Adaptive Infrastructure Management of the Angat Dam: Evaluating Water Supply Reliability Amidst Urbanization and Climate Extremes in Metropolitan Manila

Metropolitan Manila depends heavily on the Angat Dam system, while urban demand and hydroclimatic variability place increasing pressure on reservoir operations. This study evaluates monthly reservoir elevation and billed water-demand records from January 2019 to December 2025 using descriptive and inferential trend analysis, an operationally grounded analytical stress threshold of 180 m, threshold sensitivity testing, and reliability-resilience-vulnerability (RRV) indicators. Institutional and project documents were also reviewed to interpret adaptive infrastructure-management responses. Mean billed demand increased from 2,826.58 million liters per day (MLD) in 2019 to 2,946.37 MLD in 2025, peaking at 3,069.50 MLD in May 2024. The estimated annual demand slope was 23.72 MLD per year, but it narrowly missed statistical significance at the 5% level (p = 0.054). At 180 m, ten of 84 monthly observations were failures; the minimum was 160.97 m in July 2019. The system achieved 88.10% reliability, 40.00% resilience, and mean vulnerability of 5.86 m. Sensitivity testing at 175, 180, and 185 m produced reliability values of 96.43%, 88.10%, and 84.52%, respectively, while resilience remained between 33.33% and 40.00%. Results show that high overall reliability can coexist with slow recovery and concentrated seasonal risk. The evidence supports anticipatory reservoir operation, climate-informed monitoring, demand management and non-revenue-water reduction, transmission redundancy, source diversification, and institutionalized RRV monitoring. The study demonstrates a transparent, replicable screening approach for climate-sensitive urban water infrastructure where detailed hydraulic models are unavailable.