An analysis of Southeastern US prescribed burn weather windows: seasonal variability and El Niño associations

Abstract

Fire plays an important role in wildland ecosystems, critical to sustaining biodiversity, wildlife habitat and ecosystem health. By area, 70% of US prescribed burns take place in the Southeast, where treatment objectives range widely and accomplishing them depends on finding specific weather conditions for the effective and controlled application of fire. The climatological variation of the preferred weather window is examined here using two weather model reanalyses, with focus on conditions critical to smoke dispersion and erratic fire behaviour. Large spatial gradients were evident in some months (e.g. 3× change across the Appalachian Mountains in winter). Over most of the Southeast, availability of preferred conditions in summer was several (up to 8) times less than in autumn or winter. We offer explanation for this variability in terms of the mean seasonal changes of key weather conditions (especially mixing height and transport wind). We also examine the interannual variability of the preferred weather window for linkage to the tropical Pacific (1979–2010). Associations with the subset of El Niño events identified by outgoing-longwave-radiation suggest skilful seasonal fire weather forecasts are feasible. Together, these findings offer a predictive tool to prioritise allocation of scarce prescribed fire resources and maximise annual area treated across this landscape.

The role of understory phenology and productivity in the carbon dynamics of longleaf pine savannas

“…However, prolonged drought could change the system from a carbon sink to a source, as R eco would increase over GEP, which may lead to carbon starvation or hydraulic failure, depending on the severity of the event (McDowell 2011, Zeppel et al 2011, Klein 2015. Furthermore, severe drought could cause a shift in ecosystem structure, as a consequence of the inability to manage these systems with prescribed fire, as drier conditions limit prescription options for managers (Mitchell et al 2014, Chiodi et al 2018.…”

Fire Season, Overstory Density and Groundcover Composition Affect Understory Hardwood Sprout Demography in Longleaf Pine Woodlands

“…By reducing understory and midstory hardwood density, and enhancing flowering in the groundcover, growing-season fires favor grasses and other herbaceous species. Evidence for ecological benefits of growing-season burning notwithstanding, operational considerations (e.g., smoke production, hunting restrictions, heat stress for burn personnel) often restrict burning to cooler seasons [23,24].…”

Prescribed fire science: the case for a refined research agenda

“…In prescribed burn planning, weather conditions help define the fire environment used to generate a desired and expected fire behavior, subject to operational constraints. These constraints include resource availability, fuel moisture, and restricted wind directions due to smoke concerns (Fischer 1978;Waldrop and Goodrick 2012;Chiodi et al 2018). A prescribed fire requires conditions that are dry enough to burn, but not so dry as to elevate fire intensity, cause unwanted damage to the ecosystem, or compromise safety; winds must be sufficient to move the fire and disperse smoke, but not so strong as to cause control problems through elevated intensity or spot-fire ignition.…”

“…Winds also must be from directions that avoid smoke impacts to sensitive areas. The likelihood of a prescription being met on any given day becomes a problem involving several joint probabilities (e.g., Chiodi et al 2018), and current tools do not allow for fire planning to adequately vary ignition patterns simultaneously with a range of multiple micrometeorological variables coupled to combustion dynamics. One result is that prescription thresholds for individual parameters are often set conservatively without consideration of the counter-influence of other parameters that may present a broader range of conditions under which prescribed fires can be applied safely and effectively.…”

“…Prescription windows are significantly influenced by the need to minimize smoke impacts, particularly at night or near smoke-sensitive areas (e.g., Class 1 airsheds in the US [Hyde et al 2017]). The consideration of smoke for acceptable prescription windows adds meteorological variables such as mixing height and transport winds, or derived indices such as the ventilation index and atmospheric dispersion index (Chiodi et al 2018). Several tools have been developed to assist land managers in managing smoke; however, these tools currently have large uncertainties, which must be refined if air quality standards become more restrictive (Goodrick et al 2013).…”