Overpopulated, Metro Manila is sinking —and flooding— fast

Metro Manila is sinking fast due to over-pumping of groundwater by its burgeoning population, which is  exacerbating already rising water levels due to global warming, a Filipino geologist has warned.

 

In an interview with GMA News Online, Dr. Kelvin S. Rodolfo, Professor Emeritus at the University of Illinois at Chicago, explained that the over-pumping of groundwater is the main cause of land subsidence –or the sinking of land— in Metro Manila and other highly populated areas.

 

In the Philippines, he detailed, global warming is causing relative sea levels to rise by seven to eight millimeters a year. But subsidence is occurring at more than twice that rate —from 20mm to as much as 90mm a year— particularly in Bataan, Pampanga, Bulacan and CAMANAVA (cities of Caloocan, Malabon, Navotas and Valenzuela).

 

Exacerbated effects of global warming

 

Coupled with sea-level rise, land subsidence can produce higher tides that reach farther inland, as well as floods that recede more slowly. This could lead to permanent flooding, said Rodolfo, who is also a consultant for the Science and Technology Department’s (DOST's) Project NOAH (Nationwide Operational Assessment of Hazard).

 

“The main cause of our apparent local sea level rise is not (just) global warming (but also) subsidence… as sea appears to rise in the region,” explained Rodolfo.

 

“Very simply, if you are living at the coastline, with sea-level rising and land subsidence, ang epekto sa mga tao roon, babahain sila,” he added.

 

“To the local people, the effect is the same but in coastal Bataan, Pampanga, Bulacan and CAMANAVA subsidence is more than ten times faster,” the renowned geologist noted.

 

Over-pumping hastens subsidence

 

Although there are natural causes of subsidence, Rodolfo explained that over-pumping of groundwater can ‘speed up’ the process. 

 

“(The) ultimate problem is population. As population increases, groundwater use increases… and overuse of groundwater can greatly speed up the process (of land subsidence),” he said.

 

“Metro Manila’s ground water demand is still increasing… Consequent subsidence will continue and even accelerate,” the geologist claimed.

 

Overpopulation is a factor

 

Other than reducing ground water usage, Rodolfo stressed: “If you can’t control population… You need to bring water from the outside… that’s the solution — surface water from the outside.”

 

Still, the geologist warned that Metro Manila is not the only place that may experience drastic subsidence. 

 

“Any large, rapidly growing community built on a coastal river delta that uses much groundwater (is a candidate for rapid subsidence),” he added.

 

He singled out Davao City, Butuan City, Iloilo City, Lingayen City, Dagupan City and Laoag City as just such subsidence ‘candidates.’

 

Apart from carefully analyzing field data, subsidence can be recognized if nipa palms advance upstream; soil becomes salty and unproductive; and, water-well pipes “rise up out the ground.” — TJD, GMA News