Reversal of Australian drought trends over recent decades

Australia frequently experiences severe and widespread droughts, causing impacts on agriculture, the economy, and human health. The effects of these droughts can extend beyond national boundaries, influencing the global carbon cycle and global food markets owing to Australia’s position as one of the world’s leading grain exporters. Yet we lack comprehensive understanding of how Australian droughts have evolved over the past century. In this study, we analyse the past changes in seasonal-scale meteorological, agricultural, and hydrological droughts – defined using the 15th percentile threshold of precipitation, soil moisture, and runoff, respectively. We complement these traditional metrics with an impact-based drought indicator built from government drought reports using machine learning. We find that although there have been widespread decreases in Australian droughts since the early 20th century, extensive regions have experienced an increase in recent decades. However, these recent changes largely remain within the range of observed variability, suggesting that they are not unprecedented in the context of the historical drought events. The drivers of these drought trends are multi-faceted, and we show that the trends can be driven by both mean and variability changes in the underlying hydrological variable. Additionally, using explainable machine learning techniques, we unpick the key hydrometeorological variables contributing to agricultural and hydrological drought trends. The influence of these variables varies considerably between regions and seasons, with precipitation often shown to be important but rarely the main driver behind observed drought trends. This suggests the need to consider multiple drivers when assessing drought trends.