The 2019 flash droughts in subtropical eastern Australia and their association with large-scale climate drivers

During 2017-2019, drought existed in many parts of Australia with varying degrees of severity and varied timing of development and intensification. In a broad sense, the surface climate conditions went from anomalously wet in 2016 to an official government-declared drought from the end of 2017. The drought subsequently intensified further to become most severe in mid to late 2019. Here we explore the more detailed evolution of the 2019 conditions over subtropical eastern Australia and infer its predictability through linear relationships with large-scale climate drivers. To monitor the detailed drought evolution, we use the Evaporative Stress Index (ESI) computed over a 4-week running window on a 5 km grid. Flash drought onset is defined as when there is a rapid decline in the ESI that is sustained over at least 2 weeks which ends in drought conditions. For the Central Slopes area of the upper Darling River basin, flash drought onset occurred in June, persisted over 6 months, and rapidly terminated through a flash recovery in February 2020. In the far east of Australia (East Coast regions), flash drought onset was identified later, in November and December. For the Central Slopes area, less than half the magnitude of the flash drought development in June could be explained through linear relationships with the positive Indian Ocean Dipole mode (IOD) and the central Pacific El Nino, together with the long-term trend in ESI in the region. Similarly, only about half the magnitude of the East Coast flash drought developments in November and December could be explained by the ongoing positive IOD, central Pacific El Nino, negative Southern Annular Mode, and ongoing global warming trend. Therefore, although these large-scale drivers set the stage for the likelihood of drought, successful prediction of flash drought will require more local and current information than those large-scale climate drivers alone.

Automated summary

During 2017-2019, Australia experienced severe drought with varied development and intensity, the impact of large-scale climate drivers on drought was limited, successful prediction of drought requires more local and current information.