China's weather bureau said the chance of an El Nino weather event this year is about 70 percent, which may affect China's crop output and bring conditions for drought and flooding across the country.

"An El Nino is very likely, and if formed, it is expected to reach its maximum strength during December," said Ding Yihui, a climate change adviser at the China Meteorological Administration.

El Nino is a warming of sea temperatures in the Pacific, affecting wind patterns and triggering both floods and drought worldwide. Previous El Nino events have affected crop harvests in China and caused severe droughts and water shortages.

The worst El Nino on record, in 1997 and 1998, was blamed for massive flooding along the Yangtze River that claimed thousands of lives.

Some scientists said ocean data has increased concerns that the weather pattern this year will be very strong. "We cannot tell how strong the phenomenon this year will be currently," Ding said, adding that preparations should be made.

Zheng Dawei, a professor at China Agricultural University, agreed that the authorities should take measures to reduce the potential impact of the weather pattern.

Zheng said agricultural authorities have already handed out calendars to farmers setting out early planting dates and giving them tips on managing water supplies.

Farmers in southern China should prepare for possible floods, according to Zhang.

Ding said data showed the global annual crop output can be decreased by 2 to 3 percent due to El Nino.

Zheng Fei, a researcher at the Institute of Atmospheric Physics under the Chinese Academy of Sciences, said a monthly report will be made to analyze the development and future trend of weather patterns.

El Nino - Spanish for "the boy"- is a recurring weather pattern that affects the world every two to seven years. El Nino events usually tend to develop during April and June and tend to reach their peak strength from December to February. The event typically persists for nine to 12 months, but can last up to two years.

wangqian@chinadaily.com.cn