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For much of Mid-South More rain needed to end drought

Nothing about rain has been normal in Mississippi in the last three to four years, and the state went from a serious deficit in 2007 to continually soggy ground this spring.

2007 was a hot, dry year, and row crop farmers had to irrigate extensively in places to keep their crops growing. Catfish producers saw pond water levels drop dangerously, and hay dried up on pastures, which increased feed costs for cattle producers.

Charlie Wax, state meteorologist at Mississippi State University, said the state is probably at the end of a three- to four-year drought. At the end of 2007, the state's moisture deficit was 15 to 20 inches, although wet and dry areas of the state could be identified on geographic east/west lines.

“I hope this drought is about to end, but it hasn't yet. The drought is still lingering in the southeastern part of the United States, and we're still in it a bit,” Wax said.

He said the state was completely out of the drought rating in late April, but by mid-May, the southwest part of the state was back in a moderate drought. “About one-fourth of the state is under short soil moisture, 53 percent is adequate and 21 percent is at surplus,” Wax said.

Actively growing crops need an inch of water a week to maintain adequate soil moisture during the growing season. Overall, state soils demand an average of 36 inches of rain a year to compensate for what is lost through evaporation.

The Southern Region Climate Center keeps track of cumulative rainfall each calendar year. To date, most of the state is on track or just behind average. This year, selected Mississippi cities, with their average rainfall and actual accumulation in inches, include:

Stoneville — 25 average/22 received.

Starkville — 22 average/25.5 received.

Jackson — 26 average/22 received.

Natchez — 27 average/21 received.

Biloxi — 25 average/22 received.

“My assessment is that it's a whole lot better than it was this time last year,” Wax said. “The outlook is for moderate improvement and some hope that the drought will let up and we'll get more normal conditions through the summer. As stressed as the environment has been, we can't afford to go three to four weeks without a rain.”

Glenn Wilson, a soil physicist at the U.S. Department of Agriculture/Agricultural Research Service's National Sedimentation Lab in Oxford, Miss., said the vadose zone, or upper layer of soil above the water table, responds quickly to both drought and rainfall or irrigation.

“We have recharged the vadose zone, which is the zone that plant roots use for growth,” Wilson said of this year's rains.

From about April until September, the moisture demand on this zone is high as water is drawn away through evaporation and plant use.

When more rain falls than is necessary, the excess goes to surface water reserves, such as lakes, ponds and streams, and a small amount seeps deep into the soil to recharge groundwater supplies.

“Even with sufficient rainfall, we don't get much recharge until November or December,” Wilson said.

To recharge the groundwater table, located below the vadose zone, a region needs rainfall that exceeds the rate at which the water is used up daily. Aquifers — ground formations of coarse gravel and small rocks filled with water in the cracks and empty spaces — are recharged slowly by underground water supplies farther north and are mostly not affected by local rain.

“Water tables are dropping, and not just in this region. Part of this is caused by increased usage of the groundwater, and part of it has to do with global climate change, which is resulting in increased extreme periods or regions of drought or excess rainfall,” Wilson said.

“Management of water will be much more important than it has in the past and will become an even bigger issue than water quality.”

Larry Oldham, Extension soil specialist, said recharged soils and refilled lakes, ponds and streams must continue to get good rains for the state to again move out of and stay out of drought conditions.

“Even though we are recharged now, that doesn't mean we will have sufficient water throughout the growing season to make a crop,” Oldham said.

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