The Influence of Meltwater on Centennial Variability of Australian Summer Monsoon Precipitation and Its Relevance to Sustainable Water Resources and Climate Adaptation

Research on centennial-scale precipitation variability within the Australian summer monsoon (AUSM) remains limited, particularly regarding its driving mechanisms and the sustainability-relevant implications for long-term water security and climate adaptation. Here, we use the TraCE-21ka transient simulation, which credibly reproduces the centennial periodicities documented in Holocene proxy records, to attribute the physical drivers of AUSM centennial variability. Attribution is conducted by contrasting the all-forcing (AF) simulation with four single-forcing experiments that isolate the effects of orbital parameters, ice sheets, meltwater flux, and greenhouse gases. Among these experiments, the meltwater-forcing run best reproduces the centennial periodicities found in the AF simulation, indicating that meltwater input is the leading contributor to Holocene AUSM centennial variability. We further identify a dynamical pathway in which Atlantic Meridional Overturning Circulation (AMOC) variability acts as the key mediator linking meltwater perturbations to Australian hydroclimate. The enhanced AMOC amplitude during the meltwater interval (0.14 at 9–8 ka BP), compared with much weaker fluctuations during the non-meltwater interval (0.01 at 4–3 ka BP), is accompanied by a ~200-year periodicity in AUSM precipitation. This periodicity arises through an interhemispheric teleconnection: a strengthened AMOC cools Southern Hemisphere sea surface temperatures, reduces moisture availability for northern Australia, and promotes large-scale subsidence that suppresses monsoon rainfall. By contrast, during 4–3 ka BP, when meltwater forcing was negligible, weaker AMOC variability coincides with warmer Southern Hemisphere sea surface temperature (SST), favoring cyclonic circulation over northwestern Australia, enhanced moisture convergence, and stronger ascent, ultimately intensifying AUSM precipitation. Beyond advancing process understanding, these results provide a sustainability-oriented framework for interpreting low-frequency hydroclimate variability relevant to Australia’s water resources and climate adaptation. Specifically, the identified meltwater–AMOC–SST–AUSM pathway offers a physical basis for developing and evaluating long-horizon indicators of monsoon-driven rainfall variability, informing monitoring strategies and scenario planning for drought–flood risk management, water allocation, and climate-resilient infrastructure. By linking centennial-scale monsoon variability to an identifiable remote driver, this study contributes to quantifying and contextualizing natural hydroclimate variability that can confound near-term trends, thereby supporting more robust sustainability assessments, adaptation policy design, and integrated water-resource management under ongoing climate change.