Extreme rainfall events can lead to devastating floods, landslides, and widespread damage, yet predicting them remains a significant challenge. While scientists typically focus on how frequently and intensely it rains, the duration of rainfall is equally important in assessing its impact. However, research on prolonged extreme rainfall has been limited-until now.
A recent study reveals that global ocean patterns can act as early warning signals for extreme summer rainfall in China. Published in Advances in Atmospheric Sciences, the research identifies how six major oceanic modes influence Summer Extreme Persistent Precipitation (SEPP)-a phenomenon characterized by prolonged heavy rainfall that can lead to severe flooding.
Analyzing data from 1961 to 2020, the researchers examined rainfall duration, total precipitation, and daily intensity to understand SEPP patterns. They then connected these trends to global oceanic conditions using advanced statistical modeling and climate simulations.
"This is like discovering hidden messages in our oceans," said the lead author, LIU Xiaoyu, from Guangdong Ocean University. "Winter sea temperatures in the tropical Pacific, for instance, provide clear signals about summer flood potential."
The study shows that winter ocean temperatures can predict summer rainfall persistence with 75% accuracy. Additionally, combined patterns from the Pacific and Indian Oceans account for 85% of the duration of these prolonged events. Moreover, new forecasting models can predict rainfall persistence six to eight months in advance.
But how do oceans influence extreme rainfall? The key factor is moisture transport, as demonstrated in the study. For China's summer, warmer ocean surfaces contribute more water vapor to the atmosphere, which is then transported over China by prevailing wind patterns.
"Our experiments illustrated that warming in the Pacific and Indian Oceans-particularly during winter and summer-intensifies rainfall over China," explained Prof. ZHANG Yu, the study's corresponding author. "The subtropical high and monsoon winds function like a conveyor belt, drawing in moisture from the western Pacific and Indian Ocean, while stronger upward air motion leads to heavier downpours."
The team's findings are being integrated into China's national flood warning system, with pilot testing set to begin in the 2025 rainy season.
