What was done
In the words of the authors, they "developed a Tropical Cyclone Potential Impact Index (TCPI) based on the air mass trajectories, disaster information, intensity, duration and frequency of tropical cyclones," using observational data obtained from the China Meteorological Administration's Yearbook of Tropical (Typhoon) Cyclones in China for the years 1951-2009, plus the Annual Climate Impact Assessment and the Yearbook of Meteorological Disasters in China, also compiled by the China Meteorological Administration, but for the years 2005-2009.

What was learned
Xiao et al. say their results reveal that "China's TCPI appears to be a weak decreasing trend over the period [1949-2009], which is not significant overall, but significant in some periods." They also report that over one of those periods, i.e., "over the past 20 years, the TCPI decreased in the southern China coastal provinces of Hainan, Guangdong and Guangxi, while it increased in the southeastern coastal provinces of Zhejiang, Fujian and Taiwan." And they confirm that "the TCPI has a good correlation (P = 0.01) with direct economic loss, rainfall and maximum wind speed."

What it means
Once again -- and in a huge regional contradiction of the claims of the IPCC (2001, 2007), which are made for the world as a whole -- the work of Xiao et al. (2011), like that of Ying et al. (2011), indicates that tropical cyclones impacting China have not been increasing in either frequency or ferocity over the past half-century or more, which has also been the case in many other parts of the world (see Tropical Cyclones in our Subject Index).

References
IPCC. 2001. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom.

IPCC. 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom.

Ying, M., Yang, Y-H., Chen, B-D. and Zhang, W. 2011. Climatic variation of tropical cyclones affecting China during the past 50 years. Science China Earth Sciences 54: 10.1007/s11430-011-4213-2.