By Katie Nichols
The El Niño weather event of 2015-2016 brought drought and other agricultural hardships to the southern United States. Dr. Brenda Ortiz, an Alabama Cooperative Extension System scientist, said a La Nina phase is on the horizon.
The El Niño Southern Oscillation (ENSO) is a driving force in southeastern climate variability. Periodic warming and cooling of the eastern Pacific Ocean waters along the equator cause atmospheric and oceanic fluctuations of pressure, winds, sea level and precipitation in the equatorial Pacific.
The La Niña phase is characterized by unusually cold waters across the east-central equatorial Pacific. This causes warmer and drier conditions during the winter, especially in areas closer to the Gulf Coast.
El Niño and La Niña
El Niño and La Niña phases occur semi-regularly at two- to five-year intervals, generally lasting from nine to 12 months. The phase develops during the early part of midsummer and reaches peak intensity during the winter months (December to February). Phases may weaken between May and July. El Niño rarely lasts for more than one year. The La Niña phase can last for close to two years when it is very strong.
A number of international science agencies keep track of the ENSO phases (El Niño, La Niña, or Neutral). Data collected on the strength of each episode helps scientists to predict future phases months in advance.
Ortiz, an Alabama Extension precision agriculture specialist, said the comprehensive understanding of previous ENSO phases enables scientists to anticipate the potential effects associated with future ENSO events.
“All involved in agriculture should track the ENSO forecast and use it to guide their farming decisions,” Ortiz said. “Growers should keep in mind, however, that each ENSO phase is different. While statistics provide general guidance for the effects on climate, a particular event may not play out as expected.”
Though only a general rule, La Niña effects on the global climate tend to be the opposite of El Niño.
During La Niña, sea-surface temperatures are generally four to six degrees Fahrenheit below average. These temperature fluctuations occur between the International Dateline and the west coast of South America.
In the southeastern U.S., this phase coincides with warmer and drier-than-normal conditions during winter and spring months. During La Niña, storms move up the Mississippi Valley and Ohio Valley, which means northern Alabama and northern Georgia may have more rainfall than normal, while the rest of the Southeast remains warm and dry. However, this varies between individual events.
A La Niña phase can last as many as two to three years. Longer La Niña events have preceded some of the most severe historic droughts in the Southeast. La Niña also corresponds with a very active Atlantic hurricane season.
Ortiz and her colleagues have conducted extensive ENSO-related crop research. Their research suggests early maturity varieties of wheat do well when planted in southern counties of Alabama and Georgia compared to late maturity varieties.
Farmers should be aware of the potential wheat yield losses associated with Hessian fly damage, especially in warmer winters influenced by La Niña.
ENSO not only causes changes in rainfall and temperature but also alters the path of the jet stream, which is visible in different weather patterns across regions of Alabama.
During the La Niña phase, winters are drier in the central and southern parts of the state, but wetter in the northern part. Spring is slightly drier than normal throughout the state. Summers may have more rainfall than normal, except in the southern counties where it is slightly drier. Fall rainfall may increase in the central and southern areas of the state, while conditions are slightly drier than normal in the northern parts of Alabama.
Climate and Crops iBook
Alabama Extension’s Climate and Crops iBook details impacts of the different ENSO phases on the major southeast row crops. The iBook also outlines potential adaptation strategies to minimize those impacts.
Climate and Crops is a free, comprehensive resource not only for farmers, crop consultants and Cooperative Extension professionals but also for school teachers who want to introduce their students to how farming practices are increasingly being adapted to new findings about climate variability.
Each chapter includes basic crop production considerations. In addition, each chapter covers potential climatic conditions that may occur during the growing season and how these affect each of Alabama’s principal crops in terms of planting, crop growth and development, insect, weed and disease pressure and harvesting. This guidance equips farmers with the most effective management strategies to deal with each of these climate scenarios and risks.