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7. The basin of Mexico

The socio-economic background
Recent environmental in the basin
The driving forces of environmental change
The vulnerability of the basin
The response to the environmental problem
Review and conclusions
References

Adrian Guillermo Aguilar, Exequiel Ezcurra, Teresa García, Marisa Mazari Hiriart, and Irene Pisanty

The Basin of Mexico lies on the southern edge of the Central Volcanic Axis, an upland formation of Late Tertiary origin. It is a naturally closed (but now artificially drained) hydrological unit of approximately 7,500 km² (fig. 7.1), the lowest part, a lacustrine plain, averaging about 2,240 m above mean sea level. The basin is surrounded on three sides by a succession of volcanic sierras (the Ajusco and Chichinautzin to the south, the Sierra Nevada to the east, and the Sierra de las Cruces to the west). To the north, it is bounded by a series of low ranges (Los Pitos, Tepotzotlán, Patlachique, Santa Catarina, and others). The highest and snowcapped peaks, Popocatepetl and Ixtaccihuatl (at 5,465 m and 5,230 m, respectively) lie south-east of the basin, but many other peaks reach elevations of around 4,000 m.

Prior to the Spanish conquest in 1519, the lacustrine system in the floor of the Basin of Mexico covered approximately 1,500 km² and was formed by five shallow lakes running in a north-south chain: Tzompanco (Zumpango), Xaltocan, Texcoco, Xochimilco, and Chalco. Texcoco was the largest and lowest-elevated of the lakes, so that the entire system drained toward it. During high water, the lakes were connected as a surface system, but during extreme drought they may have desiccated sufficiently to have separated. The northern three lakes were saline and the southern two were fresh water, owing to the greater amount of precipitation and springs located in that area of the basin. This drainage was altered somewhat during the fifteenth century by the Aztec state, which first diked the connection between lakes Xochimilco and Texcoco and then did the same within Texcoco to protect the southwestern portion of that lake in which the island capital of Tenochtitlán was situated (Palerm 1973).

Sanders, Parsons, and Santley (1979) and Sanders (1976) recognize nine major environmental zones (seven located between 2,240 m and 2,500 m elevation) within the basin during its Amerindian occupation:

1. the lake system, which was an important habitat for migratory waterfowl;

2. the saline lakeshore, with halophyllous plants;

3. the deep-soil alluvium, covered by sedges and swamp cypresses (Taxodium mucronatum);

4. the thin-soil alluvium, dominated by grasses and agaves;

5. the upland alluvium, vegetated by oaks and acacias;

6. the lower piedmont, gently sloping and with low oak forests;

7. the middle piedmont with broadleaf oaks;

8. the upper piedmont, occupying elevations above 2,500 m and vegetated by oaks (Quercus spp.), tepozanes (Buddlea

spp.), alder (Alnus sp.), and madrones (Arbutus xalapensis), and, finally,

9. the sierras, above 2,700 m and harbouring temperate plant communities with pines, fir, and juniper.

Fig. 7.1 The Basin of Mexico: Political and geographical boundaries

The Basin of Mexico has been one of the most densely populated areas of the world for a long time. During the height of the Teotihuacan Culture (Middle Horizon, A.D. 300-750), the basin had a population of around 300,000, and at the time of the Spanish Conquest (A.D. 1519) the population was around 1.2 million people, which is much higher than the population densities of any comparable region in Europe at that time (Whitmore and Turner 1986; Whitmore et al. 1990). At this time, dikes and sluices controlled the entire lake system, and lakes Chalco, Xochirmilco, and the south-west portion of Texcoco were taken to chinampa cultivation (wetland or raised field cultivation) and much of the surrounding land (i.e. environments 2-8 above) was terraced and irrigated (Sanders, Parsons, and Stanley 1979; Whitmore and Turner 1992). Williams (1989) believes that serious erosion had taken place on much of the slope lands.

The conquest instigated a series of changes that followed from a drastic decline in the Amerindian population and the introduction of new biota and technologies from Europe (Whitmore and Turner 1992). Ultimately, the central lakes were drained as modern Mexico City expanded and land uses throughout the basin changed during colonial and post-colonial times. Today, metropolitan Mexico City, estimated to be the largest city in the world by the beginning of the next century, has completely transformed the basin (Ezcurra 1990a,b). The lakes are gone and much of the basin is paved or lies under structures of some type. The city's water must be partially pumped from elsewhere, and its effluent must be pumped out. The old basin floor is sinking under the enormous pressures of the city, and the air pollution is so bad that the surrounding mountains cannot be seen.

Although human-induced environmental change in the ancient basin was significant, this study focuses on the effects of the rapid change in the Basin of Mexico in recent times. Our study concentrates on the past 100 years, with particular emphasis on the period 1950-1990. This is the time marked by gigantic growth in population numbers and large-scale industrialization, as Mexico City changed from a relatively small third world capital city into the largest urban conglomeration in the world (table 7.1).

