Document(s) 3 of 14

One of the main features of the recent historic and geographic evolution of Latin America and the Caribbean (LAC) has been a concentration of the population in urban areas. The urban population of the region is estimated to be increasing at the rate of 3.6% per year (Bartone 1990).

At the end of the 1980s, there were over 280 cities of more than 100 000 inhabitants; the 210 million people in these cities represented about 46% of the region’s population. About 25% of these cities have populations above 0.5 million people, constituting 35% of the total population. Extremely high concentrations occur in the 13 largest urban centres, whose populations exceed 3 million (Table 1). The total population of these metropolises is 105 million or 23% of the total for Latin America and the Caribbean.

It is difficult to provide accurate or comparable figures for the populations of metropolitan areas. Large cities often encroach beyond their municipal or provincial boundaries. Other cities, formerly separated, may merge into the main urban area. Equally, the rate of annual urban growth for any growing city is hard to define, because the census units may become noncomparable during the intercensal period (i.e., because satellite cities are incorporated). I have tried to surmount these difficulties using different sources for some cities that appeared clearly uncomparable¹ in some data sources. Population growth projections are only indicative. In all cases, an average population growth for the period was estimated based on the growth of the last intercensal period and this figure was cumulatively applied for the projected period. I could not apply the same criteria for all cities but, in some obvious cases, corrections were made.

¹ In some cities, the problems are almost insurmountable. It is difficult to decide if Campinas, São Jose dos Campos, or Santos belong to the metropolitan area of São Paulo. This Brazilian city is growing through the Paraiba Valley along the Via Dutra Highway toward Rio de Janeiro: some people are already forecasting a megacity to be called São-Rio. A similar problem occurs in Mexico City because of the merging of some large, formerly independent, urban areas (i.e., Toluca, Cuemavaca, Puebla, Querétaro, and Cuautla). In the last censal survey, growth of Mexico City appeared somewhat curtailed if only the Valley of Mexico is considered, but if the other cities listed are included, the growth is even further accelerated. In the table, I have tried to conciliate statistical data (often not reflecting reality) with the actual ground truth.

Table 1. Current and projected populations (millions) for some major cities of the LAC region.

Note: na = not available.

Sources: 1 – Wilkie et al. (1988); 2 – Abril (1993); 3 – Europa (1991).

The largest cities have experienced the greatest increases, and demographic statistics leave little hope of any dramatic reversal of present trends. If the rate of growth is not significantly reduced, by the year 2020, more than 500 million inhabitants of Latin America (or two-thirds of its population) will be living in cities of over 100 000 people.

Overconcentration has reached alarming levels in three megacities: Ciudad de México (19.5 million), São Paulo (16.5 million), and Buenos Aires (12.2 million). Forecasters predict that the populations of Mexico City and São Paulo will soar to 25 and 22 million, respectively, well before the year 2010. By that time, several other cities will exceed 10 million, including Rio de Janeiro (12 million) and Lima (10 million) and many more will exceed or approach 5 million (Belo Horizonte, Bogotá, Caracas, Guadalajara, Monterrey, Pôrto Alegre, Recife, Salvador, and Santiago).

This degree of urban concentration is much higher than that expected in cities of developed countries, whose growth is slower. These populations are also higher than expected for the largest megacities of the most densely populated countries in the Third World. The People’s Republic of China, with a population of over 1.1 billion, does not contain any city with more than 15 million people: Shanghai, the largest city in China has “only” 12 million. São Paulo and Mexico City are larger, in spite of the much smaller populations of their countries (14 and 9 times smaller, respectively). In India, with a population of 800 million, the two largest cities Calcutta (15 million) and Bombay (14 million) also have populations considerably smaller than the two largest LAC megalopolises.

