Mexico City's Water Supply: Improving the Outlook for Sustainability (1995)

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THE MEXICO CITY METROPOLITAN AREA 4 2 The Mexico City Metropolitan Area For historical and political reasons, Mexico is a very centralized country in spite of efforts made by the government in recent years to move towards decentralization. Consequently, government services and industrial development have concentrated in Mexico City. Forty-five percent of the country's industrial activity and 38 percent of its gross national product are located here. The city houses nearly all government offices, international businesses, cultural activities, and the most important universities and research institutions. Rapid growth over the past 50 years has been characterized both by planned urban and residential areas for the middle and upper class, and by unplanned and illegal land appropriations by immigrants to the peripheral areas. Over time, government authorities have intervened in these irregular settlements to supply urban services, including water supply; although, the services remain inadequate for long periods of time. Mexico City is situated in the southern part of the Basin of Mexico, an extensive, high mountain valley at approximately 2,200 meters above sea level, and surrounded by mountains of volcanic origin that reach altitudes of over 5,000 meters above sea level. The major political jurisdictions of the basin are the Federal District that houses the nation's capital, most of the state of Mexico, and smaller portions of the states of Hidalgo, Tlaxcala, and Puebla (see Figure 2–1 ). The area commonly known as Mexico City was traditionally associated with the north central area of the Federal District. With the increased urbanization that has occurred over the past decades, a larger metropolitan area has been designated that contains the entire Federal District and all or portions of the states of 17 counties in the neighboring State of Mexico. Political divisions of 

THE MEXICO CITY METROPOLITAN AREA 5 FIGURE 2–1 The Mexico City Metropolitan Area (MCMA) is composed of the entire Federal District (with 16 counties) and all or portions of 17 counties of the State of Mexico. The approximate MCMA boundary is indicated by the wide, patterned line. The inset shows the location of the MCMA within the hydrologic boundary of the Basin of Mexico, and boundaries of other states—Mexico, Hidalgo, Tlaxcala, and Puebla—that partially fall within the Basin. 

THE MEXICO CITY METROPOLITAN AREA 6 Photo 2–1 Aerial view of downtown Mexico City. Courtesy of Robert Farvolden. Mexican states are known as municipios. Likewise, the Federal District is divided into 16 political delegaciones. For the purposes of this study, the metropolitan area is known as the Mexico City Metropolitan Area or MCMA, and the political subdivisions of both jurisdictions will be referred to as counties (Figure 2–1). With an area of 3,773 square kilometers, the Mexico City Metropolitan Area is one of the largest and most rapidly growing urban centers in the world. Population figures for the MCMA are inexact. In 1990, the population was officially estimated at 15 million people and projected to exceed 22 million by the year 2000 (INEGI, 1991a). Population and development pressures have 

THE MEXICO CITY METROPOLITAN AREA 7 naturally led to difficulties in planning and provision of the limited water resources available. While the rate of population growth within the north central urbanized portions of the Federal District has slowed and even declined since the 1980s, immigration to the surrounding jurisdictions, especially in the State of Mexico, has been responsible for significant population increase and urban expansion within the greater metropolitan area. Various forms of illegal or irregular settlements have been of particular concern for water resource planning. Many of these settlements, known as “lost cities” (ciudades perdidas) or “popular colonies” (colonias populares), become more or less established over time. Public services are eventually provided, but often remain incomplete for long periods. The newest immigrants often occupy the steep upland areas, which further complicates the delivery of water and sewer service (see AIC-ANIAC, 1995 for further details on population growth in the MCMA). The long history of the southern portion of the basin as an urban center, beginning with the Aztec capital of Tenochtitlán in the fourteenth century, attests to its attraction. The hydrology of this region includes an excellent aquifer system and natural springs. Nevertheless, the unusual physical setting of Mexico City— situated in a high, naturally closed basin—uniquely challenges the provision of water for a large urban population. The location of the city on an old saline lake bed and the absence of natural drainage from the valley, combined with a seasonally intense rainfall pattern, have led to difficulty in managing storm runoff. There are no large surface water sources nearby that can be used conjunctively with the local ground water source, and the high elevation of the valley makes water importation an expensive alternative. Finally, clay soils under the metropolitan area tend to consolidate from the dewatering and depressuring that accompany depletion of the underlying aquifer, resulting in regional land subsidence.