Due to climate change, droughts become more frequent and longer. For the first time, researchers have dared to forecast which places will be affected by extreme water shortages in the future, so-called “Day-Zero-Dürren”. Accordingly, almost three quarters of all regions, which are already drought today, will suffer from acute lack of water by 2100. However, the first hotspots with water bottlenecks will probably occur in the 2020s. Urban areas in the Mediterranean, in southern Africa and parts of North America are particularly at risk.
“Day-Zero-Düren” means phases of extreme water lacks in which more water is needed locally than is available. The urban water supply can then no longer be guaranteed. Such events are caused if it rains too little, evaporating too much, rivers and reservoirs are added too little water reserves and a lot of water is used. So far, such droughts have not occurred, but the cities of Cape Town and Chennai were already very close.
With the climate change, low -precipitation is becoming low -precipitation and droughts more and last longer, sometimes for several years. This increases the risk of “day-zero-villas”. So far, however, it is unclear when and where there will be such a strong water shortage. This, in turn, makes it difficult for people to divide their water reserves and to make them for phases of the water shortage.
Water shortage affects cities in particular
Now Vecchia Ravinandrasana and Christian Franzke from the University of Busan in South Korea have made a forecast for future “Day-Zero-Düren” for the first time. Based on a large ensemble of the latest climate models, they calculated the likelihood of extreme water shortages at the local level until the end of the 21st century. Your assumption: Humanity will either continue to release high emissions (SSP3-7.0) or at least take moderate climate protection measures (SSP2-4.5). In both cases, however, it will not be possible to contain global warming to 1.5 degrees above the pre -industrial level.
The evaluation showed: Under the SSP3-7.0 scenario, 74 percent of the regions that are already drought today will be exposed to a high risk of severe and persistent droughts worldwide and have experienced a “day zero” at least once. It would be 51 percent under the SSP2-4.5 scenario. “Day-Zero-Vürren” endangered would be up to 753 million people worldwide by the end of the century, including 467 million in urban areas and 286 million in rural areas. From the water bottleneck, not only agriculture and rural population would suffer, but also and above all the city population, as the two climate scientists report.
“Day zero” of the water supply comes earlier than expected
Some regions could also affect much earlier than expected: Depending on the climate scenario, 22 or even 35 percent of the drought -at -risk regions could be confronted with strong water shortages for the first time in this decade, between 2020 and 2030. These hotspots include areas in the Mediterranean, in southern Africa and in parts of North America. “Day-Zero-Dürren are no longer a distant scenario: they are already passing,” concludes Ravinandrasana.
This also applies to regions with currently large reservoirs. “According to our calculations, 14 percent of the large water reservoirs could already dry out at the first DZD events, which would have serious effects on people’s livelihood,” says Franzke. In addition, the calculations showed that the gap between successive “Day-Zero Dürren” could be shorter than the duration of the individual events. The affected regions then hardly had time to recover from the water shortage and fill water reservoir again, which also exacerbates the situation in the long run.
Plans for saving water also necessary for Central Europe
“Our study shows that global warming causes and accelerates the global warming worldwide. Even if we reach the 1.5-degree goal, hundreds of millions of people will still be faced with unprecedented shortage of water,” says Ravinandrasana. She and Franzke did not take into account the role of groundwater and from glaciers as a buffer in Dürren in the forecasts. Therefore, the real water development in individual cases could be somewhat different than calculated in the model based on the surface water.
Nevertheless, the results of the researchers show that people have to develop urgent and proactively strategies for water management in order to prepare themselves in front of upcoming “Day-Zero-Düren”. In the event of impending bottlenecks, for example, regional limit values for water consumption and other strict measures for saving water could be determined. “We need such decision -making models for adjustments, especially for Central Europe. Other regions are dryer, but we have adapted to high water availability and are therefore often more sensitive to future droughts,” comments Thorsten Wagener from the University of Potsdam.
Source: Vecchia Ravinandrasana and Christian Franzke (University of Busan); Nature communications, DOI: 10.1038/S41467-025-63784-6