This uncontrolled growth of LAC urban areas has occurred at the same time as one of the worst financial crises of the region’s history. In almost all LAC countries, foreign debt has increased at an even faster pace than the growth of their urban populations. This problem became particularly acute at the end of the I980s in Brazil (foreign debt at that time of US$116.9 billion), Mexico (US$105.6 billion), and Argentina (US$S6.2 billion),

but is also found in many smaller countries. In some cases, lack of resources prevented even the payment of interest on these debts over a relatively long period (e.g., Peru and Argentina in 1988–1989). In other countries, net transfers of resources as a result of profit repatriation and debt servicing or payment have also depleted available funds in public coffers and have jeopardized the acquisition of new credit. Little (if any) new money has been available for investment in infrastructure of any magnitude at a time when such investment is most needed to provide the necessary services for the booming urban population.

One of the public services most affected is urban water supply. Historically, Latin American cities have relied on their closest sources of water, which in most cases were freshwater streams, lakes, or springs. Soon, these resources were exhausted or degraded, and the cities were forced to invest considerable funds in the construction of dams and pipelines to bring water from more remote sources. Continually expanding cities have outgrown most water-supply systems, and new sources must be tapped to satisfy the needs of their populations.

However, funds are not available. Few new reservoirs are being built and few pipelines are being installed. In fact, expansion of the systems has been almost completely halted. Less water is available per person and this situation is gradually becoming worse.

In addition, distribution systems (originally designed for much smaller populations and for limited use) are becoming not only inadequate, but also obsolete — they increasingly require repairs at a time when less money is available to carry them out. As a result, the amount of leakage is increasing, augmenting water “consumption” from the systems. Breakages (and subsequent water losses) are common, with frequent drops in pressure increasing the risk of contamination of waterlines.

Old reservoirs are also decaying. Their storage capacity is decreasing due to silting, watershed basins are being invaded by urban and rural dwellers, and uncontrolled industrial activity is producing changes both in hydrological regime and water quality. Many reservoirs serving urban areas have become useless because of inappropriate use of their basins.

New reservoirs will be much more expensive than old ones. New dams must be built in basins unaffected by urban growth, which are often far from the people who will use the water. In some cases, water must be pumped from lower lying valleys (as in Mexico City); in other cases, interbasin water transfer may be needed (Lima). In almost all cases, increased distances and water conduction costs are unavoidable.

At the same time, consumption practices are frequently wasteful. Water policies (i.e., cost of water and available water-appliance technology) do not encourage conservation. In many cases, water costs are higher in the poorly served, low-consumption, low-income urban areas and lower in affluent neighbourhoods that have a more wasteful consumption pattern.

Sewage systems are not much better. Only 41% of the urban population is linked to sewerage systems, and over 90% of wastewater is discharged into the environment with no treatment. By the year 2000, an additional 141 million people will require these services. It is not very likely, given the financial crisis, that LAC countries will be able to obtain even a significant portion of the resources required to finance this badly needed infrastructure.

New surface-water supplies require expensive dams and pipelines.

Treatment of wastewater is rare in most cities. Wastes are discharged untreated into the environment with obvious health hazards for the population living nearby or downstream of the effluent outlets.

The consequences of this situation can be catastrophic. Millions of people are being excluded from water-distribution systems, forcing many urban communities to use various (often imaginative) ways to obtain water — what little water can be acquired is usually of poor quality. Many more millions are becoming increasingly exposed to health hazards that are affecting mortality rates in these populations, e.g., the cholera outbreak in Peru that spread throughout most of the continent in the early 1990s.

In spite of this apparently hopeless situation, in many cases means are available to obtain better quality water at a much lower cost, by using groundwater reservoirs lying close to urban areas. Groundwater volumes are normally much higher than surface water, it is less vulnerable to contamination, and initial investment is only a fraction of what is needed to develop analogous surface-water resources.

Large volumes of groundwater are available close to many of the larger LAC cities; in most cases, they are only marginally used. Mexico City, the largest LAC city, draws about 55 m³/second (80% of its consumption) from groundwater sources located beneath the urban area and in a neighbouring basin. The city also obtains surface water from the Cutzamala River basin at a much higher cost and by depriving populations downstream.

