• Firefighters battled wildfires in Turkey and France and more than 50,000 people were evacuated as an early summer heatwave hit Europe on June 30.

• Health alerts were issued in France, Spain, Italy, Portugal and Germany. Even the Netherlands, used to a milder climate, issued a warning for high temperatures in the coming days, coupled with high humidity.

• Large parts of Western Europe were in the grip of a severe heatwave, with temperatures breaching 40°C and wildfires breaking out in France.

• Scientists said the extreme temperatures in the region were related to a ‘heat dome’.

• Experts link the rising frequency and intensity of these heatwaves to climate change, warning that such extreme weather events are becoming increasingly common across Europe.

What is ‘heat dome’?

• A heat dome is an area of high-pressure air in the atmosphere which gets stuck in place over a region because atmospheric dynamics around it block it from moving.

• A heat dome occurs when a persistent region of high-pressure traps heat over a particular area, and it can linger for days to weeks. 

• It works like putting a lid on a boiling pot. The high-pressure system traps hot air below it, which heats up and compresses to form a dome. 

• Heat domes are typically linked to the behavior of the jet stream, which is a band of fast-moving winds high in the atmosphere that move in meandering wavelike patterns. When the jet stream meanders north, it moves slower and can sink, which lowers humidity. This allows the Sun to create progressively hotter conditions on the ground. 

• Air descending down mountains can also contribute to heat domes, as it warms even more. 

• Heat domes are not a new type of weather pattern.

• It builds up over time. The longer the “dome” is stuck over one area, the more that dark surfaces below, such as roads and buildings, absorb and retain heat, and the more that the ground dries out. 

• It also makes wildfires more likely, because the heat dries out vegetation.

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