| 16 Feb 2026
Comparing drivers of hydrological shifts across regions: the case of southern Australia
Abstract. Several regions globally have recently experienced persistent shifts in the relationship between rainfall and runoff, triggered by multi-annual drought. These regions are climatically diverse; however, few assessments have yet been undertaken to draw parallels (if any) between the processes responsible. We present a comparative analysis of these hydrological shifts between south-west Australia and south-east Australia, two regions separated by over 2,700 km (~1,700 miles). We apply existing methods based on Hidden Markov modelling to characterise shifts in rainfall-runoff relationships in 254 catchments in Eastern and 54 in Western Australia. Of the catchments analysed, 51 % of Eastern and 63 % of Western catchments displayed a movement away from the historical rainfall-runoff relationship to one of reduced flow generation following a multi-year period of drier climate. The reduced flow state persisted in 31 % of catchments in Eastern Australia despite a return to near-normal climatic conditions after multi-year drought, whereas in Western Australia neither the climate nor the flow states have returned to earlier norms (i.e. nearly all shifted catchments have stayed shifted). Interestingly, some catchment characteristics that were correlated with shifts in one region were anticorrelated in the other, possibly indicative of different causative processes. For example, in Western Australia the shifted catchments are typically those that have not been cleared for agriculture and thus retain forest coverage; the opposite is true in Eastern Australia. We suggest a possible link to pre-existing trends in groundwater for cleared catchments, where those in Western Australia may have been experiencing rising groundwater levels due to clearing occurring recently (mid-1900s) relative to Eastern Australia (late-1800s). These findings suggest the importance of land use history when considering changes in rainfall-runoff relationship. We recommend further comparative studies be conducted to synthesise understanding across geographies and better inform water planning decisions under climate change.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Hydrology and Earth System Sciences.
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