São Paulo, Brazil, the second largest city of the region, gets most of its water from surface resources (43 m³/second from six reservoirs located in the upper Tietê River basin). However, about one-third of the suburban and urban population and industrial establishments draw their water from underlying aquifers. The suburban areas of the city are expected to become increasingly dependent on the groundwater supply. The available

volume of groundwater in São Paulo and neighbouring basins is relatively large, and its use would require a smaller investment than needed to expand the surface-water system.

Buenos Aires, capital and largest city of Argentina, is next to the huge Río de la Plata estuary and draws the bulk of its water supply (about 80 m³/second) from this surface source. However, because of the rapid expansion of the city, many suburban communities have developed groundwater-based systems tapping a relatively shallow alluvial aquifer that underlies the urban area. La Plata (600 000 inhabitants), the capital of the province of Buenos Aires and now practically a suburb of Buenos Aires, depends on groundwater for about 40% of its requirements. This resource is of higher quality than the local river water because of the high level of contamination of the Río de la Plata near the shore.

The city of Buenos Aires discharges its untreated effluent into the Río de la Plata estuary. Use of groundwater is expected to increase in the Buenos Aires-La Plata region as this contamination of surface water near the river bank increases, thus raising the cost of treatment and conduction. However, inadequate sewage systems are affecting groundwater quality in many suburban areas of greater Buenos Aires and, ultimately, jeopardizing the present and potential use of this alternative water source.

Lima, Peru, is also heavily dependent on groundwater. The city obtains its water from the Rímac and Chillón rivers, at the rate of about 12 m³/second, after treatment at the La Atarjea plant. The balance of the city’s water (about 9 m³/second) is drawn from an underlying shallow aquifer, which, in turn, is recharged by the two rivers. Surface-water use has become more difficult because of an increased load of suspended sediments and pollutants (including those from upstream mining areas) that raises treatment costs considerably.

During the last few decades, the aquifer has been overpumped resulting in widespread saline intrusion along the coastal zones. In addition, the volume of water recharging the groundwater reservoir has diminished because the irrigation areas have been reduced and impermeability of river beds in the urban area has increased. A gradually growing water crisis will require careful management of the existing water resources. Adequate regulation of these resources should include artificial recharging of the aquifer with large volumes of surface water and intelligent extraction of water over a dispersed area of the groundwater reservoir.

In addition to the examples cited, many other urban areas in the continent obtain part or most of their water supply from groundwater sources. This is particularly true in the Caribbean region where surface water is scarce, but excellent aquifers (mainly karstic) are often suited for urban supply. In Havana, almost 100% of the water supply is drawn from groundwater; other cities using groundwater extensively include Kingston and Montego Bay in Jamaica; San Juan, Puerto Rico; Miami; Florida (which can be considered in many senses a Latin American city); Mérida and Torreón-Gómez Palacios in Mexico; Port-au-Prince, Haiti; Nassau in the Bahamas; Bridgetown, Barbados; and several others.

Many cities in volcanic areas are also well situated to draw their water supply from groundwater sources (Table 2). This is particularly true of cities located close to thick pyroclastic and associated formations and to lava rocks. Guatemala City, Managua, Mexico City, Quito, and San José, for example, have important volcanic aquifers that are tapped for their water supply. In fact, Guatemala, Managua, Mexico, and San José get most of their water from groundwater reservoirs or related springs. Quito draws about 40% of its water from groundwater sources.

A large number of other cities depend partially or totally on alluvial valley aquifers, particularly those in the Andean region. Some examples are Cochabamba, Bolivia; Valencia and Maracay in Venezuela; and Querétaro and San Luis Potosí in Mexico.

In some cases, the current water supply is obtained from surface sources that are being gradually exhausted. Groundwater may become the main source for expansion of urban supply systems in Montevideo in Uruguay, Recife and Salvador in Brazil, and others.

Often, groundwater is the only safe alternative. The quality of surface water is deteriorating in all LAC urban environments. Where stream flows are large (e.g., Asunción on the Paraguay River and Manaus on the Amazon), the effects of the various waste discharges may be small, even negligible. In other cases, when rivers are smaller or waste discharges large, surface water may be steadily deteriorating and additional treatment may be required. Below a certain quality level, water treatment becomes very costly (and sometimes technically unfeasible) and other options must be considered.

