UF Study: Local, Regional Weather Patterns Sway Impact Of El Niño, La Niña

March 29, 2004

GAINESVILLE, Fla. — Climatologists can improve the accuracy of computer models that predict El Niño- or La Niña-induced droughts by taking into account how local and regional weather patterns influence these global weather anomalies, according to a new University of Florida study.

Peter Waylen, a UF professor of geography, will present the conclusions of a study about the interplay of the so-called El Niño/Southern Oscillation, or ENSO, with other weather trends in Central America on Thursday at a sectional meeting of the Geological Society of America in St. Louis.

Countries have a critical need to predict the severity of coming ENSO events, Waylen said, because the climatic changes they bring can have a severe effect on agriculture, water supply and hydroelectric generation. Hoping to sharpen computer-modeling capabilities, he and two Colombian scientists looked at how regional weather patterns affected Columbia, Panama and Costa Rica.

Those three countries all get at least 75 percent of their electricity from hydroelectric dams that rely on huge reservoirs. The longer the advance warning of an El Niño drought, the more water managers could fill the reservoirs to compensate for expected loss of rainfall, Waylan said. The team figured out that if current models had incorporated their findings, the Columbian government could have reserved enough water during the last decade to save an estimated $200 million on fossil fuels used for thermal power plants.

El Niño occurs when winds in the tropical Pacific, which normally blow east to west, ease or reverse, warming the surface waters in the Eastern Pacific. The phenomenon variously spurs floods and droughts in different areas around the world. La Niña frequently follows an El Niño event and tends to have the opposite effects. The most recent major El Niño and La Niña occurred in 1997-98 and 1998-99, respectively, with the weather patterns causing floods, major drought and widespread fires in Florida, among other calamities.

Typically, Waylen said, El Nino causes droughts and La Niña causes floods in Central America. Using data recorded as far back as 1950, the researchers discovered the temperatures of the tropical North Atlantic affect the strength of ocean trade winds, which in turn affect the development of tropical storms and hurricanes in the Caribbean. Also affected are the frequency and paths of tropical easterly waves bringing in rainfall. The higher the North Atlantic temperatures, the less the effect of El Niño and La Niña.

The researchers also found a fourth factor influenced ENSO’s severity: The moisture content of the rain forest. If an El Niño occurred following a year of heavy rains, the drought would less severe, because evaporation of the moisture in the forest would lead to more local rainfall.

Waylen can be reached at (352) 392-0494 ext. 204,prwaylen@geog.ufl.edu.