Chinese records show typhoon cycles - Climate - Brief Article

Science News, Sept 14, 2002

Historical records compiled by local governments along China's southeastern coast during the past 1,000 years suggest that there's a regular cycle in the annual number of typhoons that strike the area.

Officials in many counties in China record events of importance in semiofficial local gazettes, or fang zhi, says Kambiu Liu, a geographer at Louisiana State University in Baton Rouge. Because gazetteers as long ago as the fifth century A.D. discriminated between typhoons and other types of storms, these archives provide a wealth of information about long-term variations in the frequency of typhoons that hit a particular area.

The documents compiled in southeastern China's Guangdong province show that since A.D. 975, at least 571 typhoons have hit land there, says Liu. Although the fang zhi probably don't record all the typhoons that struck during that period, the instrument-supplemented weather data from 1884 to 1909 suggest that the gazettes are reliable enough to reflect variations in typhoon frequency.

Guangdong province's fang zhi show that over the past 500 years, there's been a 50-year cycle in the frequency of typhoons there. That periodicity matches a long-term variation in atmospheric conditions in the northern Pacific Ocean region, says Liu. Furthermore, the two periods during which typhoons struck Guangdong province most frequently--from 1660 to 1680 and from 1850 to 1880--coincide with two of the coldest and driest periods in northern and central China. These correlations suggest that there may be a predictable cycle in atmospheric patterns that steer weather systems over southern China, Liu notes.--S. P.