A new perspective on the genesis of the 2019/2020 Australian bushfire and its atmospheric radiative impacts

Abstract

Extensive investigations of the genesis and atmospheric radiative impacts of the Australian bushfires of August 2019 to January 2020 (also known as the black summer event) have been carried out using in-situ, multi-satellite, and reanalysis data. We present the observational evidence for the role of total water storage in the initiation of this event. A strong correlation was found between the depletion of the total water storage (sum of surface and sub-surface water storage) caused by the hydrological drought and the burnt area in southeast Australia. Notably, a decadal low of Liquid Water Equivalent Thickness (LWET) going below −5 cm in December 2019 strongly suggests the crucial role of hydrological drought in the genesis of the black summer event.

The hydrological drought provided favorable conditions for intense fire activity during the black summer event and increased the aerosol loading across Australia. The assimilated Aerosol Optical Depth revealed that the impact of the black summer event on the aerosol loading is higher than previously reported. The amplified aerosol backscattering, coupled with the increased surface albedo due to the prevailing drought, led to a significant surge in outgoing shortwave flux and contributed to regional cooling. Along with the increased aerosol loading, it has also been observed that the co-emitted carbon monoxide enhanced the ozone production at 850 hPa, further degrading the air quality. These findings will offer crucial insights for predicting extreme bushfire events and their mitigation policies.