Stress testing water allocations across large river basins

Water scarcity is a growing global challenge, with climate change exacerbating pressures on water security and allocation. Traditional top-down climate impact assessments rely on downscaled global climate models and complex hydrological models, limiting the range of climate futures that can be modelled. Bottom-up approaches such as stress testing offer an alternative means of identifying system vulnerabilities by systematically varying climate inputs to better understand the system response and thresholds of impacts. However, implementing this approach for large river basins poses technical challenges to make the computational process tractable. This study presents 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 methodology combines stochastic climate projections, rainfall-runoff modeling, and statistical allocation modeling to assess how changes in precipitation, temperature, and runoff influence water availability and allocations. We look to understand the implication of spatial differences in changing climate, rainfall runoff response and allocation policy across the major rivers in the basin. Our results highlight spatial variations in climate sensitivity across the basin and demonstrate the importance of water allocation policies in how climate impacts are distributed. Of the three factors considered, the structure of the water allocation policy was the most influential in determining impacts of change and had a large influence of the degree of system resilience. 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.