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The situation is unsustainable, even where adequate distribution systems make inter-basin transfers of water possible; even then increased migration and changing precipitation patterns make future water allocations uncertain. For example, snowmelt water is allocated and conveyed from the Sierra Nevadas (and a portion of the Colorado River) to southern California, which is home to more than 20 million people but only has enough precipitation to provide water for about 1 million people. Because of decreasing snowfalls in the Sierra Nevadas, we have created a situation that precludes further growth in southern California. In fact, even the current population is at risk in times of drought.

Climate Change
In 2007, the United Nations Intergovernmental Panel on Climate Change (IPCC) issued its fourth assessment, a consensus report based on work by hundreds of scientists in dozens of countries (IPCC, 2007). According to the IPCC, our climate is changing, primarily as a result of emissions of greenhouse gases (GHGs) (i.e., human activities). The temperature is already 0.76°C warmer than it was from 1850 to 1899 (Figure 2), and it is likely to increase by 2.0 to 4.5°C (with a best estimate of about 3°C) during the 21st century. In addition, extreme events, such as heat waves, droughts, and increased-precipitation events (floods) will become more frequent.

FIGURE 2 Global temperature changes from 1880 to 2005. The annual average temperature (averaged for the entire planet for all seasons) has increased about 0.8°C in the past 125 years. Source: Adapted from Hansen et al., 2007.

Increases in precipitation are very likely in high latitudes, while decreases are likely to occur in most subtropical regions, continuing recent trends. This means that regions like the southwestern United States and Mexico, Central America, Brazil, southern Europe and the Mediterranean, northern and southern Africa, the Middle East, and western Australia will receive much less precipitation (10 to 30 percent less than they did from 1980 to 1999). Decreases in precipitation in Africa, Latin America, and southern Asia already threaten billions of poor people who can least afford to respond to the challenges of a warmer, drier world.

We are already experiencing human-induced changes in climate. Arctic ice, permafrost, and continental glaciers are melting rapidly. The Ganges River, which supplies water to 450 million people and is fed by glaciers, is destined for eventual decline. Stationarity, the scientific term for when statistics are not changing and conditions are constant, is a thing of the past (Milly et al., 2008). We can no longer count on the mean precipitation or even on traditional annual variability in precipitation.

In such a scenario, it is almost impossible to plan for the future. Most climatologists are less concerned about the increase in mean global temperature and precipitation than they are about the extremes (heat waves, droughts, and floods). We must, somehow, make plans for living in a world with rapidly changing water resources.

Changes in Land Use and Energy Choices
In an effort to develop systems in which citizens can prosper, we convert land to agricultural and industrial uses that require large amounts of water and, in the end, degrade water quality. Every year in the tropics, countries such as Brazil, Malaysia, India, and Indonesia clear huge tracts of forest for agricultural development. Every year in the United States, almost a million acres of land are converted to impervious cover, mostly highways, parking lots, and strip malls, which increases runoff and decimates urban stream ecology. Development is greatest in coastal counties where 53 percent of Americans now live.

In addition, because oil is in short supply and extremely expensive, many countries, such as Brazil, countries in Europe, Malaysia, Japan, China, and the United States, have adopted biofuels as a strategy for reducing, or at least stabilizing, oil imports. “Energy security” and “energy independence” have become the watchwords in these countries. In the United States the emphasis is on ethanol production from corn. In other countries, ethanol is produced from sugar cane and sugar beets, and biodiesel is produced from canola, sunflower, palm, and soybean oils.

However, biofuels are not sustainable, at least not in the way we practice row-crop agriculture today. Far too many nutrients run off the land causing eutrophication of nearby waters, and far too much soil erodes for biofuels to be considered sustainable in the long run. We need a crop system that is perennial, that minimizes (or eliminates) tillage, and that holds soils and nutrients in place.

As Figure 3 shows, ethanol production in the United States depends on intensive, high-input corn as feedstock. The intensive agriculture necessary to supply this corn requires about 8 grams of nitrogen (as N) fertilizer and results in 10 to 20 kilograms of soil loss for every gallon of ethanol produced. All of these nutrients run down the Mississippi River to the Gulf of Mexico where they exacerbate hypoxia (i.e., low concentration of dissolved oxygen), which causes shrimp, crabs, and fish to vacate large sections of the Gulf, 20,000 km² in 2007 (Alexander et al., 2008).

Figure 3 also shows that most U.S. ethanol production facilities are located in the rain-fed Midwest (NRC, 2008). But in the high plains of Nebraska, Kansas, and Texas, cornfields are irrigated with water from the Ogallala Aquifer, which is already overdrawn. It takes about 1,000 gallons of water to produce one gallon of ethanol from corn grown with irrigation water. Therefore, it would take the equivalent of the water supply of a city of more than 2 million for a single facility (a single dark circle in Figure 3) to produce 100 million gallons of ethanol per year.

FIGURE 3 Locations of ethanol-production facilities, both existing and under construction in 2007. Source: Renewable Fuels Association, 2008.

