Can Landsat-Derived Variables Related to Energy Balance Improve Understanding of Burn Severity From Current Operational Techniques?

Alfonso Fernández-Manso,Dar A Roberts,Carmen Quintano

doi:10.3390/rs12050890

Alfonso Fernández-Manso, Dar A Roberts + Show 1 more

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https://doi.org/10.3390/rs12050890

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Abstract

Forest managers rely on accurate burn severity estimates to evaluate post-fire damage and to establish revegetation policies. Burn severity estimates based on reflective data acquired from sensors onboard satellites are increasingly complementing field-based ones. However, fire not only induces changes in reflected and emitted radiation measured by the sensor, but also on energy balance. Evapotranspiration (ET), land surface temperature (LST) and land surface albedo (LSA) are greatly affected by wildfires. In this study, we examine the usefulness of these elements of energy balance as indicators of burn severity and compare the accuracy of burn severity estimates based on them to the accuracy of widely used approaches based on spectral indexes. We studied a mega-fire (more than 450 km2 burned) in Central Portugal, which occurred from 17 to 24 June 2017. The official burn severity map acted as a ground reference. Variations induced by fire during the first year following the fire event were evaluated through changes in ET, LST and LSA derived from Landsat data and related to burn severity. Fisher’s least significant difference test (ANOVA) revealed that ET and LST images could discriminate three burn severity levels with statistical significance (uni-temporal and multi-temporal approaches). Burn severity was estimated from ET, LST and LSA using thresholding. Accuracy of ET and LST based on burn severity estimates was adequate (κ = 0.63 and 0.57, respectively), similar to the accuracy of the estimate based on dNBR (κ = 0.66). We conclude that Landsat-derived surface energy balance variables, in particular ET and LST, in addition to acting as useful indicators of burn severity for mega-fires in Mediterranean ecosystems, may provide critical information about how energy balance changes due to fire.

Highlights

Fire is one of the major disturbance processes in many ecosystems and is prevalent in Mediterranean ecosystems, where it impacts biodiversity [1,2] and other important ecosystem properties
We examine the usefulness of these elements of energy balance as indicators of burn severity and compare the accuracy of burn severity estimates based on them to the accuracy of widely used approaches based on spectral indexes
Our study proved the usefulness of Landsat-derived variables related to energy balance to estimate burn severity with a similar accuracy to other well-established satellite-based methods, with the added advantage of providing a better understanding of fire-induced changes in energy balance

Summary

Introduction

Fire is one of the major disturbance processes in many ecosystems and is prevalent in Mediterranean ecosystems, where it impacts biodiversity [1,2] and other important ecosystem properties. The frequency, severity and size of fires have been increasing in recent decades in Mediterranean ecosystems, due mainly to climate change and modifications in land use [3]. One of the most commonly used metrics is fire/burn severity [4]. Burn severity groups short- and long-term fire effects on vegetation and soil [5]. Increases in burn severity due to changes in climate and land cover may modify vegetation characteristics (composition, resilience, structure) and soil attributes, even in Mediterranean ecosystems that are well adapted to fire [7,8]

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