Green hydrogen production in a semi-arid region: A system dynamics analysis of water supply alternatives

• A system dynamics model compares circular and linear water supply structures. • Circular water systems can deliver the highest green hydrogen output. • Circular water systems can strengthen sanitation and broaden territorial benefits. • Transition penalties arise where policy misaligns infrastructure evolution. • Desalination-led systems boost hydrogen output but heighten brine and energy use. This study applies a system dynamics model to assess how alternative water-supply strategies, recycled water and seawater desalination, shape the viability of large-scale green hydrogen production in Ceará. Simulations from 2026 to 2050 show that water architecture is a strategic determinant of hydrogen output and operational burdens. Desalination-based scenarios produce moderate hydrogen volumes, reaching ≈397 kt/year and ≈509 kt/year, but impose the highest energy demand and brine loads, reinforcing pressures on coastal ecosystems and communities. A transitional configuration with gradually increasing recycled water yields the lowest output, ≈252 kt/year, due to the misaligned timing of desalination decline and recycled water expansion, a transition penalty relevant for incremental or poorly coordinated policy approaches. In contrast, a fully circular scenario based on recycled water delivers the highest production, ≈862 kt/year, eliminates brine discharge and lowers energy intensity while strengthening wastewater infrastructure and generating broader territorial co-benefits. Although ecological and social impacts are not modelled directly, the magnitude of brine and sludge flows identifies where regulatory oversight and multi-sectoral coordination are most urgently required. The findings send a clear message to policymakers: water choices are not operational details but structural decisions that can lock Ceará into an extractive, marine-burdening model or enable a regenerative pathway that expands productive capacity while distributing benefits across urban and industrial systems. Aligning hydrogen development with sanitation expansion, water governance and long-term environmental safeguards is therefore essential to prevent new inequalities and ensure that the emerging hydrogen economy contributes to a just and resilient future for semi-arid regions.