This story was originally published by Yale Environment 360 and appears here as part of the Climate Desk collaboration.

Along the fabled Danube River, which snakes its way for 1,800 miles from the Black Forest in Germany to the Black Sea in Romania, scores of towns — such as the small Romanian port of Zimnicea on the Bulgarian border — depend on the waterway for their livelihood. But this summer’s epic drought and historic high temperatures, now in a fifth gruelling month, have depleted the once-mighty Danube, upending everything that Zimnicea’s residents — port workers, farmers, the shipping industry, anglers, restaurant owners and families — had for generations counted on to sustain themselves. Never in living memory has the river run so low, with large areas of mud-cracked river bottom exposed along Zimnicea’s shorelines, the dead mollusks evidence of the devastating toll on riverine life.

With the Danube flowing at less than half its usual summer volume, dozens of cargo barges lie motionless in Zimnicea’s harbour waiting for a turn to use the only channel deep enough for passage. Locals are collecting the scant rainwater to use for household purposes in order to save potable water from the Danube for drinking. Children play along the shoreline’s new beaches.

As elsewhere along the Danube — and, indeed, across much of Europe this summer — emergency dredging teams have been called in to deepen the riverway to break the cargo jam. Nevertheless, grain transports emanating from Ukraine — with many of its Black Sea ports controlled by Russia, the Danube is an alternative route for the war-wracked country to export foodstuffs — have been forced to shed cargo weight in order to pass, when they can pass at all.

Across southern Romania, much of which relies on the Danube for fresh drinking water, hundreds of villages are rationing water supplies and curtailing the irrigation of farmland that Europe relies upon for corn, grain, sunflowers and vegetables. The cruise ships that normally ferry tourists along the iconic waterway are docked. In the first six months of 2022, Romania’s hydropower utility Hidroelectrica generated a third less electricity than it normally does. And Romanian wheat farmers say that drought has cost them a fifth of their harvest. Romania is one of Europe’s largest wheat producers, and all the more important for the international market in light of Russia’s blockage of much of Ukraine’s wheat exports.

“At towns up and down the Danube, drought and climate change take on an existential meaning,” explains Nick Thorpe, author of The Danube: A Journey Upriver from the Black Sea to the Black Forest. “In contrast to city dwellers, they’re having this disaster unfold before their eyes.”

Nearly two-thirds of Europe has suffered drought conditions this year — the worst dry spell in 500 years — and scientists say global warming has played a large role in the crisis. The heat wave has wreaked havoc on many of the continent’s waterways — great and small, from the Loire to the Rhine — with wide-ranging knock-on effects for Europe’s food supply, commerce, water access, energy systems and ecology. And scientists warn that if hot, dry summers become a long-term trend, some of these waterways may never recover.

Map of the Danube, the largest river in Central Europe. Photo by Shannon/Wikimedia Commons (CC BY-SA 4.0)

Along the Rhine, barges that carry coal, oil and commodities that supply millions of people are waylaid. By July, water levels in Italy’s Po were so low that the government declared a state of emergency in northern Italy, where vast fields of crops were abandoned. In France, the warmed waters of the Rhône and Garonne can no longer cool the systems of nuclear power plants, forcing numerous plants to shut down. And hundreds of tributaries to the larger rivers are in even worse shape: bone dry.

In early August, France’s prime minister, Élisabeth Borne, said that France is in the midst of the “most severe drought” the country has ever experienced, which has so sapped rivers — including the Loire, the Doubs, the Dordogne and the Garonne — that hundreds of municipalities now require that drinking water be delivered by truck.

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“This year is exceptional in terms of [the drought’s] intensity and duration, and yet it’s the new normal,” says Karsten Rinke of Germany’s Helmholtz Center for Environmental Research (UFZ). “There’s a huge water deficit in Europe’s landscape, which is only getting worse every year that it’s not replenished.” Rinke says that drought conditions in four of the past five years have sapped groundwater, further shrunk the glaciers that feed rivers and transformed the landscape that has long nourished communities and ecosystems.

“Perhaps most alarming this year is the scope of the low-water levels across the entire Danube basin, from Bavaria to the Black Sea,” says Thomas Hein of the University of Natural Resources and Life Sciences, Vienna. The basin covers more than 800,000 square kilometres (300,000 square miles) and encompasses 19 countries — 10 per cent of continental Europe. “The entire river is affected, which means we can’t just pump water from one section to another to make up for the shortfall.”

