Philippine Cities Are Sinking Faster Than We Realize. What Now?
It's no secret that countries like the Philippines are among the most especially vulnerable countries when it comes to climate change. With 60 percent of the Philippines' 110-plus million population found in the coastal zone, subsidence and rising sea levels have been quiet underlying fears among urban planners, environmentalists, and researchers alike.
The Philippine Climate Change Assessment report recently confirmed that the sea level in Manila has increased by roughly 2.6 centimeters annually, as compared to the average rate of 1.3 millimeters a year in the early 20th century. To make matters worse, other cities outside the urban center are experiencing the same vulnerability.
“Manila has experienced a rapid increase in sea level, primarily attributed to long-term land subsidence caused by excessive groundwater extraction. In contrast, Legazpi and Davao have witnessed gradual sea level rises, while no clear trend has been observed in Cebu and Jolo, Sulu,” the report also noted.
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To put things into perspective, a sea level rise of just one meter could affect about 7,000 square kilometers and 1.8 million Filipinos across roughly 2,500 barangays. Three meters, on the other hand, certainly double those figures, leaving about 3.4 people vulnerable. In the past, the Department of Environment and Natural Resources (DENR) has warned that almost 17 percent of Philippine islands will be submerged by 2100, potentially displacing 14 million individuals.
Land Subsidence in the Philippines
Most of the time, we often blame the worsening floods in the Metro and perhaps even Bulacan on deforestation, urbanization, encroachment, and the like, which are all valid causes for concern. But we rarely consider land subsidence from excessive groundwater extraction for coastal aquaculture and mining as contributors to the dilemma.
While the issue of land subsidence itself has been a problem since the '90s, the rates for such are rising by the year. A recent study also confirmed the large-scale land subsidence in and around Metro Manila.
Areas around northern Manila Bay from 1991 to 2003 would have land subsidence rates of around 1.7 to 8.3 cm per year. Recently, however, data suggests that such rates from 1993 to 2010 show a 15 cm increase per year.
Unfortunately, It's Not Just Metro Manila
The thing is, areas like Metro Cebu, Metro Davao, and Metro Iloilo have each recorded their own land subsidence.
In the eastern coastal plain of mainland Cebu from Liloan in the northeast towards Naga City in the southwest, built-up developments are found. Dense vegetation and sparse distribution of agricultural domain, coupled with the less-inhabited mountain ranges have exacerbated the intrusion.
Meanwhile, densely populated areas in Metro Davao show movement. The highest rate of subsidence is −38 mm/yr at Panabo City, primarily because of mixed land-use development. Cumulative ground movement in Metro Davao from August 2019 to July 2020 shows a steady rise, as well.
The urbanized center of Iloilo City suffers from the same diminishing rates, particularly in the easter coastal districts of La Paz to Villa Arevalo. Here, the highest rates of subsidence were found within Mandurriao and Molo Districts and La Paz District. Such subsidence has also caused worse flooding and tidal disruption in the city proper.
Development Issue?
Alternative water sources are integral to establishing more commercial opportunities. From factories and plantations to fishponds and more, these moves could threaten the distribution system overall.
“I think the problem is fundamentally a development issue, where we have unabated conversion of landscapes and seascapes. For example, the subsiding areas in Manila City are mostly reclaimed land. Same as some other places too, like in Dagat-Dagatan, which was reclaimed during the Marcos dictatorship. Before that, it was a communal fishing ground,” Rodrigo Narod Eco, a former researcher at the Marine Science Institute at the University of the Philippines, told SciDev.Net.
A country like Indonesia, for example, moved its capital from Jakarta to Nusantara partly due to how the capital subsides two centimeters a year on average. Of course, the last time the Philippines changed capitals was back in 1976, and the circumstances then and now are drastically different. And the past five administrations haven't been too keen on changing the capital because of subsidence, as well.
President Ferdinand "Bongbong" Marcos Jr. would, nevertheless, lead the adoption of a new National Adaptation Plan (NAP), which it acknowledged the increasing rates and how groundwater used has enhanced the risk of sea level rise in Manila. “The implications of rising sea levels are compounded by the occurrence of land subsidence in certain areas, exacerbating the impact of sea level rise and leading to increased vulnerability to flooding and extreme sea levels,” the report revealed.
It further explained in the conclusion: “Human-induced factors, such as climate change and the subsequent warming of the oceans and melting of ice sheets, are primarily responsible for this phenomenon."
