The megacities of today
Many cities of 10 or more million people concentrated in a
relatively small area are trying to survive. Some, such as Tokyo and Los
Angeles, are in the old industrial countries. However, the majority
are found in the Third World. Some of the problems they are experiencing are
representative of the challenges affecting all urban areas today.
Mexico: a thirsty city
There are few cases in the world in which the physical
environment has been so completely transfigured by urban development as it was
in Mexico City. The valley of Mexico is a 9 600 square kilometre closed basin
that is more than 2 200 metres above sea level, in the heart of the Mexican
neovolcanic belt. Before the arrival of Europeans in 1521, the valley was a
depression in whose bottom several large lakes had developed because of volcanic
obstruction of their outlets about 700 thousand years ago. The lakes covered a
total area of about 2 thousand square kilometres and were partly connected,
especially during periods of high water. Three of the lakes contained fresh
water - Chalco, Mexico, and Xochimilco - and the other three, brackish water -
Ecatepec, Texcoco, the largest at 800 square kilometres, and Zumpango.
The area was, and to a certain extent still is, subhumid.
Rainfall was probably slightly more than the current amount, which ranges from
600 millimetres per year at the bottom of the valley to l 200 millimetres per
year in the nearby mountains. The average temperature was relatively cool for
the subtropic latitude at which the city is located, ranging from 8° to
15°C depending on the altitude. Soils were deep, highly fertile, and easy
The land was completely covered by thick forests, particularly
on the slopes of the mountains and highland areas. The plains in the valley,
which were originally also covered by forests, were soon allocated for
agriculture, and parts of the forest were cleared to make way for farms. In
addition to the freshwater lakes, a large number of springs around the lakes and
in the foothills of the nearby mountains provided considerable volumes of
Because of its abundant resources, the valley was occupied early
by a number of indigenous peoples, who based their economy on locally
domesticated crops and farm animals: corn, tomatoes, chili peppers, cacao,
turkeys, dogs, honey bees, and fish. Because these people did not have draft
animals or use the wheel, most trade was carried out by boat (or walking).
Several peoples successively inhabited and established political
control over the lacustrine area during the few centuries before the arrival of
the Europeans. The last group was the Aztecs, who arrived from the legendary
land of Aztlan (probably in the northern arid territories) during the 14th
The Aztecs probably maintained a livelihood by fishing and
trading with neighbouring groups. Gradually, they managed to build an island in
the centre of the Lake of Mexico on which a town developed: Tenochtitlan.
Through alliances and wars, the Aztecs built an empire, and Tenochtitlan became
a thriving city of several hundred thousand people. A bridge was built to
connect the island with the mainland, and large boats transported people and
merchandise. The Aztecs also built earth dikes to control flooding and to
separate the brackish lakes from the fresh water. Aqueducts carried fresh water
from springs to the city through the lake and along the dikes.
It is difficult to comprehend the extent of the changes that
took place in the few centuries after the Spanish conquest. Today, the proud
Tenochtitlan has disappeared, and only scattered archaeological remnants can be
found. In its place stands the highly urbanized downtown area of Mexico City.
The Lake of Mexico is gone. In its place are several hundred
square kilometres of urban neighbourhoods built on what used to be the lake
bottom. A few canals and small lakes are the only remnants of Chalco and
Xochimilco lakes. Like the southern lakes, the three northern lakes were
gradually drained (beginning in 1786), and the former Texcoco Lake has become a
vast flat plain on which little vegetation grows because of the highly alkaline
soil (pH is over 10). An intricate maze of wells and pipes pump brine from the
lacustrine sediments for sodium carbonate and sodium chloride extraction.
The old springs that provided water to the riverine populations
are also gone. Now over 5 thousand wells draw more than 50 cubic metres of water
per second from an average depth of 100 metres, causing the level of water in
the aquifers to subside by as much as 1 metre per year. As a result of this
overpumping and the compaction of the upper layers of sediments, widespread
subsidence is occurring. The surface has dropped 6 metres in several places and,
because of differential rates of subsidence, many structures have been weakened.
This phenomenon has been exacerbated by frequent seismic activity, of which the
most recent destructive example was the earthquake of September 1985.
