They were disabled residents of a care home, the Lebenshilfe Haus, asleep when the waters of the flash flood suddenly rose early Thursday morning. Trapped on the first floor, they drowned before aid could arrive.

As calamitous floods hit Germany, the deaths of 12 people at a care home in Sinzig, a small town between the Rhine and Ahr rivers, have broken hearts all over the country and demonstrated how tragedy could have been avoided had flood warnings been better heeded.

“Every person who dies is a tragedy,” said Tabera Irrle, 23, a train driver who came to Sinzig to help with the cleanup. “But this is a special sadness.”

Neighbors could hear screaming, they said later, but all that emergency workers could do was save the other 24 residents on higher floors some three hours later, bringing them out the windows in small boats. The disabled residents had been under the care of a lone watchman.

Dominik Gasper, 17, was helping his parents and uncle clean out the mud and ruined belongings of his grandparents’ house near the care home. He knew about the 12 dead, he said.

“It was so horrible,” he said. “You can’t really understand such a thing.”

The waters crested in Sinzig at more than 7 meters, about 23 feet, the highest in a century, said Andreas Geron, the mayor. He said emergency workers in fire trucks had tried to warn residents late Wednesday night, but few said they had heard an alarm.

Two other Sinzig residents died in this town of 20,000, and a newly renovated bridge over the Ahr collapsed.

Luis Rufino, 50, a lifelong resident of Sinzig, was angry about what happened. He said some of it could have been prevented.

“Our health system is better than in the U.S., but they are still trying to avoid costs,” he said. “So there was only one guy watching over these poor people, and when the lights went out, they went into a panic, and when the flood came through, they had no chance.”

Ulrich van Bebber, the chairman of Lebenshilfe, which has operated the care home since it was built 27 years ago, told journalists that “we are all horrified, stunned and infinitely sad.”

He said those who survived were being cared for. “We want to keep the Lebenshilfe Haus as a residential facility and, if necessary, rebuild it.”

Usually a national leader faced with floods as severe as those in Germany would be expected to break off whatever she was doing and rush to the crisis area.

But Chancellor Angela Merkel of Germany completed an official visit to Washington that ended Friday, and she was not expected to visit the flood zone until Sunday, long after most other German political leaders had come and gone. (Saturday was also her 67th birthday.)

Ms. Merkel did express from Washington her sympathy to the victims, saying during an appearance with President Biden on Thursday: “My heart goes out to all of those who, in this catastrophe, lost their loved ones or who are still worrying about the fate of people still missing.”

And hours after touching down in Germany on Friday morning, Ms. Merkel took part in a crisis meeting with leaders of the state of Rhineland Palatinate, where many of the hardest-hit communities are. She also spoke by telephone with Armin Laschet, the leader of North Rhine Westphalia, which also suffered major devastation and loss of life.

Mr. Laschet — who, like Ms. Merkel, is a member of the conservative Christian Democratic Union party — is the party’s candidate to succeed her after the country holds elections in September.

So far Ms. Merkel has not faced major criticism for taking several days to see the damage for herself. She has never been one for political theater, and does not need to worry about opinion polls because she is stepping down from politics after the elections.

Germans also seemed to understand the importance of her trip to Washington — probably her last as chancellor — and meetings with Mr. Biden.

Germany is anxious to repair its relationship with the United States, a crucial ally and trading partner, after four tense years of dealing with President Donald J. Trump, who treated Germany like a rival and threatened to impose punitive tariffs on German cars. At a news conference with Mr. Biden on Thursday, Ms. Merkel seemed almost buoyant to be dealing with a new administration.

“We’re not only partners and allies, but we’re very close friends,” she said of Mr. Biden.

Addressing an underlying cause of Western Europe’s worst floods in centuries, the two leaders signed a pact to take “urgent action to address the climate crisis.”

“There is a dramatic increase in such unusual weather phenomena, and we have to contend with this,” Ms. Merkel said while standing alongside Mr. Biden.

