Time of First Emergence (ToFE) of Day Zero Drought (DZD) conditions and global hotspot regions. (a) Spatial distribution of the decadal ToFE of DZD events across the globe from 1900 to 2100. Color shading indicates the first decade during which DZD becomes statistically attributable to anthropogenic climate change, defined as the first decade in which the Fraction of Attributable Risk is greater than 0.99 (FAR ≥ 0.99). Gray regions indicate grid cells where no DZD event attributable to anthropogenic climate change is projected to emerge before 2100. (b) Circular diagram illustrating the temporal distribution of ToFE by decades. The color scale indicates the percentages of DZD grid cells (land areas) experiencing their ToFE distribution in each decade from 1900 to 2100. It provides a temporal overview of how the ToFE is distributed over time and the trends in DZD emergence. Credit: Institute for Basic Science
A new study in the journal Nature Communications by researchers from the IBS Center for Climate Â鶹ÒùÔºics (ICCP) at Pusan National University in the Republic of Korea reveals that global warming is accelerating the risk of multi-year droughts that can lead to extreme water scarcity, threatening water demands in cities, agriculture, and livelihoods worldwide, already within the coming decades.
The study uses the latest generation of climate model simulations to determine the time when local water demands will exceed the regional water supply from precipitation, rivers, and reservoirs. This time is commonly referred to as the Day Zero Drought (DZD). Cities, such as Cape Town (South Africa) in 2018 and Chennai (India) in 2019, have already been close to DZD conditions, highlighting the growing vulnerability of urban water supply systems for drinking water and agriculture.
Understanding where and when these conditions will emerge is crucial for developing effective water management strategies for rural and urban communities. The new study shows that the frequency of DZDs will increase sharply over the coming decades, much sooner than previously anticipated.
The climate models used by the authors were forced with the SSP3-7.0 and SSP2-4.5 greenhouse gas emission scenarios. Focusing on hydrological compound extremes, including prolonged rainfall deficits, reduced river flow, and increasing water consumption, but excluding groundwater reservoirs, the study identifies robust DZD hotspots across the Mediterranean, southern Africa, and parts of North America. Urban areas are particularly vulnerable.
According to the simulations, DZDs are likely to emerge in 35% of the vulnerable regions already within the next 15 years. By the end of this century, DZD conditions could threaten about 750 million people globally, including 470 million city residents and 290 million people in rural areas. The Mediterranean region is projected to have the highest urban exposure, whereas Northern and Southern Africa and parts of Asia face the most severe rural impacts.
"Our study shows that global warming causes and accelerates Day Zero Drought conditions worldwide. Even if we meet the 1.5°C target, hundreds of millions of people will still face unprecedented water shortages," says Ph.D. candidate Ravinandrasana, first author of the study.
"According to our calculations, and due to the increasing severity of hydrological stress, 14% of major water reservoirs could dry out already during their first DZD events, with severe impacts on people's livelihoods," says corresponding author Prof. Christian Franzke from the IBS Center for Climate Â鶹ÒùÔºics.
"Day Zero Droughts are no longer a distant scenario: they are already happening. Without immediate adaptation and sustainable water management, hundreds of millions of people are likely to face unprecedented future water shortages," says Ravinandrasana.
More information: Vecchia P. Ravinandrasana et al, The first emergence of unprecedented global water scarcity in the Anthropocene, Nature Communications (2025). .
Journal information: Nature Communications
Provided by Institute for Basic Science
