Gap between water supply and demand will increase as climate shifts

Water is necessary for life. It’s also tremendously important for food and energy security and ecosystem health. Despite this, many people live in areas that experience water scarcity at least one month out of the year.

Press Release – Washington, DC—Robust water-management strategies will be necessary to overcome discrepancies between water supply and demand in a warming world, according to a new analysis by Carnegie Science’s Lorenzo Rosa and Matteo Sangiorgio of the Polytechnic University of Milan.

Their work, recently published in Nature Communications, quantifies water scarcity issues under both warming scenarios of 1.5 degrees Celsius and 3 degrees Celsius.

Water is the most vital substance on our planet. Life cannot exist without it and is also central to a range of human activities. Water availability is critical for human health, environmental resilience, economic development, and food and energy security. Despite this, in many parts of the world the demand for water is greater than the available supply.

“Water scarcity is one of the greatest challenges facing humanity this century,” Rosa said. “About 4 billion people reside and about half the world’s irrigated agriculture is in regions that experience water scarcity for at least one month each year.”

The term water gap is used to describe a scenario in which water consumption surpasses the naturally available water supply at any given point within a month. Over time, this type of unsustainable water use leads to the depletion of groundwater, rivers, lakes, aquifers, and other natural reserves of water.

“Water gaps are already an issue for communities around the world, resulting in either inadequate supplies of water or environmental degradation,” Rosa explained. “And as climate change further disrupts precipitation patterns and alters the water cycle, it will add even more stress.”

Previous research efforts have approached this growing challenge from two perspectives. Some investigators quantified the depletion of groundwater or other reductions in environmental water availability on a global scale. And other studies explored unsustainable water use at the regional level. Combining these two sides of water gap research was necessary to comprehensively understand the scope of the issue and make informed water management plans and policies for the future.

“We must be able to balance environmental resilience and the growing need for water in a warming world with a burgeoning population,” Rosa added. “As cities grow, pollution, industrial water use, and irrigation will all increase, which will, in turn, exacerbate the water gap.”

In order to fully assess the future of water scarcity and inform policymakers, Rosa and Sangiorgio quantified water gaps under baseline, 1.5-degree Celsius, and 3-degree Celsius scenarios, accounting for a variety of factors including: groundwater depletion, surface water depletion, and water needs for aquatic ecosystems.

Their work shows that water gaps amounting to nearly 458 billion cubic meters of water per year already exist. These are projected to increase by 6 percent under 1.5 degrees Celsius warming and by 15 percent under 3 degrees Celsius warming.

“Even relatively modest increases in the water gap can put pressure on ecosystems and lead to severe shortages for agricultural use, resulting in food insecurity,” Rosa said.

Resource managers and lawmakers can consider options for increasing water supplies, including investing in resilient infrastructure to enhance water storage capabilities, desalinating saltwater, reusing treated wastewater, and transporting water from other areas to overcome these hurdles. Additionally, farmers could prepare for water scarcity by shifting to less water-intensive crops and investing in more efficient irrigation technologies.

This work contributes to Rosa’s overall research program, which aims to understand the agricultural challenges posed by climate change and assess various ways to improve agricultural sustainability.

Rosa joined Carnegie in 2022 as a Staff Associate—a prestigious program designed to give early career scientists the freedom and independence to pursue bold and unconventional research. Since then, his efforts have included analyses of irrigation strategies, soil moisture-retention techniques, and water storage needs, as well as evaluating solutions to reduce the carbon footprint of fertilizer production and achieve net-zero emissions in agriculture.