A New Application of the Disturbance Index for Fire Severity in Coastal Dunes

Abstract

Fires are a disturbance that can lead to short term dune destabilisation and have been suggested to be an initiation mechanism of a transgressive dune phase when paired with changing climatic conditions. Fire severity is one potential factor that could explain subsequent coastal dune destabilisations, but contemporary evidence of destabilisation following fire is lacking. In addition, the suitability of conventional satellite Earth Observation methods to detect the impacts of fire and the relative fire severity in coastal dune environments is in question. Widely applied satellite-derived burn indices (Normalised Burn Index and Normalised Difference Vegetation Index) have been suggested to underestimate the effects of fire in heterogenous landscapes or areas with sparse vegetation cover. This work assesses burn severity from high resolution aerial and Sentinel 2 satellite imagery following the 2019/2020 Black Summer fires on Kangaroo Island in South Australia, to assess the efficacy of commonly used satellite indices, and validate a new method for assessing fire severity in coastal dune systems. The results presented here show that the widely applied burn indices derived from NBR differentially assess vegetation loss and fire severity when compared in discrete soil groups across a landscape that experienced a very high severity fire. A new application of the Tasselled Cap Transformation (TCT) and Disturbance Index (DI) is presented. The differenced Disturbance Index (dDI) improves the estimation of burn severity, relative vegetation loss, and minimises the effects of differing soil conditions in the highly heterogenous landscape of Kangaroo Island. Results suggest that this new application of TCT is better suited to diverse environments like Mediterranean and semi-arid coastal regions than existing indices and can be used to better assess the effects of fire and potential remobilisation of coastal dune systems.

Post‐wildfire coastal dunefield response using photogrammetry and satellite indices

“…To measure significant surface and vegetation changes between surveys, the M3C2-PM plugin of CC was used. M3C2 was developed by Indices were chosen due to their widespread application (Chuvieco et al, 2020) and according to related work in burnt coastal dune environments (DaSilva et al, 2021). The normalised burn ratio (NBR) using bands 8 842 and 12 2190 of S2 imagery is given by…”

“…Fires are common and occur annually, principally from intentionally human‐initiated burn‐offs and dry lightning strikes (Peace, 2012). For further information on KI, DaSilva et al (2021) provide a review of the island's geography as it relates to fire severity, and Bonney, He and Myint (2020) review its recent fire history.…”

“…Three spectral indices used in fire severity studies were calculated from S2 geomedians and compared in pre‐ (November 2015 to December 2019) and post‐fire groups (January 2020 to May 2022). Indices were chosen due to their widespread application (Chuvieco et al, 2020) and according to related work in burnt coastal dune environments (DaSilva et al, 2021). The normalised burn ratio (NBR) using bands 8 842 and 12 2190 of S2 imagery is given by …”

“…GS Normals/D = 0.3 information and facilitates landscape-specific variables such as soil brightness to be mitigated(DaSilva et al, 2021).Geomedian pixels within survey areas were masked to burnt areas according to a differenced NBR (dNBR) threshold of 0.2, calculated by the cloud-free images before and after the fire. Pre-fire minimum and maximum index values were calculated to show the relative range and index trajectory of dunefields as seen from satellite indices.To analyse the M3C2-PM changes according to the pre-fire ground-cover types, spectral thresholds were used to separate pixels into three sub-analysis groups: bare sand and burnt or unburnt vegetated surfaces.…”

Short-Term Recovery of the Aboveground Carbon Stock in Iberian Shrublands at the Extremes of an Environmental Gradient and as a Function of Burn Severity

“…Despite the influence of soil background signal and transferability issues that may hinder the performance of Normalized Burn Ratio (NBR)-based indices in burn severity initial assessments [21,59,60], threshold-based classification of the differenced NBR (dNBR; [61]) index is the most widely accepted approach for this purpose [62,63]. In fact, the dNBR is the primary spectral index within the Rapid Damage Assessment (RDA) module of European Forest Fire Information System (EFFIS) and the Monitoring Trends in Burn Severity (MTBS) project (together with RdNBR; [64]) in the United States.…”