Natural variability of multi-year droughts in Australia in Last Millennium simulations

Fluctuations in Australia's hydroclimate have severe societal and environmental implications, with devastating consequences associated with precipitation deficits or droughts. However, the short length of instrumental records (i.e., ~100 years since 1900s onwards) restricts our understanding of the full range of natural variability of droughts, including features such as the persistence, frequency, and severity of droughts. Here, we assess drought variability using climate model simulations of the last millennium. We investigate the length and magnitude of consecutive dry years and accumulated precipitation deficits using the Community Earth System Model (CESM) Last Millennium Ensemble (LME), and compare these distributions to a lag-one autoregressive (AR(1)) model and to white noise. We also compare these distributions to observations over Australia since 1900 CE. We further assess how sensitive recent hydroclimatic trends are to the length of climate simulation, and explore the role of external forcings, such as volcanic eruptions on drought variability. This work helps contextualize current hydroclimatic changes under anthropogenic climate change and provides further insight into the full range of natural variability of drought in Australia.