Cascading Hazards in the Aftermath of Australia's 2019/2020 Black Summer Wildfires

M Kemter,A Banerjee,E Schönfeldt,J Vogel,O Korup,M Fischer,L V Luna,K Thonicke

doi:10.1029/2020ef001884

Abstract

AbstractFollowing an unprecedented drought, Australia's 2019/2020 “Black Summer” fire season caused severe damage, gravely impacting both humans and ecosystems, and increasing susceptibility to other hazards. Heavy precipitation in early 2020 led to flooding and runoff that entrained ash and soil in burned areas, increasing sediment concentration in rivers, and reducing water quality. We exemplify this hazard cascade in a catchment in New South Wales by mapping burn severity, flood, and rainfall recurrence; estimating changes in soil erosion; and comparing them with river turbidity data. We show that following the extreme drought and wildfires, even moderate rain and floods led to undue increases in soil erosion and reductions in water quality. While natural risk analysis and planning commonly focuses on a single hazard, we emphasize the need to consider the entire hazard cascade, and highlight the impacts of ongoing climate change beyond its direct effect on wildfires.

Highlights

Australia's 2019/2020 “Black Summer” fire season was exceptional in terms of the number of fires, burned area, and fire severity (Baldwin & Ross, 2020; Deb et al, 2020; Hughes et al, 2020)
We show that following the extreme drought and wildfires, even moderate rain and floods led to undue increases in soil erosion and reductions in water quality
The 2019/2020 hazard cascade observed in the Manning River catchment in southeast Australia highlights how the impact of ongoing climate change on wildfires affects the likelihood and magnitude of adverse consequences from other hazards that are in parts physically linked to each other

Summary

Introduction

Australia's 2019/2020 “Black Summer” fire season was exceptional in terms of the number of fires, burned area, and fire severity (Baldwin & Ross, 2020; Deb et al, 2020; Hughes et al, 2020). Wildfires cause hydrometeorological and geomorphic changes that can heighten the susceptibility of burned areas to other hazards; for example, raised soil water repellency after a fire can lead to increased runoff (Shakesby & Doerr, 2006). This was the case with the 2019/2020 fires: following an extreme drought, the fires were the second step in an entire cascade of adverse processes (Figure 1). The ash-laden water contaminated water bodies such as the Lake Burragorang reservoir, Sydney's main drinking water supply (Figure S1) Extreme impacts, like those observed in Australia in early 2020, are often caused by a combination of several drivers (Figure 1). By moving through the sequence of hazards, we explore how certain events triggered and influenced each other, changing their susceptibility as the event chain developed and its effects propagated throughout the catchment

Cascade Onset

Initial Impact

Subsequent Effects

Conclusions and Outlook

Findings

Data Availability Statement