In addition, ethanol production facilities require considerable amounts of water. Each dark circle requires 3 to 4 gallons of water to produce one gallon of ethanol. Thus a facility that produces 100 million gallons per year would use more than 300 million gallons of water, which would come either from surface water or an aquifer. Many aquifers in the Midwest, such as the Cambrian-Ordovician unit in Iowa and Illinois, have already lost more than 100 feet of pressure head through excessive withdrawals.

Most Americans do not realize how far we are from the balance necessary for sustainability. Even if we devoted all of our agricultural land to biofuels, we would still not produce the transportation fuel necessary to supply our 220 million cars and trucks. Americans consume 3 to 4 gallons of petroleum per person per day. We have neither the land nor the water to grow our way out of this problem.

In addition, biofuels policies in Europe and the United States contribute to higher prices for corn and, thus, higher prices for food, which is increasing hunger and poverty around the world. According to life-cycle analyses, biofuels may not even help reduce greenhouse gases.

Perennial prairie grasses or trees would provide cellulosic feedstock for ethanol production far superior to feedstock from corn. Switchgrass, which was once ubiquitous on the Great Plains, could be so again. This would restore bird habitats, improve water quality, and sequester carbon dioxide in the soil.

However, using switchgrass (or agricultural wastes) effectively as a feedstock for ethanol would require a breakthrough in technology, such as the development of enzymes that can break down cellulose into starch and sugars for fermentation or a commercially viable process for the thermochemical conversion of cellulosic materials by gasification. Either of these may take several years.

Global Poverty
One of the UN Millennium Development Goals is the alleviation of global poverty, reflecting a consensus among development professionals that we cannot solve other problems until the issue of global poverty is addressed. More than 2 billion people live on less than $2 per day. As long as 1.1 billion people do not have clean drinking water, and 2.4 billion do not have adequate sanitation, and 1.4 million children die every year from clearly preventable waterborne diseases, no progress can be made on reversing climate change, deforestation, or the loss of species. The developed world must help developing countries solve their pressing problems before they can help us address global issues. Today, however, their children are still dying.

Will there be enough fresh water for 9 to 10 billion people in 2050? We already appropriate 54 percent of fresh water resources (Postel et al., 1996), and the average supply of water per person is decreasing as the number of megacities and coastal development increases and rainfall distributions continue to change. The United Nations estimates that 700 million people suffer from water scarcity today, and as many as 3 billion could face water shortages by 2025 (UN News Service, 2007).

Egypt has the smallest amount of fresh water per capita of any major country, less than 26 cubic meters per year. Survival is possible because Egypt imports “virtual water,” that is, liquids from fruits, vegetables, and other products that require a great deal of water where they are grown. In addition, the country has large national agricultural areas in the Nile River Basin and, more recently, in the middle of the desert (e.g., the Toshka project, an oasis where crops are raised using groundwater and drip irrigation) (Martin, 2008). However, as Elie Elhadj, author and water specialist in the Middle East, has said, “You can bring in money and water, and you can make the desert green until either the water runs out or the money” (Martin, 2008). In the long run, this scenario is simply not sustainable.

The Next Steps
Mitigation, Treatment, Action
The first thing we must do is to mitigate the causes of water shortages as much as possible. According to most demographers, population growth will level off sometime in the 21st century. Through education and the empowerment of women, we may be able to limit population at the “medium” projection in Figure 1.

The prospects for mitigating climate change depend on global governmental resolve to decrease emissions of GHGs by 80 percent by the end of the 21st century. At that level the atmospheric concentration of carbon dioxide would be stabilized at approximately 450 parts per million (Hansen et al., 2007; IPCC, 2007). Developed countries would have to take on the heaviest responsibility for early cutbacks in emissions (25 to 40 percent by 2025 and 80 to 95 percent by 2050), and developing countries would be required to follow suit as their economies begin to prosper.

Governments in developed countries must challenge their people to use less energy and encourage a massive conversion to wind power (which is already economical), plug-in hybrid or electric cars refueled by electricity produced from wind energy, and water- and energy-efficient buildings. In the United States, this will require daring changes in policy, such as a revenue-neutral decrease in income taxes and an increase in carbon taxes.

Energy efficiency and renewable technologies can be the engine for economic growth and the creation of green-collar jobs. In Iowa, for example, five new wind-power manufacturers now provide thousands of high-paying manufacturing jobs. The end of the age of fossil fuels will prove to be the turning point of this century. The transition away from dependence on nonrenewable resources will be what Harvard economist Joseph Schumpeter once called “creative destruction,” an economic revival that replaces an old system with a better one for the future.

Water Conservation
Water conservation in the United States will be essential. Many people think that water is scarce only in the Southwest, but a large portion of the country is using up its water supplies through the exploitation of aquifers and the degradation of surface waters from non-point source pollution. Figure 4 shows the geographical areas where water is under stress as a result of industrial and agricultural withdrawals from the water supply. We can only hope to address our future water needs through better water-treatment systems, the recharging and reuse of aquifers, and water conservation.

FIGURE 4 Water stress (water withdrawals/annual precipitation) in the contiguous United States. Areas with water stress greater than 1.0 (darkest categories) use more water than falls on that area of the country via precipitation. Source: K.J. Hutchinson, M.S. thesis, University of Iowa, 2008, adapted from PRISM, 2006 and USGS, 2005.

