Stress testing water allocations across large river basins

Abstract Water scarcity is a growing global challenge, with climate change exacerbating pressures on water security and allocation. Increasingly approaches such as stress testing, scenario neutral methods and decisions scaling are being suggested to identifying system vulnerabilities by systematically varying climate inputs to better understand the system response and thresholds of impacts. However, applying such approaches to large river basins presents technical challenges in making the computational process tractable. This study develops a novel, rapid-assessment method to stress test water allocations in large, complex river basins, applying it to the Southern Connected Murray-Darling Basin in Australia. The method combines stochastic climate projections, rainfall–runoff modelling, and statistical allocation modelling to evaluate how changes in precipitation, temperature, and runoff affect water availability and allocations. We assess the implications of spatial differences in climate, runoff response, and allocation policy across major rivers in the basin. Our results highlight substantial spatial variation in climate sensitivity and demonstrate that water allocation policy plays a critical role in mediating climate impacts. Among the three factors examined, the structure of the water allocation policy had the greatest influence on system robustness (i.e. is the inherent capacity of a system to withstand a range of conditions). This is particularly evident in the Murray reservoirs, where two different allocation systems produce markedly different outcomes under climate change. The approach offers a scalable framework for evaluating climate risks to water resources in regulated river systems worldwide, and an additional tool for rapid assessment of water allocation impacts in large river basins.