Background
The authors note that "two recent studies argued that tropical cyclone intensity has increased markedly in recent decades," citing the works of Emanuel (2005) and Webster et al. (2005); and they say that because those researchers "argued that topical cyclone activity over the western North Pacific has been changed in response to the ongoing global warming," they decided to see if any related increases in tropical cyclone activity occurred over China between 1957 and 2004.

What was done
Ren et al. analyzed tropical cyclone (TC) precipitation (TCP) data from 677 Chinese weather stations for the period 1957 to 2004, searching for evidence of long-term changes in TCP and TC-induced torrential precipitation events.

What was learned
Interestingly, the seven Chinese researchers report that "significant downward [our italics] trends are found in the TCP volume, the annual frequency of torrential TCP events, and the contribution of TCP to the annual precipitation over the past 48 years." In addition, they say that the downward trends were accompanied by "decreases in the numbers of TCs and typhoons that affected China during the period 1957-2004."

What it means
In a conclusion that differs dramatically from the recent provocative claims of Emanuel (2005) and Webster et al. (2005) relative to inferred increases in topical cyclone activity over the western North Pacific in recent decades, Ren et al. say their findings "strongly suggest that China has experienced decreasing [our italics] TC influence over the past 48 years, especially in terms of the TCP."

References
Emanuel, K.A. 2005. Increasing destructiveness of tropical cyclones over the past 30 years. Nature 436: 686-688.

Webster, P.J., Holland, G.J, Curry, J.A. and Chang, H.-R. 2005. Changes in tropical cyclone number, duration, and intensity in a warming environment. Science 309: 1844-1846.