Deadly April rainfall in US South and Midwest was intensified by climate change, scientists say

Human-caused climate change intensified deadly rainfall in Arkansas, Kentucky, Tennessee and other states in early April and made those storms more likely to occur, according to an analysis released Thursday by the World Weather Attribution group of scientists.

The series of storms unleashed tornadoes, strong winds and extreme rainfall in the central Mississippi Valley region from April 3-6 and caused at least 24 deaths. Homes, roads and vehicles were inundated and 15 deaths were likely caused by catastrophic floods.

The WWA analysis found that climate change increased rainfall intensity in the storms by 9% and made them 40% more likely compared to probability of such events in the pre-industrial age climate.

Some of the moisture that fueled the storms came from the Gulf of Mexico, where water temperatures were abnormally warm by 1.2°C (2.2°F) compared to pre-industrial temperatures. That warming was made 14 times more likely due to climate change, according to the researchers from universities and meteorological agencies in the United States and Europe.

Rapid analyses from the WWA use peer-reviewed methods to study an extreme weather event and distill it down to the factors that caused it. This approach lets scientists analyze which contributing factors had the biggest influence and how the event could have played out in a world without climate change.

The analysis found a rainfall event of April’s intensity could occur in the central Mississippi Valley region about once every 100 years. Even heavier downpours are expected to hit the region in the future unless the world rapidly slashes emissions of polluting gases such as carbon dioxide and methane that causes temperatures to rise, the study said.

“That one in 100 years … is likely to go down to once every few decades,” said Ben Clarke, a researcher at the Centre for Environmental Policy at Imperial College London and the study’s lead author. “If we continue to burn fossil fuels, events like this will not only continue to occur, but they’ll keep getting more dangerous.”

Heavier and more persistent rainfall is expected with climate change because the atmosphere holds more moisture as it warms. Warming ocean temperatures result in higher evaporation rates, which means more moisture is available to fuel storms.

Forecast information and weather alerts from the National Weather Service communicated the risks of the April heavy rain days in advance, which the WWA says likely reduced the death toll. But workforce and budget cuts made by the Trump administration have left nearly half of NWS offices with 20% vacancy rates or higher, raising concerns for public safety during future extreme weather events and the upcoming Atlantic hurricane season that officially begins June 1.

“If we start cutting back on these offices or reducing the staff … the unfortunate result is going to be more death. We’re going to have more people dying because the warnings are not going to get out, the warnings are not going to be as fine-tuned as they are today,” said Randall Cerveny, a climate professor at Arizona State University who was not involved in the study.
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