A recent study has revealed that the devastating biennial floods along China's Yangtze River are not merely a product of local atmospheric conditions, but are significantly influenced by subsurface oceanic fluctuations thousands of kilometers away in the Indian Ocean.

Researchers at the Korea Institute of Ocean Science and Technology (KIOST), led by Dr. Kang Dong-jin, have identified that 'Rossby waves'—massive, rotating water currents caused by the Earth’s rotation—play a pivotal role in these climate disasters. By analyzing 65 years of hydrological and atmospheric data since 1960, the team demonstrated how these waves travel eastward across the Indian Ocean, suppressing the upwelling of cold deep-sea water. This process results in an abnormal rise in sea surface temperatures.

The heated Indian Ocean waters warm the surrounding atmosphere, which in turn strengthens the North Pacific subtropical high-pressure system. This atmospheric shift funnels a massive amount of hot, humid air toward the Yangtze River basin, triggering intense torrential rains.

The study highlights that this cycle has increasingly occurred on a biennial basis. As the speed of the Indian Ocean's Rossby waves has accelerated, the timing of the ocean-heating effect now aligns more precisely with East Asia’s summer monsoon season. Consequently, major summer floods in the Yangtze basin, which occurred only five times in the 30 years prior to 1990, have surged to 11 instances since then. Notably, since 2010, almost all catastrophic floods have occurred in even-numbered years (2010, 2016, 2020, 2024).

This research, published in the international journal Nature Communications, underscores the growing need to view climate change through a global lens. Dr. Kang noted, "We can no longer explain the weather patterns of the Korean Peninsula by looking at our immediate vicinity alone. Small changes in the distant Indian Ocean can trigger extreme weather events in East Asia."

The findings have direct implications for Korea. The massive volume of low-salinity water generated by Yangtze River floods often drifts toward the West Sea and Jeju Island, posing a significant threat to sedentary marine life such as abalone and conch. Given the clear biennial pattern observed in the past—specifically in 1996, 2016, and 2024—experts are urging extra vigilance for the summer of 2026.

Professor Nam Sung-hyun of Seoul National University emphasized, "While it may not be a perfect two-year cycle, the pattern has become increasingly regular. Given that this is an even-numbered year, thorough preparation for potential flooding and the subsequent influx of low-salinity water is essential."

This collaborative study involved the participation of Seoul National University, the U.S. National Oceanic and Atmospheric Administration (NOAA), and the Indian Institute of Tropical Meteorology.

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