Science Source

A Revised U.S. Climate Extremes Index

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