Changes in Drought Characteristics and Heatwave Propagation Over Groundwater Basins in Australia

Abstract The commitment to reduce emissions in global climate change science meetings shows collective responsibility to mitigate the risk of climatic extremes in the Anthropocene. However, growing anthropogenic footprint and climate change will exacerbate the impacts of extreme events on freshwater systems, necessitating the need to enhance contemporary understanding of future changes in drought characteristics (e.g., severity, duration, etc.) and climatic extremes in groundwater basins to assess their implications for water supplies and allocation. Using bias-corrected ensemble mean of nine Coupled Model Intercomparison Project Phase 6 (CMIP6) models, drought characteristics are assessed for two future socio-economic scenarios (SSP 370 and 585). Two drought indicators (standardised precipitation index and standardised runoff index) were combined with Heatwave total length (HWTL) to measure changes in drought characteristics and heatwave propagation, respectively, over four groundwater basins (South West Western Australia-SWWA; Murray Darling Basin-MDB; Cambrian Limestone Aquifer-CLA; and South Australia-SA) in Australia. Our findings indicate that as Australian summers become considerably warmer, particularly toward the late twenty-first century, the relationship between rainfall and runoff extremes, which exhibited strong connections historically (e.g., in CLA; r = 0.87), will vary in the future. This relationship is expected to increase in SA, showing stronger correlations ( r = 0.67 and 0.82 for SSP 370 and SSP 585, respectively) but decrease in SWWA ( r = 0.43 and 0.20, for SSP 370 and SSP 585, respectively). In the MDB, heatwaves are projected to propagate more rapidly into hydrological drought during summer and autumn under the SSP 585 scenario. Even though drought-affected areas are expected to decline in between decades across Australia, the duration and intensity in some locations show no signs of reduction. Increasing drought duration and intensity could limit freshwater availability, and such impact can potentially be exacerbated by the observed shifts and considerable changes in the propagation time of meteorological drought and HTWL to hydrological drought in some basins.