Desalination will also be important for meeting future water needs. More than 15,000 desalination plants (mostly using reverse osmosis) are in operation in 125 countries with a total capacity of 32 million cubic meters of water. As the cost of desalination processes come down, capacity will continue to rise (Zimmerman et al., 2008).

Ideally, water reuse, such as flushing toilets with gray water, will become the norm. Aquifer storage and recovery will prevent the evaporation of precious water supplies and help to recharge depleted aquifers. Novel, high-quality treatment regimes will ensure that water is treated appropriately for different uses. Engineers and scientists will find ways to protect watersheds from pathogens, pesticides, and endocrine-disrupting chemicals like hormones and pharmaceuticals, which are now present in both wastewater and drinking water.

Adapting to a Changing World
Some things cannot be changed or mitigated, and for those we must adapt as best we can. The average availability of fresh water from rivers and ground-water (Figure 5) is likely to decrease drastically. Many countries in Africa, the Middle East, and parts of Asia that are particularly short of water also have the largest, fastest growing populations and the highest levels of poverty. It is incumbent on the developed world to help them meet their water-supply and sanitation needs.

FIGURE 5 Map of global freshwater resources per capita from accessible rivers and groundwater indicating that in many countries less water is available than is recommended (<1700 m3/capita/year) according to the World Resources Institute and the United Nations Environment Programme. Sources: UNEP, 2002. Reprinted with permission.

Engineers are well suited to make a positive difference. We can teach, we can create appropriate technologies, and we can serve in ways that scientists are sometimes reluctant to undertake. For example, Engineers for a Sustainable World, Engineers without Borders, Inter-national Rotary, and many other groups offer people-to-people programs that provide assistance for professional development.

Adapting to a changing world may simply mean working together within a common framework to improve water quality. For example, World Water Monitoring Day (WWMD), sponsored by the Water Environment Federation, was initiated in 2002 as an international outreach program to increase public awareness and involvement in protecting water resources. More than 80,000 participants worldwide are monitoring streams, rivers, lakes, and estuaries in 50 countries for dissolved oxygen, transparency, temperature, and pH. To join, one simply registers a monitoring site, purchases a rudimentary test kit for about $20, monitors during the test period of September 18 through October 18, and enters the results on the organization’s website (www.worldmonitoringday.org).

Imagine if millions of 5th graders throughout the world were enlisted to monitor water sites. Just suppose that tomorrow at noon every schoolchild walks to a creek, stream, lake, or drinking water source near his or her home and records a scientific observation—the temperature, clarity, pH, or dissolved oxygen in the water at that site. They then file their data via the Internet, and the next day they collectively publish a map of worldwide water quality. We can hope that they will also think, or are taught, about the science behind the results and that they will be motivated to improve the environment. These volunteers would constitute a network of “water watchdogs” for the entire planet. This is the kind of project that can transcend geopolitics.

Modeling, Predicting, and Forecasting
Some engineers are already embracing new technologies that are capable of making a positive difference for the environment. One such effort is the WATERS Network (Water and Environmental Research Systems Network), a $300 million proposal to the National Science Foundation for a capital investment to revolutionize the modeling, predicting, and forecasting of the quantity and quality of water (Montgomery et al., 2007).

Figure 6 is a schematic drawing of a field facility, one node in a national network of sites that span the physiographic characteristics of water resources throughout the country. The facility makes use of breakthroughs in technology, like novel sensors, wireless and broadband technologies, high-performance computing, and real-time data assimilation, to predict and forecast the types and amounts of water constituents (nutrients, sediments, pathogens, and emerging chemical contaminants). Such a system could be used to control or warn of the likelihood of floods, harmful algal blooms, the entry of disease-causing microorganisms into a water supply, or Gulf hypoxia.

FIGURE 6 An environmental field facility in the proposed WATERS Network. The facility uses breakthrough technologies to predict and forecast capabilities for water-quality constituents (e.g., nutrients, sediments, pathogens, and emerging chemical contaminants).

This national initiative will use real-time environmental sensing to conduct multi-scale research and experimentation on U.S. water resources. The WATERS Network will integrate, complement, and leverage existing investments in water monitoring operated by various federal and state agencies, as well as river-basin commissions and others.

The goal of the WATERS Network is to improve our understanding of Earth’s water resources and related biogeochemical cycles, which could lead to better management of critical water processes that interact with human activities. Through the WATERS Network, hydrologists and environmental engineers will develop skills in predicting water availability and quality, and economists and social scientists will improve forecasts of water availability and provide reliable input for decision makers.

Modern networks like WATERS can provide a way for us to address critical science and engineering questions to mitigate and adapt to the changes threatening our water resources. Data fusion and assimilation techniques that can “bootstrap” model performance, prediction, and forecasting of water quality and quantity throughout the country could lead to more efficient and effective water and wastewater treatment and collection systems. WATERS represents just one initiative that might help us learn to live with a changing water environment.

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About the Author
Jerald L. Schnoor is Allen S. Henry Chair Professor, Department of Civil and Environmental Engineering, University of Iowa, and an NAE member.

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