Warmer Winters Tied to Increased Drownings in Falls Through Ice

By Lisa Rapaport

December 07, 2020

(Reuters Health) - During warm winters, ice drownings increase exponentially in regions where winter air temperatures hover just below water's freezing point of 0 degrees Celsius, a new study suggests.

Researchers examined data from medical examiners, coroners, and other government sources on more than 4,000 fatal drownings in 10 countries in the Northern Hemisphere where inland waters are typically covered in ice in the winter: Canada, Estonia, Finland, Germany, Italy, Japan, Latvia, Russia, Sweden, and the United States. The period of data collection varied by country, and spanned from as early as 1991 to as recently as 2017.

In addition, researchers examined regional data on mean air temperature and precipitation during the winter months to calculate seasonal averages. Most winter ice drownings in the study happened in the final month of winter.

Winter drownings represented from 15% to 50% of total annual drownings across all the countries in the analysis, the study found. Winter temperatures explained 48% of the variation, researchers report in PLoS ONE.

The largest number of drownings occurred when winter air temperatures were between -5 degrees C and 0 degrees C, and also in regions where indigenous traditions and livelihood require extended time on ice, the authors note. At winter air temperatures below -10 degrees C, the number of winter drownings was relatively low and similar across countries and regions.

At winter air temperatures between -10 degrees C and -5 degrees C, the variability of drownings among countries began to increase substantially, the authors write. As winter air temperatures approached 0 degrees C, the number of drownings was five times higher and varied by an order of magnitude among countries, they found.

"Freshwater requires consistently cold air temperatures for the water column to sufficiently freeze and form strong black, clear ice to bear people, snowmobiles, and trucks," said lead study author Sapna Sharma, an associate professor of biology at York University in Toronto.

"A bright, sunny day, even if temperatures are slightly below 0 degrees Celsius, promotes melting of ice, as does a heavy blanket of snow, or rain, or temperatures above 0 degrees Celsius," Sharma said by email.

Children and young adults may be more susceptible to winter ice drownings based on an analysis of a subset of data from Minnesota. Children under 9 years old and teens and young adults 15 to 39 years old accounted for more total winter drownings than older individuals.

While vehicular accidents contribute to many of these drownings, children under 9 years old accounted for 44% of drownings that didn't involve a vehicle. This suggests that these younger children are particularly vulnerable to fatalities while playing or skating on the ice, or due to curiosity or lack of supervision, the study team notes.

However, the melting process as temperatures rise closer to 0 degrees C weakens the structural integrity of the ice sheet and the ice may turn into gray, slushy ice, which is significantly weaker than black ice, Sharma said. Even if temperatures get very cold again, the gray, slushy ice remains, making ice weaker and more brittle, he added.

"Climate change is already changing ice in northern countries," Sharma said. "We're seeing later ice formation, earlier ice thaw, weaker and thinner ice and this warming has accelerated in recent decades."

While this may indeed contribute to more winter ice drownings, additional research is needed to confirm this connection, said Dr. Gary Smith, president of the Child Injury Prevention Alliance and director of the Center for Injury Research and Policy at Nationwide Children's Hospital in Columbus, Ohio.

"This study is valuable because it presents initial data and a provocative hypothesis that is relevant to the important concerns about the public health effects of global warming," Dr. Smith, who wasn't involved in the study, said by email.

"Clinicians, public health and safety professionals, and others should continue to recommend that individuals in cold climates carefully assess ice conditions before engaging in activities in or around ice-covered bodies of water to prevent drowning," Dr. Smith added.

SOURCE: https://bit.ly/39PP6Iy PLoS ONE, online November 18, 2020.

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