Canadian Forest Service Publications
Extending the National Burned Area Composite time series of wildfires in Canada. 2022. Skakun, R.; Castilla, G.; Metsaranta, J.; Whitman, E.; Rodrigue, S.; Little, J.; Groenewegen, K.; Coyle, M. Remote Sensing 14(13):3050.
Issued by: Northern Forestry Centre
Catalog ID: 40758
Availability: PDF (download)
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Wildfires are a major natural disturbance in Canada that are postulated to increase under a warming climate. To derive accurate trends in burned area and to quantify the effects of fire frequency, duration, and extent, a sufficiently long time series of reliable burned area maps is required. With that in mind, we extended Canada’s National Burned Area Composite (NBAC) dataset from its previous start year (2004) back to 1986. NBAC consists of annual maps in polygon format where the area burned in each fire event is represented by the best available delineation among various mapping methods and data sources of varying quality. Ordered from more to less reliability, in the new 35-year time series (1986 to 2020), 10% of the total burned area was derived from airborne and high-resolution ( < 5 m) satellite imagery, 81% from change detection methods using 30 m Landsat satellite imagery, and the remaining 9% was largely from aerial surveys. Total (Canada-wide) annual burned area estimates ranged from 215,797 ha in 2020 to 6.7 million ha (Mha) in 1989. We computed 95% confidence intervals for the estimate of each year from 1986 to 2020 based on the accuracy and relative contribution in that year of the different data sources, for both the new NBAC time series and the polygon version of the Canadian National Fire Database (CNFDB), a commonly used source of spatially explicit data on burned area in Canada. NBAC confidence intervals were on average ±9.7% of the annual figure, about one-third the width of the confidence intervals derived for CNFDB. The NBAC time series also included nearly 5000 fire events (totalling 4 Mha, with the largest event being 120,661 ha in size) that are missing in the CNFDB. In a regional analysis for the Northwest Territories, retroactive fire mapping from Landsat imagery reduced historical estimates by 3 Mha (16%), which would result in a 1.6 Mha increase in the reported undisturbed critical habitat for threatened woodland caribou. The NBAC dataset is freely downloadable from the Canadian Wildland Fire Information System.
Plain Language Summary
Every year in Canada, wildfires burn hundreds of thousands to millions of hectares of forest. To keep track of how much burned each year and where, fire maps are created by government agencies and then compiled into the Canadian National Fire Database (CNFDB). While some of these maps are accurate, many consist of broad delineations that often encompass areas that actually did not burn, and sometimes entire fires are missed. To tackle this, we used satellite imagery to enhance and expand an alternative fire database called the National Burned Area Composite (NBAC) that the Canadian Forest Service uses for forest carbon emissions reporting. The extended NBAC time series spans from 1986 to 2020 and includes thousands of fires unreported in the CNFDB. Furthermore, we assessed the uncertainty of annual burned area estimates in both NBAC and CNFDB and found that on average NBAC is three times more accurate than CNFDB. As an example of the impact of the increased accuracy on applications such as wildlife conservation, we show there are over a million more hectares of undisturbed woodland caribou habitat in the Northwest Territories than previously reported. The NBAC annual maps of forest fires in Canada are freely downloadable from the internet.