Fire severity and recovery for the Chimney Tops 2 fire, TN, 2016-2023
The fall 2016 Chimney Tops 2 fire is of particular interest because of its unexpectedly high severity and impacts to communities and the Great Smoky Mountains National Park. Until 2016, fall fires in the southern Appalachians were not well appreciated. Before then, most wildfires and prescribed fires occurred in the spring, with most severe wildfire behavior either associated with the rare summer fire or short fire runs. Fall fires tend to occur during drought as freshly fallen leaf litter provides sufficient fuel to carry fire across the topography. In spring, rising humidity with green-up normally checks fire growth and extreme behavior, but phenological constraints are loosened as the fall progresses without rain as transpiration drops regionally with leaf-fall. This historic fire burned just after Thanksgiving and became the capstone of a fire season that began in mid October.
Monitoring fire severity and recovery is relatively straightforward with NDVI. Thanks to the extreme weather, most severely burned patches were larger than elsewhere that fall, with strong departures much lower across the south facing slopes than observed earlier. The largest single severe fire patch seen across the Southern Appalachians was on Bull Head, an area with ericaceous shrubs and table mountain pine that burned so severely that its NDVI recovery trailed other severely burned areas by several years as shown in this map sequence.
One of the most remarkable discoveries from our fire research is a sequential disturbance from wind that occurred five months after the fire. Wind impacts persisted through that next growing season both within and adjacent to the Chimney Tops 2 burn area. The severe weather experienced on May 4 resulted from a Mountain Wave wind event, as was the wind that caused the erratic Chimney Tops 2 fire behavior. Mountain Wave events are common in this area, with multiple events happening each year, typically from fall to spring. This highlights the peculiar extreme wind-wildfire hazard of the Tennessee foothills that may be far greater than across the rest of the southern Appalachian region. This is not to say that wind and fire are not of concern elsewhere; rather that this peculiarly virulent inherent Mountain Wave wind-fire hazard is of particular concern here. This has implications for how fire hazard and associated risks are predicted here.