the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Burned Area and Carbon Emissions Across Northwestern Boreal North America from 2001–2019
Stefano Potter
Sol Cooperdock
Sander Veraverbeke
Xanthe Walker
Michelle C. Mack
Scott J. Goetz
Jennifer Baltzer
Laura Bourgeau-Chavez
Arden Burrell
Catherine Dieleman
Nancy French
Stijn Hantson
Elizabeth E. Hoy
Liza Jenkins
Jill F. Johnstone
Evan S. Kane
Susan M. Natali
James T. Randerson
Merritt R. Turetsky
Ellen Whitman
Elizabeth Wiggins
Brendan M. Rogers
Abstract. Fire is the dominant disturbance agent in Alaskan and Canadian boreal ecosystems and releases large amounts of carbon into the atmosphere. Burned area and carbon emissions have been increasing with climate change, which have the potential to alter the carbon balance and shift the region from a historic sink to a source. It is therefore critically important to track the spatiotemporal changes in burned area and fire carbon emissions over time. Here we developed a new burned area detection algorithm between 2001–2019 across Alaska and Canada at 500 meters (m) resolution that utilizes finer-scale 30 m Landsat imagery to account for land cover unsuitable for burning. This method strictly balances omission and commission errors at 500 m to derive accurate landscape- and regional-scale burned area estimates. Using this new burned area product, we developed statistical models to predict burn depth and carbon combustion for the same period within the NASA Arctic-Boreal Vulnerability Experiment (ABoVE) core and extended domain. Statistical models were constrained using a database of field observations across the domain and were related to a variety of response variables including remotely-sensed indicators of fire severity, fire weather indices, local climate, soils, and topographic indicators. The burn depth and aboveground combustion models performed best, with poorer performance for belowground combustion. We estimate 2.37 million hectares (Mha) burned annually between 2001–2019 over the ABoVE domain (2.87 Mha across all of Alaska and Canada), emitting 79.3 +/- 27.96 (+/- 1 standard deviation) Teragrams of carbon (C) per year, with a mean combustion rate of 3.13 +/- 1.17 kilograms C m-2. Mean combustion and burn depth displayed a general gradient of higher severity in the northwestern portion of the domain to lower severity in the south and east. We also found larger fire years and later season burning were generally associated with greater mean combustion. Our estimates are generally consistent with previous efforts to quantify burned area, fire carbon emissions, and their drivers in regions within boreal North America; however, we generally estimate higher burned area and carbon emissions due to our use of Landsat imagery, greater availability of field observations, and improvements in modeling. The burned area and combustion data sets described here (the ABoVE Fire Emissions Database, or ABoVE-FED) can be used for local to continental-scale applications of boreal fire science.
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Stefano Potter et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2022-364', João Silva, 22 Dec 2022
In this work burnt area maps and carbon emissions are derived for Canada and Alaska for a period of 19 years, based on satellite imagery and a large data base of field observation. Concerning the carbon combustion estimation, both aboveground models and belowground models are used. The latter is very important since in the Canadian and Alaskan boreal ecosystems fire typically burns deeply into the organic soil layer, which limits the application of remotely sensed data. Results area compared with several data sources.
Major comments:
- Although the manuscript is well structured and clear, due to the large number of analysis performed, it would be easier to fallow the work done if a flowchart was available, describing the methods, data, variables, etc. Or two flowcharts, one for the burnt area mapping model, and one for the combustion and burn depth models.
- Burned area estimates are compared with other products (regional, from Canada, and global, such as MODIS), and total annual burnt area values are very similar (Fig. 3), but it would be useful to actually validate the burnt area maps. If possible, at least for the areas covered with Landsat, the burnt area maps could be validated with manually digitized burnt area maps over Landsat images, or with Sentinel-2 burnt images for the last years.
- If the validation suggested in 2 is not possible, a sample of individual fires could be selected and the different burnt area maps discussed (as done in Fig. 4, and Fig. S10), to better understand the impacts (e.g. commission and omission errors) of the different methods.
Other comments:
- In line 223 is not clear what are “burned and paired control sites”.
- Line 387 and 389: dNBR is repeated.
- Line 475: how was the 3% standard deviation value obtained? A normal distribution was fitted to the data? The same for the 20% value in the next line; how was it obtained?
- Line 503: I think it should be “We quantified uncertainty in our predictions in three ways”, instated of ““We quantified uncertainty in our predictions three ways”. This was the only grammar issue I found, but my mother tongue is Portuguese.
- Line 549: “substantially” does not make sense looking to results (Fig. 3).
- Line 554: GFED4 is not in Fig. 3.
- 4: f) e g) fire perimeters look the same.
- Line 789: should be Figure S22 instead of Figure 22.
- Line 850: for these kind of data with very large inter-annual variability, with some years that are strong outliers, it is better to use non-parametric methods to assess the trends, such as the Theil-Sen slope, which is very robust to outliers (significance is given by the associated test of Mann-Kendell).
- This is a suggestion since already many analyses were done in this work (but may be used in future research): it would be very ingesting to have maps of the trends in burned area and emissions. I mean to run spatiotemporal trends for Alaska and Canada and for the 19 years at the pixel level, done in a contextual way to account for the effect of the neighboring pixels. Some examples: https://link.springer.com/article/10.1007/s10113-018-1415-6, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0150663
Citation: https://doi.org/10.5194/egusphere-2022-364-RC1 -
RC2: 'Comment on egusphere-2022-364', Anonymous Referee #4, 21 Feb 2023
In this work the authors evaluated the burned area and carbon emissions across Canada and Alaska over a 19-year period, using remote sensing data, field observation and modeling. The paper is well structured and clear, especially the introduction, results and discussion. However, the methodology could be resumed with flowcharts or some information added as supplementary material and the discussion could explore more perspectives and applications from the ABoVe-FED.
Specific comments:
- Line 149: The meaning of ABoVE domain is not cited early.
- Lines 175-180: Fig 1: The colors in the legend can be resumed by parenthesis instead of repeating “is shown in..”
- In this figure its would interesting to show the final land cover map (for i.e. the last year of study, 2019)
- Line 187: What did you mean by “burn depth”?
- Lines of burned area mapping approach could be more resumed in a flowchart, for example.
- Figure 8: add how much is “low fire occurrence”
Citation: https://doi.org/10.5194/egusphere-2022-364-RC2
Stefano Potter et al.
Stefano Potter et al.
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