Published on 06/01/00

Dry May Intensifies Drought in Georgia

ATHENS, Ga. -- Georgia's dry May has intensified drought conditions statewide.

Many places in middle and south Georgia had less than an inch of rain in May. Across north Georgia, May rainfall totals were generally less than 2.5 inches. Normal rain totals for May should be between 3.5 inches along the coast to almost 5 inches in the mountains.

In middle and south Georgia, rainfall totals for May include 0.04 inches at Tifton, 0.21 at Newton and Vidalia, 0.30 at Macon, 0.34 at Camilla, 0.36 at Augusta, 0.41 at Dublin, 0.57 at Fort Valley, 0.66 at Alma, 0.78 at Columbus, 0.96 at Savannah, 1.08 at Valdosta, and 1.18 at Midville.

Rainfall was greater in north Georgia but still well below normal. May totals were 1.07 inches at Rome, 1.14 at Watkinsville, 1.51 at Griffin, 1.62 at Blairsville, 1.85 at Atlanta, 2.02 at Duluth, 2.17 at Athens, 2.52 at Jonesboro, and 2.77 at Gainesville.

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Source: Climate Prediction Center, NOAA

Soil Moisture Low ...

A bigger concern than the lack of rain is the lack of soil moisture. Soil-moisture models from the National Oceanic and Atmospheric Administration's Climate Prediction Center indicate that soil moisture across the state is between the first and 10th percentiles for the last day of May.

At the first percentile, we would expect soils to have more moisture in 99 of 100 years. At the 10th, we would expect the soils to have more moisture in nine out of 10 years.

With little soil-moisture recharge last winter, reserves are quickly being depleted. One measure of the rate at which soil moisture is changing is the water balance, a simple moisture accounting system.

... And Getting Lower

To calculate the water balance, take the rainfall during a given period and subtract the soil-moisture loss due to evaporation and plants' water use during that period. A negative water balance means that the soils lost moisture during the period. A positive value means the soils gained moisture.

Between April 1 and May 30, all Georgia locations lost soil moisture. Some water-balance values include -10.74 inches at Dublin, -10.50 at Tifton, -10.48 at Newton, -9.65 at Midville, -9.51 at Fort Valley, -9.09 at Vidalia, -7.98 at Griffin, -6.96 at Camilla, -6.93 at Watkinsville, -6.66 at Alma, -5.54 at Valdosta, -4.86 at Jonesboro, -4.39 at Duluth, -3.44 at Gainesville, -2.48 at Rome and -0.75 at Blairsville.

Stream flows statewide remain at record- to near-record-low flows for the end of May. The Altamaha, Flint, Little, Ocmulgee, Oconee, Ohoopee and St. Mary's rivers set daily low-flow records for May 31.

Keetch-Byram Drought Index
June 1, 2000

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The higher the KBDI numbers, the greater the danger of wildfire. In areas where the numbers are 600 or greater, just putting fires out becomes a problem. Most of south Georgia is above 600.

Wildfire Dangers Rising

Wildfire dangers are increasing. A measure of wildfire drought is the Keetch-Byram Drought Index from the U.S. Forest Service. The KBDI scale runs from zero to 800.

As of May 30, KBDI values were greater than 600 across the southern quarter of Georgia. KBDI values greater than 500 were south of the fall line (Columbus to Macon to Augusta).

With KBDI values greater than 500, expect excessive site damage when fires break out. With values greater than 600, just suppressing fires becomes a major problem.

Drought Likely to Continue

I expect the drought to continue through the summer, barring a tropical weather system. This outlook is based on two factors.

The first is that with normal weather, soils in Georgia lose moisture during the summer. Thus, even if Georgia returns to normal rainfall patterns, the soils will keep getting drier.

The second factor is the lack of soil moisture for thunderstorms. During the summer, most of Georgia's rain is the result of scattered afternoon and evening storms. Without a readily available local supply of moisture, these storms will be diminished.

David Emory Stooksbury is associate professor of Biological and Agricultural Engineering at University of Georgia's College of Agricultural and Environmental Sciences.