La Nina conditions may hit rain, lead to drought

China faces a potential winter-to-spring drought in its eastern and southern regions, as climate experts link current weather patterns to a persistent cooling of the equatorial Pacific Ocean, known as La Nina conditions.

While experts say a full-fledged La Nina event is unlikely this winter, the present conditions are still affecting precipitation patterns.

La Nina refers to a prolonged period where the sea surface temperatures across the central and eastern equatorial Pacific Ocean are unusually cool. Monitoring by the National Climate Center shows that these conditions emerged in October.

Meteorologists track these temperatures using the Nino 3.4 index, the standard metric for defining such events. When this index falls below minus 0.5 C, the region is considered to have entered La Nina conditions, said Zhang Daquan, deputy director of the center's climate prediction division.

Entering La Nina conditions is not the same as having a full La Nina event. According to the national standard, an event is officially declared only when the index remains below minus 0.5 C for at least five consecutive months.

Forecasters expect the current cooling to persist for the next two to three months before shifting toward neutral conditions around February or March of next year, which would likely prevent it from meeting the five-month threshold for an official event.

Nevertheless, sustained La Nina conditions can still influence China's climate, particularly precipitation patterns, Zhang said.

La Nina tends to create a cyclonic circulation anomaly over the western North Pacific and the South China Sea. The resulting prevailing northeasterly winds suppress the transport of water vapor from tropical regions — China's main moisture source in the winter.

As a result, precipitation in eastern and southern China may remain below normal, raising the possibility of a drought in these regions during the winter and the following spring, according to the center.

After news that China had entered La Nina conditions trended online, many netizens wondered whether this winter would be colder than usual.

Zhang responded that rather than simply linking the condition with a colder winter, China's average winter temperature is actually expected to be near or slightly above the long-term average, though overall precipitation is likely to be lower than normal.

He noted that La Nina is only one of several factors influencing China's autumn and winter climate. Arctic sea ice, Eurasian snow cover and natural variability in the atmospheric circulation systems also play important roles.

According to the center, temperatures may fluctuate sharply this winter, along with more pronounced swings between cold and warm periods.

zhaoyimeng@chinadaily.com.cn