Climatological relevance of major USA weather losses during 1991–1994

Abstract

Two insurance indices, which integrate storm types with their losses from 1948 to 1994, were examined to assess the frequency and intensity of damaging weather in the USA from 1991 to 1994. These indices adjust for changing socio‒economic conditions, allowing meaningful temporal assessment of 1991–1994 conditions against those in earlier years. Catastrophes, as defined by property loss insurers, were assessed for two groups, those 707 storms with insured losses between $10 and $100 million and those 189 with greater than $100 million. Both categories experienced their greatest frequency and caused more loss during the 1991–1994 period than in any prior period. However, the temporal behaviour of annual frequency and losses for both categories were very different, with steady increases found for the $10 to $100 million catastrophes, while the number of >$100 million catastrophes exhibited a high‒low‒high distribution and the annual cost distribution was flat with a few isolated peaks. For both categories the temporal behaviour of storm intensity was similar, with moderate intensities found in the recent period and the highest intensities in the 1950s. The crop‒hail losses were high in 1992–1994, and the annual loss costs for the 1948–1994 period had a U‒shaped time distribution similar to that of the >$100 million catastrophes. Weather conditions (USA mean temperature and surface cyclone frequency) were found to largely define: (i) when major, highly expensive weather events occur (and their annual losses), and (ii) how intense catastrophic storm conditions and crop‒damaging hailstorms are during each year. Conversely, the shifting target (population as an index) for damaging (non‒hurricane) storms across the USA is the major factor in ‘creating’ storms with losses reaching into the low ($10 million) to moderate ($100 million) range. © 1998 Royal Meteorological Society.