How did epidemic effect the land?

The port of Pago Pago, where "Rain" is set, receives an unusual amount of rainfall because of the shape of the mountains above it. For the characters in the story, the persistent rain creates an ominous, "maddening" atmosphere. At one point, Dr. Macphail thinks of the rain as possessing its own "fury" that it is unleashing on the stranded travelers. The inhospitable weather forces the characters to stay inside most of the time, where interpersonal tensions intensify with the rain pounding all day on the corrugated metal roof.