Is rain a drought killer?

Heavy rain has filled local reservoirs, replenishing the Charlotte region's water supplies and is making a major dent in the long-lasting drought.

Enough rain has fallen since Tuesday to likely improve drought conditions by one full stage, said Patricia Tanner, a National Weather Service hydrologist in Greer. An updated U.S. Drought Monitor will be released by Thursday.

Twenty-one Western N.C. counties, including Gaston, Lincoln and Catawba, are now categorized in exceptional drought, the severest stage. Mecklenburg County is one step better, in extreme drought.

The western counties got up to 8.5 inches of rain in the past 24 hours. Both Old Fort, near the headwaters of the Catawba River, and Charlotte's airport reported 7.5 inches.

Lake levels responded quickly. Lake James, the northern-most of the Catawba reservoirs, is up 1 foot since Monday; Mountain Island Lake, Charlotte-Mecklenburg's major water source, nearly 2 feet; Lake Norman, 1 foot; and Lake Wylie, 3 feet.

Duke Energy said it expects lakes James, Rhodhiss, Hickory and Lookout Shoals to reach full pond, or above, by this afternoon. It advised lake residents to prepare for high water.

“The (water) storage is vastly improved, for sure,” said Ed Bruce, a Duke engineer and coordinator of a Catawba River drought-advisory group.

It's a good time of year to have full reservoirs, Bruce said. With cooler weather on the way, consumers will use less water, and the rate of evaporation from lakes will drop. That's a good hedge against any future dry spells.

But experts aren't ready to call the drought over. It's lasted more than a year, leaving Charlotte with a nearly 15-inch rainfall deficit in 2007, followed by below-normal rain this year. Reversing those conditions will likely take months.

A key indicator will be how groundwater responds to this week's rain. Groundwater supplies much of the water in streams and rivers, which in turn feed reservoirs. When groundwater is low, as it is now, rainwater fills streams but then quickly subsides.

A shallow well at Mecklenburg's Hornet's Nest Park has risen nearly 2 feet in the past day alone. But the reaction of deeper wells will take longer, depending on soil types.

“It's really going to take us a couple of weeks to sort it out,” said U.S. Geological Survey hydrologist Curtis Weaver. “When you get upwards of 10 inches of rain overnight, you're going to have flooding. The question is how quickly will these streams fall off after the rain stops?”

The good news, Tanner said, is that a major weather influence, the cooling of Pacific waters called La Nina, is going into a neutral phase. For the Carolinas, that means a return to normal rainfall is expected by late November.

“So it shouldn't get any worse,” she said.