AsianScientist (May. 19, 2025) – Extreme rainfall events in China, from flash floods to devastating landslides, often leave a trail of destruction. While their frequency and intensity have been studied extensively, one crucial element has remained elusive: duration. How long it rains can be just as critical as how hard it rains. Now, a team of climate scientists may have found the key to predicting such prolonged rainfall — hidden in the oceans.
A new study published in Advances in Atmospheric Sciences reveals that global oceanic patterns can serve as early warning signals for extreme summer rainfall in China. The study identifies how six major oceanic modes influence Summer Extreme Persistent Precipitation (SEPP) or prolonged heavy rainfall that can lead to severe flooding.
“This is like finding hidden messages in our oceans,” said lead author Xiaoyu Liu of Guangdong Ocean University. “Winter sea temperatures in the tropical Pacific, for example, give us clear signals about summer flood potential.”
China is especially vulnerable to extreme rainfall, in part due to its sensitivity to climate change and its location in the East Asian monsoon region. The IPCC (2021) reported that rainfall is expected to be stronger and more frequent under global warming as well as result in frequent and severe floods. Therefore, analysing the patterns behind long-lasting summer rainfall events is crucial for improving preparedness and reducing risks.
To understand this, the researchers used climate data from 1961 to 2020 to identify six major oceanic modes —long-term sea temperature patterns— that influence rainfall duration, total precipitation, and daily rainfall intensity. Among the most significant drivers were the tropical Pacific and Indian Oceans, whose temperature fluctuations were linked with 85 percent of prolonged rainfall events.
Their model demonstrated impressive predictive power: winter ocean temperatures alone could forecast summer SEPP events with up to 75 percent accuracy, six to eight months in advance.
But how exactly do oceans drive extreme rainfall?
The key lies in moisture transport. In case of China’s summer, warmer ocean surfaces pump more water vapour into the atmosphere, which is then carried over China by wind patterns.
“Our experiments showed that warming in the Pacific and Indian Oceans, especially in winter and summer, intensifies rainfall over China,” explained Yu Zhang, the study’s corresponding author. “The subtropical high and monsoon winds act like a conveyor belt, pulling in moisture from the western Pacific and Indian Ocean, while stronger upward air motion fuels heavier downpours.”
The team’s findings are being incorporated into China’s national flood warning system, with pilot testing beginning in the 2025 rainy season.
However, some challenges still remain.
Bian He, another corresponding author from the Institute of Atmospheric Physics at the Chinese Academy of Sciences, said that current models can’t fully predict ocean-rainfall interactions beyond one year, and some complex relationships are still missing.
“Our next step is to use more advanced climate models to refine these forecasts, He added.
As global warming alters ocean temperatures, understanding these connections could help improve seasonal rainfall forecasts, giving governments and disaster agencies more time for disaster preparedness.
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Source: Guangdong Ocean University; Image: Shutterstock
The study can be found at: The Month-to-Year Precursory and Synchronous Inherent Connections between Global Oceanic Modes and Extreme Precipitation over China
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