The German flood warning system leaves it up to local officials to decide what action to take, on the theory that they are best informed about local terrain and what people or property lies in the path of an overflowing river.
In some cases it appears that warnings were issued in time. In the city of Wuppertal, located in a valley bisected by the Wupper River, a crisis committee including police, the fire department and city officials used social media to urge people to stay at home.
Early on Thursday, shortly after midnight, they sounded a warning siren, which sounds eerily like the kind used during World War II, to alert residents to move to higher floors or evacuate as the waters surged.
Wuppertal suffered property damage, such as flooding in the orchestra pit of the local opera house, but no fatalities, said Martina Eckermann, a spokeswoman for the city.
But in other places the warnings came too late.
In the Ahrweiler district of neighboring Rhineland-Palatinate, regional officials issued their first warning to residents living near the banks of the river as it approached its record level of 3 meters, or nearly 10 feet. It wasn’t until three hours later, as the waters pushed beyond the previous flood record that a state of emergency was declared.
By that time, many people had fled to the upper levels of their homes, but those who could not move fast enough died, such as 12 handicapped residents of a care home in Sinzig, who were not alerted in time to be helped from their ground-floor rooms before the waters surged in.
“The warnings arrived,” Mr. Kirsche of the German Weather Service said. “But the question is why didn’t evacuations take place sooner? That’s something we have to think about.”
Melissa Eddy reported from Berlin, Jack Ewing from Frankfurt, Megan Specia from London and Steven Erlanger from Müsch, Germany.