1201. Water Gap under Future Climate Change

Freshwater, essential for ecosystems and human existence, is becoming increasingly scarce. Population growth, urbanization, and socio-economic development are driving increasing demand for the world's limited water resources. At the same time, climate change is changing precipitation patterns and affecting water supplies. Currently, about 4 billion people experience water shortages for at least one month each year. Irrigated agriculture, which accounts for about 90% of global water consumption, is the main driver of this water shortage. Without significant reductions in greenhouse gas emissions, global temperatures could rise by 3°C by the end of the century, exacerbating water scarcity and affecting an additional 800 million to 2.2 billion people.

A new study published in Nature Communications quantifies and maps the current "water gap" (the shortage where water demand exceeds supply) around the world and predicts how warming will affect water supplies. It predicts that global water scarcity will increase by nearly 6% if warming is below 1.5°C and by nearly 15% if warming is below 3°C.

The study introduces the concept of the "water gap," defined as the difference in the amount of water when demand exceeds supply. When water supply falls below consumption, it is a sign of severe water scarcity and leads to unsustainable water use. Such water scarcity threatens human needs, agriculture, industry, energy production, and ecosystems, and can have severe social, economic, and environmental consequences. The paper used historical water use data and water availability from a water resources model to map the average global water gap from 2001 to 2010.

The analysis found that the current global water deficit is about 458 cubic kilometers (km³) per year (1 cubic kilometer is equal to 1 billion cubic meters). The countries with the largest individual water deficits are India, the United States, Pakistan, Iran, and China, but water shortages are projected on every continent. In areas with water shortages, humans must make up for the shortfall by depleting groundwater, rivers, lakes, and aquatic ecosystems.

The paper also predicts how future climate change will magnify water shortages. A 1.5-degree increase in temperature is projected to increase global water shortages by about 26.5 km³ per year, a 5.8% increase from the current baseline. A 3-degree increase in temperature would result in a more severe increase of 67.4 km³ per year, or a 14.7% increase. These results suggest that continued climate change mitigation measures are essential to minimize the impacts on water resources.

Regional variations in water scarcity highlight the uneven impacts of climate change, with some countries and river basins facing significant vulnerability. India, which has the largest baseline water scarcity of 124.3 km³ per year, is also expected to experience the most pronounced increase in water scarcity. Other countries, including China, Pakistan, the United States, Spain, and Turkey, also experience notable increases. Currently, significant water scarcity is found in the Ganges-Brahmaputra basin in India and Bangladesh, the Sabarmati basin in India, and the Tigris-Euphrates basin, which covers much of the Middle East. In both warming scenarios, water scarcity is expected to increase significantly in the Ganges-Brahmaputra basin and the Mississippi-Missouri basin in the United States.

On the other hand, the model projects that water scarcity will be slightly reduced in some countries, including Nigeria, Niger, Chad, Sudan, Ethiopia, Vietnam, and the Philippines.

No single solution can ensure global water security. Effective solutions require both reducing water consumption and increasing water availability. Reducing consumption includes switching to less water-intensive crops, minimizing food waste, and improving irrigation efficiency. On the supply side, expanding water storage infrastructure, investing in desalination technologies, and reusing treated wastewater can help augment freshwater resources. A combination of these approaches, tailored to local needs, is essential to address water scarcity and ensure long-term water security.

Reference
Rosa, L., Sangiorgio, M. Global water gaps under future warming levels. Nat Commun 16, 1192 (2025). https://doi.org/10.1038/s41467-025-56517-2

Contributor: IIYAMA Miyuki, Information Program