On the brink: Sari, 35, stands in front of a slum near Jakarta Bay seawall in Muara Baru, North Jakarta, where she has lived for the past 25 years. Sari has to put up with flooding every time heavy rain soaks the area or the tide from Jakarta Bay rises.(JP/Nina A. Loasana)

For 25 years, Sari, a 35-year-old woman living in a kampung in Muara Baru, North Jakarta, has had to put up with flooding from heavy rainfall and the rising tides of Jakarta Bay. A four-meter-high seawall erected along the water’s edge does not always protect the area, which is located less than 300 M from the sea.

“Tidal flooding is an almost daily threat for us, especially during the rainy season. Just last month, our community unit was flooded about 20 centimeters after heavy rainfall. I really want to move to another, better, place, but I just can’t afford it,” Sari told The Jakarta Post on Friday.

Her neighborhood, along with the rest of North Jakarta, is under constant threat from rising sea levels and rapid land subsidence. A team of researchers from the Bandung Institute of Technology (ITB) studied data from 1925 to 2015 and concluded that significant land subsidence had affected the capital city since 1975. The team predicted that Sari’s house, along with 90 percent of North Jakarta, would be submerged by 2050.

The study also found that North Jakarta was the worst affected area. Marunda and Cilincing had sunk 1.5 m, Kelapa Gading had sunk 2.4 m and Pluit had sunk 4 m as of 2015. Jakarta is still sinking about 1 to 15 cm per year, making it one of the fastest-sinking cities in the world.

Recent developments in the study, however, have shown that the rates of land subsidence in Muara Baru and several other areas in North Jakarta have slowed.

“The land subsidence rate in Muara Baru had decreased about fifty percent, from about 20 to 26 cm per year to 10 to 12 cm a year. Even though the area is still sinking at a rapid pace, the data carries good news. It means that we have hope for slowing down the subsidence or even stopping it,” Heri Andreas, an expert from the ITB team told the Post.

Heri said that besides Muara Baru, several other areas in the capital city had also experienced a slower rate of land subsidence. The data showed that the pace of land subsidence in Pluit and Mutiara Beach in North Jakarta had decreased about 50 percent from 20 cm a year to 10 to 12 cm a year. Cengkareng and Daan Mogot in West Jakarta showed about a 66 percent decrease from 15 cm a year to 5 cm a year.

Heri said the declining rate of land subsidence was caused by many companies moving their factories to other parts of Java due to high labor costs in North Jakarta.

“Over the past years, many companies decided to move their factories to West Java and East Java for cost efficiency. This caused a decline in groundwater consumption, causing the rate of land subsidence in the area to slow down,” he said.

Based on data from the Jakarta Industry and Energy Agency, from 2016 to 2018, the number of industrial plants in North Jakarta decreased by 42 percent from 5,313 to 3,089. The decrease was partly caused by the rise of Jakarta’s minimum wage and rapid land subsidence.

This has resulted in an increase in the number of plants operating in the neighboring municipality of West Jakarta. The municipality has seen the number of factories increase, over the same period, from 7,102 to 9,694.

Heri said the latest data also showed that land subsidence had spread further inland to the eastern and southern parts of the capital city.

“Based on our latest data, the land subsidence rate in Kamal Muara, North Jakarta, had increased by 50 percent from 5 cm to 10 cm a year. Cilincing, also in North Jakarta, saw a 20 percent increase from 4 to 5 cm a year to 6 to 7 cm a year. The research also shows even more alarming results, as the area affected [by land subsidence] has almost doubled in width. The problem has spread to Depok and Bekasi, West Java and North Tangerang, Banten,” he said.

Kosambi in Banten is currently sinking at 5 to 8 cm a year, and some areas in Bekasi, West Java, are sinking about 10 cm a year. Depok, West Java, is sinking 1 to 5 cm a year.

Heri said that regulating residents’ groundwater is one of the most important steps to reduce the rate of land subsidence in the capital city.

“Massive use of groundwater is the main reason Jakarta is sinking at such a rapid pace. About 40 percent of the residents in the capital city still rely on groundwater, destroying the aquifer below the city and causing the ground to sink in an alarming rate,” Heri said.