Assessing long-term urban water supply and demand balance using system dynamics modelling: A case study of Auckland, New Zealand

Rapid population growth, economic expansion, and constrained water supply capacity pose increasing challenges for Auckland, New Zealand’s long-term water security. This study develops an exploratory, aggregated, policy-aligned system dynamics model to assess Auckland’s urban water supply–demand balance from 2024 to 2050. The model integrates population growth, domestic and industrial demand, non-revenue water, and constrained supply capacity, and evaluates four policy-aligned scenarios: rainwater harvesting, supply augmentation, demand efficiency, and integrated intervention. The model was calibrated and validated against historical population, Gross Industrial Product (GIP), and total water demand data, showing acceptable reproduction of historical demand-side behaviour. Under baseline conditions, total water demand increases from approximately 134 million m³ yr⁻¹ in the mid-2020s to nearly 197 million m³ yr⁻¹ by 2050, while effective supply reaches a capacity limit of approximately 154 million m³ yr⁻¹ by the early 2030 s. The supply–demand ratio falls below unity in 2033 and declines to approximately 0.78 by 2050. Individual interventions delay, but do not prevent, long-term deficits. In contrast, the integrated scenario maintains a supply–demand ratio above 1.0 throughout the simulation period, reaching approximately 1.19 by 2050. These findings suggest that Auckland’s long-term water security requires coordinated demand management and supply diversification. The model provides a transparent decision-support framework for long-term urban water planning, while recognising that climate variability, source-specific reliability, and operational supply constraints are not explicitly simulated.