May 15, 2008

A Revised U.S. Climate Extremes Index

Karin L. Gleason, Jay H. Lawrimore, David H. Levinson, Thomas R. Karl, and David J. Karoly
American Meteorological Society
  • Presents a revised framework that quantifies observed changes in the climate of the contiguous United States through analysis of a revised version of the U.S. Climate Extremes Index (CEI)
  • States that CEI is based on a set of climate extremes indicators that measure the fraction of the area of the United States experiencing extremes in monthly mean surface temperature, daily precipitation, and drought (or moisture surplus)
  • The revised CEI incorporates auxiliary station data, including recently digitized pre-1948 data to extend further back in time and to improve spatial coverage
  • Finds that observations over the past decade continue to support the finding that the area experiencing much above-normal maximum and minimum temperatures in recent years has been on the rise, with infrequent occurrence of much below- normal mean maximum and minimum temperatures
  • Finds, conversely, that extremes in much below-normal mean maximum and minimum temperatures indicate a decline from about 1910 to 1930
  • Observes an increasing trend in the area experiencing much above-normal proportion of heavy daily precipitation from about 1950 to the present
  • Identifies a period with a much greater-than-normal number of days without precipitation from about 1910 to the mid-1930s
  • Finds that warm extremes in mean maximum and minimum temperature observed during the summer and warm seasons show a more pronounced increasing trend since the mid-1970s
  • Results from the winter season show large variability in extremes and little evidence of a trend
  • The cold season CEI indicates an increase in extremes since the early 1970s yet has large multidecadal variability