Climate Change and Subsidence in Metro Manila: Relative Sea Level Projections Through Tide Gauge Records and Satellite Altimetry up to 2150

Metro Manila, one of the world’s most densely populated megacities, is highly vulnerable to sea-level rise due to its low-lying deltaic location, frequent tropical cyclones, and rapid anthropogenic subsidence from groundwater extraction. This study integrates historical PSMSL tide-gauge records from Manila Harbour with IPCC AR6 projections under Shared Socioeconomic Pathways, incorporating vertical land motion (VLM) and sea-level fingerprints to estimate local relative sea-level (RSL) changes. Assuming constant subsidence, cumulative VLM reaches –0.785 m by 2100 and –1.289 m by 2150. Including climatic contributions (amplified 10–20% by fingerprints, particularly under high-emission scenarios from far-field Antarctic ice loss in the western Pacific), projected RSL ranges from 1.09–1.42 m (SSP1-2.6) to 1.51–2.00 m (SSP5-8.5) by 2100, and from 1.70–2.28 m to 2.41–3.54 m by 2150. Results indicate 7.95–11.15 km² (1.2–1.8%) of land could face permanent ocean-connected inundation under high scenarios, mainly in Malabon (~18%), Navotas (~20%), and Manila (~7%). These conservative estimates (excluding aquaculture areas) are much lower than prior mid-century projections of up to 30%. Intensified chronic flooding, erosion, and saltwater intrusion threaten millions, requiring urgent integrated adaptation, groundwater regulation, and combined nature-based and engineered solutions.