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Large wildfire driven increases in nighttime fire activity observed across CONUS from 2003-2020

Large wildfire driven increases in nighttime fire activity observed across CONUS from 2003-2020
Large wildfire driven increases in nighttime fire activity observed across CONUS from 2003-2020

Despite the ecological and socioeconomic impacts of wildfires, little attention has been paid to the spatiotemporal patterns of nighttime fire activity across the conterminous United States (CONUS). Daytime fire radiative power (FRP) detected by the Moderate Resolution Imaging Spectroradiometer (MODIS) was nearly evenly split (54% vs. 46%) between inside and outside wildfires from 2003 to 2020. In contrast, 94% of nighttime FRP was detected within wildfires, of which 95% was detected within large wildfires (> 2023 ha). Nighttime proportions (i.e., the proportion of total summed FRP detected by MODIS at night) were lowest (3%) outside wildfires when coincident 1000-hr fuel moistures were highest and vegetation fires were smaller and less intense. As 1000-hr fuel moistures decreased, MODIS active fire pixels shifted out of agricultural and prescribed fires and into wildfires with higher nighttime per-pixel values of FRP such that nighttime proportions peaked at 29% for the largest wildfires. Increases in nighttime proportions within larger wildfires were attributed to increases in nighttime persistence whereby under the driest conditions, daytime fire activity detected by MODIS was more likely to continue burning with sufficient vigour to be detected again at night. From 2003–2020, MODIS detected significant (p < 0.01) increasing trends in nighttime wildfire fire activity, with a +54%, +42% and +21% increase in the annual nighttime sum of FRP, annual nighttime active fire pixel counts and annual mean nighttime per-pixel values of FRP, respectively, detected in the latter half of the study period. Nighttime trends were corroborated using observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) as well annual wildfire statistics reported by U.S. federal, state and local agencies. Moreover, MODIS detected a significant positive trend in the nighttime proportion of FRP emitted from wildfires, indicating that in the absence of diurnal differences in detection biases, increases in nighttime fire activity since 2003 have outpaced daytime increases. However an analysis of MODIS omission rates revealed that increasing nighttime proportions were at least partially attributed to a relatively greater improvement in nighttime detection performance compared to the daytime for larger wildfires burning during drier conditions. Nighttime fire activity already poses additional risks to firefighters and communities, and this work suggests that projected increases in the frequency of large wildfires will be accompanied by increases in the extent and intensity of nighttime fire activity.

Large wildfires, Nighttime fire activity, Nighttime persistence, Nighttime proportion
0034-4257
Freeborn, Patrick
84628116-80f4-40f3-9836-6f16d0b7295c
Jolly, Matt
f7fa37e6-7973-42ae-b235-81c7d441a88c
Cochrane, Mark
6478c9eb-c1f7-4390-b646-6faf14d42dab
Roberts, Gareth
fa1fc728-44bf-4dc2-8a66-166034093ef2
Freeborn, Patrick
84628116-80f4-40f3-9836-6f16d0b7295c
Jolly, Matt
f7fa37e6-7973-42ae-b235-81c7d441a88c
Cochrane, Mark
6478c9eb-c1f7-4390-b646-6faf14d42dab
Roberts, Gareth
fa1fc728-44bf-4dc2-8a66-166034093ef2

Freeborn, Patrick, Jolly, Matt, Cochrane, Mark and Roberts, Gareth (2022) Large wildfire driven increases in nighttime fire activity observed across CONUS from 2003-2020. Remote Sensing of Environment, 268, [112777]. (doi:10.1016/j.rse.2021.112777).

Record type: Article

Abstract

Despite the ecological and socioeconomic impacts of wildfires, little attention has been paid to the spatiotemporal patterns of nighttime fire activity across the conterminous United States (CONUS). Daytime fire radiative power (FRP) detected by the Moderate Resolution Imaging Spectroradiometer (MODIS) was nearly evenly split (54% vs. 46%) between inside and outside wildfires from 2003 to 2020. In contrast, 94% of nighttime FRP was detected within wildfires, of which 95% was detected within large wildfires (> 2023 ha). Nighttime proportions (i.e., the proportion of total summed FRP detected by MODIS at night) were lowest (3%) outside wildfires when coincident 1000-hr fuel moistures were highest and vegetation fires were smaller and less intense. As 1000-hr fuel moistures decreased, MODIS active fire pixels shifted out of agricultural and prescribed fires and into wildfires with higher nighttime per-pixel values of FRP such that nighttime proportions peaked at 29% for the largest wildfires. Increases in nighttime proportions within larger wildfires were attributed to increases in nighttime persistence whereby under the driest conditions, daytime fire activity detected by MODIS was more likely to continue burning with sufficient vigour to be detected again at night. From 2003–2020, MODIS detected significant (p < 0.01) increasing trends in nighttime wildfire fire activity, with a +54%, +42% and +21% increase in the annual nighttime sum of FRP, annual nighttime active fire pixel counts and annual mean nighttime per-pixel values of FRP, respectively, detected in the latter half of the study period. Nighttime trends were corroborated using observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) as well annual wildfire statistics reported by U.S. federal, state and local agencies. Moreover, MODIS detected a significant positive trend in the nighttime proportion of FRP emitted from wildfires, indicating that in the absence of diurnal differences in detection biases, increases in nighttime fire activity since 2003 have outpaced daytime increases. However an analysis of MODIS omission rates revealed that increasing nighttime proportions were at least partially attributed to a relatively greater improvement in nighttime detection performance compared to the daytime for larger wildfires burning during drier conditions. Nighttime fire activity already poses additional risks to firefighters and communities, and this work suggests that projected increases in the frequency of large wildfires will be accompanied by increases in the extent and intensity of nighttime fire activity.

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Accepted/In Press date: 26 October 2021
Published date: January 2022
Additional Information: Funding Information: The authors would like to thank the two anonymous reviewers and the editors for their comments and suggestions that helped improve this paper. M.A.C. participated in this work with support from NASA grant NNX11AB89G . Publisher Copyright: © 2021
Keywords: Large wildfires, Nighttime fire activity, Nighttime persistence, Nighttime proportion

Identifiers

Local EPrints ID: 452586
URI: http://eprints.soton.ac.uk/id/eprint/452586
ISSN: 0034-4257
PURE UUID: 965ebb2e-5bbb-4a8b-844e-fdbc216fb8c0
ORCID for Gareth Roberts: ORCID iD orcid.org/0009-0007-3431-041X

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Date deposited: 11 Dec 2021 11:27
Last modified: 17 Mar 2024 03:24

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Contributors

Author: Patrick Freeborn
Author: Matt Jolly
Author: Mark Cochrane
Author: Gareth Roberts ORCID iD

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