BERLIN — Days before roiling waters tore through western Germany, a European weather agency issued an “extreme” flood warning after detailed models showed storms that threatened to send rivers surging to levels that a German meteorologist said on Friday had not been seen in 500 or even 1,000 years.
By Friday those predictions proved devastatingly accurate, with more than 100 people dead and 1,300 unaccounted for, as helicopter rescue crews plucked marooned residents from villages inundated sometimes within minutes, raising questions about lapses in Germany’s elaborate flood warning system.
Numerous areas, victims and officials said, were caught unprepared when normally placid brooks and streams turned into torrents that swept away cars, houses and bridges and everything else in their paths.
“It went so fast. You tried to do something, and it was already too late,” a resident of Schuld told Germany’s ARD public television, after the Ahr River swelled its banks, ripping apart tidy wood-framed houses and sending vehicles bobbing like bath toys.
Extreme downpours like the ones that occurred in Germany are one of the most visible signs that the climate is changing as a result of warming caused by greenhouse gas emissions. Studies have found that they are now happening more frequently for a simple reason: A warmer atmosphere can hold more moisture, generating more, and more powerful, rainfall.
But even as extreme weather events become increasingly common around the globe — whether wildfires in the American West, or more intense hurricanes in the Caribbean — the floods that cut a wide path of destruction through Germany, Belgium, Switzerland and the Netherlands this week were virtually unheard-of, according to meteorologists and German officials.
Even so, they were not unforeseen.
“There should not have been so many deaths from this event,” said Dr. Linda Speight, a hydrometeorologist at the University of Reading in Britain, who studies how flooding occurs. She blamed poor communication about the high risk posed by the flooding as contributing to the significant loss of life.
For now German politicians made a point of not wanting to appear to be politicizing a calamity, and Chancellor Angela Merkel’s spokesman said she planned to visit the stricken state of Rhineland-Palatinate, after returning from talks in Washington.
But the natural disaster had all the hallmarks of an event that has in the past reshaped political fortunes in German election seasons like this one.
Armin Laschet, the conservative leader of North Rhine-Westphalia, who is vying to succeed Ms. Merkel after national elections on Sept. 26, told a news conference Friday, “Our state is experiencing a flood catastrophe of historic scale.”
“We have to make the state more climate-proof,” said Mr. Laschet, who is facing his strongest challenge from the environmentalist Green party. “We have to make Germany climate neutral even faster.”
But his state was among the hardest hit, and once the floodwaters recede he and Ms. Merkel may yet face questions about why their political strongholds were not better prepared.
German officials said Friday their warning system, which includes a network of sensors that measure river levels in real time, functioned as it was supposed to. The problem, they said, was an amount of rain they had never seen before — falling so rapidly that it engorged even small streams and rivers not normally considered threats.
To describe the events of recent days as a 100-year flood would be an understatement, said Uwe Kirsche, a spokesman for the German Weather Service, calling it a flood the likes of which had not been seen in perhaps a millennium.
“With these small rivers, they have never experienced anything like that,” Mr. Kirsche said. “Nobody could prepare because no one expected something like this.”
On Tuesday Felix Dietsch, a meteorologist for the German Weather Service, went on YouTube to warn that some areas of southwest Germany could receive previously unimaginable volumes of rain. Up to 70 liters, or more than 18 gallons, of water could pour down on an area of one square meter within a few hours, he warned.
The weather service, a government agency, assigned its most extreme storm warning, code purple, to the Eifel and Mosel regions. It was one of numerous warnings that the weather service issued on Twitter and other media earlier this week that were also transmitted to state officials and local officials, fire departments and police.
But the waters rose so swiftly, to heights beyond previously recorded record levels, that some communities’ response plans were rendered utterly insufficient while others were caught off guard entirely.
A spokesman for the office responsible for monitoring floods and alerting local officials in Rhineland-Palatinate said that all warnings had been received from the weather service and passed along to local communities as planned.
But what happened after that is critical, and not entirely clear.
In the village of Müsch, at the junction of the Ahr and Trierbach Rivers, Michael Stoffels, 32, said that he had gotten no warning from the government, but that a neighbor had called to alert him to the rapidly rising waters on Wednesday.
He rushed home from the retail store he manages nearby to salvage what he could. He was lucky, he said, since he has storage on the ground level and his living area is above that so the 12 feet of water that his home took on did not inflict significant damage.
But the village of 220 people got clobbered by flash floods that one resident, Maria Vazquez, said did their work in less than two hours. On Friday evening, it was without electricity, running water or cellphone coverage.
The river banks were scenes of devastation, with crushed cars and huge tree stumps, while many of the cobbled streets were covered with mud and debris. Truckloads of broken furniture, tree branches and chunks of stone were being driven slowly over downed power lines.
“A lot of good cars crashed or got crushed,’’ said Ms. Vazquez, who works in a nearby auto repair shop. “I work with cars, so that’s sad, but I just hope that all the people are OK”
Across the border in Belgium, 20 people were confirmed dead and 20 remained missing, the country’s prime minister, Alexander De Croo, said on Friday, calling the floods “the most disastrous that our country has ever known.”
Waters rose on lakes in Switzerland and across waterways in the Netherlands, leaving hundreds of houses without power and submerging the city center of Valkenburg in the Netherlands, although neither country suffered deaths or the destruction inflicted on German towns.
Medard Roth, the mayor of Kordel, in the state of Rhineland-Palatinate, defended the warning systems and said that he activated his town’s emergency flood response once he had been alerted that the waters of the Kyll River were approaching dangerous levels. But the waters rose too rapidly to be held back by the usual measures.
“Already on Wednesday afternoon at 3:30 p.m. the Kordel fire brigade began setting up the security measures,” Mr. Roth told Bild, a German newspaper. “By 6 p.m., everything was already under water. Nobody could have predicted that.”
Ursula Heinen-Esser, the environment minister for the state of North Rhine-Westphalia, said during an online presentation Friday that floodwaters had reached “levels never before recorded.”
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.