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.

More than 70% of typhoon-related rainfall in North China comes not from the storms' direct landfall but from long-distance moisture transport. "A typhoon acts like a giant offshore water pump," Li explained. Even when a storm remains over the South China Sea or waters east of China's Taiwan, it can channel a stream of warm, moist air from the Pacific and the South China Sea all the way to north China, triggering heavy downpours far from the storm's center.

A warmer world, a wetter north

The findings align with a broader global pattern. The Intergovernmental Panel on Climate Change's Sixth Assessment Report expresses high confidence that human-induced climate change increases heavy precipitation associated with tropical cyclones. Global average tropical cyclone rainfall rates are projected to increase by about 7% per 1 degree Celsius of warming. Meanwhile, a study published in Proceedings of the National Academy of Sciences this year found that tropical cyclone-induced storm surges have increased globally by 20% over the 1982-2024 period.

For China, these global trends are playing out in real time. "Against the backdrop of climate change, typhoons are making landfall farther north, their paths are shifting northward, and their maximum intensity is stronger," Li said. "The number of typhoons affecting north China has increased." Warmer sea surface temperatures – a direct consequence of global warming – are creating more favorable conditions for typhoon intensification. An El Nino event developing in the equatorial Pacific is expected to further boost typhoon activity.

The implications are twofold. In the short term, the immediate risks are severe: urban flooding, mountain torrents and agricultural losses. In early July, Typhoon Maysak triggered flooding that left 159 dead and 10 missing in Guangxi, affecting more than 1.65 million people. In the longer term, shifting rainfall patterns are reshaping water resource distribution, soil moisture regimes and ecosystem dynamics across the region.