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Flash floods around the world over the past week have been exacerbated by high temperatures baking the ground and reducing its ability to absorb moisture, scientists say, following a record heatwave season.
Hong Kong was paralyzed on Friday as rains from Typhoon Shahura flooded subway stations, trapped vehicles, shut down schools and the stock exchange, and shut down schools and the stock exchange, following extreme rainfall in Europe and the United States last week.
The Hong Kong Observatory recorded more than 158 millimeters of rainfall between 11pm and midnight local time, the highest hourly rainfall since records began in 1884, the government said.
In Japan, Tropical Storm Yunyang brought some of the worst daily rainfall on record to some eastern areas, officials said. Mobara recorded 392 millimeters of rain on Saturday, the most in a 24-hour period since tracking began in 1976.
Storm Daniel battered parts of southern Europe and the Mediterranean this week, causing flooding in central Greece.
After weeks of record-breaking summer heatwaves, the Greek plains have seen up to 800 millimeters of rain fall in 24 hours, equivalent to more than a year’s rainfall.
Larissa, a large agricultural center, suffered damage to crops and houses when its river banks burst, while in the city of Volos houses and roads were flooded and cars were swept away. and the popular tourist island of Skiathos.
Spain has also seen unusually high amounts of rainfall in a short period of time compared to historical rainfall. Toledo received 91.8 mm of rainfall in 24 hours, while Puerto Navacerrada received 114.8 mm of rainfall in 48 hours.
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Scientists say record temperatures could lead to increased rainfall and flooding. The Copernicus Climate Change Service reported that June to August this year was the hottest period on record, with an average temperature of 16.77 degrees, 0.66 degrees higher than the average temperature from 1990 to 2020.
Europe experienced its fifth-highest summer temperature on record, with an average temperature of 19.63 degrees, 0.83 degrees above average.
Copernicus also said above-average rainfall affected Western Europe, Turkey, Central Europe, Scandinavia, California and western Mexico, causing flooding in these areas between June and August.
“There are well-known thermodynamic arguments that indicate that rising temperatures will lead to an increase in the amount of water vapor that can be held in the atmosphere,” said Copernicus Director Carlo Buontempo. “Climate models predict that the increase in water vapor will translate into an increase in the heaviest precipitation.
“As global warming increases, heavy precipitation will generally become more frequent and intense.”
Flooding is exacerbated by high temperatures that dry out the ground, making it unable to absorb moisture from rainwater and producing excess runoff, leading to flooding.
Professor Mark McLean, director of the Lincoln Center for Water and Planetary Health, said: “Heatwaves and wildfires have not solved the problem because the ground has been baked and much of the vegetation has been burned away.”
However, Buontempo noted that while “the intensity of the most extreme precipitation is on an upward trend across much of Europe, the evidence is less strong in the Mediterranean”.
“The impact of ocean and atmospheric warming . . . is inconclusive, but thermodynamic arguments (again) suggest that the intensity of precipitation associated with this event is likely to increase due to warming.”
Experts also pointed out that Greece’s mountainous terrain contributed to the flooding.
“Whenever there is a heavy downpour, the runoff rates are very high because many catchments have large areas of exposed bedrock, so the precipitation is almost immediately converted into flooding,” McLean said.
The extreme conditions across Europe can also be explained by the “Omega Block” over Europe. If the jet stream – the strong winds in the area above the Earth’s surface that controls atmospheric pressure – is disrupted by storm activity in the North Atlantic, areas of high pressure could become trapped between areas of low pressure.
High-pressure areas within Omega, such as the UK, may experience unusually hot weather, while outer areas such as Spain and Greece experience stormy weather.
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