Strong El Nino foments extreme weather risks

Editor's note: A rapidly intensifying El Nino in the tropical Pacific could potentially become the strongest on record. Xinhua News Agency spoke to Zhang Ling, a senior engineer at the Hubei Climate Center, and Zhu Dingzhen, a former chief expert of the China Meteorological Administration, on the potential impact on the country's weather. Below are excerpts of the interviews. The views don't necessarily represent those of China Daily.

El Nino is linked to abnormal weather patterns. Under normal conditions, sea surface temperatures across the equatorial Pacific follow a pattern of "warm in the west and cool in the east". But during an El Nino, the sea surface temperatures in the central and eastern equatorial Pacific are unusually warm for a long period.

When the sea surface temperatures rise above normal, they release heat into the atmosphere, altering atmospheric circulation and eventually contributing to floods, droughts, heat waves and other extreme weather events. This process unfolds over time.

Think of the ocean as a giant hot-water bottle. If you put a hot-water bottle in a room, it will not immediately warm up the place. Instead, the temperature will gradually increase. Similarly, atmospheric circulation takes time to adjust, just like how ripples from a stone thrown into a lake take time to reach the shore.

The current El Nino stands out for its rapid development, strong intensity and significant impact on weather. However, it has not yet been officially declared an El Nino event.

An El Nino event is defined when the three-month average sea surface temperature index reaches or exceeds 0.5 C and remains at that level for at least five consecutive months. The current period of high sea surface temperatures has not lasted that long.

At the same time, ocean warming is clearly on an upward trend, and there is a high probability that a strong El Nino event will eventually develop. It is expected to peak between November and December this year, and potentially become the strongest ever recorded.

The weather's response to El Nino doesn't necessarily coincide with changes in sea surface temperatures. Often, the effects occur several months later, a phenomenon known as the "lag effect" of El Nino. The impact on global climate typically peaks in the decaying year of the event when sea surface temperatures have started declining.

The summer following an El Nino usually sees the western Pacific subtropical high circulation system becoming stronger and shifting southward. This can take large amounts of moisture toward the Yangtze River basin, increasing the risks of heavy precipitation and widespread flooding.

In the year of an El Nino, regions south of the lower Yangtze River and South China may experience above-average autumn rainfall, while a warmer-than-normal winter is more likely across China.

The next year, multiple river basins, particularly the Yangtze River basin, can expect significantly above-average rainfall, heightening the risk of widespread flooding. Consequently, flood-control efforts will focus on these regions. Heat waves are also likely to intensify in these regions.

While El Nino has a significant influence on China's climate, it is not the only factor at work. China's geographical location and complex terrain mean that climate patterns are also affected by conditions in other oceans, as well as factors such as sea ice and snow cover.

The weather and climate patterns in China during El Nino events can vary significantly, shaped by a complex combination of factors. How strong the current El Nino will ultimately become, and exactly how it will affect China's climate and the global climate next year remains uncertain and requires further observation.