Improving Counts of Global Intense Tropical Cyclone Events Back to 1970

The impact of climate change on tropical cyclone frequency and intensity is a topic of great interest. Observational studies of changes in the frequency and intensity of tropical cyclones rely on the historical records of tropical cyclones being homogenous. However, changes in the numbers and coverage of satellites, the resolution of satellite imagery and increases in available frequency bands may have introduced significant inhomogeneity issues. To properly establish the current role of climate change on tropical cyclone characteristics it is necessary to identify these inhomogeneities and make corrections to the tropical cyclone datasets to account for them. Our analysis looks at global intense tropical cyclone counts (1-minute sustained winds > 95kts) back to 1970. Intense tropical cyclones cause the majority of global tropical cyclone-related economic losses. We compare the inter-annual variability of intense tropical cyclone counts to that of weaker storms within individual tropical cyclone basins and for the Northern and Southern hemispheres as a whole. We look for clear changes in variance, trends and abrupt changes in the ratio of intense tropical cyclone numbers to total storm numbers, which we would expect to be due to data inhomogeneity issues. We find that there are clear inhomogeneity issues in the 1970s and early 1980s in the Southern Hemisphere and, to a lesser extent, the Northern Hemisphere. This is due to an under-reporting of intense tropical cyclone numbers. We suggest that global intense tropical cyclone counts in the 70s and early 80s are revised upward.