Abstract
Alaska’s boreal region stores large amounts of carbon both in its woodlands and in the grounds that sustain them. Any alteration to the fire system that has naturally regulated the region’s ecology for centuries poses a concern regarding global climate change. Satellite-based remote sensors are key to analyzing those spatial and temporal patterns of fire occurrence. This paper compiles four burned area (BA) time series based on remote sensing imagery for the Alaska region between 1982–2015: Burned Areas Boundaries Dataset-Monitoring Trends in Burn Severity (BABD-MTBS) derived from Landsat sensors, Fire Climate Change Initiative (Fire_CCI) (2001–2015) and Moderate-Resolution Imaging Spectroradiometer (MODIS) Direct Broadcast Monthly Burned Area Product (MCD64A1) (2000–2015) with MODIS data, and Burned Area-Long-Term Data Record (BA-LTDR) using Advanced Very High Resolution Radiometer LTDR (AVHRR-LTDR) dataset. All products were analyzed and compared against one another, and their accuracy was assessed through reference data obtained by the Alaskan Fire Service (AFS). The BABD-MTBS product, with the highest spatial resolution (30 m), shows the best overall estimation of BA (81%), however, for the years before 2000 (pre-MODIS era), the BA sensed by this product was only 44.3%, against the 55.5% obtained by the BA-LTDR product with a lower spatial resolution (5 km). In contrast, for the MODIS era (after 2000), BABD-MTBS virtually matches the reference data (98.5%), while the other three time series showed similar results of around 60%. Based on the theoretical limits of their corresponding Pareto boundaries, the lower resolution BA products could be improved, although those based on MODIS data are currently limited by the algorithm’s reliance on the active fire MODIS product, with a 1 km nominal spatial resolution. The large inter-annual variation found in the commission and omission errors in this study suggests that for a fair assessment of the accuracy of any BA product, all available reference data for space and time should be considered and should not be carried out by selective sampling.
Highlights
Boreal regions store large quantities of carbon in the vegetation, permafrost, and peatlands that are usually stored for hundreds of years, unless released into the atmosphere by a disturbance [1,2,3]
Four burned area (BA) time series based on satellite imagery with different spatial resolution, Burned Areas Boundaries Dataset (BABD)-Monitoring Trends in Burn Severity (MTBS)
For the pre-Moderate Resolution Imaging Spectroradiometer (MODIS) era, the product resulting from LTDR images shows the best results in terms of BA estimation
Summary
Boreal regions store large quantities of carbon in the vegetation, permafrost, and peatlands that are usually stored for hundreds of years, unless released into the atmosphere by a disturbance (e.g., a wildfire) [1,2,3]. In the past six decades, Alaska’s average temperature has increased by about 3 ◦ F, and models forecast a potential increase of up to an additional 4 ◦ F by 2050 [7]. This rise in the average temperature is causing a modification of the surface energy balance and soil thermal conditions, the exposure of permafrost to thawing due to the decrease in organic soil depth, the decrease in the humidity of forest fuels, the extension of the natural fire season and, an abnormal spatial and temporal dynamic in these fires.
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