Illustration of extreme drought conditions and projected water shortage in urban areas.
Credit: Institute for Basic Science
Climate simulations reveal that Day Zero Drought conditions are approaching rapidly worldwide, putting vast populations at risk of severe water scarcity.
A new study in Nature Communications from researchers at the IBS Center for Climate Physics (ICCP) at Pusan National University in the Republic of Korea finds that global warming is speeding up the likelihood of multi-year droughts. These prolonged dry periods can push regions toward severe water shortages, putting pressure on drinking water supplies, agriculture, and communities around the world within the next few decades.
To investigate this risk, the team used state-of-the-art climate model simulations to estimate when local water demand will surpass the available supply from rainfall, rivers, and reservoirs. This tipping point is known as the Day Zero Drought (DZD). Recent close calls in Cape Town (South Africa) in 2018 and Chennai (India) in 2019 have already demonstrated how vulnerable cities are to running out of water.
Identifying when and where these thresholds will occur is essential for planning effective water management for both urban and rural regions. According to the study, DZD events are projected to rise rapidly in the coming years, happening far earlier than once expected.
Climate model projections reveal accelerating Day Zero Drought events
The team relied on climate simulations based on the SSP3-7.0 and SSP2-4.5 greenhouse gas scenarios. By examining prolonged rainfall shortages, declines in river flow, and growing water use, the researchers identified clear DZD hotspots across the Mediterranean, southern Africa, and sections of North America. The analysis shows that cities in these regions are especially at risk.
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
According to the simulations, DZDs are likely to emerge in 35% of the vulnerable regions already within the next 15 years (Figure 1). 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.
Projected impacts on reservoirs and global communities
“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 PhD candidate Ms. 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 Frankze from the IBS Center for Climate Physics.
“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 Ms. Ravinandrasana.
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