COMOROS — Hundreds of brightly clad women flock to the banks of the river each week to scrub their way through bundles of laundry. Some of them travel hours from tiny villages to access a critical but increasingly endangered resource here on the island of Anjouan: water.

The island, part of the nation of the Comoros off the East African coast, receives more annual rainfall than most of Europe. But a combination of deforestation and climate change has caused at least half of its permanent rivers to stop flowing in the dry season.

Since the 1950s, the island has been clearing forests to make way for farmland and in the process disrupted a delicate ecosystem. With so many trees and plants cut down, the water they would normally collect and feed back into the ground and rivers is disappearing. Families in parts of the island now struggle to meet their domestic needs, and farmers are finding it increasingly difficult to irrigate their fields.

“We’ve lost 40 permanent rivers in the last 50 years,” said Mohamed Misbahou, the technical director of Dahari, a nonprofit focused on reforesting land in some of the hardest hit areas on the island. “In some parts of the country, there’s now a big problem getting water.”