 "How soon could ‘Day Zero droughts’ become a reality?")
The warning signs of a deepening global water crisis are flashing red.
With the planet warming, rainfall patterns shifting, and water demands surging, experts are sounding the alarm that so-called “Day Zero droughts” — moments when entire cities risk turning on taps to find nothing coming out — could arrive sooner than many policymakers or residents might expect.
A major international study, published in Nature Communications on Tuesday (September 23, 2025), has revealed that regions across the Mediterranean, southern Africa, and North America could face these extreme water scarcity events as early as the late 2020s and 2030s.
For urban centres, rural communities, and agricultural systems alike, the findings highlight the scale of the threat posed by a changing climate and increasing pressure on freshwater resources.
The research points to a startling conclusion: “Day Zero” is not a distant possibility but a near-term reality for many areas if current warming and consumption trends continue.
The origins and meaning of “Day Zero drought”
The term “Day Zero drought” first entered public discourse in dramatic fashion during the Cape Town water crisis of 2017-2018.
Over the course of several years starting in 2015, the South African city experienced its worst drought in more than a century, driven by record-low rainfall and mounting water demand.
By early 2018, the city’s largest reservoir, Theewaterskloof, had plunged to critically low levels. River flows in the surrounding region reached their lowest point since 1904.
The local government announced that unless consumption dropped sharply and rains returned, Cape Town would hit “Day Zero” — the moment when the city would have to shut off most taps, with residents queuing at distribution points for emergency water supplies.
The crisis was only narrowly averted when above-average rainfall arrived later that year, refilling dams just in time. Still, it exposed the vulnerability of urban water systems to multi-year droughts, especially in cities that depend almost entirely on surface water.
Cape Town sourced 96 per cent of its supply from reservoirs and rivers, with only 4 per cent coming from groundwater, leaving it dangerously exposed when surface flows collapsed.
Researchers studying the event have classified Day Zero droughts as “compound extreme events.”
Unlike conventional meteorological or agricultural droughts, which are usually defined by rainfall deficits or soil moisture conditions, Day Zero events occur when multiple factors converge simultaneously: prolonged dry spells, plummeting river flows, shrinking reservoirs, and surging water demand from households, farms, and industries.
What the new study reveals
The Nature Communications study, conducted by an international team of scientists from institutions including Pusan National University in South Korea, used the latest climate models to project when and where Day Zero droughts are most likely to strike in the coming decades.
Researchers analysed how warming temperatures disrupt the global water cycle, affect precipitation patterns, and interact with rising consumption to create severe water shortages.
They simulated conditions where rainfall, river flows, and reservoirs could no longer meet human and environmental needs — a situation signalling Day Zero.
The conclusions were sobering.
According to the study, 35 per cent of drought-prone regions worldwide could face Day Zero conditions within the next 15 years.
By the end of the century, nearly three-quarters of such regions are projected to be at risk if greenhouse gas emissions remain high and water management practices do not improve.
Christian Franzke, one of the study’s authors, explained to CNN, “These are unprecedented water scarcity events, events which haven’t occurred so far. It’s when you turn on your water tap and no water comes out.”
The models revealed several hotspots where risks are particularly acute:
The Mediterranean Basin: Home to hundreds of millions of people, the region combines a drying climate with dense urban populations and heavy agricultural water use.
Southern Africa: Already prone to severe droughts, the region faces overlapping pressures from population growth, industrial demand, and warming temperatures.
North America: Parts of the western United States, including California, Arizona, and Texas, are likely to face Day Zero scenarios in the coming decades, exacerbated by industries such as semiconductor manufacturing and data centres that require vast amounts of water.
The study also estimates that under a high-emissions scenario, up to 750 million people globally could be exposed to Day Zero drought conditions by 2100 — two-thirds in urban areas and the rest in rural regions.
Urban centres in the Mediterranean could see nearly 196 million residents at risk, while rural communities in Asia and both northern and southern Africa face disproportionate vulnerabilities due to limited infrastructure and resources.
Lessons from past crises: Cape Town and Chennai
While the study looks forward, recent history provides stark reminders of what Day Zero droughts look like on the ground.
Cape Town’s close call in 2018 was followed by another major urban crisis in 2019 when Chennai, India’s sixth-largest city, nearly ran out of water after failed monsoon rains left its main reservoirs virtually dry.
For weeks, water had to be delivered by truck to parched neighbourhoods, with residents queuing for hours under scorching temperatures.
