Spatial partitioning and temporal evolution of Australia's total water storage under extreme hydroclimatic impacts

Australia experienced one of the worst droughts in history during the early 21st-century (termed the ‘big dry’), exerting negative impacts on food production and water supply, with increased forest die-back and bushfires across large areas. Following the ‘big dry’, one of the largest La Niña events in the past century, in conjunction with an extreme positive excursion of the Southern Annular Mode (SAM), resulted in dramatic increased precipitation from 2010 to 2011 (termed the ‘big wet’), causing widespread flooding and a recorded sea level drop. Despite these extreme hydroclimatic impacts, the spatial partitioning and temporal evolution of total water storage across Australia remains unknown. In this study we investigated the spatial-temporal impacts of the recent ‘big dry’ and ‘big wet’ events on Australia's water storage dynamics using the total water storage anomaly (TWSA) data derived from the Gravity Recovery and Climate Experiment (GRACE) satellites. Results showed widespread, continental-scale decreases in TWS during the ‘big dry’, resulting in a net loss of 3.89 ± 0.47 cm (299 km3) total water, while the ‘big wet’ induced a sharp increase in TWS, equivalent to 11.68 ± 0.52 cm (898 km3) of water, or three times the total water loss during the ‘big dry’. We found highly variable continental patterns in water resources, involving differences in the direction, magnitude, and duration of TWS responses to drought and wet periods. These responses clustered into three distinct geographic zones that correlated well with the influences from multiple large-scale climate modes. Specifically, a persistent increasing trend in TWS was recorded over northern and northeastern Australia, where the climate is strongly influenced by El Niño-Southern Oscillation (ENSO). By contrast, western Australia, a region predominantly controlled by the Indian Ocean Dipole (IOD), exhibited a continuous decline in TWS during the ‘big dry’ and only a subtle increase during the ‘big wet’, indicating a weak recovery of water storage. Southeastern Australia, influenced by combined ENSO, IOD and SAM interactions, exhibited a pronounced TWS drying trend during the ‘big dry’ followed by rapid TWS increases during the ‘big wet’, with complete water storage recoveries. A spatial intensification of the water cycle was further identified, with a wetting trend over wetter regions (northern and northeastern Australia) and a drying trend over drier regions (western Australia). Our results highlight the value of GRACE derived TWSA as an important indicator of hydrological system performance for improved water impact assessments and management of water resources across space and time