Imminent “Day Zero” Droughts Threaten Global Water Security Amid Climate Change

By April 2023, Lake Mead had fallen dramatically due to a megadrought and decades of overuse.
Will Lanzoni/CNN

Many regions of the world are already facing the risk of so-called zero-drought days – periods of extreme water crisis when freshwater supplies disappear quickly and suddenly. Such scenarios could unfold in the coming years in certain regions, including North America, the Mediterranean region, and southern Africa.

Climate change driven by burning fossil fuels disrupts the global water cycle and intensifies water scarcity. Scientists had previously considered several possible time frames, but the question of exactly when peak water deficit would occur and where it would be expected earlier than anticipated remained open. A new study provides answers, some of which are surprising, notes climatologist Christian Francke from Pusan National University and one of the study’s authors.

Scientists employed a wide range of climate models to assess the time frames and the probability of zero-drought days – phenomena not previously observed.

“Unprecedented events of water scarcity, events that have never occurred before.”

“That’s when you turn on the tap and no water comes out.”

Zero-drought days arise from a combination of factors: extended periods without rainfall, low river flows, depletion of reservoirs, and growing demand for water for people, agriculture, and industry.

According to the study, nearly three-quarters of regions already facing droughts and including regions with large reservoirs are at high risk of severe and prolonged droughts by the end of the century, assuming continued fossil-fuel use in energy.

More than a third of such regions, including the western United States, could find themselves in this scenario as early as the 2020s or 2030s. The very fact that zero-drought days could arrive so early given the current pace of global warming “shocked us,” Francke noted, even though some cities were already close to this scenario.

As an example, Cape Town in South Africa endured a water crisis in 2017–2018 after one of the longest droughts on record. The disaster was averted thanks to strict water-saving measures and increased rainfall in 2018.

Governments and cities around the world today are grappling with the risk of a “zero-drought day”: Tehran, Kabul, Mexico City, and Los Angeles – just a few examples. Cities with rapidly growing populations and limited water resources are under increased pressure, and vulnerable low-income communities bear the heaviest consequences.

Some regions, including the Mediterranean region, Southern Africa, parts of Asia and Australia, could face longer sequences of zero-drought days and a shorter inter-drought recovery interval between them, making it harder to restore water resources. Such trends threaten agriculture, ecosystems, and even long-term habitation in some areas.

The authors emphasize the urgent need to accelerate the shift to clean energy and to manage water resources more efficiently – a substantial portion of water is lost through leaks and pipeline seepage. The study could also serve as a guide for industries, particularly for semiconductor manufacturing and data centers in water-stressed regions such as Texas and Arizona.

One limitation of the study is that groundwater stocks were not included in the calculations because they were not part of the models. However, the authors note that the analysis includes provisions to address this aspect.

“Important new evidence of how drought will emerge when climate warming combines with society’s demand for fresh water.”

“The study is ‘a guide, not a perfect forecast,’ Allen told CNN, but it ‘paints a picture of a growing assault on water resources from several fronts that are already taking shape’.”

In short, the study not only points to the possibility of an early onset of zero-drought days but also underscores the need for society and economic sectors to adapt to harsher water conditions. This means greater investment in infrastructure, higher energy efficiency, and the rapid modernization of water-management systems.

Additionally, it is worth noting that for a fuller understanding of the scenarios, groundwater resources and regional differences in access to water should also be considered. Policy and planning for urban water supply are moving in the same direction, which will significantly influence future decisions about water and energy use.

Overall, the study lays out a framework for understanding how the water crisis may unfold in the era of a warming climate. Investors, cities, and national governments should view these data as a signal for action: the need for clean energy, modernization of water infrastructure, and stricter controls on water losses – to reduce risk and mitigate impacts on human lives and the economy.