Flooding is a common occurrence in the cities of Navotas and Malabon, located in densely populated areas north of Metro Manila in the Philippines.
These cities have adapted to the constant threat of floods. For example, the iconic jeepney vehicles are now made of stainless steel to prevent corrosion from seawater. Additionally, roads have been continuously elevated, reaching heights higher than people’s doors in some areas.
“They keep raising the roads higher and higher, and it’s a challenge to sustain this,” says Dr. Mahal Ragmay, Executive Director of the University of the Philippines Resilience Institute.
The struggle to combat floods in these cities is not just due to rising sea levels, but also to the lowering of the ground level. A study led by Lagmay and his team revealed that parts of Metro Manila sank by 10.6 centimeters (4.2 inches) per year between 2014 and 2020, significantly higher than the global average sea level rise.
This rapid decline has been a growing concern, especially in certain coastal areas around Manila Bay where floods have left half of the houses submerged, forcing rice farmers to turn to fishing for their livelihood.
Similar subsidence issues are observed in various highly urbanized regions worldwide, as highlighted by land subsidence expert Dr. Matt Way, who studies urban subsidence on a global scale.
The Impact of Land Subsidence
Subsidence measurements are now conducted using advanced technologies like satellite data, allowing researchers to make more accurate estimates of ground movement. With tools like GNSS and InSAR, scientists can track ground movement in 3D at specific points, providing detailed insights into subsidence patterns.
By analyzing subsidence data from various cities globally, researchers have found that many urban areas are experiencing significant sinking rates, posing a threat to millions of people.
Causes of Subsidence
Subsidence in cities like New York and Manila has various causes, including post-glacial rebound and human activities like excessive groundwater pumping. While natural phenomena like seismic faults contribute to ground movements, human interventions play a significant role in accelerating subsidence rates.
Addressing subsidence requires a multi-faceted approach, from regulating groundwater extraction to monitoring and mitigating the impact of sinking urban areas.
Mitigating Urban Subsidence
Cities like Jakarta, Tokyo, and Houston have made strides in slowing subsidence rates by implementing stricter water regulations and alternative water supply solutions. In Manila, efforts to ban deep well drilling and reduce reliance on groundwater are underway to address subsidence issues.
While some areas may face relocation due to flooding and sinking, careful management of groundwater resources and proactive monitoring can help cities bounce back from subsidence challenges.
About our experts
Dr. Matt Way is an expert in oceanography and studies natural disasters and crustal geodesy at the University of Rhode Island.
Dr. Mahal Lagmay is the Executive Director of the University of the Philippines Resilience Institute, focusing on projects related to flooding and groundwater management in the Philippines.
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Source: www.sciencefocus.com
