Southeast Climate Consortium
November 1, 2011
The El Niño-Southern Oscillation (ENSO) phenomenon is the biggest player in the game of year-to-year climate variability. El Niño and La Niña events tend to develop during April-June and tend to reach maximum strength during December-February.
Typically they persist for 9 to 12 months. La Niña conditions take place when surface water temperatures in the tropical Pacific Ocean along the equator turns colder than normal.
La Niña can be thought as the opposite of El Niño conditions, in which the same area of the Pacific is warmer than normal. La Niña affects weather patterns in many areas of the world. In the case of the
Southeast U.S.A. it usually brings a drier and warmer winter and spring (November through March).
For Florida, central and lower Alabama, and central and southern Georgia rainfall may be 40 to 60 percent lower than normal and temperatures 3 to 4 degrees warmer than normal.
La Niña events may last more than one year, in fact, they do tend to last longer on average than El Niño events.
Examples of events that lasted longer than one year include the La Niñas of 1954-56 (extreme drought in the southeastern U.S.), 1973-75, and 1999-2001.This year is the second year of a la Niña pattern that started back in July of 2010 and returned after a brief period of neutral conditions during the summer. Figure 1 shows average rainfall anomalies (Nov-Jan) observed during the 2nd year of La Niñas events in the past.
Although La Niña events are never the same, it indicates that drier than normal conditions are generally observed in most of the southern U.S.A.
Figure 2. Average rainfall anomalies observed during second year La Niña events. Potential Impacts of La Niña Events on Crops
Winter Vegetables: Tomato and green peppers generally yield more during La Niña years than during Neutral or El Niño years. Dry weather generally decreases fungal and bacterial diseases and help growers reduce the number of fungicide applications, however viruses caused by thrips (Tomato Spotted Wilt [TSW]) and white fly (Tomato Yellow Leaf Curl [TYLCV]) are problems. High nighttime temperatures (above 65°F) can be a problem for fruit setting. For more information on how to apply climate information for reducing tomato production risks check the following UF- Extension EDIS publication.
Using Seasonal Climate Variability Forecasts: Risk Management for Tomato Production in South Florida (Click for access to report from UF-IFAS)