Table 7.1 Evolution of the urban area and population densities in Mexico City, 1600-1989

Sources: DDF (1986); and projections by the authors.
a. Projected values.
b. Preliminary values of the 1990 population census.

The socio-economic background

Mexico City is a spatially continuous urban area, originally contained within the boundaries of the Federal District, but during the 1950s spreading beyond into adjacent municipalities of the State of Mexico. The current urban area of Mexico City encompasses all 16 subunits or delegaciones of the Federal District and 21 municipios in the neighbouring State of Mexico (henceforth, both delegaciones and municipios are referred to as "municipalities"). The urban area, therefore, does not coincide with political administrative divisions. The Metropolitan Area of Mexico City (hereafter Mexico City) corresponds to the territorial extension of the old central city in the Federal District into the urbanized political-administrative units contiguous to it (fig. 7.2; see Negrete and Salazar 1986).

In contrast, the Basin of Mexico is a larger, hydrologically defined unit integrated by 84 municipalities of four different political administrative units: the Federal District, and the states of Mexico, Hidalgo, and Puebla. Mexico City represents the most important social, economic, and spatial unit within the basin, concentrating 93 per cent of the basin's population. Thus, the Basin of Mexico and Mexico City are almost synonyms in demographic terms, but the latter is a subset of the former in geographic terms.

Fig. 7.2 Municipalities and industrialization trends in Mexico City, 1960-1980 (Source: Garza, 1987,103)

The economy of the basin

The Basin of Mexico concentrates almost 25 per cent of the country's total population, and an even greater percentage of the country's economic output. These circumstances were not always so. In the 1940s, Mexico City, being the seat of the federal government, had an extensive urban infrastructure, a concentrated market for industrial products, a variety of professional and financial services, and abundant facilities for administrative transactions. A flow of government investments and fiscal incentives stimulated the concentration of economic development in the area - maintaining a tradition of concentration that can be traced back to pre-Hispanic times. The basin contained, in 1940, 8 per cent of the nation's total population and its share of the national industrial output was 32 per cent; by 1980, however, it had grown to include 21 per cent of the national population and contributed 48 per cent of the industrial output. The Federal District alone contributed 35 per cent of the gross national product.

In the early 1950s, industrial activity in the basin became especially dynamic, and, at a national level, a clear trend appeared towards concentration in the capital city. In 1930, 6.8 per cent of all the industrial establishments of the country were located in Mexico City. This number increased without interruption: in 1970 the capital contained 27.9 per cent, and in 1980, 29.5 per cent of the industries in the nation. Between 1970 and 1980 the number of industries increased 15 per cent (from 33,185 to 38,492), and with it the investment of industrial capital also went up. This dramatic industrial concentration in the capital during the present century has created a situation in which the city produces almost half the total of the national industrial production.

To understand the economic dynamics of the basin, it is important to analyse the diversification and internal structure of industry in Mexico City. This structure is divided into two broad sectors (table 7.2), the means of production and consumer goods. The first sector represented 27.4 per cent of all industry in 1970, including capital goods (11.1 per cent) such as machinery and tools, and intermediate goods (16.3 per cent), which are basically raw materials for other industries. On the other hand, industries that produced consumer goods were the most important within the basin, representing 73 per cent of the total. This sector is in turn divided into two groups: immediate consumer goods (56 per cent; e.g. food, beverages, tobacco, clothing) and durable goods (16.5 per cent; e.g. electric appliances, automobiles, furniture). As table 7.2 indicates, the durable goods and capital goods sectors showed the highest increases in the 19501970 period (Garza 1984).

The economic predominance of Mexico City over the rest of the country also shows up in other economic sectors. The city holds an enormous share of the major financial exchanges, private businesses, and central offices in the country; it also has the largest number of institutions of higher education and centres of culture.

Table 7.2 Industrial structure of Mexico City according to the type of value aggregated, 1950-1970

Source: Garza (1984).

Indeed, compared with industry, services show an even higher trend to concentrate in Mexico City. Many industries have begun to relocate their manufacturing operations to outlying cities, although their administrative headquarters remain in the capital. In general and aggregate terms, the economic base of the city rests mainly on industry, construction, commerce, restaurants and hotels, and financial services. In 1980, 4.9 per cent of the active population were employed in the primary sector, 41.4 per cent were occupied in industrial activities, and 53.7 per cent were economically active in services.

Urban growth and social distribution

The spatial development of Mexico City until 1950 was characterized by a pattern of concentration in the four central municipalities of the Federal District, which contained around 70 per cent of the urban area at that time. Thereafter, the expansion of the city underwent a rapid process of suburbanization that affected the surrounding municipalities and finally produced a demographic spillover into the adjacent municipalities of the other states. In this process the city occupied agricultural land or, more frequently, land unsuited for urbanization, such as the desiccated lake-bed of Texcoco in the east, the unused open-cast mines and sand quarries to the west, and the mountain slopes of the south.