On the Danube, the river is so low at Novi Sad, Serbia’s secondlargest city, that people can wade across it — something even the city’s oldest citizens have never before witnessed. Whole wharfs and their vessels are stranded on dried riverbed, with never-before-seen islands now dotting the shallow waters. Farmers from the rich agricultural regions surrounding Novi Sad have requested that the government declare a state of emergency. And a grim symbol from the past has emerged: Dozens of sunken German Second World War-era warships, some still harbouring live ammunition, are now visible in the diminished river.

The drought is taking a huge toll on commerce: Europe’s waterways transport about one ton of freight a year for every EU resident and contribute, in terms of transportation alone, roughly $80 billion to the economy. The Rhine is so emaciated today that massive sandbars breach its midsection, rendering fully loaded barges unable to transport coal, diesel and commodities to the industrial cities of Germany’s Ruhr Valley.

The coal and fuel that travel the Rhine and other rivers are particularly vital now in light of Russia’s embargoes on gas and coal. And the outages at France’s nuclear power plants due to a lack of cooling water have contributed to the soaring price of French electricity, which has shot up to the unheard-of 900 euros per megawatt-hour — more than 10 times last year’s price.

Scientists say that the economic cost of the rivers’ decimation is only part of the problem. The less water in the water system as a whole, explains Gabriel Singer, an ecologist at the University of Innsbruck, Austria, the less dilution for salts and the slower a river flows. This leads to higher saline content and higher water temperatures, which can be lethal for many species of riverine life, such as Danube salmon, barbel, and European grayling, among many others.

Higher temperatures also feed algae blooms, Singer explains, which can be toxic for river systems. This is what has happened in several German rivers, including the Moselle and Neckar, as well as perhaps the Oder River, where in mid-August more than 100 metric tons (220,000 pounds) of dead fish — among them perch, catfish, pike, and asp — washed up on its shores within a week. (Experts are currently investigating the cause of the die-off.)

Scientists point out that while the predicament of the great rivers of Europe has grabbed the headlines, it is the smaller rivers that suffer disproportionately. “So many of them are completely dried up, not a drop of water left,” says Rinke. “When this happens, they lose their entire community of biodiversity, forever. It won’t just return the next time it rains.”

Scientists say that millennia of engineering and human activity along Europe’s rivers have also played a role. The straightening of once-wild rivers, deforestation, damming, industrial pollution, wastewater discharges and agriculture’s usurpation of shorelines and wetlands have made Europe’s rivers all the more susceptible to heat waves and low-water conditions, as well as floods.

“All of our river systems are highly fragmented and vulnerable,” says Singer, underscoring that while the lower Danube is plagued by drought, the upper Danube in Germany and Austria can be at risk of flooding, as happened so spectacularly last July in the Rhine borderlands of Germany and Belgium. The underlying problem, he says, is essentially the same: the inability of highly modified rivers and river basins to hold water for longer periods of time. “Healthy natural ecosystems function as a sponge that gives and takes water, but ours have lost this ability,” he says.

Christian Griebler, a limnologist at the University of Vienna, explains: “We lose high amounts of water because rain cannot infiltrate sealed surfaces, and heavy rain after a drought does not infiltrate dry soils. Surface overflow goes into channelized and fast-flowing rivers that hardly communicate with the surrounding aquifers.”

Thus, the authorities’ reflex reaction — namely to dredge deeper — doesn’t address the essential problem, say Singer and Griebler. In fact, it exacerbates it.

Solving the crisis unfolding this summer along Europe’s rivers will of course involve the long-term endeavour of slowing global warming. In the short term, scientists say governments need to address other factors stressing the continent’s waterways, including enforcing stronger wetland protections.

On that front, some progress is being made, says Singer. Last year, UNESCO established the world’s first five-country biosphere reserve along the Mura, Drava, and Danube rivers — a total area of almost one million hectares (3,860 square miles).

The Danube Delta, Europe’s largest wetland, has enjoyed such protection since 1998. But the delta’s special status has not spared it from the extreme weather. Freshwater springs in the Delta’s Letea Forest went dry in August, endangering the lives of Romania’s famed wild horses. Officials bulldozed the mud-caked springs, enabling water to flow again and the horses to drink.

“Fortunately we still have the glaciers that act as a reserve for the bigger rivers in times of lower precipitation,” says Hein. “But climate change modellers say they’ll be gone in 30 years. This is extremely worrisome.”

Robert Lichtner, the Vienna-based coordinator of the European Union’s Strategy for the Danube Region, says that adaptation measures ultimately must be part of the basin’s future. “We want to slow these processes down, but [the extreme weather] is not going away,” he says. “We’ll have to adapt and learn to live with it.”