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Southeastern Geogrujìher Vol. 26, No. 1. May 1986, pp. 2.5-3.5 CLIMATIC CHANGE IN GEORGIA AS ILLUSTRATED BY THE FREQUENCY OF FREEZING AND HOT DAYS* Philip W. Suckling Most assessments of climatic change have considered long term trends of average temperature or precipitation conditions utilizing mean annual, mean seasonal or mean monthly values over a number of years (1). Some studies have assessed climatic change with alternative data such as maximum and minimum temperatures (2), the length of the growing season (3), or the frequency of establishing record temperatures (4). Variations or trends in these latter values or events do not always correspond to the trends evident for mean annual, seasonal or monthly temperature data. In the case of Georgia, recent studies have suggested that climatic variability as represented by the occurrence of extreme (either above or below normal) mean monthly temperatures or water budget values has not generally increased in recent years (5). Despite this finding, general climatic trends may exist. For example, it has been shown that the dates for the last spring freeze in central Georgia and much of the southeast have occurred considerably later, on average, in recent years compared to earlier this century (6). It is the goal of this study to further investigate recent climatic trends in Georgia utilizing special event data; in this case, the frequency of days per year with temperatures reaching 320F (00C) and below, and 900F (32.2°C) and above. METHODOLOGY. The number of days in a year experiencing temperatures of 32°F and below, and 9O0F and above are routinely tabulated for many weather stations in publications produced by the National Climatic Center (7). For this study, 13 sites in Georgia and three sites in Tennessee and Florida were utilized (Fig. 1). The sites were chosen to provide uniform spatial coverage for the state. No missing data existed for any of the sites for the 1948-1984 study period. However, some stations were relocated during the period, most noteworthy of which included Tallahassee (moved 3 miles SSW in 1961), Jacksonville (moved * The technical assistance of Mitch Wilkins is gratefully acknowledged. Dr. Suckling is Associate Professor of Geography at the University of Georgia in Athens, GA 30602. 26 Southeastern Geographer I ._*_Chaltanf3qga________ ^ Dahlonega / 50 Miles S \ · Rome Atlanta )»Columbus > i »Blakely -s Toccoa Athens ? N ? •\ Augustan *? ?. •\. •Macon Savannahi Tifton Tallahassee« Waycross Brunswick ? ) Jacksonville* Fig. 1. Meterological stations in Georgia and adjacent states used in the study. 5 miles NW in 1971) and Columbus (moved 0.4 miles NW in 1978). Savannah and Augusta also experienced substantial site moves; however , these occurred very early in the study period during 1950. Mean and standard deviation values of the number of days with Vol. XXVI, No. 1 27 freezing temperatures (32°F and below) and hot temperatures (900F and above) for the entire 37-year period are given in Tables 1 and 2, respectively . For days with freezing temperatures, there is a general decrease in frequency from north to south with especially low values on the southeast coast due to the moderating effects of the Atlantic Ocean. The number of hot days increases from north to south peaking in central and southern Georgia but decreasing for southeastern coastal sites (Savannah , Brunswick, Jacksonville) and for Tallahassee (near the Gulf of Mexico), where the moderating effects of the sea are felt. Standard deviation values for the number of hot days are generally much higher than that for the frequency of days with freezing temperatures. The southern sites of Waycross and Tallahassee are the only exceptions. In order to detect climatic change as represented by temporal trends in the frequency of days experiencing 32°F and below or 900F and above, 10-year running means were calculated (8). These are plotted in Figures 2 and 3, respectively. Values are plotted for the center of 10-year periods (i.e., the 1948-1957 average is plotted between 1952 and 1953, and so on). Also, t-statistic values were calculated comparing the mean of the last 10-year period (1975-1984) to all other TABLE 1 AVERAGE NUMBER OF DAYS PER YEAR EXPERIENCING FREEZING TEMPERATURES (32°F AND BELOW) WITH STANDARD DEVIATION VALUES...

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