When the floods are bad, Ms. Villarmia has learned to subsist on cold rice and coffee. She has grown skilled at tying up her valuables so they don’t float away.

She is 80, and she knows the logic of actuarial tables.

“I will be gone before Batasan is gone,” she said. “But Batasan will also disappear.”

Around the time of every new and full moon, the sea rushes soundlessly past the trash-strewn shores, up over the single road running along the spine of Batasan, population 1,400, and into people’s homes. The island, part of the Tubigon chain in the central Philippines, is waterlogged at least one-third of the year.

The highest floods are taller than any man here, and they inundate the basketball court. They drown a painting of sea life at the primary school, adding verisimilitude to the cartoonish renderings of grinning sharks and manta rays.

When the tides come, Batasan, densely packed with houses and shacks, smells not of clean sea air but of a deeper rot — sodden sofas, drowned documents and saturated sewers that expel human waste into the brine washing through houses.

Only a few of Batasan’s coconut palms have survived. The rest have been choked by seawater.

“People say this is because of the Arctic melting,” said Dennis Sucanto, a local resident whose job is to measure the water levels in Batasan each year. “I don’t understand but that’s what they say.”