ILOILO CITY — The reports that put this city in the spotlight after a scientific study revealed that it is sinking at an average of 9 millimeters (mm) per year did not sit well with Mayor Jerry Treñas. Treñas, in a press conference on Monday, questioned the media's focus on Iloilo City in its coverage of a University of the Philippines (UP) study on land subsidence rate among metropolitan areas in the country. "Iloilo has the lowest since it only has a subsidence rate of 9 millimeters per year. Others have higher rates but the focus has been in Iloilo and I don't really know why the focus is in Iloilo," he said. The UP study, which examined data from 2014 to 2020, revealed that Metro Iloilo — including Iloilo City and the towns of Pavia, Oton, San Miguel, Sta. Barbara, Cabatuan, and Leganes — has experienced land subsidence rates ranging from 4.0 to 8.8 mm per year. Specific subsidence rates identified in various areas of Metro Iloilo include San Rafael in Mandurriao, Iloilo City at 8.8 mm per year; Banuyao in Lapaz, Iloilo City at 8.1 mm per year; Calahunan in Mandurriao, Iloilo City at 4.0 mm per year; Alibay Norte in Oton at 4.6 mm per year; Ungka 1 in Pavia at 4.7 mm per year; and Poblacion in Leganes at 2.6 mm per year. In contrast, other metropolitan areas such as Bulacan province in Greater Manila experience a subsidence rate of 109 mm per year, Metro Davao at 38 mm per year, Legazpi City at 29 mm per year, and Metro Cebu at 11 mm per year. "We only have 9 mm per year and Bulacan has [109 mm per year] so they should have more 'screaming headlines,'" the mayor said, noting that the city's rate is "significantly lower" compared to other areas. Treñas also called for further evidence-based scientific studies to confirm the land subsidence reportedly experienced by the city. "If there's a study, it should be thoroughly reviewed, and if published, it should emphasize that our subsidence rate is the lowest," he said. "The study is a scientific study; let's leave it at that. However, I think there should be more studies on the issue because when you read the study in its entirety, it seems that there are no specific measurements and it is only based on images," he said. The UP study used interferometric synthetic aperture radar (Insar) time series analysis validated by Global Navigation Satellite System (GNSS) data to identify deforming areas in major metropolitan cities in the country. In simpler terms, Insar involves using radar data from satellites to detect and measure ground deformation. GNSS, like the Global Positioning System, provides highly accurate location data from ground-based stations. Treñas previously expressed skepticism to the study, citing the lack of visible signs of sinking in the city's historic infrastructures. "Iloilo City is one of the oldest cities in the Philippines, with historic churches, buildings, mansions, houses, and plazas. It seems there have been no reports of sinking," he said in a statement on August 29. This statement was later taken down and replaced an hour after being posted on the official Facebook page of the Iloilo City Government. In his new statement, Treñas has changed his perspective and welcomed the UP study, noting his openness to the conduct of additional studies that would help the city in its preparation and mitigation measures against climatic and geological threats.
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