New Study: 21 Global Water Scarcity Hotspots Identified, Classified into 7 Hotspot “Clusters” with Shared Water Challenges

WASHINGTON, D.C. (April 25, 2024) - A new study released today identifies 21 global water scarcity “hotspots,” where there is a significant “water gap” between human demand for water and renewable available supply. The team of Utrecht University researchers analyzed each of the 21 hotspots to determine what’s driving water scarcity at each location. Hydroclimatic change, population growth, and agricultural, domestic, and municipal water use are the biggest pressures affecting both the quality and quantity of available water, researchers found. The study in Environmental Research Letters also classifies the 21 hotspots into seven “clusters,” based on common drivers of water scarcity.

About one third of the global population is affected by water scarcity for at least one month per year. In these areas, the overuse of freshwater resources can lead to a “water gap” and threat of depletion, making them global water scarcity hotspots, said the study, which is supported by the National Geographic Society’s World Water Map and Freshwater Initiative.

Researchers identified the 21 hotspots through a combined approach of hydrological modeling and a literature review of 300 case studies. Hotspots were classified as water provinces where the water gap exceeds 0.015 meters per year. Additionally, to identify and characterize hotspot clusters by similarities and differences, the team applied a Drivers, Pressures, States, Impacts and Responses (DPSIR) framework to the literature.

Example of the most important water scarcity Drivers, Pressures, States, Impacts and Responses (DPSIR) in the Indus Basin. The colors of the text boxes with system processes correspond to the respective DPSIR component from the legend in the bottom right. Black arrows in the legend indicate how DPSIR components affect each other. Colored arrows in the figure give spatial direction to corresponding system processes. Image courtesy of Utrecht University.

Myrthe Leijnse, Utrecht University

“We started with two questions: where does water scarcity occur, and why is it happening? While we found water scarcity has similar drivers in some hotspots, the impacts on people, ecosystems, and economies - as well as societal and policy responses - could vary widely place to place,” said Myrthe Leijnse, the lead author of the study and a researcher at Utrecht University. “We hope this study demonstrates to policymakers that if there are common contributors to water scarcity, there could be common solutions to addressing it.”

The seven “hotspot” clusters are:

1. Water treatment and desalination: Arabian Peninsula. Unlike other hotspots, this region faces a unique combination: low natural water availability (highlighted in 89% of case studies) and high per capita water consumption (42%), leading to groundwater depletion and reliance on unconventional water sources (desalination and water treatment). Economic growth from oil and natural gas discovery has also fueled urbanization and population growth, further intensifying water demand.
   
2. Hydroclimatic change: Central Chile, Spain, Murray-Darling (Australia), Japan. These hotspots have faced consecutive droughts and a decline of total annual rainfall. At the same time, these hotspots have effective acts and agreements that support sustainable use of water resources (including water treatment, water rights, and increased storage capacity). Unlike most other hotspots, population growth is not a major driver of water scarcity in these locations.
   
3. Agricultural water use: North China Plain, Central Valley California, US High Plains, White Nile Sudan, Nile Delta, Italy, Greece, and Turkey. This is the largest cluster by number of hotspots, containing eight of the 21. Their single commonality is high agricultural water use (mentioned in 29-100% of case studies).
   
4. Population growth: Indus and Ganges River Basins: The Indus and Ganges River Basins have experienced rapid population growth over the last decade (reported in 40-67% of case studies), impacting society and the ecosystem. Water scarcity has led to reduced food production (24-33%), conflict and migration (28-33%), and health concerns (17-56%). The lack of water regulation has also resulted in unregulated private wells and subsequent groundwater depletion (52-61%).
   
5. Surface and groundwater depletion: Coastal Peru and Iran. Peru and Iran are the only hotspots where both surface and groundwater depletion are reported in over 60% of case studies. Both hotspots report contamination and salinization of water resources. Conflict and rural-urban migration (45-50%) are also prevalent due to water scarcity and inequality of water supply.
   
6. Land subsidence: Mexico, Java (Indonesia), and Vietnam. All show above average values of industrial (30-71%), municipal (40-75%) and agricultural (70-100%) water use. While these values are also reported in other clusters, Mexico, Java and Vietnam have one common impact that is unique compared to other hotspots: land subsistence (10-27%), the gradual settling or sudden sinking of the Earth's surface. This is likely due to groundwater overexploitation.
   
7. Virtual water trade: Thailand. In Thailand, virtual water trade (43%) is a significant factor driving water scarcity. Thailand is one of the world’s biggest rice exporters, shipping about one third of its rice production. However, case studies had limited information on policy responses to address water scarcity in Thailand.

Myrthe Leijnse, Utrecht University

"Water scarcity doesn’t always look like a lake or river drying up in an arid climate, but can also manifest itself in wetter climates as temporarily low streamflow or falling groundwater levels. It has many diverse, complex drivers, whether that’s producing water-intensive crops or goods for global trade, rapid population growth, or inefficient use of water in our towns and cities,” said Marc Bierkens, National Geographic Explorer and professor of hydrology at Utrecht University.

Niko Wanders, project lead and associate professor of hydrological extremes at Utrecht University, adds, “by zooming in on these hotspots, we can understand the development of water scarcity in a regional context. We hope these insights can help us find better targeted solutions to alleviate water scarcity. Also, by comparing drivers and solutions between hotspots, we hope to equip policymakers with insights to help close the water gap.”

The Society’s World Freshwater Initiative supports grantees in science, conservation, education, and storytelling, who are illuminating water scarcity issues - as well as sustainable solutions - in these hotspot areas and beyond.

“The identification of these 21 water scarcity hotspots is a critical addition to our understanding of global water and how people, wildlife, and nature use it. A complement to the World Water Map, the hotspots help tell the story of our irreplaceable freshwater resource and are part of our ongoing commitment to illuminate and protect the wonder of our world,” said Alex Tait, The Geographer at the National Geographic Society. “This study embodies the power of the geographic approach: observe the world around us, gather and analyze data, and generate powerful insights about how people interact with water.”

Myrthe Leijnse, Utrecht University

Data Availability Statement

The model output of PCR-GLOBWB for the global water gap are openly available on https://worldwatermap.nationalgeographic.org/. Supplementary data is available on Zenodo https://doi.org/10.5281/zenodo.10591425.