Water resources represent one of the most serious environmental issues of the twentieth century. Water is abundant globally, yet millions of people have inadequate fresh water, and droughts plague rich and poor countries alike. Water pollution compounds the scarcity of usable fresh water and threatens the health of millions of people each year. At the same time, the ravages of flooding and catastrophes associated with excessive rainfall or snowmelt cause death and destruction of property. To cope with these problems, water resource management has become a high priority worldwide.
Concerns about water scarcity seem unwarranted, considering that there are 326 million mi3 (1.36 billion km3) of water on earth. Although 99% of this water is either unusable (too salty) or unavailable (ice caps and deep groundwater storage), the remaining 1% can meet all future water needs. The total volume of fresh water on earth is not the problem. Scarcity of fresh water results from the unequal distribution of water on earth and water pollution that renders water unusable.
Fresh water is not always available where or when it is needed the most. In Lquique, Chile, for example, no rainfall was measured for 14 consecutive years, from 1903 to 1918. At the other extreme, Mount Waialeale, Kauai, Hawaii, averages 460 in (1,168 cm) of rainfall per year. Even such extremes in annual precipitation do not tell the complete story of water scarcity. For example, in the tropics, storms in the rainy season can deposit from 16 to over 39 in (40.6 to 99 cm) of rainfall in two to three days, often resulting in widespread flooding. However, the same areas can experience negligible rainfall for two to three months during the dry season.
The demand for water varies worldwide, with wealthier countries consuming an average of about 264,000 gallons (1,000 m3) per person, per year. In contrast, over one-half of the population in the developing countries of North Africa and the Middle East live on a fraction of this amount. Population growth and droughts have forced people to use water more efficiently. However, water conservation alone will not solve water scarcity problems.
Increasing demands for water and the disparity of water distribution have sparked the imagination of hydrologists and engineers. Grandiose schemes have emerged, including towing icebergs from polar regions to the lower latitudes, desalinization of ocean water, cloud seeding, and transporting water thousands of kilometers from water-rich to water-poor regions. Although many of these ideas are fraught with environmental, economic, and political concerns, they have placed water supply issues in the international spotlight.
Historically, more conventional, large public investment water development schemes have been a vehicle for economic development. As a result, about 75% of the fresh water used worldwide is used for irrigation , with 90% used for this purpose in some developing countries. Much of this water is being wasted. Poorer countries do not have the technology to irrigate efficiently, using twice as much water to produce one-half the crop yields of wealthier countries.
Multi-purpose reservoir projects that generate hydroelectric power, control flood, provide recreational benefits, and supply water have become commonplace worldwide. Hydroelectric power has fostered both municipal and industrial development. Since 1972, 45% of the dams constructed with World Bank support were primarily for hydropower, in contrast to 55% for irrigation and/or flood control. Although the pace of dam construction has slowed worldwide, large projects are still being constructed. For example, the proposed Three Gorges Dam on the Yangtze River, China, will cost at least $10 billion and will be the largest hydroelectric power project in the world. It will generate one-eighth of the total electrical power that was generated in China in 1991.
Dams and water transfer systems constructed for economic benefit often carry with them environmental costs. Wildlife habitat is flooded by reservoir pools, and streamflow volumes and patterns are altered, affecting aquatic ecosystems. The modification of flow by dams in the Columbia River of the United States has either eliminated or severely reduced natural spawning runs of salmon in much of the river. The reservoir created by the Three Gorges Dam will flood one of China's most scenic spots and will force over one million people to relocate. Already there are concerns that high rates of soil erosion and sediment deposition behind the dam will threaten the usefulness of the project. The relocation of people in response to water resource development can also bring unwanted environmental consequences. In developing countries, relocated people seek new land to cultivate, graze livestock, or build new villages, often accelerating deforestation and land degradation.
Small-scale projects offer environmentally attractive alternatives to large dams and reservoirs. Mini-hydroelectric power projects, which do not necessarily require dams, provide electricity to many small villages. Rainfall harvesting methods in drylands provide fresh water for drinking, livestock, and crops. Flood plain management is environmentally and economically preferable to large flood control dams in most instances.
Groundwater provides large volumes of fresh water in many regions of the world. A proposed $25 billion irrigation project in Libya would pump nearly 980 million yd3 (750 million m3) of groundwater per year in the Sahara to be transported 1,180 mi (1,900 km) north. Groundwater supplies in the Sahara are thought to be nearly 20 trillion yd3(15 trillion m3). However, there is concern that such pumping will drop water levels 8–20 in (20–50 cm) per year, eventually causing water that is too salty for irrigation to intrude. Groundwater mining occurs if water is pumped faster than it is replenished. Such mining is occurring in many parts of the world and cannot provide sustainable sources of water.
Water requirements for urban areas pose formidable challenges in the coming years. With 90% of the population growth expected to occur in urban areas over the next few decades, competition for fresh water between rural agricultural areas and cities will become severe. With urban areas able to pay higher prices for water than rural areas, legal and political battles over water rights and subsidy issues will likely ensue. In many cities, however, finding sufficient sources of fresh water will be difficult. For example, Mexico City has a rapidly growing population of over 22 million as of 2002. Fresh water from lakes and springs have already been exhausted. Groundwater is being mined three times faster than the rate of recharge. Also, a daily discharge of 29 million lb (13 million kg) of sewage plus industrial wastes threaten groundwater quality. Furthermore, groundwater pumping is causing land to subside around the city. Unfortunately, many other large cities around the world are faced with equally challenging problems of water supply and pollution.
Flooding and droughts are global concerns that lead to famine in the poorer countries and will persist until solutions are found. Flood avoidance or flood plain management are not commonplace in many such countries because people have no alternative places to live and farm. The recurring floods and devastation in Bangladesh, and the droughts of North Africa emphasize the dilemma of the poorest of countries.
In contrast to problems of water quantity, water pollution accounts for over 5 million deaths per year, largely the result of drinking water that is contaminated by human and livestock waste. Inadequate sewage treatment and a lack of alternative fresh water supplies can be blamed. These problems can be solved but will require that water quality issues become a high priority in terms of policies, institutions, and financial support.
Water pollution plagues rich and poor countries alike. Municipalities and industries pollute streams and ground-water with toxic chemicals , sewage, disease-causing agents, oil, heavy metals , thermal pollution , and radioactive waste . Polluted water from municipalities and industries can and should be treated before it is discharged. Environmental laws and enforcement can ensure that this happens.
Agricultural development has made significant strides in solving food problems in the world, but it has also contributed to water pollution. Water supplies have become polluted as a result of heavy fertilizer and pesticide use. The focus on sustainable agricultural practices that do not rely so heavily upon fertilizers and pesticides offer some promise. Sensible use of chemicals and the adoption of "best management practices" also offer a means of meeting food requirements of growing populations without contaminating water supplies.
Just as food security issues attracted global attention through the 1950s to 1970s, similar efforts will be needed to provide for water security in the twenty-first century. Long-term, holistic, and interdisciplinary solutions are needed. The crises management approach of the past—that of attempting to deal with droughts, floods, and contaminated water only when they are upon us—cannot continue.
We currently have the technology to solve most water resource problems. Implementing solutions are often constrained by inadequate policies, institutions, financial resources, and political instability. In many ways, people management is more critical than water resource management. With human populations continuing to grow, water scarcity, flooding, and disease and death from contaminated drinking water will become even more pronounced.
[Kenneth N. Brooks ]
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"Water Resources." Environmental Encyclopedia. . Encyclopedia.com. (May 22, 2019). https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/water-resources
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