Huge cleanup efforts were underway after days of flooding inundated parts of Western Europe this week.

President Frank-Walter Steinmeier of Germany on Saturday visited the city of Erftstadt, where floods had ripped away homes, setting off a landslide that wrought further destruction.

An entire stretch of highway remained submerged there on Saturday as fears mounted that people who had tried to flee this week’s torrential rains could have been trapped in their cars by flash flooding — and may still be found when the waters recede.

Already, at least 43 people are known to have died.

Mr. Steinmeier, who is seeking a second term in office after his current one ends in February, urged Germans to help in any way they could.

“Many people in this region have nothing left but hope,” Mr. Steinmeier said. “And we cannot disappoint these hopes.”

A president’s role in Germany is largely ceremonial, but in times of national tragedy or crisis, the head of state often helps set the tone and serve as a representative of the people.

Mr. Steinmeier was joined by Armin Laschet, governor of North Rhine-Westphalia, home to Erftstadt, and the leading candidate to succeed Chancellor Angela Merkel when Germans vote for a new government in the fall.

Ms. Merkel planned to travel on Sunday to the town of Schuld (not Stuhr as an earlier version of this item said) in Rhineland-Palatinate.

Extreme weather disasters across Europe and North America have highlighted two essential facts of science and history: The world as a whole is neither prepared to slow down climate change, nor live with it.

Some of Europe’s richest countries lay in disarray this weekend, as rivers burst through banks in Germany and Belgium, leaving people shellshocked at the intensity of the destruction.

Days before in the Northwestern United States, hundreds had died of heat. In Canada, wildfire had burned a village off the map. Moscow reeled from record temperatures. And the northern Rocky Mountains were bracing for another heat wave.

The events have ravaged some of the world’s wealthiest nations, whose affluence has been enabled by more than a century of burning coal, oil and gas — activities that pumped the greenhouse gases into the atmosphere that are warming the world.

“I say this as a German: The idea that you could possibly die from weather is completely alien,” said Friederike Otto, a physicist at Oxford University who studies the links between extreme weather and climate change. “There’s not even a realization that adaptation is something we have to do right now. We have to save peoples’ lives.”

Disasters magnified by global warming have left a trail of death and loss across much of the developing world, wiping out crops in Bangladesh, leveling villages in Honduras and threatening the very existence of small island nations.

A big question is whether the disasters in the developed world will have a bearing on what the world’s most influential countries and companies will do to reduce their own emissions of planet-warming gases.

“This tragic event is a reminder that, in the climate emergency, no one is safe,” Mohamed Nasheed, the former president of the Maldives, said in a statement about the flooding.

The floods devastating Europe have killed scores of people, leaving at least 1,300 missing, uprooting families, causing immense financial damage and reducing homes and cars to the state of floating bath toys. But it is not the first time the continent has been buffeted by a deluge.

Here are some of the other major lethal floods and flooding caused by storms in recent years.

February and May 2014

A 7-year-old boy dead after falling ill in a flooded home in Surrey. A kayaker drowned on a swollen Welsh river. A coastal railroad ripped up by waves in Cornwall.

In a matter of months in 2014, at least 5,000 houses in Britain were damaged in what was then seen as one of the rainiest seasons in nearly 250 years. While some blamed the flooding on the austerity measures of David Cameron, the prime minister at the time, others pointed to climate change.

In May of that year, the heaviest rains and floods in 120 years hit Bosnia and Serbia, killing at least 33 people, forcing thousands out of their homes, and cutting off power in 100,000 households in Serbia, as several months’ worth of rainfall fell in a matter of days.

June 2013

Germany is no stranger to flooding.

In Bitterfeld, in eastern Germany, about 10,000 people were asked to leave their homes in June 2013 after a levee on the Mulde River burst, amid some of the worst flooding that some German regions had seen in centuries. More than 600 residents of Dresden were brought to safety as electricity and water services to the city’s affected center were cut off.

