Spain's heavy flood death toll raises questions about how one of the world's most developed nations failed to respond adequately to extreme storms likely to intensify as climate change accelerates.

Torrential rains that began at the start of the week sparked flooding that has left at least 95 people dead, the deadliest such disaster in the western European country since 1973.

National weather agency AEMET launched a red alert for the hardest-hit eastern Valencia region on Tuesday morning and conditions deteriorated throughout the day.