Various factors, including drivers becoming trapped in their cars, poor planning by officials and extreme rainfall being exacerbated by climate change are all likely to have contributed.
In a nutshell: those responsible to warn the population to stay at home or seek shelter did not do it on time, normal activity (many people on cars returning home) was carried out on the streets when the flood (which all online station readings and related agencies were reporting for a while, if not threatening it along the whole day) arrived to those regions.
UPDATE: The news show an image marking Turia as “burst river”, but the flood did not come from it, it indeed stoped it to reach Valencia town and did not overflow, the flood came from dry ravines that typically carry rain water up hill. Also, the civil alert was sent when people in cars on the street got already the water at their chest.
In a nutshell: those responsible to warn the population to stay at home or seek shelter did not do it on time, normal activity (many people on cars returning home) was carried out on the streets when the flood (which all online station readings and related agencies were reporting for a while, if not threatening it along the whole day) arrived to those regions.
UPDATE: The news show an image marking Turia as “burst river”, but the flood did not come from it, it indeed stoped it to reach Valencia town and did not overflow, the flood came from dry ravines that typically carry rain water up hill. Also, the civil alert was sent when people in cars on the street got already the water at their chest.