Wednesday, 15 May 2002: 11:15 AM
Climate Stability in the Great Plains
Given our growing knowledge of climate variability and change and the many factors that can cause adjustments in the climate system, there is a need to better address the question: How stable is the current climate? In his 1965 monograph on drought, Palmer made a strong case for his water balance-based drought severity index (PDSI) and he presented (in Appendix D) an index of climatic stability. The index examines the number of months with the absolute value of PDSI exceeding a threshold. For his climatic stability index, Palmer summed the number of months with PDSI greater than or equal to 1.0 and that sum was a measure of instability for the year. Palmer's initial work, done solely for western Kansas, clearly indicated that climatic stability varied over time. The goal of this research was to assess both temporal and spatial variations in Palmer's climatic stability index. Climatic data for a north-south transect in the Great Plains were assessed. Climatic Division data for PDSI, obtained from NCDC, for the time period 1895 to 2000 were used in the analyses. In addition to Palmer's suggested threshold, using an absolute value of 1.0, we also examined setting the threshold at 2.0, 3.0, and 4.0. The results from this analysis indicate that unstable months occur more often than not using Palmer's threshold at 1.0 and that instability tends to decrease from north to south. The pattern changes dramatically when using a threshold at 4.0; highest values of instability are found in Nebraska with a rapid decline toward the south. At all threshold levels, Oklahoma Climate Divisions have the lowest values (suggesting the most stable climate along the transect analyzed).