Urban water demand will increase by 80% by 2050, while climate change will alter the timing and distribution of water. Here we quantify the magnitude of these twin challenges to urban water security, combining a dataset of urban water sources of 482 of the world’s largest cities with estimates of future water demand, based on the Intergovernmental Panel on Climate Change (IPCC)’s Fifth Assessment scenarios, and predictions of future water availability, using the WaterGAP3 modelling framework.

We project an urban surface-water deficit of 1,386–6,764 million m³. More than 27% of cities studied, containing 233 million people, will have water demands that exceed surface-water availability. An additional 19% of cities, which are dependent on surface-water transfers, have a high potential for conflict between the urban and agricultural sectors, since both sectors cannot obtain their estimated future water demands. In 80% of these high-conflict watersheds, improvements in agricultural water-use efficiency could free up enough water for urban use. Investments in improving agricultural water use could thus serve as an important global change adaptation strategy.

Cities around the world are markedly expanding in size, as global urban growth (that is, increasing urban population) leads to more than two billion additional urban residents by 20301. Today, approximately 54% of the global population (that is, 3.9 billion people1) lives in cities, a fraction that is likely to grow to between 60% and 92% by the end of the twentyfirst century, according to the scenarios from shared socioeconomic pathways2 (SSPs). Domestic water use almost quadrupled over the last 60 years due to increasing population, wealth and access to drinking-water infrastructure3, and there was an even higher increase in water use in cities4. Read more

The South African city plans to shut off the taps to 4 million people. But it’s just one of many cities around the world facing a future with too little water.

HOW CAPE TOWN IS COPING WITH ITS WORST DROUGHT ON RECORD

Editor’s Note: Since this story was first published on February 2, the “Day Zero” when Cape Town is set to turn off its water supply has been moved back several times, first to May, and then even later. As of March 5, the day was set for July 15. The city has gotten “a slight reprieve” thanks to area fruit growers using up their annual water allocation, making more available for the city, and some water routing and conservation measures.

By summer, four million people in the city of Cape Town—one of Africa’s most affluent metropolises—may have to stand in line surrounded by armed guards to collect rations of the region’s most precious commodity: drinking water. Read more

Many more cities than Cape Town face an uncertain future over water. But there are emerging solutions.

“Day Zero,” when at least a million homes in the city of Cape Town, South Africa, will no longer have any running water, was originally scheduled for April. It was recently moved to July. The three-year long drought hasn’t ended, but severe water rationing—limiting people to a mere 13 gallons (50 litres) per person per day—has made a difference. (To put this into perspective, an average U.S. citizen uses 100 gallons (375 liters) per day.)

“No person in Cape Town should be flushing potable water down a toilet any more.… No one should be showering more than twice a week now,” said Helen Zille, the premier of the Western Cape province, where Cape Town is located.

Like many places in the world, Cape Town and the surrounding region has likely reached “peak water,” or the limit of how much water can be reasonably taken from the area, says water scientist Peter Gleick, president-emeritus of the Pacific Institute. Gleick, who has spent substantial time in South Africa, says the country generally has good water managers. Read more

The European Space Agency is developing technology to allow satellites to identify the concentration, movement and origin of plastic debris across the world’s oceans.

A European Space Agency satellite. European Space Agency

PAOLO CORRADI AND Luca Maresi had the same idea: tracking plastic trash from space.

Corradi, an engineer with the European Space Agency’s (ESA) optics division in the Netherlands, had been hearing about plastic marine litter from a friend at a nonprofit working on the issue. Maresi, Corradi’s boss, had seen the problem firsthand during sailing trips.

“We actually had the same study idea independently and inspired by different reasons,” Corradi said.

The men figured that deploying satellites to monitor marine litter on a global scale could give researchers working on plastic pollution data about its abundance, concentrations and movement. But it remains to be seen whether such satellite tracking will be possible and whether it will be useful in the effort to combat a huge and growing problem that has spawned “gyres” of plastic trash in the world’s oceans. Read more

Water is the common denominator of life.

All around the world, water is a precious resource, the common denominator of life. When it’s reliable and clean, people tend to take it for granted. When it’s the opposite, it can become the crucial fact of a person’s existence, something that, if left unaddressed, prevents anything else from happening.

Roughly 2 billion people don’t have reliable sources of clean drinking water and one child every minute dies from preventable waterborne diarrheal disease.

By 2050, demand for fresh water is expected to grow by more than 40% and around a quarter of the world’s population will live in places where water resources are endangered, according to the United Nations. Read more