Deadly floods in Germany, China and North America’s sizzling heatwaves have one common link: jet stream
- Jet stream is generated when cold air from the poles clashes against hot air from the tropics, creating storms, rain and drought
- Water and mudslides overran houses and roads in Germany, killing more than 170 people and leaving hundreds missing
But the link between these far-flung extremes goes beyond warming global temperatures. All of these events are touched by jet streams, strong and narrow bands of westerly winds blowing above the Earth’s surface. The currents are generated when cold air from the poles clashes against hot air from the tropics, creating storms and other phenomena such as rain and drought.
“Jet streams are the weather – they create it and they steer it,” said Jennifer Francis, a senior scientist at the Woodwell Climate Research Center. “Sometimes the jet stream takes on a very convoluted pattern. When we see it taking big swings north and big dips southward we know we’re going to see some unusual weather conditions.”
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Aerial footage shows extent of deadly landslides in Germany
Meteorologists worry whenever those swings and dips form omega-shaped curves that look like waves. When that happens, warm air travels further north and cold air penetrates further south.
The result is a succession of unusually hot and cold weather systems along the same latitude. Under these conditions, winds often weaken and dangerous weather can remain stuck in the same place for days or weeks at a time – rather than just a few hours or a day – leading to prolonged rains and heatwaves.
“It’s just like when waves in the ocean get to a beach, overturn and break,” said Tess Parker, a research fellow at the ARC Centre for Excellence for Climate Extremes at Monash University in Melbourne. “That can happen in the atmosphere as well, and if that happens you tend to catch a high- or low-pressure system that will become stationary.”
That’s what sunk parts of Germany into floods earlier this month, as a low pressure system became pinned above the country’s western region. Heavy rains soaked the terrain for the first two days, followed by a few hours of even more intense precipitation that caused rivers to overflow.