Los Angeles, Mexico City, Kabul, and Tehran are among other major cities identified as facing high water stress, with limited resilience if severe multi-year droughts strike.
Many rely heavily on surface water sources or ageing infrastructure, leaving them exposed to both climate shocks and mismanagement.
As Franzke noted, “The finding that day-zero droughts could happen so soon, at current levels of global warming, was something that surprised us,” given that several cities have already approached this tipping point in recent years.
The role of climate change & human activity
One of the study’s most significant conclusions is that both climate change and human activity are driving Day Zero drought risks.
Global warming intensifies the hydrological cycle, leading to longer and more frequent droughts in many regions while causing extreme rainfall and flooding in others.
Rising temperatures increase evaporation rates, dry out soils, and reduce river flows, shrinking available freshwater supplies just as demand climbs.
At the same time, booming populations, rapid urbanisation, and industrial expansion are straining water systems already under pressure.
Agriculture accounts for around 70 per cent of global freshwater withdrawals, while industries such as energy production, mining, and manufacturing consume vast additional volumes.
In many regions, poor infrastructure worsens the problem. Leaky distribution networks lose significant amounts of treated water before it even reaches consumers. Pollution from untreated wastewater further limits usable supplies.
Low-income communities are expected to bear the brunt of these shortages, as wealthier households and businesses often secure access through private wells, storage facilities, or costly desalination projects, leaving poorer populations more exposed when public systems fail.
Regional breakdown: Where Day Zero may strike first
Based on the study’s modeling, the timing and severity of Day Zero drought risks vary by region:
Mediterranean Europe and North Africa: With warming temperatures, declining rainfall, and growing populations, cities from Spain to Morocco face mounting risks within the next two decades. Agricultural irrigation in water-scarce environments adds further pressure.
Southern Africa: Countries like South Africa, Namibia, and Botswana already endure recurring droughts, with urban centers and rural farming communities alike confronting severe water stress.
Western United States: Prolonged droughts across California, Arizona, Nevada, and Texas threaten both cities and industries. The growth of water-intensive sectors, including semiconductor fabs and data centers, is accelerating concerns over supply sustainability.
South and Central Asia: Fast-growing megacities combined with glacier retreat, erratic monsoons, and rising demand put regions like northern India, Pakistan, and Afghanistan at particular risk.
Australia: Repeated droughts across southeastern Australia are projected to worsen, threatening both agriculture and urban water security.
Some areas are expected to experience not only more frequent Day Zero events but also shorter recovery times between crises, leaving less opportunity for ecosystems, agriculture, and infrastructure to rebound.
Limitations and data gaps
While the study provides one of the most comprehensive global assessments to date, the authors acknowledge certain limitations.
Notably, groundwater resources were not fully included in the climate models used. In many regions, aquifers act as critical buffers during droughts, supplying water when surface sources fail.
However, groundwater itself is under pressure from over-extraction, pollution, and slow recharge rates, meaning it cannot be seen as an unlimited safety net.
Franzke explained that while the research incorporated some measures to approximate groundwater availability, the lack of detailed global data on aquifer conditions prevents precise modelling of how long they might sustain supplies during prolonged droughts.
What needs to happen next
Experts agree that preventing or mitigating Day Zero droughts requires urgent action on multiple fronts.
First, cutting greenhouse gas emissions remains essential to slow the warming that intensifies drought risks. The study notes that even limiting global temperature rise to 1.5 degrees Celsius above preindustrial levels — the goal of the Paris Agreement — would still leave hundreds of millions facing unprecedented water shortages.
As Vecchia Ravinandrasana, one of the study’s authors, stated, “Even if global warming is held at 1.5 degrees Celsius above preindustrial levels, hundreds of millions of people will still face unprecedented water shortages.”
Second, improving water management is critical.
This includes repairing leaky infrastructure, adopting water-efficient irrigation technologies, recycling wastewater, and protecting watersheds from deforestation and pollution.
Urban planning also needs to factor in water limits. Industries with high water footprints, such as semiconductor manufacturing and large-scale agriculture, must evaluate the risks of operating in already water-stressed regions.
Finally, better early-warning systems, drought preparedness plans, and public awareness campaigns can help communities adapt before crises hit.
Cape Town’s experience showed that aggressive conservation measures, public communication, and contingency planning can buy valuable time when reservoirs run low.
With inputs from agencies
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