Extract from ABC News
First it was heatwaves and fires. Now, Greece and southern Europe have been slammed by torrential rain and devastating flooding.
Key points:
- A meteorologist says an omega block weather pattern has caused flooding in southern Europe
- The same pattern is driving heatwave temperatures in countries further north
- A researcher says the patterns are not usually so intense
Climate scientists say extraordinarily high ocean temperatures are likely to blame, turning a "fairly common" weather set-up into a powerhouse of energy.
Scenes of water pounding down streets and rivers, while cars were washed away, were captured across Greece, Turkiye, Spain and Bulgaria as torrential rains engulfed the regions, killing at least 14 people.
The rain has smashed records in parts of Central Greece.
The coastal village of Zagora received more than 750 millimetres of rain – more than a years' worth — in the space of just 18 hours on Tuesday, according to the country's national meteorological service.
Data shows its nearest major city, Larissa, which has also been hit with heavy rain – usually receives 413mm of rainfall in an entire year.
"For Greece, this has never happened before," climatologist Monica Ionita said.
"There has been floods and damage, but the amount of rainfall that has fallen is really unprecedented."
Meanwhile, countries to the north including the UK and France are sweltering under heatwave conditions.
London was expecting its hottest day of the year on Saturday with a forecast of 33 degrees Celsius.
What's causing it?
Monash University meteorologist Michael Barnes said the downpours and the heat were connected to an atmospheric phenomenon known as an "omega block" – named after its resemblance to the Greek letter "Ω" when looking at a weather map.
The horseshoe shaped weather pattern features a high pressure system – known to bring warm, clear weather – wedged between two "cut-off" lows – which trigger storms and rain.
The arrangement causes a "block" – like a traffic jam of weather systems – with each system remaining over one place for days on end, rather than flowing from west to east as it usually would.
For those stuck underneath the low pressure system, the result is days upon days of rain, while the heat builds for those under the high pressure system.
Dr Barnes said that weather pattern had been observed across the region the past few days.
"So the western cut-off low resulted in the heavy rainfall in Spain, and the second one, which is the eastern part of this omega pattern, resulted in the heavy rainfall over Greece," he said.
He said similar scenarios had played out in Australia before, including the Lismore flooding which featured a cut-off low that "sat there and rained out for several days".
Unusual intensity
Omega blocks are a fairly regular occurrence across Europe during spring and summer, according to Dr Ionita from Germany's Alfred Wegner Institute for Polar and Marine Research.
But she said they didn't always deliver extreme weather — especially not to the degree that Greece had experienced.
She said high sea surface temperatures in the Mediterranean Sea had contributed to the situation in Greece.
"I want to emphasise, the situation would be this bad if the Mediterranean Sea were not so hot," she said.
"Basically, the waters were boiling.
"If you went there on summer vacation, it was almost impossible to actually go swim because it was so hot.
"All this water, all this energy, it's just creating the damage that we see now."
Data from the Copernicus Marine Environment Service shows temperatures in the Mediterranean have decreased from their peak in July, but remained well above normal.
Dr Barnes said the hot ocean temperatures likely played a role in its intensity, but they weren't the only reason.
"It's probably quite an intricate and complex process to unpack exactly what went on," he said.
"And there can be local effects as well, which can pay into it."
University of Melbourne climate scientist Andrew King was more cautious about making the link between the two, but said the hot oceans "might be contributing".
Role of climate change
Dr King said climate change could be another factor.
"It's likely that climate change is intensifying the events a bit, mainly through the fact that we know that in a warmer atmosphere, the moisture holding capacity increases, and so there's more moisture available for heavy rain to occur on very short timescales," he said.
"And we do see that in Europe, generally, this trend towards more extreme short duration rain events."
He said the influence climate change was having on the weather system itself was more uncertain.
"But there is a bit of evidence to suggest that having more persistent high and low pressure systems around the northern hemisphere in the warmer half of the year … that climate change is making this set up more frequent," he said.
Rainfall has started to wane across Spain and Greece as each system loses its power, but high temperatures are expected to continue for several more days in the UK.
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