CYCLICITY IN PRECIPITATION AND STREAM DISCHARGE IN GEORGIA AND RELATIONSHIPS WITH THE SOUTHERN OSCILLATION

Abstract

Maximum entropy spectrum analysis of 10 stream discharge time series from four physiographic provinces in Georgia has revealed clear and statistically significant cycles in water-year discharge (October to September) over the period 1938 to 1994 at 15 to 17 and 5 to 6 years in all 10 series, and at 8 to 9 years in 9 series. Analysis of 13 precipitation records uncovered cycles at 15 to 18 years (10 stations), 8 to 10 years (8 stations), and 5 to 6 years (13 stations). The cycles are much more consistent and better defined in the stream discharge time series suggesting that large intra-annual variations in precipitation, possibly caused by spatial variations in summer convectional rainfall, are filtered in the stream records. Spectrum analysis of the Southern Oscillation (SO) for the 98-year period from 1897 to 1994 revealed water-year cycles at about 18, 10, and 6 to 7 years, which are not in phase with the stream-flow and precipitation cycles. However, a strong relationship is apparent between cool-season (December through March) precipitation and stream flow in the southern part of the state (the Coastal Plain) and the sum of SO values in the same four months. In addition, cycles in cool-season precipitation at about 19, 10, and 6 years agree well with those in the SO and appear in phase suggesting a causal relationship.