An analysis of all global heatwaves occurring between 1979 and 2020 has revealed that these extreme hot spells, which initially lasted for an average of 8 days at the start of the study period, now linger for an average of 12 days. The findings of the study were published on March 29th in Science Advances.
Amsterdam in the Heat Wave. Image Source: Koen van Weel/AFP via Getty Images
According to Zhang Wei, the corresponding author of the paper and a researcher at Utah State University, as the Earth continues to warm, heatwaves will last longer. "According to this trend, by around 2060, it could double to 16 days."
The study found that not only are heatwaves lasting longer, but they're also becoming more frequent and moving slower. This means that specific regions must endure more frequent heatwaves for longer durations.
Although heatwaves are typically thought of as localized weather events, the areas affected by extreme heat are changing over time as the weather systems causing the hot conditions move.
The research team found that the speed at which heatwaves move has slowed from around 340 kilometers per day in the 1980s to about 280 kilometers per day now. More importantly, the deceleration rate is increasing.
Despite the slower average speed, because they last longer, they spread over greater distances – the total distance affected has risen from about 2500 kilometers to around 3000 kilometers, impacting a larger area.
The study did not explore the reasons for these trends. However, researchers caution that as the Earth warms, heatwaves becoming more frequent, slower, and longer-lasting will have increasingly destructive impacts on society and nature unless more measures are taken to prevent further warming.
Most previous studies on heatwaves have focused on specific places or regions. Zhang Wei's team is among the few studying how heatwaves change over time. To do this, they divided the world into grids. Heatwaves were defined as temperatures in one or more grids far above the average temperatures from 1981 to 2010, specifically exceeding 95% of temperatures during that period, and lasting more than three days.
The results found that due to the influence of prevailing weather conditions, heatwaves tend to move in specific directions. For example, in Australia, there's a strong tendency for heatwaves to move southeast, while in Africa, they tend to move westward.
David Keellings from the University of Florida says other studies have shown that hurricanes are also moving slower. "This means that these incredibly dangerous events will last longer in any given place, and their impacts will be more pronounced." Generally, the longer people are exposed to heatwaves, the higher the hospitalization and mortality rates.
Andrea Böhnisch from the University of Munich states that the data on the duration of heatwaves largely depends on how research groups define them. If defined differently, the overall trend will remain the same, but the numbers could vary greatly. "This should be considered when studying precise numerical values," she says.
Related paper information: https://doi.org/10.1126/sciadv.adl1598
