Has the frequency of intense tropical cyclones increased in the north Indian Ocean?

An effort has been made to settle the question whether the intense cyclones have become more frequent over the north Indian Ocean, posing a more serio us threat to the vulnerable coastal population of the region. The results o f the study, which has considered the entire existing data of 122 years of tropical cyclone frequency over the north Indian Ocean from 1877 to 1998, h ave shown that there is indeed a trend in the enhanced cyclogenesis during November and May. These months account for the maximum number of severe cyc lones over the north Indian Ocean, The increasing trend in the cyclone freq uency during these months has been primarily due to the significant positiv e trends over the Bay of Bengal, where the majority of north Indian Ocean c yclones develop. Thus the coastal regions of Bangladesh, India and Myanmar have indeed become more prone to the incidence of severe cyclones during No vember and May. There has been a two-fold increase in the tropical cyclone frequency over the Bay of Bengal during November in the past 122 years. There has been a 17% increase in the intensification rate of cyclonic distu rbances to the cyclone stage, and a 25% increase to severe cyclone stage ov er the north Indian Ocean during November, which accounts for highest month ly average of severe cyclone frequency, All these linear trends are statist ically significant at 99% level. The increasing trend in the cyclone freque ncy during May is also highly significant but the intensification rates to cyclone and severe cyclone stages have registered only slight increasing te ndencies. The cyclonic frequencies during transitional monsoon months, June and September, have diminished considerably. The detailed results have bee n presented for November and May only.