The world’s 100 most-populated river basins are indispensable resources for billions of people, companies, farms, and ecosystems. But many of these river basins are also increasingly at risk. As water demand from irrigated agriculture, industrialization, and domestic users explodes, major rivers on several continents are becoming so depleted that they sometimes fail to reach their ocean destinations. Add climate change, nutrient and chemical pollution, and physical alterations like dams and other infrastructure development to the mix and it’s clear that many communities rely on water resources that face an increasingly risky future.
WRI’s Aqueduct project recently evaluated, mapped, and scored stresses on water supplies in the 100 river basins with the highest populations, 100 largest river basins, and 180 nations. We found that 18 river basins— flowing through countries with a collective $US 27 trillion in GDP —face “extremely high” levels of baseline water stress. This means that more than 80 percent of the water naturally available to agricultural, domestic, and industrial users is withdrawn annually—leaving businesses, farms, and communities vulnerable to scarcity.
Periodic, and often serious, droughts only make the situation worse. Stressed river basins can severely threaten regional water security and economic growth, and may even contribute to political instability—especially if a basin does not have adequate water-management plans in place.
Managing Extremely High Water Stress: A Look at the Colorado River
Decision-makers in many of world’s water-stressed basins have attempted to put management plans in place—with mixed results. The United States’ Colorado River is a prime example of a plan that, while well-intentioned, may ultimately be unsustainable. Starting in Colorado and running 1,400 miles to the Gulf of California, the Colorado River is the 14th most stressed among the world’s most populated river basins, and the sixth most stressed if ranked by size. More than 30 million people depend on it for water. The seven states receiving its water comprised 19 percent of the United States’ total GDP in 2010.
Because of its naturally arid setting—and due to its large and growing number of users and resulting high level of baseline water stress—the Colorado has become one of the most physically and legally managed rivers in the world. It is also under serious duress, exacerbated by a decades-long drought. This imbalance between supply and demand means that the river often runs dry before it reaches the Pacific Ocean—posing significant problems for wildlife, ecosystems, and communities that depend on it.
The Colorado River is an example of a basin where natural water stress is already severe. The complex web of infrastructure and governance structures around the river was, in a sense, created to ensure predictable, steady water supplies in a stressed region. On the other hand, that same development has driven increasing demands for limited supplies. Aqueduct’s country and river basin rankings deliberately do not include the effects of such extensive management, instead focusing on objective measures of underlying hydrological conditions. But the overall picture is clear: Even the most-established, iron-clad management systems start to crumble under increasing scarcity and stress.
Managing Stress through Global River Basin Assessments
While each river basin in the world faces unique challenges, Aqueduct’s stress scores and rankings provide a valuable common foundation for stakeholders to manage water-related risks.
Standardized scores help all stakeholders—from governments to development banks to civil society organizations—understand the nature of water security challenges and their potential social, economic, and environmental effects. This information is vital for making better, high-level decisions about where and how to begin to respond to river basin-level risks.
For companies, standardized scores inform better decisions about responding to basin-level hazards. Sustainability managers or operations supervisors know they are comparing each of their facilities in different basins around the world to the same standard. Investors benefit similarly, as they are able to more accurately compare water risks among their portfolio companies.
Shareholders, governments, civil society groups, and others also stand to gain when companies report river basin stress rankings. CDP’s water questionnaire – the leading corporate water risk disclosure platform –asks companies to disclose their water-risk exposure at the river-basin level. As a result, shareholder groups will be more informed when engaging with corporate boards. Public sector stakeholders, such as teachers’ pension funds, can act upon more comprehensive and standardized insights into how river basin-level risks can affect corporate operations.
As the world marks another World Water Day, we must become more knowledgeable about the water security threats we face. River basin-level water risk data is a key tool in moving toward a water-secure future.
What Is Water Stress?
Water stress is the ratio of total water withdrawals to available renewable supply in an area. In high-stress areas, 40 percent or more of the available supply is withdrawn every year. In extremely high-stress areas, that number goes up to 80 percent or higher. A higher percentage means more water users are competing for limited supplies. See the high and extremely high-stress areas highlighted in red and dark red on the maps. For more detailed information, please see Aqueduct’s Global Maps 2.0 metadata document.
A Look at River Basins’ Water Risks
- Baseline water stress: the ratio of total annual water withdrawals to total available annual renewable supply.
- Inter-annual variability: the variation in water supply between years.
- Seasonal variability: the variation in water supply between months of the year.
- Flood occurrence: the number of floods recorded from 1985 to 2011.
- Drought severity: the average length of droughts times the dryness of the droughts from 1901 to 2008.