"Thermocouple Probe Orientation Affects Prescribed Fire Behavior Estimation"

Published December 14, 2017

Abstract:

Understanding the relationship between fire intensity and fuel mass is essential information for scientists and forest managers seeking to manage forests using prescribed fires. Peak burning temperature, duration of heating, and area under the temperature profile are fire behavior metrics obtained from thermocouple-datalogger assemblies used to characterize prescribed burns. Despite their recurrent usage in prescribed burn studies, there is no simple protocol established to guide the orientation of thermocouple installation. Our results from dormant and growing season burns in coastal longleaf pine (Pinus palustris Mill.) forests in South Carolina suggest that thermocouples located horizontally at the litter-soil interface record significantly higher estimates of peak burning temperature, duration of heating, and area under the temperature profile than thermocouples extending 28 cm vertically above the litter-soil interface (p < 0.01). Surprisingly, vertical and horizontal estimates of these measures did not show strong correlation with one another (r2 ≤ 0.14). The horizontal duration of heating values were greater in growing season burns than in dormant season burns (p < 0.01), but the vertical values did not indicate this difference (p = 0.52). Field measures of fuel mass and depth before and after fire showed promise as significant predictive variables (p ≤ 0.05) for the fire behavior metrics. However, all correlation coefficients were less than or equal to r2 = 0.41. Given these findings, we encourage scientists, researchers, and managers to carefully consider thermocouple orientation when investigating fire behavior metrics, as orientation may affect estimates of fire intensity and the distinction of fire treatment effects, particularly in forests with litter-dominated surface fuels.

Citation:

Coates, T. A., A. T. Chow, D. L. Hagan, T. A. Waldrop, G. G. Wang, W. C. Bridges, M. Rogers, and J. H. Dozier. 2017. Thermocouple Probe Orientation Affects Prescribed Fire Behavior Estimation. J. Environ. Qual. 0. doi:10.2134/jeq2017.02.0055

Corresponding author: Alex T. Chow (achow "at" clemson.edu)

“What is an anomaly?”*

TPOS note:

New research on the 2016 drought in the southern Appalachians demonstrates this event was an anomaly given recent regional climate trends. Since the 1950s, average fall weather has seen higher than average precipitation and lower than average daily high temperatures. The drought of 2016 (sometimes called a "flash drought") was notable for the "...intensity and rapid onset... and its destructive impact on wildfire and human water resources..."

However, the authors also reviewed longer-term climate data and concluded, "...droughts as strong as the 2016 event are more likely than indicated from a shorter 60 year perspective."

The infamous Chimney Tops 2 Fire occured during this flash drought. Following ignition by an arsonist, this fire burned from Great Smokey Mountains National Park to Gatlinburg, Tennessee. With severe drought, strong winds, steep terrain, and high fuel loads (including recent leaf fall and dry heavy fuels) the fire covered 14,000 acres, destroyed structures, and resulted in 14 fatalities.

Here are two questions we hope will lead to further discussion on this blog or elsewhere:

• do these events suggest wildfire risk assessments for the Midwest should be reviewed to determine if models include parameters adequate to modeling wildfire spread in worst case (so-called "unthinkable") scenarios?
• what questions do you have for the authors about this research?

Read the abstract below or check out the article "The 2016 southeastern U.S.drought: An extreme departure from centennial wetting and cooling" at http://onlinelibrary.wiley.com/doi/10.1002/2017JD027523/full

* thanks to Megan Sebasky, Northeast Region LANDFIRE coordinator, for helpful comments on this post and suggesting this title (read LANDFIRE's interview with Megan). Thanks also to Jed Meunier, Wisconsin DNR fire ecologist, for reviewing and sharing comments on this post.

Abstract

The fall 2016 drought in the southeastern United States (SE U.S.) appeared exceptional based on its widespread impacts, but the current monitoring framework that only extends from 1979 to present does not readily facilitate evaluation of soil-moisture anomalies in a centennial context. A new method to extend monthly gridded soil-moisture estimates back to 1895 is developed, indicating that since 1895, October–November 2016 soil moisture (0–200 cm) in the SE U.S. was likely the second lowest on record, behind 1954. This severe drought developed rapidly and was brought on by low September–November precipitation and record-high September–November daily maximum temperatures (Tmax). Record-high Tmax drove record-high atmospheric moisture demand, accounting for 28% of the October–November 2016 soil-moisture anomaly. Drought and heat in fall 2016 contrasted with 20th century wetting and cooling in the region but resembled conditions more common from 1895–1956. Dynamically, the exceptional drying in fall 2016 was driven by anomalous ridging over the central United States that reduced south-southwesterly moisture transports into the SE U.S. by approximately 75%. These circulation anomalies were partly promoted by a moderate La Niña and warmth in the tropical Atlantic, but these processes accounted for very little of the SE U.S. drying in fall 2016, implying a large role for internal atmospheric variability. The extended analysis back to 1895 indicates that SE U.S. droughts as strong as the 2016 event are more likely than indicated from a shorter 60 year perspective and continued multidecadal swings in precipitation may combine with future warming to further enhance the likelihood of such events.

Citation

Park Williams, A., Cook, B. I., Smerdon, J. E., Bishop, D. A., Seager, R., & Mankin, J. S. (2017). The 2016 southeastern U.S.drought: An extreme departure from centennial wetting and cooling. Journal of Geophysical Research: Atmospheres, 122. https://doi.org/10.1002/2017JD027523

Corresponding author: A. Park Williams, williams "at" ldeo.columbia.edu