Alternative surface sources are usually farther away than the outdated ones, requiring hundreds of millions of dollars in infrastructure to tap and transport water to the cities (e.g., Lima and Mexico City). However, there is frequently a nearby groundwater source that could be exploited at a much lower cost. In some areas, quantity is also a problem. Surface sources do not provide the required volumes and underground sources are the best available alternative.

Often, even when the main sources of water supply for the urban core are bodies of surface water, the use of groundwater can be the most economical and feasible option for some sections of the city. This is the case in Bogotá, where although surface water is the best source for the northern and central neighbourhoods, it is expensive and unpractical for some of the fast-growing southern suburbs, where it could be more economical and convenient to use the underlying aquifer. Although this solution has not been implemented, it is repeatedly advocated by Colombian hydrogeologists.

Table 2. Current and potential sources of water supply for major cities of the LAC region.

Note: 5 = surface water; G = groundwater

Where water is not supplied directly to the home, it must be carried from the nearest source.

In Buenos Aires and São Paulo, many of the new neighbourhoods and industries get their water from wells, because their distance from the municipal system and their low population density do not justify the expense of extending municipal waterlines or because the financial resources of the water companies are insufficient to install the connections. When potable groundwater is easily available, fringe communities use this resource, even in cities where surface water is abundant, cheap, and of good quality. For example, in Asunción, Paraguay, many industrial factories depend on wells in spite of the good quality and reliability of the river water in the core of the urban area.

The number of people experiencing these limitations is gradually increasing, not only because of growth of the urban population, but also as a consequence of financial difficulties of water companies to obtain funds for expansion of municipal systems. Whatever the reason, the trend is clear: Latin American urban water supply will depend more and more on groundwater reservoirs. In 1990, about 30% of the water consumed in LAC cities came from nearby aquifers. At the present and projected rate of increase in groundwater extraction, by the year 2020, up to 40% of urban water will come from aquifers.

At that time, about 850 m³/second will be pumped from the ground to satisfy the requirements of the urban populations of the big cities. This is 3.5 times the present extraction rate (about 260 m³/second) for the whole urban groundwater supply, including only cities with more than 100 000 people. If smaller towns and agricultural areas are included (present rate of use, 2500 m³/second), it is easy to project the importance of groundwater use in the 21st century.

However, Latin America is not prepared to deal with this issue. In fact, lack of awareness of this resource is appalling. Few trained hydrogeologists or groundwater engineers can be found in the LAC area. There are fewer than 200 formally trained

hydrogeologists in the 30 countries of the LAC (almost half are in Brazil): one for every 3 million people or one for every 3 000 wells. There are not many more groundwater engineers.

Partly as a consequence of the lack of expertise in the region, groundwater resources are poorly understood and, therefore, frequently underused. Sometimes, large amounts of money are spent on surface water-supply schemes, when readily available groundwater of good quality is within the financial and technical means of city authorities. In other cases, aquifers are overexploited and degraded because of improper management, lack of protection of recharge areas, and overpumping. As a result, some groundwater reservoirs become irreversibly contaminated, or subsidence or saline intrusion take place.

As previously stated, groundwater is much less vulnerable to degradation than surface water. However, this may become a double-edged sword. In many cases, this apparent invulnerability may give a sense of false security and no protective measures may be taken when they are required. Although groundwater is relatively safe from contamination, with time it may become contaminated in such a way as to render it completely unusable. The lack of understanding of groundwater dynamics may ultimately result in destruction of the resource. In the long term, underground water can be damaged more than surface water, because reversing the “environmental messes” is more difficult, expensive, and often impossible.

How is the LAC region going to cope with the need to understand the nature, dynamics, and vulnerability of groundwater systems? How is it going to deal with the contradiction arising from growing needs, increasing environmental degradation, and lack of expertise and financial resources? This book is intended to try to answer these questions using the limited available information and some common sense. I hope it will shed light on the not easily predictable future of Latin American cities in the next century.

Document(s) 3 of 14