Climate change is not slowing down. It is linked to more frequent and intense extreme weather events. A scientific study confirms that hurricanes and tropical cyclones bring heavier rainfall. Hurricane Ian, which affected several Caribbean nations and parts of the United States and caused over a hundred fatalities, exemplifies researchers warning that unprecedented rainfall can accompany such storms.
Theoretical models suggested that rainfall rates in tropical cyclones should rise as environments warm, but this idea had not been tested on a global scale. Two researchers from Florida International University undertook that analysis.
Óscar Guzmán and Haiyan Jiang examined tropical cyclone rainfall from 1998 to 2016 and found an upward trend around 1.3 percent per year. They explain that the rise was more pronounced in the Pacific Northwest and the North Atlantic and remained fairly uniform across different cyclone intensities.
Their results indicate a link with higher sea surface temperatures and with the total amount of water available in the cyclone environment, not the water contained within the storm core. The scientists also note that the region’s destructive power has increased recently, though it has been debated whether cyclone numbers and intensities are rising due to global warming because long term, consistent data are limited.
Differences between the two hemispheres
The study shows warming and added humidity in the northern hemisphere during the study period, supporting higher rainfall rates in that region.
In the southern hemisphere the data do not show a clear upward trend in rainfall during tropical cyclones. The authors attribute this to a smaller rise in sea surface temperatures compared with the northern hemisphere on average.
Effects of Hurricane Ian off the coast of Florida are depicted in photographs from EFE.
All signs point to warming and greater moisture in the southern hemisphere having slightly less pronounced effects on precipitation during tropical cyclones.
A key finding is that the amount of rain during a hurricane depends on the surrounding water, not the water in the storm’s core. In other words, higher temperature and humidity amplify rainfall.
The researchers also tracked changes in the maximum sustained wind speeds over the study period and found no clear upward shift in intensity.
Their interpretation is that the global rise in cyclone precipitation likely stems from increased moisture availability driven by warmer sea surface temperatures under stable relative humidity.
This work is part of a broader study titled missing from the original publication details but issued with the title Assessing Tropical Cyclones and Climate Change Part II which focuses on how anthropogenic warming may alter cyclone behavior. Resulting insights were published in 2020 by a collaboration of American, Chinese, Japanese, South Korean, Australian, and Indian researchers.
Big storm surges
The research team sought to identify what changes in tropical cyclone activity could accompany a two degree Celsius rise in global warming. The main projections include higher storm surges as sea levels rise. There is moderate to high confidence that global precipitation in close storm scenarios would increase by around 14 percent with a two degree rise due to more atmospheric water vapor. For cyclones in categories 1 to 3, most authors expect a global average intensity increase, with a projection near five percent for a two degree warming. For the most intense category 4 and 5 storms, the predicted accompanying rainfall increase is about thirteen percent.
Photographs of Hurricane Ian near Cuba and Florida are attributed to NOAA.
However, a notable difference exists between this study and estimates from the University of Florida. While the Florida model suggests about fourteen percent more rainfall for a two degree warming, the newer study projects a twenty one percent rise for a much smaller temperature change of 0.21 degrees Celsius across nineteen years.
The researchers attribute this disparity primarily to the stronger role of increased precipitation within the tropical cyclone environment and the surrounding atmosphere.
Reference work: a Nature Communications article that discusses these findings and related methods.
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The environment department acknowledges the study findings and continues to explore implications for weather prediction and climate policy.