Terrestrial water storage in Australia under stress from compound climate extremes

Abstract

A large proportion of human population could be exposed to future risks from compound climate extremes, which are threatening food and water security. To understand the far-reaching impacts of these extremes on the livelihoods of current and future generations, we need models that are less ambiguous, better suited for impact studies, and more capable of advancing our understanding of future climatic conditions (e.g., rainfall and temperature). To advance such modelling capabilities for impact assessment of compound extremes in Australia, we develop a new framework to combine satellite gravity data with in-situ data and outputs from hydrological models to adjust for biases in the latest Coupled Model Intercomparison Project Phase general circulation models' projections of water budget parameters. The impacts of compound climate extremes under different climate scenarios on the freshwater derived from these parameters were then assessed. Our findings show that the Australian east coast will experience a rise in compound hot and wet extremes, and changes to these compound extremes under different climate scenarios will drive freshwater deficits in Australia. The consequences of limiting global warming to different levels (historical, SSP 245, 370, and 585) on freshwater were also identified. We found significant freshwater declines over Australia with Western Australia being the most affected by compound climate extremes (wet and hot extremes) across all global warming scenarios. Considerable percentage changes exceeding-125% in freshwater have been linked to these compound extremes. Our results also reveal that evapotranspiration will emerge as a more crucial indicator to freshwater availability, and that atmospheric dynamics and moisture transport are expected to contribute to considerable changes in freshwater availability.