Chancellor Angela Merkel, now tested by the current flooding, showed her mettle at the time, touring three of the hardest-hit areas to wade through ankle-deep floodwaters and visit victims of the flood.

January 2007

The storm was called Kyrill by German meteorologists, and it spurred unrelenting rain in Britain, Ireland, France, Belgium and the Netherlands.

The howling gale churned through the British Isles and Northern Europe, uprooting trees, shattering windows, flooding beaches and forcing the cancellation of hundreds of flights at airports from London to Frankfurt.

According to the European Environment Agency, Kyrill killed 46 people and resulted in overall losses worth 8 billion euros. At the time, it was one of the most damaging extreme weather episodes ever recorded in Europe.

The name Kyrill stemmed from a German practice of naming weather systems. Anyone may name one, for a fee, and three siblings had paid to name the system as a 65th birthday gift for their father, not realizing it would grow into a fierce storm.

August 2005

Such was the deluge in Central and Southern Europe in 2005 that in the Alps, military helicopters were deployed to ferry in supplies, evacuate stranded tourists and even stranded cows in mountain pastures threatened by rising water.

The floods left dozens dead. In Romania, which was badly affected by the flooding, victims were drowned as torrents of water rushed into their homes. Austria, Bulgaria, Germany and Switzerland were also buffeted by the flooding.

The scenes of devastation were visceral and shocking. The Aare River broke through the windows of a children’s clothes shop in Bern, leaving baby strollers and toys floating in muddy water. Much of the historic old city of Lucerne remained underwater.

Meanwhile, in southern Poland, rivers broke their banks and at least seven bridges collapsed.

August 2002

In 2002, some of the worst rains since 1890 pelted the Czech Republic, putting part of the historic center of Prague underwater and resulting in 50,000 residents being ordered to evacuate, as rivers swelled by near constant rain.

The death toll from the floods, which ravaged East and Central Europe, including Germany and Austria, and southern Russia, was more than 110. The flooding caused billions of dollars’ worth of damage.

The management of the crisis by Germany’s chancellor, Gerhard Schröder, helped propel him to re-election.

In Austria, the Salzach River burst its banks south of Salzburg and threatened to inundate the city at the height of its famous summer festival, forcing the authorities to close most bridges and major roads.

Floodwaters rose in Hungary and Germany, and in northern Austria the authorities halted river traffic on parts of the Danube.

Was the flooding caused by climate change?

Tying a single weather event to climate change requires extensive attribution analysis, and that takes time, but scientists know one thing for sure: Warmer air holds more moisture, and that makes it more likely that any given storm will produce more precipitation.

For every 1 Celsius degree of warming, air can hold 7 percent more moisture.

On average, the world has warmed by a little more than 1 degree Celsius (about 2 degrees Fahrenheit) since the 19th century, when societies began pumping huge amounts of greenhouse gases into the atmosphere.

“Any storm that comes along now has more moisture to work with,” said Jennifer Francis, a senior scientist with the Woodwell Climate Research Center in Massachusetts. “That’s the straightforward connection to the increased frequency of heavy downpours.”

And although it is still a subject of debate, some scientists say climate change might be causing storms to linger longer.

Some studies suggest that rapid warming in the Arctic is affecting the jet stream. One consequence of that, said Hayley Fowler, a professor of climate change impacts at Newcastle University in England, is that the river of wind is weakening and slowing down at certain times during the year, including summer. That, in turn, affects weather systems farther south.

“That means the storms have to move more slowly,” Dr. Fowler said. The storm that caused the flooding was practically stationary, she noted.

The combination of more moisture and a stalled storm system means that a lot of rain can fall over a given area.

Geert Jan van Oldenborgh, one of the primary scientists with World Weather Attribution, a group that quickly analyzes extreme weather events to see whether they were made more likely by climate change, said the group was discussing whether to study the German floods.

