Excessive groundwater extraction, rapid urbanization, tectonic motion, and the natural compaction of sediments contribute to land subsidence worldwide. This issue is worsened by rising sea levels due to climate change, leading to frequent and severe flooding especially during high tides or typhoons, as well as local contexts of hazard management regulations.
Jolly Joyce Sulapas, Audrei Anne Ybañez, and Dr. Alfredo Mahar Francisco Lagmay of the University of the Philippines – Diliman College of Science (UPD-CS), along with Kayla Milcah Marasigan and Julian Marie Bernice Grageda of the UP Resilience Institute Nationwide Operational Assessment of Hazards (UPRI-NOAH) analyzed land subsidence in major Philippine cities from 2014 to 2020.
Their land subsidence analysis showed that Bulacan, which is located in Greater Manila, has the highest sinking rate at 109 millimeters (mm) per year. This was also the first study to examine land subsidence in other cities, with rates of 11 mm per year in Metro Cebu, 38 mm per year in Metro Davao, 9 mm per year in Metro Iloilo, and 29 mm per year in Legazpi City.
“The high population density of cities makes the information more relevant to the public, as its impact on people is greater,” Sulapas said. “Cities are also more vulnerable to land subsidence because the subsurface strata, or the rocks beneath the cities, are relatively younger.”
