Thoughts From Engineers: Water Scarcity is Common: The Grim Reality of Freshwater Supplies Worldwide
Most news headlines barely get my attention, but it was startling to come across a list of 11 cities projected to experience serious water shortages within the next 50 years due to a combination of polluted and diminishing water supplies, climate change and population growth (bbc.in/2Mj16HR). Some of the major urban centers at risk for severe water shortages won’t surprise you; others surely will. The mix of cities with looming water shortages include Beijing, Cairo, Cape Town, Tokyo, London, Miami and a few others. A more recent list (bit.ly/33ufD8Z) includes Lincoln, Neb., San Francisco and Denver.
These are cities with tens of millions of inhabitants. These are long-established, productive metropolitan areas where, in most cases, a continuous supply of drinkable water was a near certainty. Desperate populations are elsewhere, we reason, in rural, impoverished regions on the other side of the planet. Yet water-supply issues are occurring in areas that previously were considered “safe” from water shortages and in a range of communities: affluent and poor, historically water rich and not. This is becoming a defining feature of life in the 21st century: Water supply is the new equalizer, as it spares no one.
Global Water Scarcity, Month to Month and Region to Region
In an article published in the February 2016 issue of Science Advances, “Four billion people facing severe water scarcity” (bit.ly/2H5jmAk), Mesfin Mekonnen and Arjen Hoekstra from the University of Twente in the Netherlands reveal that severe water scarcity is common, and communities across the globe are grappling with water scarcity much more frequently than previously thought.
Mekonen and Hoekstra looked at the issue of global water scarcity at a much smaller geographic and time scale than had previously been carried out in earlier investigations. Previous studies examined the question of water scarcity at a much larger geographic scale (e.g., a river basin) and from year to year. The authors of this study argue that the extreme variability in water supply and demand which can occur from month to month are hidden when only the yearly average is considered. To truly understand inter-basin supply and demand, the authors argue it’s important to look at a region’s monthly need for surface water and groundwater in relation to monthly water supply.
Each Community has a “Blue Water Footprint”
This study focused on the ratio of the blue water footprint to the total blue water availability in a region. The “blue water footprint” is equal to the fresh surface water and groundwater not returned to the watershed because it’s either consumed by irrigation or lost through evapotranspiration or other usage. The “blue water availability” value is the sum of the runoff found within the study area, minus natural flow requirements and the water footprint of the adjacent region located directly upstream. This way, water consumed upstream also is considered.
Who Needs Water and When?
The results showed that high variability in water scarcity occurs from month to month due to seasonal water demands and fluctuating rainfall patterns. Some countries experience moderate to severe water scarcity for more than six months of the year (northern Mexico, parts of the western United States, Southern Africa, Pakistan and the Middle East, among others). Cities in which there are large populations (e.g., London) as well as high levels of water-intensive agriculture or a combination of the two, such as in China and India, experience high water scarcity as well.
In some areas, rates of water consumption are highest during months when water availability is low. This is the case in the Limpopo river basin in South Africa as well as the Ganges river basin in India. Their analysis showed that at certain times of the year when agriculture is most intense, river flows and groundwater levels are low due to reduced precipitation due to climate change. Rivers now are running dry before reaching their natural outlets, as the Colorado River does before reaching the Pacific Ocean.
Up to 4 Billion People Scramble for Water at Least One Month a Year
Their study made a number of major conclusions, namely that up to 4 billion people experience severe water scarcity at least one month every year. In the authors’ words: “freshwater scarcity is becoming a threat to the sustainable development of human society.”
How do communities worldwide deal with recurring shortages? Strategies take a variety of forms depending on municipal resources and other factors. In large, wealthy municipalities, the scramble to secure water gets done quietly under the radar to keep panic at bay. Las Vegas, for example, has stringent water-recycling regulations in place; more than 90 percent of the water used is recaptured, and new housing construction can’t come with a lawn. By contrast, in India, residents walk miles to find clean water. In Mexico City, water is imported by train and truck.
Developing Sustainable Water Footprints
Mekonnen and Hoekstra acknowledge that their investigation didn’t include the impacts of water withdrawal or evaporation from artificial reservoirs or inter-basin transfers. Also, changing patterns in precipitation due to climate change weren’t considered, but they suggested climate change variability would likely aggravate existing findings.
As economies and populations continue to grow unfettered and the demand for agricultural irrigation, modern living and other uses increase, long-entrenched patterns of water usage will need to be questioned and reexamined.