Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) reveals continued ground deformation in and around Metro Manila, Philippines, associated with groundwater exploitation

Uneven ground deformations resulting from excessive groundwater exploitation have been causing problems in metropolitan cities worldwide. Metro Manila and its adjoining provinces have been recognized as undergoing ground deformations due to excessive groundwater pumping, meeting the continued population growth rate demands. Previous studies have identified widespread subsidence using advanced Differential Interferometric Synthetic Aperture Radar (D-InSAR) techniques, but with insufficient archived SAR data, which suffered from the extended perpendicular and temporal baselines covering long periods from 1993 to 2011. This study presents a Sentinel-1 Permanent Scatterer InSAR (PS-InSAR) application from 2015 to 2019 as a continued effort to monitor ground deformations caused by groundwater extraction and recharge in and around Metro Manila. The results revealed that several areas manifest apparent subsidence and uplift within the image’s footprint. The line-of-sight (LOS) subsidence rates in Manila, Caloocan, Malabon, Navotas, and Valenzuela are between 1 and 2 cm/year, except for some coastal communities. Other parts of the region are detected to be experiencing an uplift of 0.1 to 1 cm/year. LOS subsidence rates exceeding 4 cm/year were recorded in the adjoining provinces of Metro Manila, specifically in Bulacan, Cavite, and Laguna. These observations are consistent when correlated with groundwater levels during the same period. Moreover, a high correlation was observed with coefficients of determination (R 2 ) > 0.95 in Makati, Bagumbayan (in Quezon City), and Dasmariñas (in Cavite). With the results obtained, a better understanding of these subtle ground deformations affecting various areas in the Philippines can help mitigate possible disasters and damages by this geohazard.