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

Abstract

Metro Manila, one of the world's most densely populated megacities, is highly vulnerable to sea-level rise because of its low-lying deltaic location, frequent tropical cyclones, and rapid anthropogenic subsidence caused mainly by groundwater extraction. This study brings together historical tide-gauge records from the Port of Manila (PSMSL) with the Sixth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR6) projections under Shared Socioeconomic Pathways, adding in vertical land motion (VLM) and sea-level fingerprints to work out local relative sea-level (RSL) changes. Assuming a constant subsidence rate, cumulative VLM reaches similar to 0.785 m by 2100 and similar to 1.289 m by 2150. When you factor in climatic contributions (amplified 10-20\% by fingerprints, especially under high-emission scenarios thanks to far-field Antarctic ice-loss effects 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 show that 7.95-11.15 km(2) (1.2-1.8\% of land area under SSP5-8.5) could face permanent inundation, mostly in Malabon (similar to 18\%), Navotas (similar to 20\%), and Manila (similar to 7\%). Our conservative estimates (permanent ocean-connected flooding, excluding existing aquaculture areas) come in much lower than earlier mid-century projections of up to a 30\% area affected. All this will worsen chronic tidal flooding, erosion, saltwater intrusion, and risks to millions in low-lying districts. We urgently need integrated adaptation, better groundwater regulation, and a mix of nature-based and engineered solutions.