Development of an index to monitor national extreme weather-climate impacts in the United States

This study has developed a weather-climate extremes index based on economic measures of the impacts from the major weather and climate extremes occurring in each year in the contiguous United States. The index is designed to serve as a measure of how the climate, as defined by those conditions that cause major financial losses in the U.S., has been and will be fluctuating over time. This annual measure of impacts is labeled the "National Extreme Weather-Climate Impact Index," or NEWCLI.

The index was developed after an assessment of a wide variety of historical data on extremes, each with at least 40 years duration. The variables ultimately chosen for the index would also have to be available in future years to allow for a continuing assessment of the future fluctuations exhibited by the index. After much assessment, nine variables, each expressed in monetary amounts adjusted for changing dollar values and other conditions affecting losses, were identified for inclusion in calculating the annual index values for the U.S. These are: 1) hurricane losses, 2) costs of temperature extremes in energy use, 3) flood losses, 4) drought and wetness effects on crop losses, 5) severe storm property losses, 6) tornado losses, 7) crop-hail losses, 8) winter storm losses, and 9) wind storm losses. Loss-index values for each year from 1950 to 1997 show wide fluctuations with no indication of an upward or downward time trend since 1950. The index values ranged from a low of $3 billion in 1963 to a high of $54 billion in 1972, and the average annual index value is $17.47 billion (1997 dollars).