Long-term assessment of urban water supply–demand dynamics in a semi-arid multi-source system: the case of Maghnia, Northwestern Algeria

ABSTRACT

Supply diversification through desalination is widely promoted as a climate adaptation strategy in semi-arid regions; however, whether diversification improves overall system performance beyond increasing production capacity remains insufficiently assessed. This study evaluates the urban water supply system of Maghnia (northwestern Algeria) during pre-diversification (2006–2010) and post-diversification (2011–2023) phases. Structural break detection, substitution analysis, supply–demand diagnostics, and reliability–vulnerability–resilience metrics were applied to annual production and demand data. Total potable water production increased by 155%, rising from 5.44 to 13.89 million m³, while production variability declined substantially (CV: 0.320 to 0.144). Desalination contributed 28.64% of total production and showed a strong inverse relationship with surface water production (r = −0.85), consistent with compensatory operational dynamics. Despite improved volumetric stability, reliability declined from 1.00 to 0.31, vulnerability increased to 0.76 million m³ per deficit year, and nine deficit years occurred after 2013. Production gains were partly redirected toward external withdrawals, tightening supply–demand margins. The findings indicate that diversification improved production stability but did not fully secure reliable supply under sustained demand growth and evolving allocation dynamics.