EXPLAINER: What caused the record rainfall in Beijing and northern China?

Beijing — Record-breaking rainfall with an unusually long duration triggered by the arrival of Typhoon Doksuri in late July has battered northern China for a week, causing huge flooding and disrupting the lives of millions.

After pelting the Chinese capital Beijing in the worst storms in 140 years and lashing nearby cities in a region the size of Britain, the rain finally shifted to China’s northeast near its border with Russia and North Korea where their power, though weakened, remained potent.

How severe was the rainfall? 

The amount of rainfall since Saturday broke many local records in Beijing and northern China, with the vast Haihe river basin experiencing the worst flooding caused by storms since 1963.

A reservoir in Beijing’s Changping district logged 744.8mm of precipitation between Saturday and Wednesday, the most in the city in over 140 years.

In the populous province of Hebei, one weather station recorded 1,003mm of rain from Saturday to Monday, an amount normally seen over a year and a half.

What caused the extreme and prolonged rainfall? 

As Doksuri’s rain clouds headed north, a subtropical and continental high-pressure system in the atmosphere blocked their passage, leading to the continuing convergence of water vapour that acted like a dam storing the water, the meteorologists say.

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, Typhoon Khanun was gathering strength in the Western Pacific and as it approached China’s coast, a large amount of moisture was fed into Doksuri’s weakened circulation.

The interaction of the two typhoons sustained the circulation while increasing the amount of precipitation, leading to an extended and intensified impact from the storms, Chinese meteorologists told media.

How damaging was the rain? 

In urban parts of Beijing, hundreds of roads were flooded. Hundreds of flights were either delayed or cancelled.

The impact was more pronounced in the city’s western suburbs. In Mentougou and Fangshan districts, raging water coursed down roads, sweeping away cars. Villages in mountainous areas were cut off, prompting 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-submerged, with about 134,000 residents affected and one-sixth of the city's population evacuated.

Have similar weather events happened in the past? 

Rain with such intensity and duration following typhoons is unusual in northern and northeastern China. The Chinese capital has observed just 12 incidences of significant rain brought by typhoons since authorities started keeping records, according to state media.

In 2017 and 2018, Typhoon Haitang and Ampil both dumped over 100mm of rain on Beijing. Typhoon Wanda in 1956 unleashed more than 400mm of precipitation on the densely populated city.

For China’s northeast, the impact of typhoons is also rare. Most typhoons would move way west or northwest after making landfall in China, experts say.

Reuters