Mari Luz Sánchez’s body lay on top of an overturned refrigerator in a corner of her kitchen when her family found her. A wave of water in the village of Chiva, in southeastern Spain, had deposited her there after devastating flooding across the region on Tuesday night.

“The torrent of water took her away,” said Ms. Sánchez’s daughter-in-law, Pilar Zahonero. “Nothing like this has ever happened before.”

Never had locals in Chiva seen their streets turn into such furious surges of muddy water that tore through their homes. Not in the 1983 floods, nor in the ones in 2019, had waves over six feet high trapped people inside their cars and homes and taken so many lives.

“I’d never seen rain like this,” said Concepción Feijoo Martínez, 66, as she stood in her house in Chiva, which had been torn open on one side by the rushing waters let loose when a nearby river overflowed its banks.

“They say there is no climate change,” she added. “Then what is this atrocity?”

Days after their country’s deadliest natural catastrophe in recent decades, as they swept mud off their floors and mourned their dead, Spaniards started to try to make sense of the tragedy that had struck them: Why were the floods on such an enormous scale, and why did so many die?