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THE EFFECT OF PRESCRIBED BURNS AND WILDFIRES ON SMOKE COVER AND PM2.5 IN CALIFORNIA

Authors:
THE EFFECT OF PRESCRIBED BURNS AND WILDFIRES ON
SMOKE COVER AND PM2.5 IN CALIFORNIA
Anna Boser1, Samuel Evans1,2 & Matthew D. Potts1
1 Department of Environmental Science, Policy, and Management, UC, Berkeley 2 Dept. of Public Policy, Mills College
METHODS
We used prescribed burn and wildfire data from CAL FIRE’s Fire
Resource Assessment Program (FRAP)2in conjunction with NOAA’s
HMS plumes3and NASA’s high resolution PM2.5 estimates.4High
and medium density HMS plumes have been shown to be associated
with increases in ground level PM2.5 during wildfire events.5
FRAP Fire Perimeters NOAA HMS Plumes NASA PM2.5 Estimates
+ +
We considered 4248 wildfires and 2113 prescribed burns between
October 2005 and December 2018.We divided them by acres
burned into three categories: “small” (150- acres), “medium” (150-
22000 acres), and “large” (22000+ acres).
We calculated the area covered by plumes of each density within a
1km distance from the fire perimeter boundary and mean PM2.5 at
the site of each fire from aperiod from 7 days before until 14 days
after the start of the fire.We then used t-tests with aBonferroni
correction to understand whether there was a difference in log plume
area (area was far from normally distributed) and PM2.5 in the period
prior to the start of the fire and each day after the fire’s start date.
BACKGROUND
Prescribed burns are an important forest management tool, and their
increased use in California is proposed to help mitigate catastrophic
wildfires. However, the smoke they produce has been cause for
public health concern. Smoke exposure from wildfires, particularly
due to fine particulate matter (PM2.5), has been shown to increase
adverse health outcomes across the Western United States.1
However, it is not well understood how emissions from prescribed
burns compare to those from wildfires, and thus compare in terms of
public health impacts.
1. Lui, J.C., et.al. (2017)Wildfire-specific Fine Particulate Matter and Risk of Hospital Admissions in Urban and Rural Counties.Epidemiology.2017 Jan; 28(1):77-85.
2. California Department of Forestry and Fire Protection (CAL FIRE), Fire Resource Assessment Program (FRAP). (2018)Fire Perimeters.
3. National Oceanic and Atmospheric Administration (NOAA) (2005) Hazard Mapping System (HMS)
4. Al-Hamdan, M., et al. (2009)Methods for Characterizing Fine Particulate Matter Using Ground Observations and Remotely Sensed Data:Potential Use for
Environmental Public Health Surveillance. Air & Waste Manage. Assoc. 59:865881.
5. Preisler, H. et.al. (2015) A statistical model for determining impact of wildland fires on Particulate Matter (PM2.5)in Central California aided by satellite imagery of
smoke. Environmental Pollution.205:340-349.
REFERENCES
RESULTS
Guiding Research Questions
1. How do prescribed burns compare to wildfires in terms of the
area covered by smoke over time?
2. How do prescribed burns and wildfires compare in terms of
increases in ground level particulate matter, which is associated
with adverse health outcomes?
All sizes of wildfires were associated with statistically significant
increases in log10 area of plumes of all densities for all two-weeks
after fire onset, except the first day, where increases in coverage by high
density plumes was not significant. Prescribed burns of both small and
medium size only showed a statistically significant increase in log area
covered by low density plumes on the first day of the fire only.
Small wildfires showed statistically significant increases in PM2.5 for 10
days,medium wildfires for 12 days,and large wildfires for all 14
days.By contrast, prescribed burns did not show astatistically
significant increase in PM2.5 at any point in the two week period.
Preisler et.al.5suggested that only medium and high density plumes are associated with increases in ground level PM2.5, so these results indicate that
wildfires, and not prescribed burns, would correspond to increased exposure days to elevated PM2.5. Consistent with these findings, our analysis of the
PM2.5 increases show that wildfires of all sizes contributed detectable increases for at least two weeks, while prescribed burns did not.
These results suggest that HMS plumes and NASA PM2.5 estimates are not fine enough data to accurately capture the nuanced increases in smoke
cover and PM2.5 that prescribed burns surely contribute. However, these results clearly show that whatever contributions prescribed burns do make,
they are of significantly smaller magnitude, cover a significantly smaller area, and persist for significantly shorter periods of time than those of
prescribed burns.This has important forest management and public health implications, as it may suggest that prescribed burns may be an effective
way to decrease smoke exposure in the long run, in addition to their wildfire mitigation potential.
DISCUSSION AND CONCLUSION
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