Australia’s Tinderbox Drought: An extreme natural event likely worsened by human-caused climate change

We examine the characteristics and causes of southeast Australia’s
Tinderbox Drought (2017–2019) that preceded the Black Summer fire
disaster. The Tinderbox Drought was characterised by cool season rainfall
deficits of around –50% in three consecutive years, which was
exceptionally unlikely in the context of natural variability alone. The
precipitation deficits were initiated and sustained by an anomalous
atmospheric circulation that diverted oceanic moisture away from the
region, despite traditional indicators of drought risk in southeast
Australia generally being in neutral states. Moisture deficits were
intensified by unusually high temperatures, high vapour pressure deficits
and sustained reductions in terrestrial water availability. Anthropogenic
forcing intensified the rainfall deficits of the Tinderbox Drought by
around 18% with an interquartile range of 34.9% to –13.3% highlighting the
considerable uncertainty in attributing droughts of this kind to human
activity. Skillful predictability of this drought was possible by
incorporating multiple remote and local predictors through machine
learning, providing prospects for improving forecasting of multi-year
droughts.