Springer Science and Business Media LLC

The 2019/20 Australian black summer bushfires were particularly severe in many respects, including its early commencement, large spatial coverage, and large number of burning days, preceded by record dry and hot anomalies. Determining whether greenhouse warming has played a role is an important issue. Here, we examine known modes of tropical climate variability that contribute to droughts in Australia to provide a gauge. We find that a two-year consecutive concurrence of the 2018 and 2019 positive Indian Ocean Dipole and the 2018 and 2019 Central Pacific El Niño, with the former affecting Southeast Australia, and the latter influencing eastern and northeastern Australia, may explain many characteristics of the fires. Such consecutive events occurred only once in the observations since 1911. Using two generations of state-of-the-art climate models under historical and a business-as-usual emission scenario, we show that the frequency of such consecutive concurrences increases slightly, but rainfall anomalies during such events are stronger in the future climate, and there are drying trends across Australia. The impact of the stronger rainfall anomalies during such events under drying trends is likely to be exacerbated by greenhouse warming-induced rise in temperatures, making such events in the future even more extreme.

Truths of the Riverscape refer to the use of geomorphological principles to inform sustainable approaches to nature-based river management. Across much of the world a command-and-control philosophy continues to assert human authority over rivers. Tasked to treat rivers as stable and predictable entities, engineers have ‘fixed rivers in place’ and ‘locked them in time’. Unsustainable outcomes ensue. Legacy effects and path dependencies of silenced and strangled (zombified) rivers are difficult and increasingly expensive to address. Nature fights back, and eventually it wins, with disastrous consequences for the environment, society, culture and the economy. The failure to meet the transformative potential of nature-based applications is expressed here as a disregard for ‘Truths of the Riverscape’. The first truth emphasises the imperative torespect diversity, protecting and/or enhancing the distinctive values and attributes of each and every river. A cross-scalar (nested hierarchical) lens underpins practices that ‘know your catchment’. The second truth envisages management practices thatwork with processes, interpreting the behaviour of each river. This recognises that erosion and deposition are intrinsic functions of a healthy living river—in appropriate places, at appropriate rates. This premise underpins the third truth,assess river condition, highlighting the importance of what to measure and what to measure against in approaches that address the causes rather than the symptoms of unexpected river adjustment. The fourth truthinterprets evolutionary trajectory to determine what is realistically achievablein the management of a given river system. Analysis of whether the river sits on a degradation or recovery pathway (i.e., condition is deteriorating or improving), alongside assessment of catchment-specific recovery potential, is used to foresight river futures. Viewed collectively, Truths of the Riverscape provide a coherent platform to develop and apply proactive and precautionary catchment management plans that address concerns for biodiversity loss and climate change adaptation.