Tropical cyclones rank with floods as the most devastating of all natural catastrophes. Vulnerability to tropical cyclones is increasing due to the rapid population growth in coastal tropical regions. Most of the damage and loss of life is caused by intense (maximum sustained winds of 33ms-1) and super-intense (maximum sustained winds winds of 50ms-1) tropical cyclones. In the US, for example, super-intense events (called intense hurricanes) cause 84% of the total damage. In recent years studies have examined trends in tropical cyclone numbers in the Atlantic, northwest Pacific and around Australia to look for changes linked to climate change. Based largely on these studies, the Henderson-Sellers report (1998) concluded there was little or no expectation for a change in global tropical cyclone frequency due to greenhouse warming.
We report the results of a study of the trends in global intense and super-intense tropical cyclone numbers for 1969-1997. We also examine trends in global intense landfalling events and ‘high-impact’ landfalling events - the latter defined by a population density threshold of 180 people/km2. Our tropical cyclone data come from the National Climatic Data Center, and our 5 arc minute global population data are obtained from the Global Demography Project, University of California. We select 1969 as the year from which global satellite identifications of tropical cyclones are regarded to be accurate, but also examine trends for the more recent 1979-1997 period during which the Dvorak technique has provided consistent intensity estimates. We find that the annual (and seasonal) number of intense and super-intense events have increased by 32% and 59% respectively for 1969-1997. These upward trends are significant to 99%. For the same period, the annual number of super-intense landfalling events has increased by 57% (significant to 91%), and the annual number of high-impact landfalling events has increased by 53% (significant to 84%). Similar trends occur for 1979-1997. We discuss possible causes for these increases.