Persistent drought to linger across southern United States

"The speed with which the drought developed across the southern United States is rather unusual considering that just last year El Niño dominated the region with abundant precipitation," said Bill Proenza, director of NOAA's National Weather Service southern region." Then it was as if a switch was flipped during the summer, changing to La Niña conditions."

One of the major aspects of the emergence of La Niña was a very busy Atlantic hurricane season, which spawned 19 tropical storms, making it the third most active on record. Despite the large number of storms, only Hurricane Alex and Tropical Storm Hermine produced any appreciable rainfall in the southern United States. Those storms only affected Texas; no significant rainfall from an organized tropical system fell along the Gulf Coast from Louisiana to Florida.

Sparse tropical rainfall and the dry conditions associated with La Niña combined to create severe to extreme drought conditions for nearly a third of the South and Southeast by late fall and early winter.

While the drought touches all of the Gulf Coast states, Texas and Florida are the most affected. From October through December, Texas received only five to 50 percent of normal precipitation, with portions of the lower Rio Grande averaging less than five percent of normal. During that period, for example, Brownsville received only 0.14 inches (normal is 6.55 inches) and Del Rio received 0.04 inch (normal is 3.89 inches). To the north in Austin, only 1.55 inches of rainfall was observed, compared to the normal of 8.34 inches.

In Florida, 51 percent of the state was in severe to extreme drought by the end of 2010. Some areas experienced the driest July 1 -- December 31 period on record. For example, Gainesville received only 12.95 inches of precipitation, compared to the previous record low of 15.25 inches. The city normally receives 27 inches. Daytona Beach ended the period with 14.71 inches compared to the previous record low of 15.35 inches − its normal is 30 inches.

In central and southern Florida, the South Florida Water Management District rain gauge network recorded an average of only 2.97 inches during the October through December period, breaking the previous record low average of 4.07 inches. Moreover, the District reports that Florida's Lake Okeechobee ended the year at 12.4 feet, 2.3 feet below average.

In addition to agricultural and water conservation concerns, one of the major threats from the drought is the growing wildfire danger. More than 42,000 fires accounted for more than 775,000 acres burned throughout the affected southern tier states during 2010.

Texas and Florida were among the hardest hit states. In Texas, the severe wildfire threat prompted Governor Rick Perry to issue a disaster proclamation for 244 of the state's 254 counties. Meanwhile, Florida lost more than 400,000 acres to wildfires last year, with more predicted to come. Florida's Forestry Division notes La Niña is expected to continue at least through spring and again anticipates greater than normal wildfire activity in 2011.

Getting the word out regarding likely La Niña impacts is imperative. "By providing information on current and future climate conditions to the public and to other federal, state and local decision makers, the National Weather Service can help them prepare for and react to such extreme weather events and to climate variability," said David Brown, Ph.D., regional climate services director for NOAA's National Weather Service southern region.

La Niña has developed 13 times since 1950, and the current La Niña ranks as the sixth strongest. The question climate experts are asking now is whether it will fade with the approach of summer or continue into next year.

"Of the five stronger La Niñas that occurred, four resulted in multi-year events," said Victor Murphy, climate program manager for NOAA's National Weather Service southern region. "If this La Niña persists until next winter, the threat of drought conditions in the south extending into next year will be heightened."