Beyond the speed of a weather system and its moisture content, there are many factors that affect flooding that can make an analysis difficult. Local topography has to be taken into account, as that can affect how much runoff gets into which rivers.

Human impacts can complicate the analysis even further. Development near rivers can make runoff worse by reducing the amount of open land that can absorb rain. And infrastructure built to cope with heavy runoff and rising rivers may be under-designed and inadequate.

While some development in cities and elsewhere can make flooding worse, other projects can reduce flooding. That appears to have been the case in the Netherlands, which was not as severely affected as neighboring Germany by this week’s storm.

After several major floods on the Meuse River in the 1990s, the Dutch government began a program called Room for the River to reduce flooding, said Nathalie Asselman, who advises the government and other clients on flood risk.

The work involved lowering and widening river beds, lowering flood plains and excavating side channels.

“The aim of these measures is to lower flood levels,” she said.

Taming water in the Netherlands, a waterlogged country, has been a matter of survival for centuries, and the imperative to keep levels under control is inextricably bound up with Dutch identity. Much of the country sits below sea level and is gradually sinking. Climate change has also exacerbated the twin threats of storms and rising tides.

While a dike near the Meuse in southern Netherlands suffered a breach that caused some flooding until it was repaired on Friday, the measures appear to have worked.

The breach, in the dike along the Juliana Canal in the southern Netherlands, was closed by the Dutch military by dumping hundreds of sandbags into the growing hole. Hours before, thousands had been told to evacuate after the dike was breached along the canal, a 22-mile waterway that regulates the Meuse River.

The river’s water level is at heights not witnessed since 1911, the Dutch national broadcaster NOS reported. Yet water levels on the Meuse were about a foot lower than would have been the case without the flood-reduction measures, Ms. Asselman said. That meant that smaller tributaries backed up less where they met the Meuse, producing less flooding.

“If we wouldn’t have implemented these measures, then the situation would have been worse,” she said. “Both on the main river and the tributaries.”

An increasingly hot, dry and deadly summer has gripped much of the Western United States, with heat claiming lives in the Pacific Northwest and Canada in record numbers, and a deepening drought threatening water supplies — all of which is setting the stage for another potentially catastrophic fire season in California and neighboring states.

A fourth major heat wave was forecast to roast parts of the region again this weekend. It comes two weeks after a record-shattering spate of high temperatures — which scientists said would been virtually impossible without climate change — killed hundreds of people in the United States and Canada.

A week ago, Death Valley hit a 130-degree high, matching a reading from last year that may be the highest reliably recorded temperature on earth. Also this past weekend, Las Vegas tied its record high, 117 degrees, and Grand Junction, Colo., topped its previous record, hitting 107 degrees.

At least 67 weather stations from Washington State through New Mexico have recorded their hottest temperatures ever this summer, the National Weather Service said this week. Those records stretched back at least 75 years.

The heat helped drive the rapid growth of a wildfire in southern Oregon, known as the Bootleg Fire, that has burned more than 240,000 acres — about a third the size of Rhode Island, America’s smallest state. The fire, the largest of dozens across the West, has destroyed about two dozen homes, threatens 1,900 more and has set off a wave of evacuations.

The fire also burned across a power line corridor that serves as a major contributor to the electrical grid in California, where officials have issued warnings this week asking residents to conserve power by turning up their thermostats and turning off appliances, or risk rolling blackouts.

One part of the West saw some relief from the crushing heat this week, as monsoon rains fell on the Southwest, including New Mexico and Arizona. But the result was yet another disaster: flash flooding that left some city streets in Arizona awash in muddy water and propelled a torrent of water through part of the Grand Canyon, washing away a camp where about 30 people on a rafting trip were spending the night, killing one.

As the Earth warms from climate change, heat waves are becoming hotter and more frequent. “And as bad as it might seem today,” Jonathan Overpeck, a climate scientist at the University of Michigan, recently told The New York Times, “this is about as good as it’s going to get if we don’t get global warming under control.”