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| LSU geography and anthropology professor Kam-biu Liu, who made the news two years ago for research showing that catastrophic hurricanes hit the Gulf Coast about once every 300 years, has taken a different tack in unearthing ancient storms. He is finding them in the libraries of China. Liu's work on the Gulf coast involved taking cores from coastal lakes and marshes, looking for places where prehistoric storm surges washed sand into the lakes. Using radiocarbon dating to date the layers, he was able to determine when, and how many, hurricanes have hit the coast for the past five millennia. His research has given birth to a new field of science called paleotempestology -- the study of past tropical cyclone activities by means of geological techniques. In his more recent work, Liu has examined more than 1,000 years of historical records from Guangdong Province on the southeastern coast of China, finding that 1,133 typhoons made landfall in this area, with clusters of more powerful storms occurring in a 50-year cycle. The 1,025-year period, beginning in 975 A.D., is the longest documentary record of tropical cyclone activity ever compiled. "In North America the record is very short. Even after Columbus it's very sketchy for the first hundred years. And the Gulf Coast has virtually nothing before the 17th century," Liu said. In China the historical record goes back 3,000 years or more. The "official history" of China was kept by each dynasty and always included lists of natural disasters, including typhoons. There are also some 2,000 local governments, or counties, in China, Liu said, and most counties kept gazettes recording every natural phenomenon worth noting -- floods, droughts, astronomical phenomena, earthquakes. And of course, for coastal counties, typhoons. Working from libraries in Hong Kong and Beijing, which contain the majority of the gazettes, Liu and his colleagues labored through hundreds of records, discovering passages like this from the Zhenhai County Gazette, Zhejiang. "In the sixth lunar month of the sixth year of the Emperor Chongzhen (1633 A.D.), a typhoon struck. Torrential rain fell for 10 days. Houses collapsed. Naval battleships were drifting in the sea; eight or nine out of 10 were destroyed, drowning numerous soldiers. Since the first year of Chongzhen there was no year without typhoon strikes. The damage was especially serious this year. It was widely believed the culprit was a mischievous dragon." Liu and his team were able to check the reliability of these accounts by comparing a 26-year period, from 1884 to 1909, when historical records overlapped with instrumental observations. The historical record under-reported the number of tropical cyclone hits, but if only typhoons were counted, the under-reporting is much smaller. More significantly, the trends in the historical record coincide positively with the trends in the instrumental data. The year-by-year accounts contained in these records are a lot more accurate than sedimentary work, Liu said. The sedimentary records are accurate only to between 100 and 200 years. They show the major cycles, but the historical record shows the annual activity imposed on these cycles. Among the interesting findings were that the most active period of typhoon landfalls, from 1660 to 1680, occurred during a time when there was virtually no sunspot activity, although the relationship between sunspots and earth's climate is unclear. Another peak in landfall activity occurred between 1850 and 1880. Both of these peaks took place during the coldest and driest periods the Northern Hemisphere has experienced in the past 500 years. Colder climate and lowered sea surface temperatures are supposed to reduce hurricane activity and intensity, but Liu speculates that climatic changes only shifted the tracks of tropical cyclones to the south, where they made landfall in Guangdong Province. His most significant discovery was that major tropical cyclone activities occur in a 50-year cycle. This is of great interest to the Chinese government because the Guangdong Province is now one of the fastest-growing economic regions in China and its long and exposed coastline makes it highly vulnerable to catastrophic storm surges and coastal flooding. Between 1949 and 1988, 158 cyclones struck Guangdong. Thirty-three of them had winds above 73 mph, marking them as typhoons. "If a typhoon the strength of Hurricane Camille were to hit Guangdong Province today, the destruction and possible loss of life would be immense," Liu said. "The logical question to ask is, what is causing these cycles?" In order to find an answer, Liu will work his way up libraries on the coast of China, then branch out into the historical records of Japan and the Philippines. "Integrating the historical data will help us understand the climatological mechanisms that control these activities," he said. "Once we understand those, it will help us predict these storms." Liu's research is supported by grants from the Risk Prediction Initiative, housed at the Bermuda Biological Station for Research and financed by the insurance industry, and the National Science Foundation. # # # |
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