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Tropical Cyclone Trends
Raghavan, S. and Rajesh, S.  2003.  Trends in tropical cyclone impact: A study in Andhra Pradesh, India.  Bulletin of the American Meteorological Society 84: 635-644.

What was done
The authors review the general state of scientific knowledge relative to trends in the frequency and intensity of tropical cyclones throughout the world, with special attention given to the Indian state of Andhra Pradesh, which borders on the Bay of Bengal.

What was learned
For the North Indian Ocean (NIO), comprising both the Bay of Bengal and the Arabian Sea, Ragnavan and Rajesh report that for the period 1891-1997 there was a significant decreasing trend (at the 99% confidence level) in the frequency of cyclones with the designation of "cyclonic storm" and above, and that "the maximum decrease was in the last four decades," citing the work of Srivastava et al. (2000).  They additionally note that Singh and Khan (1999), who studied 122 years of data, also found the annual frequency of NIO-basin tropical cyclones to be decreasing.  As in other parts of the world, however, they find increasing impacts of tropical cyclones; but their economic analysis leads them to conclude that "increasing damage due to tropical cyclones over Andhra Pradesh, India, is attributable mainly to economic and demographic factors and not to any increase in frequency or intensity of cyclones."  Hence, they find that "inflation, growth in population, and the increased wealth of people in the coastal areas (and not global warming) are the factors contributing to the increased impact."

What it means
The authors report "there is a common perception in the media, and even government and management circles [they mention "various publications including those of the U.S. Senate and of insurers], that [increased property damage from tropical cyclones] is due to an increase in tropical cyclone frequency and perhaps in intensity, probably as a result of global climate change." However, as they continue, "studies all over the world show that though there are decadal variations, there is no definite long-term trend in the frequency or intensity of tropical cyclones." Hence, they conclude that "the specter of tropical cyclones increasing alarmingly due to global climate change, portrayed in the popular media and even in some more serious publications, does not therefore have a sound scientific basis."

Sing, O.P. and Khan, T.M.A.  1999.  Changes in the frequencies of cyclonic storms and depressions over the Bay of Bengal and the Arabian Sea.  SMRC Report 2. South Asian Association for Regional Co-operation, Meteorological Research Centre, Agargaon, Dhaka, Bangladesh.

Srivastava, A.K., Sinha Ray, K.C. and De, U.S.  2000.  Trends in the frequency of cyclonic disturbances and their intensification over Indian seas.  Mausam 51: 113-118.

Reviewed 11 June 2003