane Florence in 2018 and Dorian in 2019 to local weather change as properly.

While the impact of local weather change on giant particular person hurricanes has been researched, Reed and his colleagues selected to deal with the change in rainfall over a whole season (June 1 to Nov. 30).

“What this work shows us is that even a storm, maybe it’s a tropical storm that only dumped a couple of inches of rainfall in a given region … has still been impacted by climate change,” mentioned Reed, an atmospheric scientist at Stony Brook University. “As far as we know, this is kind of the first study to objectively apply an attribution framework regardless of intensity.”

The crew used a way often called hindcasting, or the reverse of forecasting, to estimate how a lot excessive rainfall throughout the total Atlantic hurricane season may very well be attributed to the human-induced sea floor temperature will increase. They checked out the rainfall accumulation each three hours and each three days if there was a tropical storm and hurricane.

“This climate change signal actually increases. It becomes larger in more intense storms,” Reed mentioned. “If we focus just on hurricanes instead of all storms throughout the season, we see those percentages go up a little bit.”

The study’s outcomes are usually not stunning to others in the area. Climate scientist Jose Javier Hernandez Ayala mentioned his personal analysis has proven that Hurricane Maria, which unloaded 41 inches of rain in Puerto Rico in 2017, was almost 5 instances extra prone to occur attributable to situations that had been altered by human-induced local weather change.

“Climate change is enhancing ideal conditions for higher tropical cyclone activity,” mentioned Hernandez Ayala, a professor of local weather science at Sonoma State University, in an electronic mail. “A warmer tropical Atlantic can then produce record-breaking hurricane activity that can lead to extreme rainfall accumulations like we have not seen before in the basin.”

Researchers have already predicted above-average hurricane exercise for 2022 in the Atlantic basin, partly attributable to La Niña situations, which had been additionally current in 2020 and 2021.

“All countries in the corridors of these storms should prepare for the impacts of intense winds, extreme rainfall, flash flooding and storm surge associated with the passages of these tropical cyclones,” mentioned Hernandez Ayala.

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