IN an extensive study, a group of geologists from the University of the Philippines has listed highly urbanized centers in the country where land subsidence is a growing problem.The study, published in the International Journal of Applied Earth Observation and Geoinformation last September, pointed to excessive groundwater extraction and rapid urbanization as among the factors that contribute to ground subsidence, which is described as 'the gradual sinking or sudden collapse of the Earth's surface due to the settling of subsurface earth materials.'The ground sinking is helped along by rising sea levels caused by climate change, which lead to frequent and severe flooding.Subsidence is a natural occurrence, but man has accelerated the process. We dig into the ground in search of water, fuel and minerals. As these resources deplete, we dig deeper, with nary a thought about the damage we are inflicting.Now we are beginning to reap the consequences. Another study, 'Unveiling the Global Extent of Land Subsidence: The Sinking Crisis,' published earlier this year, considers land sinking as 'a significant geohazard posing serious risks to security of infrastructure, natural resources, built environment and businesses in numerous places worldwide.'It estimated that 'more than 6.3 million square kilometers of the global land is influenced by significant subsidence rates. That includes 231,000 square kilometers of urban and dense settlement areas, and a population of nearly 2 billion.'Jakarta, Indonesia, for example, is sinking up to 17 centimeters a year. 'That's an issue, because they're right at sea level,' according to Michelle Sneed, a land subsidence specialist at the US Geological Survey. 'They have this added pressure of increased flooding and sea level rise. They built seawalls. But the city is subsiding so quickly that, at high tides, water just pours over.'Parts of Mexico City are sinking by 30 cm per year, partly because the aquifer that provides half of the potable water for its 21 million people is overdrawn.The Kansai International Airport in Japan, hailed as an engineering marvel when it opened in 1994, is threatened by subsidence and rising seas.The airport, built on an artificial island at a staggering cost of $20 billion, is propped up by 2.2 million vertical pipes pounded into the clay seabed. The pipes have been slowly sinking into the seabed, and unless a fix is found soon, Kansai will be totally submerged by 2056.The UP geologists' study found the country's biggest annual subsidence rate — 109 millimeters — in Pariahan Village in Barangay Taliptip, Bulakan, Bulacan, where a major international airport is being built on reclaimed land. 'If not addressed, the new airport in the reclaimed area will continue to suffer threats from worsening floods and storm surges,' they warned.Other urban hubs are under threat as well, including Metro Manila, Metro Cebu, Metro Davao, Metro Iloilo and Legazpi City.Despite the looming threat, the global response to ground subsidence is far from encouraging. That's because it is what social scientists refer to as a 'crisis in slow motion,' where there is a lack of societal consensus that it must be addressed urgently.But a better perception about subsidence is beginning to emerge. California passed a law in 2014 to ensure that groundwater use in the state does not result in unreasonable land subsidence.In the Philippines, a growing population, urbanization and poor urban planning are the challenges to be hurdled in mitigating ground subsidence.As a starting point, the UP geologists recommended a more efficient monitoring of groundwater extraction. The National Water Regulatory Board already has this function, but the 34 water wells it is monitoring are woefully inadequate to provide an accurate picture of the extent of ground subsidence.Better monitoring could 'guide groundwater management, land use planning and mitigation efforts to prevent excessive land subsidence, especially in faulted areas prone to hazards associated with ground sinking,' the study's authors said.Fighting sea level rise and ground subsidence require a two-pronged approach. There must be global action to address sea level rise by lowering carbon emissions. At the same time, individual communities can take control of their own land subsidence.
