Circular Water Conservation Pathways for Long-term Urban Supply–demand Planning: A System Dynamics Assessment of Auckland, New Zealand

Urban water systems face increasing pressure from rising demand, constrained supply capacity, water losses, and long-term freshwater stress. This study assesses how circular water conservation pathways could influence Auckland’s long-term urban water supply–demand balance by integrating Reduce, Reuse, Recycle, and Recover scenarios into an exploratory System Dynamics Model (SDM). Literature-informed intervention ranges were translated into changes in domestic demand, industrial water intensity, leakage, and alternative usable supply. Conservative, moderate, and ambitious implementation levels were simulated from 2027 to 2050. Under the baseline, the supply–demand ratio falls below 1.0 in 2033 and reaches 0.78 by 2050. All Circular Economy (CE) scenarios improve the long-term balance, although their effectiveness depends on the model pathway and implementation level. At the conservative level, Reduce, Reuse, and Recover delay but do not avoid long-term imbalance, whereas Recycle-Conservative remains slightly above the balance threshold. Moderate and ambitious Reduce, Recycle, and Recover pathways provide larger long-term margins, while Reuse-Ambitious remains close to the threshold and is sensitive to uncertainty. The combined conservative Reduce–Recycle portfolio reaches a supply–demand ratio of 1.29 in 2050 and remains above the balance threshold in all 10,000 simulations under the uncertainty ranges tested. Uncertainty analysis shows that scenarios close to a ratio of 1.0 are more sensitive to changes in demand, supply, intervention effectiveness, and implementation timing. The findings support Auckland’s emphasis on demand efficiency, leakage reduction, and diversification of alternative water sources, while highlighting the need to consider implementation feasibility and uncertainty. The study provides a structured approach for translating CE principles into quantitative urban water-planning scenarios.