The regional U.S. climate extremes index

The U.S. Climate Extremes Index was first developed in the mid 1990s with the goal of quantifying observed changes in the climate of the contiguous United States so that the results could be easily understood and used in policy decisions made by non-specialists in the field. The U.S. CEI is based on a set of climate extremes indicators, which measure the fraction of the area of the U.S. experiencing extremes in monthly mean surface temperature, daily precipitation and drought (or moisture surplus) as measured by the Palmer Drought Severity Index. Although useful, the national index provides an overview of extremes experienced across the country rather than identifying which regions of the country experienced a large/small proportion of extremes in any given season. A regional CEI is proposed which looks at the same extremes indicators, but across the 9 U.S. Standard Regions in the Contiguous United States. Year-to-year variations in the regional index will likely have higher amplitude swings and larger/smaller percentages affected by extremes compared with the national CEI since there is a good deal of spatial consistency among the indicators and similar extremes may span across or be absent from a region in any given season.