A new NOAA study tracks the occurrence of seasonal tornadoes across the U.S.
Fewer outbreaks, but more twisters?
Staff Report
FRISCO — Tracking tornado trends is a big deal in the global warming era, as researchers seek to determine whether climate change will result in more catastrophic and life-threatening weather events.
Since the 1950s, researchers say, the overall number of annual tornadoes has remained steady, but a new analysis of data shows there are fewer days with tornadoes each year, but on those days there are more tornadoes.
A consequence of this is that communities should expect an increased number of catastrophes, said lead author Harold Brooks, research meteorologist with the NOAA National Severe Storms Laboratory.
“Concentrating tornado damage on fewer days, but increasing the total damage on those days, has implications for people who respond, such as emergency managers and insurance interests,” Brooks said. “More resources will be needed to respond, but they won’t be used as often.”
The report from the National Oceanic and Atmospheric Administration, published in the journal Science, studied historic tornado records between 1954 and 2013 to find patterns in tornado occurrences.
The scientists weren’t able to pinpoint an exact reason for the changed pattern, but speculated about a connection to weather and climate. They also concluded that the start of the tornado season has become more variable during the study period.
From 1954 to 1997, 95 percent of the time tornado season started between March 1 and April 20. But in the last 17 years, this happened only 41 percent of the time.
The scientists said the trend toward increased variability is illustrated by numbers from recent years. The June 2010 to May 2011 period brought 1,050 tornadoes of at least EF1 strength, the most in any 12-month period on record.
But about a year later, there were only 236 EF1 or stronger tornadoes between May 2012 to April 2013, the fewest on record. November 2012 had no EF1 tornadoes, but November of 2013 had the sixth most on record, with 66.
The study’s results are a first step toward understanding the relationship between changing tornado activity and a changing climate. The next step will be for climate scientists and tornado researchers to work together to identify what specific large scale pattern variations in climate may cause, or are related to, clustering of tornado activity.
