CR 17:33-43 (2001)  -  doi:10.3354/cr017033

ABSTRACT: Most climate variability studies have been conducted at a regional level in which it was assumed that the climate was uniform for each individual climatic zone. The objective of this study was to determine climate variability at a local level for the entire state of Georgia during the 20th century. Daily historical weather data for 85 weather stations were analyzed for the period 1901-1997. Annual air temperature for the century showed a statistically significant negative trend. A similar tendency was found for both the warm- and cold-half of the year, as well as the individual winter, spring and summer seasons. Georgia has experienced several drought episodes during the 20th century, especially during the 1930s, 1950s and 1980s. Drought was most severe in 1954 across central and south Georgia, with precipitation less than 35% of the normal (1961-1990) climatic values. A decrease in precipitation during the warm-half of the year (April-September) from the end of 1970s until present was found. Although there was an increase in summer precipitation from the beginning of the 1980s, the overall trend showed a decrease in summer precipitation. Most El Niño episodes during the cold-half of the year featured an increased frequency of occurrences of above normal precipitation. During the autumn El Niño events, Georgia has tended to be warmer than the normal climatic conditions. However, almost all classified winter El Niños were connected by lower mean air temperature during the winter season. This lower temperature during the winter resulted in an increase in winter wheat yield. Higher air temperatures during the growing season resulted in a shorter growing duration, causing a reduction in yield. The spring and summer crops used in this study were affected by both precipitation deficits and higher air temperatures during the warm-half of the year. Since 1961, maize yield was higher in most years when El Niño events occurred during the warm-half of the year. The statistical linear yield models that were developed in this study can be used for assessments of expected anomalies of mean winter wheat, maize, soybean, peanut and cotton yield in Georgia for a particular year.

KEY WORDS: Georgia · Climate variability · El Niño · Crop yield · Statistical models