The period 1930-1950 witnessed an important process of decentralization of urban activities towards the south along two main avenues (Insurgentes and Calzada de Tlalpan). This process set in motion a commercial invasion of properties along those thoroughfares, with the establishment of service institutions. This, in turn, stimulated the appearance of low-density neighbourhoods to the south and west (Polanco, Del Valle, and Chapultepec Morales), occupied mostly by the upper social classes. Thus, the more affluent bourgeoisie left the historic centre of Mexico City and started moving towards the west and south of the basin, where the neighbourhoods with the highest standard of living are now located (figs. 7.3 and 7.4). The most impressive impact on the urbanization pattern, however, was that of the expansion of low-income neighbourhoods, induced by the location of industry in the north. The demand for labour in the newly established factories attracted migrants into working-class municipalities such as Azcapotzalco and Gustavo A. Madero: 70-80 per cent of their growth in the decade 1940-1950 was due to migration. The central part of city also absorbed part of the migrant population, which found accommodation in the old and dilapidated buildings (vecindades) that had been abandoned by the wealthy (on Mexico City urban expansion, see Aguilar 1986; Bataillon and Rivière d'Arc 1973; Garza and Schteingart 1978; Unikel 1974; Ward 1981, 1990).

Suburbanization was stimulated at the beginning of the 1950s by the government's ban on new residential developments within the Federal District. Tax incentives in the State of Mexico encouraged industrial zones to expand, especially to the north-east (Ecatepec) and north-west (Tlanepantla, Naucalpan), around railway terminals. This expansion was accompanied by new housing developments supported by significant improvements in the road system, such as the Mexico-Queretaro freeway, which reduced the travel time from the new suburban areas to either the city centre or the industrial zones.

Fig. 7.3 Population by municipalities in Mexico City, 1980 (Source: Tamayo, Valverde, and Aguilar, 1989)

This widely encouraged the middle and upper classes to settle towards the north-west in developments around Ciudad Satelite (which opened in 1957). In contrast, the low-income groups were segregated towards new, slum-like settlements in the east. These settlements occupied the salty, inhospitable land of the old Lake Texcoco and lacked the most basic urban services. Additionally, they were vulnerable to seasonal flooding and dust storms.

Increasing immigration and the flight of the poor from the city centre into the outer urban contours spawned the proliferation of settlements, most of them products of illegal land subdivision. Perhaps the most impressive example is that of Ciudad Nezahualcoyotl, established in large part on the former lake-bed, and which increased its population from 65,000 in 1960 to 650,000 in 1970; today it contains a population of about 2 million. Accelerated urban growth led to the proliferation of illegal, usually poorly urbanized, settlements either in the State of Mexico or in the Federal District, where the ban upon new subdivisions provoked an increase in squatting. In 1968 the prohibition of new residential estates in the Federal District was overruled, and this stimulated the growth of new residential neighbourhoods, especially to the south. Between 1970 and 1975 some southern municipalities, such as Tlalpan and Xochimilco, almost doubled their urban area, while Cuajimalpa tripled in size. In the east and west of the Federal District, light industry was established in municipalities such as Iztapalapa, Iztacalco, and Alvaro Obregón.

Fig. 7.4 Social conditions as defined by a multivariate social indicator, by municipalities in Mexico City, 1980 (Source: Tamayo, Valverde, and Aguilar, 1989)

Throughout the second half of the 1970s, this suburbanization continued and reinforced previous patterns. Towards the north-west, middle classes settled in new developments along the Mexico-Queretaro highway, accompanied by the establishment of more heavy industry. In the inhospitable lands of the east and north-east, low-income sectors concentrated in Netzahualcoyotl and Ecatepec, while towards the south a boom of residential subdivisions and diverse social groups occupied the mountain slopes in an uncontrolled fashion. It is noteworthy that this expansion, in part, has been stimulated by public decisions, such as the construction of a highway between Picacho and Ajusco and the massive development of large lower-middle-income apartment buildings and housing units (usually built by government agencies) that have emerged recently in peripheral locations (fig. 7.3).

It is notorious that those municipalities located to the east represent the highest proportions of the active population that earn less than the minimum salary (fig. 7.4). In municipalities such as Chalco, Chimalhuacan, La Paz, or Ixtapalucan, this proportion is more than 50 per cent, whereas in central and western administrative units the poorer groups represent less than 30 per cent, and middle and upper classes reach percentages higher than 10 or 15 (as in, for example, Benito Juarez, Miguel Hidalgo, or Tlalpan). The high proportion of low-income population in peripheral municipalities follows from three principal factors. First, peripheral municipalities still include a large number of people engaged in agricultural occupations, and thus the populations represent the least industrialized of the city. Secondly, peripheral populations that have recently been incorporated into the urban economy are poorly qualified for higher-paying employment. And thirdly, these municipalities receive the poorer population from the centre who are looking for cheaper land or dwellings, as well as the incoming rural migrants (Aguilar Martínez and Godínez, 1989).

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