TornadoesStudying El Niño, La Niña helps predict frequency of tornadoes, hail storms

Climate scientists can spot El Niño and La Niña conditions developing months ahead of time, and they use this knowledge to make more accurate forecasts of droughts, flooding, and even hurricane activity around the world. Now, a new study shows that El Niño and La Niña conditions can also help predict the frequency of tornadoes and hail storms in some of the most susceptible regions of the United States. The study appears in the current issue of the journal Nature Geoscience.

“We can forecast how active the spring tornado season will be based on the state of El Niño or La Niña in December or even earlier,” said lead author John Allen, a postdoctoral research scientist at the International Research Institute for Climate and Society (IRI).

The El Niño-Southern Oscillation, or ENSO, is a naturally occurring climate cycle in which sea-surface temperatures in the equatorial Pacific Ocean fluctuate. When waters are warmer than normal, as they are currently, it is described as El Niño; when cooler, La Niña.

A Columbia University release reports that Allen and his coauthors show that moderately strong La Niña events lead to more tornadoes and hail storms over portions of Oklahoma, Texas, Kansas, and other parts of the southern United States. El Niño events act in the opposite manner, suppressing both types of storms in this area.

While the information cannot pinpoint when and where storms will wreak havoc, it will nevertheless be useful for governments and insurance companies to prepare for the coming season, Allen said. In recent weeks, researchers from IRI and other institutions have detected El Niño conditions over the Pacific, which implies that this spring will be a relatively quiet one for severe storms in the southern United States.

“The big contribution of the paper is that it looks at the changes in environmental conditions associated with ENSO,” said Harold Brooks, a senior research scientist at the U.S. National Oceanic and Atmospheric Administration (NOAA), who was not an author of the study. “Previous efforts have focused on tornado reports, but the connection with changes in large-scale conditions hadn’t been made,” he said.

Last year, forty-seven people died in tornadoes. But in 2011— a La Niña year — tornadoes killed more than 550 people, higher than in the previous ten years combined. Hail storms and tornadoes cause an average estimated $1.6 billion in insured losses each year in the United States, according to