Jakarta. Jakarta’s coastline is now visibly sinking below sea level, with ocean waters at Pantai Mutiara in North Jakarta standing higher than the surrounding land.

Field observations on Monday showed sea levels at Pantai Mutiara overtopping the height of nearby land, held back only by a coastal embankment. Without these barriers, seawater would flow inland. Even with them, scientists warn that the situation is increasingly precarious.

The National Research and Innovation Agency (BRIN) says parts of Jakarta are sinking by 10 to 30 centimeters every year, driven by natural soil compaction and decades-long overuse of groundwater by homes, businesses, and industries. The subsidence rate is among the fastest of any major city in the world.

Johan Risandi, a senior researcher at BRIN’s Oceanography Research Center, said the higher water levels along the coast reflect the combined impact of extreme tides, seasonal winds, high waves, and critically, the city’s rapid land subsidence.

“Tidal surges can happen twice a month, and strong winds add even more water,” Johan said. “But the main factor is land subsidence. In some areas, the ground is sinking up to 30 centimeters per year.”

He explained that Jakarta’s soft, alluvial soil naturally compacts over time. But excessive groundwater extraction, still widely practiced due to insufficient piped water services, accelerates the descent, pulling the land downward at alarming rates.

“This natural compaction is made worse by massive groundwater use from households and industries,” he said. “The more we pump, the faster the land sinks.”

To prevent seawater from spilling into residential areas, Johan said coastal defenses must be continually raised. “Sea walls have to be routinely elevated to match rising sea levels and sinking land,” he noted. “We need to calculate how much water increases due to tides and waves to determine the proper height.”

He also urged stricter rules to limit groundwater usage, supported by detailed monitoring of extraction volumes and ground movement to ensure fair and effective regulation. Beyond engineering, Johan recommended nature-based solutions such as mangrove restoration to help break incoming waves before they reach the shore.

Former Jakarta governor Basuki Tjahaja Purnama, commonly known as Ahok, previously warned that if the coastal embankment at Pantai Mutiara fails during a high tide, floodwaters could surge far inland, even reaching the National Monument (Monas) in Central Jakarta.