6 Minutes
Climate modelers warn that the next decades could bring a dramatic increase in multi-year droughts that overwhelm local water supplies. A new study from the Institute for Basic Science (IBS) suggests that so-called "Day Zero Drought" conditions — when local demand outstrips available fresh water from rainfall, rivers and reservoirs — are on course to affect hundreds of millions of people worldwide.
What researchers modeled and why it matters
Scientists at the IBS Center for Climate Physics used advanced climate simulations to estimate when and where Day Zero Droughts (DZD) will first become attributable to anthropogenic climate change. By combining rainfall deficits, reduced river flows and rising water use, the team mapped the Time of First Emergence (ToFE) for DZD across land areas between 1900 and 2100.
The analysis relies on two greenhouse-gas pathways commonly used in climate research: SSP3-7.0 and SSP2-4.5. These scenarios span a range of future emissions and allow researchers to test how sensitive water systems are to warming and human water demand. The result is a global picture of emerging drought hotspots and the likely timing of their first climate-attributable events.
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
Where and who are most at risk?
The simulations show DZD hotspots concentrated across the Mediterranean basin, large parts of southern Africa and key regions in North America and Asia. Cities in Mediterranean countries face particularly high exposure, while rural populations in Northern and Southern Africa and parts of Asia could experience the harshest impacts.
According to the study's projections, Day Zero Droughts are likely to emerge in roughly 35% of identified vulnerable regions within the next 15 years. By 2100, the researchers estimate that DZD conditions could threaten about 750 million people globally — approximately 470 million urban residents and 290 million people in rural areas.
Impacts on reservoirs and livelihoods
Beyond people counts, the study highlights infrastructure vulnerability. Models suggest that 14% of major water reservoirs could run dry during their first DZD events, magnifying the risk to agriculture, municipal supplies and industries that depend on reliable freshwater storage.
"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," said PhD candidate Ms. Ravinandrasana, first author of the paper. Corresponding author Prof. Christian Frankze added: "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."
Science behind the projections
To trace DZD emergence, the research team calculated the Fraction of Attributable Risk (FAR) for each grid cell on a decadal basis, identifying the first decade when FAR ≥ 0.99. That statistical threshold indicates a high degree of confidence that observed drought conditions are linked to human-driven climate change rather than natural variability alone.
By linking hydrological stress (shortfall in supply) with socioeconomic demand scenarios, the study provides a more operationally relevant outlook than models that focus on precipitation alone. This approach helps water managers and policymakers see where and when supply-demand imbalances could become acute.
What can cities and nations do?
Experts stress a mix of mitigation and adaptation. Reducing greenhouse gas emissions remains critical to limit the magnitude and pace of DZD emergence. At the same time, practical measures in water management can blunt impacts: improved leakage control, diversified supply portfolios (reuse, desalination where feasible), demand-side restrictions during drought windows, and investment in downstream storage and groundwater recharge.
- Prioritize early-warning and monitoring systems linked to reservoir levels and river flow.
- Invest in efficient irrigation and urban water reuse to stretch available supplies.
- Plan for social and economic impacts, especially in food systems and low-income communities.
Expert Insight
"The concept of a Day Zero makes the abstract idea of drought immediate and local," says Dr. Lena Ortiz, a water-resources scientist not involved with the study. "What this paper adds is timing: it shows where those DZD tipping points are most likely to appear first, which is vital for planning. Even with successful climate mitigation, some regions will need rapid adaptation to avoid humanitarian crises."
As the planet warms, this research underscores a troubling reality: Day Zero Droughts are not hypothetical futures but emerging events that will test water systems, institutions and communities. The next decade will be decisive in deciding how many people suffer severe water scarcity and how effectively societies adapt.
Source: scitechdaily
Comments
labcore
wow didnt expect 750 million ppl… that number hits hard. Cities prepping? Rural areas gonna suffer bad, urgent planning needed, now
Leave a Comment