LOSSES CAUSED BY WEATHER AND CLIMATE EXTREMES: A NATIONAL INDEX FOR THE UNITED STATES

Abstract

An annual index measuring past national losses and capable of measuring future loss from weather and climate extremes was developed to help measure future shifts in climate, a subject of great concern to the global warming issue and the insurance industry. Results from climate models indicate that a changed climate owing to global warming would alter and increase many extremes, and the objective of this study was to develop a national-scale index to monitor change in monetary losses and costs from weather and climate extremes. Forty-four historical variables addressing various aspects of weather and climate extremes and their effects on the U.S. economy since the late 1940s were assessed as potential input to such an index. Frequencies of most severe weather conditions from 1950 to 1997 did not correspond well with their financial impacts. However, hurricane losses did correspond with the frequency of intense hurricanes, and tornado losses corresponded well with the number of violent tornadic storms. Quality insurance loss data for several major storm types (thunder, hail, winter, and wind storms) were available, plus quality data on flood and hurricane losses, and all were adjusted to 1997 dollars. Techniques were developed to assess the effect of seasonal climate extremes on major crop yields and costs for electricity and natural gas consumed. Trends were upward for certain key variables between 1950 and 1997, including the incidence and losses associated with winter storms, flood losses, crop losses, and incidence of heavy rains. Trends were downward for other weather-driven loss variables including hurricane losses, energy costs, thunderstorm losses, wind storm losses, and hail losses. Nine loss variables were selected to develop the U.S. annual loss index, and in rank order, based on their average annual loss values, were energy costs, followed by losses from hurricanes, floods, severe convective storms, crops, tornadoes, winter storms, hail, and wind storms. The variables chosen also will be available in future years to allow a continuing assessment using the index. The 1950–1997 average annual index value was $17.47 billion (1997 dollars), with annual values ranging from a high of $54.4 billion in 1972 to a low of $2.4 billion in 1963. The 48-year trend of the index was unchanging with three notable high loss periods: 1950–1954, 1970–1974, and 1990–1994. [Key words: climate change, storms, natural hazards, weather extremes.]