Long-term rainfall deficits troublesome in Southeast

Rainfall was plentiful throughout most of the Southeast during the winter months. And, while early spring showers brought short-term relief to much of the drought-stricken area, long-term deficits still remained, according to the first May report of the U.S. Drought Monitor.

Widespread rains of 1 to 2 inches during the latter part of April improved conditions in the most drought-affected areas, but most of Alabama, Georgia, South Carolina and North Carolina are still categorized from abnormally dry to extreme drought.

And significant long-term deficits remained, ranging from 5 to 15 inches over the past six months to 12 to 20 inches over the past 12 months, with locally larger deficits.

Surface conditions improved temporarily, but deeper soil moisture remained dry and groundwater levels and multiple-day averaged stream flows continued low in many places. The Tennessee Valley Authority lakes continued low in spite of the recent rains.

Conditions especially improved in Virginia, where 4 to 8 inches of rain fell during the latter part of April.

Conservation measures and rainfall have helped to replenish many of the reservoirs in North Carolina, but low well levels and stream flows still reflected subnormal groundwater conditions.

In Georgia, State Climatologist David Stooksbury agrees that winter and early spring rains have helped the situation there, but north Georgia remains in severe to extreme drought. The northern coastal plain is abnormally dry, he says, and moisture conditions for the southern coastal plain along the Florida border are near normal for this time of year.

From Oct. 1 through the middle of April is considered Georgia’s moisture recharge period, when the state typically gets more rain than moisture losses due to evaporation and plant use.

“North Georgia didn’t receive enough rain to fully recharge soil moisture, groundwater, streams or reservoirs, says Stooksbury. “Since Oct. 1, north Georgia has received only 70 percent to 80 percent of normal rainfall. Most north Georgia streams are at or near record low flows for late April. At many locations, only 1986 and 2007 stream flows were lower than they are now.”

Both Lake Lanier and Lake Hartwell in Georgia were well below desired levels for late April, he says. “Smaller reservoirs are near full, though. However, with the extremely low stream flows across north Georgia, these smaller reservoirs must be managed well because drought conditions are expected to continue,” he says.

From the northern Coastal Plain to the North Carolina and Tennessee borders, soil moisture is abnormally low, says Stooksbury. It is especially low across the northern Piedmont and into the mountains. In northwest Georgia, soil moisture is extremely low, he adds.

“Soil moisture in south-central and southeast Georgia was near normal for late April. But levels are already decreasing. In southwest Georgia, most flows were low for late April and decreasing. The development of drought conditions over May was possible,” he says.

From late April through October, moisture loss from soils is usually greater than rainfall, says Stooksbury. If Georgia has normal weather this summer, we can expect the soils to continue to dry out and groundwater levels, stream flows and reservoir levels to drop across the entire state.

For several months, both the Southeast Climate Consortium (SCC) and NOAA’s Climate Prediction Center have been predicting an increased likelihood of drier than normal and warmer patterns for the fall, winter and early spring seasons in the Southeast, especially in Florida, south Alabama and south Georgia.

The reason is that a moderate to strong La Niña (colder than normal ocean temperatures along the equator in the eastern and central Pacific Ocean) developed this past fall. La Niña is well known to typically bring drier conditions and warmer weather to the Southeast in the colder months (November through March).

The threat of a dry winter, when most recharge of surface and groundwater takes place in Georgia and Alabama, did not bode well for any lasting relief in the drought-stricken areas of these states.

Fortunately, states the SCC, this past winter was anything but typical as far as La Niña and rainfall is concerned. January and February saw a pattern that brought frequent storms and low pressure systems along the Gulf Coast. Several heavy rainfall events impacted the Panhandle and north Florida, south Alabama, and south and central Georgia.

In other areas, rainfall has not been so plentiful and drought conditions persist, say experts with the SCC. “The hardest hit areas of north Alabama and north Georgia are still experiencing rainfall deficits. Lake and reservoir levels, such as Lake Lanier that supplies Atlanta, are still significantly below normal and have not received as much recharge as hoped during the winter season. Likewise in south Florida, where low Lake Okeechobee levels are dictating water restrictions in south and southwest Florida.”

Looking further ahead, La Niña rainfall patterns actually could reverse themselves over portions of most of Alabama, western Georgia and the Florida Panhandle, says the SCC. “May and June actually bring patterns that favor more rainfall than normal in these areas, on average from 5 percent to 10 percent. While this forecast can be viewed with optimism, there is less confidence in forecasting using La Niña climate shifts at this time of the year.

Like this current La Niña, sea surface temperatures reach their peak departure from normal in the winter months and have or are in the process of returning to normal by the summer. Also, the active jet stream has migrated north to its summer position, so the tropical Pacific has less influence on it and corresponding weather patterns.”

e-mail: [email protected]

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.