Evaluating the Differenced Normalized Burn Ratio for Assessing Fire Severity Using Sentinel-2 Imagery in Northeast Siberian Larch Forests

Clement J F Delcourt,Roman Petrov,Michelle C Mack,Tatiana A Shestakova,Dave Van Wees,Alisha Combee,Sander Veraverbeke,Brian Izbicki,Brendan M Rogers,Rebecca C Scholten,Trofim Maximov

doi:10.3390/rs13122311

Abstract

Fire severity is a key fire regime characteristic with high ecological and carbon cycle relevance. Prior studies on boreal forest fires primarily focused on mapping severity in North American boreal forests. However, the dominant tree species and their impacts on fire regimes are different between North American and Siberian boreal forests. Here, we used Sentinel-2 satellite imagery to test the potential for using the most common spectral index for assessing fire severity, the differenced Normalized Burn Ratio (dNBR), over two fire scars and 37 field plots in Northeast Siberian larch-dominated (Larix cajanderi) forests. These field plots were sampled into two different forest types: (1) dense young stands and (2) open mature stands. For this evaluation, the dNBR was compared to field measurements of the Geometrically structured Composite Burn Index (GeoCBI) and burn depth. We found a linear relationship between dNBR and GeoCBI using data from all forest types (R2 = 0.42, p < 0.001). The dNBR performed better to predict GeoCBI in open mature larch plots (R2 = 0.56, p < 0.001). The GeoCBI provides a holistic field assessment of fire severity yet is dominated by the effect of fire on vegetation. No significant relationships were found between GeoCBI components (overall and substrate stratum) and burn depth within our fires (p > 0.05 in all cases). However, the dNBR showed some potential as a predictor for burn depth, especially in the dense larch forests (R2 = 0.63, p < 0.001). In line with previous studies in boreal North America, the dNBR correlated reasonably well with field data of aboveground fire severity and showed some skills as a predictor of burn depth. More research is needed to refine spaceborne fire severity assessments in the larch forests of Northeast Siberia, including assessments of additional fire scars and integration of dNBR with other geospatial proxies of fire severity.

Highlights

Wildfire is a natural disturbance that can drastically alter ecosystem composition, structure, function, and carbon stock [1,2]
In the Yert fire scar, intermediate to high differenced Normalized Burn Ratio (dNBR) values were more homogeneously spread across the fire perimeter (Figure 5)
Our study shows that the dNBR is especially useful as a predictor of aboveground severity, as inferred from the relatively strong relationship between the dNBR and the Geometrically structured Composite Burn Index (GeoCBI) [74]

Summary

Introduction

Wildfire is a natural disturbance that can drastically alter ecosystem composition, structure, function, and carbon stock [1,2]. Fires in boreal forests occur in remote and often inaccessible areas, burning large areas, and are of particular concern given the biome’s large carbon stocks that are mostly contained in soil organic matter [3,4,5,6]. Remote sensing measurements are essential for quantifying the impact of fire in boreal forests, Remote Sens. Sensed data provide powerful and cost-effective tools for mapping fire extents from local to global scales and assessing the degree of environmental changes caused by fire [8,9,10]. The environmental impact of wildfires in boreal regions differs from fires in other climate regions due to soil composition and climate conditions [7]. Boreal soils generally consist of a thick organic layer known as duff, which stores large amounts of carbon and acts as an insulating and protective layer for the underlying mineral soils and permafrost [11]

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