Temperature Variability in Georgia in Recent Years

Southeastern Geographer Vol. 24, No. 1, May 1984, pp. 30-41 TEMPERATURE VARIARILITY IN GEORGIA IN RECENT YEARS* Philip W. Suckling In recent years several examples of temperature extremes have occurred in Georgia and across the southeast. These include extreme cold in the winter of 1976—77, above normal summer temperatures in 1980 and 1981, and the exceptionally warm Christmas season of 1982. Do these occurrences indicate that temperature variability has increased? Some writers have suggested that there has been an increase in climatic variability in recent years. The following are some relevant quotes: "droughts, floods, heat waves and cold spells unprecedented in living memory "; "record low temperatures reported with increasing frequency in many parts of the United States"; and "the range of short-term variations has widened since the middle of the century." (J) Studies have addressed the issue of whether the climatic trend is towards cooling or warming. (2) Although the issue of climatic trends of cooling versus warming is important, it is the frequency of extremes (i.e., climatic variability) that may be of more significance to man and his activities, especially in agriculture. (3) In the past, it has been suggested that overall climatic cooling should cause increased temperature variability. However, a study by Van Loon and Williams indicated this concept to be wrong. (4) Previous studies on temperature variability have supported the contention that in recent years an increase in the frequency of extremes has occurred. Asakura and Ikeda concluded that an increase in temperature extremes for the northern hemisphere has occurred in the last two decades compared to the mid-twentieth century . (5) Similarly, Jones, Wigley and Kelly found increased year-toyear variability during the 1970s in a study of northern hemisphere temperature variations over the last century. (6) By contrast, Ratcliffe, Weiler and Collison in a study covering parts of Britain found no trend toward increased climatic variability in the last century. (7) In an assessment of interannual temperature variability for the United States * The technical assistance of Jeon Lee is gratefully acknowledged. Dr. Suckling is Associate Professor of Geography at the University of Georgia in Athens, GA 30602. Vol. XXIV, No. 1 31 since 1896, Chico and Sellers found a decrease in variability for the 1930s to the 1970s. (S) Boer and Higuchi found no evidence to support the contention that the climate has generally become more variable in the northern hemisphere for the last 25 years although, in a later article, they did find evidence suggesting increased summertime temperature variability. (9) Hoyt has shown that the popular opinion that more weather "records" have been set in recent years in the United States is mistaken. If anything, less "records" are being established than statistically expected. (JO) Regional differences in climatic change and variability are to be expected. (JJ) Using a limited number of sites, the study by Van Loon and Williams found decreasing temperature variability for U.S. locations in the midwest and northeast but increasing variability in the south and west. (J2) It is the purpose of the present study to assess temperature variability for the southern state of Georgia. Has there been an increase in the occurrence of unusually above or below normal monthly temperatures in recent years? METHODOLOGY. Mean monthly temperatures for the period 19401982 for seven sites in Georgia plus the nearby locations ofChattanooga, TN, Tallahassee, FL, and Jacksonville, FL, were used for study (Fig. 1). The three non-Georgia stations were included to provide surrogate data for the far northern and southern regions ofthe state in the absence ofappropriate in-state sites. Monthly average temperature and standard deviation values for the 43-year period are given in Table 1. It is notable that winter months have much more temperature variability than summer months as indicated by consistently higher standard deviation values at all sites. In order to assess interannual changes in temperature variability, it is therefore appropriate to conduct the analysis on a month by month basis. The climatic variability index of Tavakol and Jones (J3) will be adapted for use: Temperature _ Iy |X - X|. . Variability Index ? ? s? For ? map points (i.e., sites), X is the average mean temperature for the month under consideration for...