Typhoons key driver of N China's extreme rainfall surge, study finds

This year's typhoon season in the northwest Pacific is shaping up to be one of the most active in recent memory – and a new study from the Chinese Academy of Meteorological Sciences (CAMS) shows that the trend carries profound implications for extreme rainfall across northern China.

As of August 22, 20 typhoons have formed in the northwest Pacific and the South China Sea since January, well above the historical average of 13.4 for the January-to-August period.

Typhoons have formed every month this year, with each month exceeding the long-term average.

The 20th typhoon, Gaenari, developed on Saturday afternoon, creating a rare "three typhoons simultaneously active" scenario over the region alongside Typhoons Narra and Saudel.

Several typhoons have already made landfall in China this season, and more are forecast.

The numbers behind the surge The surge in typhoon activity is not merely statistical.

A CAMS study, based on 47 years of observational data from 428 weather stations across north China from 1977 to 2023, has quantified the link between tropical cyclones and the region's escalating extreme rainfall.

The research identifies 2002 as a tipping point: while north China's rainy-season precipitation showed no clear trend from 1977 to 2002, both total rainfall and regional extreme rainstorm events increased markedly from 2003 onward.

The numbers are striking.

Typhoons are involved in 25.9% of ordinary regional extreme rainfall events – roughly one in four.

For severe regional extreme rainfall, the share rises to 30.1%.

And for the most destructive category – extreme torrential rain – typhoons play a role in 43.3% of cases.

"The stronger the rainfall, the greater the typhoon's contribution," said Li Ying, a researcher at CAMS.

She noted that some of north China's most devastating downpours – including the July 2012 Beijing flood, the July 2021 Zhengzhou disaster and the July 2023 north China flood – all had typhoon involvement.