The study, led by faculty from the UF Institute of Food and Agricultural Sciences School of Forest Resources and Conservation (SFRC), highlights trends in dry season length in the southeastern region of the United States. Jennifer Fill and Raelene Crandall from SFRC worked in partnership with Corey Davis from the State Climate Office of North Carolina at North Carolina State University.
Nine southeastern states (North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Arkansas, and eastern Texas) were chosen for the study. Selection criteria included cyclical wet and dry seasons and high lightning activity levels, which define a region’s “lightning-ignited fire season.”
“We chose to focus on the lightning-ignited fire season because lightning has a direct relationship with climate and is more predictable than human ignitions,” Fill said.
The researchers analyzed data collected by the National Oceanic and Atmospheric Administration from 1897-2017 from hundreds of randomly selected weather stations in the Southeast. After evaluating the precipitation data, they discovered that the dry season has, in fact, lengthened by as many as 156 days in some parts of the region, an alarming 130% increase over 120 years.
“Prolonged periods of dry weather allow more opportunities for fire ignitions and can also generate more severe fires due to greater drying of soils and vegetation,” Fill said.
The data showed that the dry season was extended – starting earlier and ending later. While there was less total precipitation over the years, the annual pattern of thunderstorm frequency remained the same. Nevertheless, Fill explains that this lengthened dry season means that a larger proportion of thunderstorm activity overlaps with periods of dry vegetation.
“The overlap between the dry season and high thunderstorm activity has increased over time. Toward the end of the dry season, lightning is very frequent, and fuels are at their driest,” Fill said. “The largest lightning-ignited fires typically occur within a week of the wet season onset, which has recently been in June or July across much of the southeastern United States.”
Vegetation management through prescribed burning is a proactive way to plan for and manage lightning-ignited fires, by lowering both their severity and extent. However, Fill anticipates that the dry season will only continue to lengthen.
“Looking at trends over the past 120 years, if we project that same rate of change into the future, by 2050 the dry season could be up to 42 days longer than it is now, and exponentially drier,” Fill said. “These changes will depend on tropical storm patterns and other climatic influences but could have a major influence on agriculture. We need to be proactive in our strategies for mitigating risk.”