Ernst Rauch
Peak meteorological values and never-ending loss records
The last two years have been dominated by extreme tropical cyclones. The belief that the exceptional year of 2004 would be followed by a period of calm in 2005 turned out to be mistaken. The time has come for a radical rethinking of how hurricane risks are evaluated.
The record-breaking year of 2004
2004 was marked by the highest regional frequencies and intensities of tropical cyclones in the North Atlantic since the recording of meteorological tracks began in 1851.
Hurricane Ivan was particularly significant for the insurance industry: its HDP (Hurricane Destruction Potential), which is the sum of the squares of the maximum wind speed in 6-hour periods for the duration of the storm, was 71,250. For the sake of comparison, the average HDP value of all tropical cyclones recorded in the Atlantic in each entire season between 1950 and 1990 was 70,600.
Hurricane Ivan set new records in terms of duration and intensity, but the latest scientific findings suggest it will not be an exception for very long. The study (Emanuel [2005], Nature) quoted in the section "Climate cycles and global warming — Effects on risk evaluation" shows that the Power Dissipation Index (PDI), which represents the accumulated wind energy of tropical cyclones in the North Atlantic for a whole year, increased sharply in correlation with the higher sea surface temperature. The PDI is calculated in a similar way to the HDP. A closer analysis of this change makes it clear that there has been an increasing trend in the strength and duration of hurricanes and thus in their destruction potential too.
2005 — An increase is possible
In this season, both hurricane activity, i.e. the number of tropical cyclones, and the observed intensities reached new peak levels. The new maximum values were far above the old records of 21 tropical storms (1933) and 12 hurricanes (1969). A total of 27 named tropical cyclones developed in the North Atlantic, 15 of which reached hurricane force with wind speeds exceeding 118 km/h.
The intensities were no less striking. The list of the ten strongest hurricanes ever recorded includes Wilma, Rita, and Katrina, all from the year 2005. On 19 October, Wilma had a central pressure of 882 hPa, the lowest ever recorded. This suggests that it also had higher wind speeds than any other hurricane in the Caribbean since recordings began in 1851.
The beginning and end of the hurricane season in 2005 were also marked by exceptional meteorological features. The hurricane year began very actively with seven tropical cyclones in June and July — two more than the previous record of five by the end of July. Hurricane Epsilon marked the end of the season in December, along with Tropical Storm Zeta, which was still active in the Atlantic even at the beginning of January 2006: two storms that did not observe the "official" end of the hurricane season on 30 November.