agricultural technologies, water supply and distribution, and health technologies. These achievements have certainly improved the quality of life for everyone in the twentieth century. In addition, they have accelerated the massive global shift of populations to urban centers. In this country, 50 percent of the population was engaged in farming at the turn of the previous century in contrast to 2 percent today. A century ago, cities with a million inhabitants were rarities; today megacities of 10 million are becoming all too common, mostly in countries that are ill-equipped to handle these large concentrations of people.

Urban centers are an important focus area for Earth systems engineering because they have impacts that extend far beyond their urban centers. For example, large cities create their own microclimates through local changes in albedo (light reflection), heat generation, and humidity. And their waste streams can pollute local and regional bodies of water, even such large areas as the Bay of Bengal. Cities rely not only on technologies and infrastructural concepts of the twentieth century, but also on those of the nineteenth century. To compound the problem, cities, regions, and nations spend a good portion of their gross national products enlarging, modifying, and repairing this infrastructure without examining whether the fundamental design of urban systems is appropriate or whether new approaches might be more effective. As cities grow, the size, complexity, cost, and, scale of existing technologies used to transport goods and services must be reexamined. Urban centers should be designed to meet the needs of tomorrow.

As an example, let’s look at water supply and distribution and their complements, wastewater and sewage. The provision of a potable water supply and reliable distribution have been major accelerants to the expansion of urban centers. About 200 years ago, as cities in the United States began to grow, they had to look beyond local ponds, wells, and cisterns for water supplies. In 1801, Philadelphia was the first U.S. city to install a water system; Cincinnati soon followed in the 1820s, New York in 1841, and Boston in 1848. By 1860 the 16 largest cities in the United States had installed a total of 136 water systems (NRC, 1984).

The realization of abundant (if not unlimited) water supplies enabled cities to switch technologies from the use of privy vaults, cesspools, and private sewers for wastewater and sewage disposal to a technology that used large amounts of water as the medium for diluting and transporting wastes beyond the city boundary. In the intervening years, the main supplement to these systems has been the treatment of wastewater streams before discharge.

In 1850, or even 1950, this approach might have been acceptable. But we must ask ourselves if it is the best approach for the twenty-first century megacity? If we could go back to square one and systematically examine the use of water and the disposal of wastes, would we choose to use existing technologies? Can we afford to use freshwater, our most critical resource, as a medium for diluting and transporting waste and then turn around and treat this high-volume stream to make it acceptable for discharge into the environment? Should we create more

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