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Tides can cause flooding even in the middle of a long dry spell. The reason is simple: tidal floods aren’t caused by weather, but by the gravitational pull of the moon and the sun.

The earth’s rotation is also a factor. As the planet spins it creates a centrifugal force that causes the oceans to shift like water inside a spinning glass.

“It’s basically the interaction among the oceans, sun and the moon,” said Sugarin, head of the data and information division at the Meteorology and Geophysics Agency’s maritime department.

Although they don’t get as much publicity as floods caused by rains that lead to overflowing rivers, tidal floods are potentially far more dangerous for Jakarta because the city continues to sink by 5 centimeters to 10 centimeters a year, and as much as 25 centimeters in some areas.

The tidal cycle affecting Jakarta lasts about 18 years, swinging between periods of higher and lower tides every nine years or so. The latest downswing began last year, so Jakarta residents can expect to see the tides begin their next upswing in 2018. Meanwhile, Jakarta will have been steadily sinking.

In other words, the city has nine years to avoid devastating flooding, especially in northern Jakarta, said Hongjoo Hahm, lead infrastructure specialist at the World Bank in Jakarta. “Imagine the sea rising and the ground sinking,” he said.

There are separate sea walls along the shores of Muara Baru and Pluit, but they can no longer keep water out because of continuing land subsidence across the city, said Jan Jaap Brinkman, a hydrology expert who works closely with the Ministry of Public Works.

“The temporary walls aren’t strong enough,” he said, adding that sinking land poses a far greater threat than the rising tides.

While simple tidal flooding can create devastation on its own, its effects can be multiplied by weather such as a cyclone or even strong winds, Sugarin said.

Strong winds even far offshore can cause sea waves to grow much bigger. For example, a cyclone far away in the South China Sea can produce higher waves in Jakarta. Add such conditions to regular tidal flooding, and the results could be catastrophic, especially for Jakartans living along the waterfront.

“Imagine there’s water on a plate, and we blow from one end,” Sugarin said. “Water on the other end will rumble depending on how strong we blow on it.”

However, Sugarin declined to speculate on whether Jakarta could be doomed by tidal flooding.

“There are many factors that trigger a tidal flood,” he said, including inadequate sea walls, land subsidence and the quality of city drainage.