Explained | The cause behind heavy rainfall in China that broke record of 140 years

China is currently battling with record rainfall with thecapital city Beijing and northern parts of the country drowning in floods. Typhoon Doksuri, which tore through the Pacific last week, still continues to wreak havoc triggering thousands of evacuations.

The situation is so intense in the second most populous country in the world that the weather service officials released a statement on Tuesday saying that the Chinese capital Beijing had received the "heaviest rainfall in over 140 years", since the inception of record-keeping.

"The maximum value of rainfall recorded during this storm, which was 744.8 millimetres, occurred at the Wangjiayuan Reservoir in Changping," the Beijing Meteorological Service said.

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The torrential rains, up until Tuesday (August 1), had claimed the lives of at least 20 people while 27 people were still missing.

As per reports, more than 52,000 peoplehave been evacuated from Beijing and moved to safer areas since the extreme rains battered the city in late July.

In the Fangshan district, power to some 60,000 homes was knocked out.

Doksuri, which is the most powerful typhoon to hit China this year and the second-strongest to hit the southeastern province of Fujian since 2016, has prompted the authorities to use a flood storage reservoir in Beijing for the first time since it was first built, over 25 years ago, after the rivers in the country swelled up to record levels.

On Friday (August 4), China released a statement saying that natural disasters had claimed the lives of at least 147 people, with several missing in the month of July after record rainfall hit the country's capital.

China's Ministry of Emergency Management said that 142 of the deaths or disappearances recorded in the month of July were caused by flooding or geological disasters.

The remaining five deaths or disappearances were due to other natural disasters such as drought.

Extreme rainfall

According to reports, since Saturday, the amount of rainfall that has been pouring has breached many local meteorological records.

A precipitation reading of 744.8mm (29.3 inches) was recorded by a reservoir in Beijing's Changping district between Saturday and Wednesday, which is the most to be logged in the city in over 140 years.

The previous record of 609mm was set in the year 1891.

In Hebei, 1,003mm of rain was recorded by a local weather station for a three-day period, i.e. from Saturday to Monday. Such an amount is usually witnessed over a year and a half.

What caused the extreme downpour?

As per Chinese meteorologists, besides the remnants of Doksuri, warm and humid air-flows and water vapour brought by Typhoon Khanun slowly moving in the Western Pacific also created the conditions for the heavy rains.

The meteorologists say that as the residual circulation of Doksuri's rain clouds headed north, a subtropical and continental high-pressure system in the atmosphere also barricaded their north and eastward passage, which further lead to the continuing conjunction of water vapour that acted like a dam storing the water.

Another factor that contributed to the extreme weather condition was the topographic features. As large amounts of vapour gathered in northern China, it was then lifted up by a low-altitude wind, shifting precipitation east of the Taihang mountain range, where the worst-hit areas, including Beijing's Fangshan and Mentougou districts, are located.

Meanwhile, a series of convective clouds gathered over the area, which lead to heavy rainfall for a lengthy period of time, further worsening the damage and problematising rescue operations.

The damage caused by rains

In the urban areas of the capital city of Beijing, several roads were flooded which forced the closure of parks and tourist spots.

The city's two major airports witnessed delays or cancellations of flights. Some subway lines and trains were also suspended.

The impact of rainfall was more evident in the city's western suburbs. In Mentougou and Fangshan districts, raging water rushed down roads, sweeping away cars. Villages in mountainous areas were completely cut off due to the extreme weather situation which further prompted the authorities to deploy helicopters to drop off food, water and emergency supplies.

Hebei's Zhuozhou, a city with more than 600,000 people to the southwest of Beijing, was half-immersed, with about 134,000 residents affected and one-sixth of the city's population evacuated.

Similar weather events in the past

The extreme weather conditions witnessed by Beijing currently are unusual for its surroundings. Previously, the Chinese capital has observed at least 12 incidences of significant rain brought by typhoons since authorities started keeping records, as per the state media.

Typhoon Haitang and Ampil both spilled over 100mm of rain on Beijing in the years 2017 and 2018 respectively. One of the most significant rain events was caused by Typhoon Wanda in the year 1956, which discharged more than 400mm of precipitation in the densely populated city.

(With inputs from agencies)

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