KURASHIKI, Japan — As rain poured and the creeks and rivers that course through the city of Kurashiki began to rise, Miyuki Komada repeatedly tried to call her 70-year-old mother, who was home sick with a cold.

But Ms. Komada, 37, could not get through. And heavy rain Friday drowned out the sound of evacuation sirens. When she and her sister arrived after 9 p.m. they found their mother dozing.

As they drove her out, water was already nearing knee height. Soon after, a nearby levee broke, and water surged to shoulder height within a half-hour, Ms. Komada said.

“If I hadn’t come, my mother would have stayed in bed,” she said. “I’m glad I came.”

As she searched through mud and standing water for what few valuables could be salvaged from the family home on Monday, the risk her mother would have faced was clear. The water line climbed to the second floor of the two-story house, stopping halfway up the windows.