The forests that used to cover the adjacent hills have
practically disappeared, and widespread soil erosion occurs. Most former
agricultural land has been covered by pavement, houses, and other urban
constructions. Quarries, which supplied construction materials, can be found
throughout the legion. Some have become garbage dumps, into which some of the
annual 10 million tonnes of garbage is thrown. A significant portion of the
garbage is dumped on the shores of the former Texcoco Lake,
particularly in the south. Ciudad Netzahuatcoyotl, in that area, is a
neighbourhood of 3 million people. Although recently established, this urban
area is extremely degraded; developed areas alternate with garbage dumps and
Water, which used to flow into the lakes, is channeled out of
the basin, together with urban wastewater, through a system of canals and
tunnels into the Gulf of Mexico hydrographic system. A number of pumping wells
used to supply the city are located next to the canal (the Chalco Canal). Risks
of contamination are obvious and, in fact, some wells had to be closed because
of the presence of nitrates in the water.
The atmosphere of the valley has also changed. Emissions from 4
million vehicles and 25 thousand industrial establishments in a poorly
oxygenated environment (because of the altitude) have transformed the air in
Mexico City into one of the most unhealthy urban environments for human life,
particularly near the downtown core.
Mexico City contains 21 million people, making it the largest
urban centre in the world. Every year, its population increases by 750 thousand
people, including both births and migration from the rest of the country. By the
year 2000, the city will hold 29 million people (surpassing the population of
Canada) and, by 2010, 38 million. If corrective measures are not taken, the
citys problems will continue to grow, and the ancient paradise may become
one of the worst environ mental nightmares of the 21st century.
The aquifer underlying the valley of Mexico is one of the key
natural elements in Mexicos environment. It provides the bulk of the water
that makes the existence of the city possible. Although some water is brought in
from the Lerma-Cutzamala basin, the volume is less than one-fifth of total
Any other option for bringing water from outside the valley is
becoming impractical or too expensive. The Lerma-Cutzamala resources are almost
exhausted, but using other basins (such as the Balsas basin or the Amacuzac
subbasin) may mean pumping water 1 200 to 1 500 metres upward and constructing
long pipelines, storage reservoirs, and other expensive engineering works.
Bringing this water into Mexico City will also deprive a number of communities
that now depend on it for irrigation and other uses.
Mexicos aquifer is contained in a number of Tertiary and
Quaternary units with a thickness ranging from a few hundred metres to nearly 2
thousand metres. These units comprise a wide range of sedimentary materials.
Continued volcanic activity produced huge volumes of pyroclastic material, which
has been more or less reworked by fluvial action, and intercalated lava flows.
During periods of volcanic activity, tuffs, breccias, ashes, and lava formed; at
other times, alluvial and lacustrine action was more important. The main
water-bearing layers are the Tarango formation and associated alluvia and the
Cenozoic sequence of fractured pyroclastic and lava flows. These are covered by
younger lacustrine sediments, confining the main aquifer.
The whole sequence can be up to 2 000 metres thick, but the
lower 1 500 metres are more consolidated and less porous. The upper few dozen
metres of the aquifer are too close to the upper lacustrine clays and continued
pumping might produce dewatering and consolidation of these clays, causing
subsidence. Therefore, the usable portion of the aquifer is generally between
100 and 500 metres underground.
The aquifer is recharged mainly in the mountain region (Sierra
Chichinautzin in the south, Sierra Las Cruces in the west, and Sierra Nevada to
the east). The total available recharge volume has been estimated to be 25 to
50% of precipitation: 25% in Sierra Las Cruces, 35% in Sierra Nevada, and 50% in
Sierra Chichinautzin. Of these volumes, about half flows toward the valley of
Mexico and the rest outward to other basins. An accurate figure for inflow to
the aquifer itself is difficult to estimate (probably 30 to 40 cubic metres per
second). However, it is certainly below 50 cubic metres per second - the amount
being pumped out - because the water level is sinking.
Additional lowering of water levels will increase inflow from
the Sierras because of an increase in gradient. This will not compensate for the
deficit, however, particularly if pumping is increased. Precise forecasting of
the aquifers reaction to prolonged extraction requires accurate modeling.
Only recently has adequate information on the geometry and hydraulic properties
of the reservoir been available. Modeling of the aquifer has been carried out at
the Instituto de Geofisica, and it is expected to allow prediction of the actual
potential of the groundwater resources of the valley.
It has recently become clear that the groundwater resources of
the valley of Mexico are limited and that additional water will have to come
from external sources. Such external sources are all found at elevations lower
that that of the city. Therefore, tapping this water will not only require
enormous energy consumption but will also deprive downstream communities of this
vital resource. The bottom line is that the urban model of Mexico City is
unsustainable. It has become too large for its territorial base. The city has
not only run out of water, but also its air is heavily polluted, the local
ecosystems have been destroyed or critically damaged, and the surrounding soils
are under severe strain as a result of heavy urbanization. To check this
continuous destruction of resources, radical policy shifts are essential. The
window of opportunity to save Mexico City is rapidly closing.
Los Angeles: setting priorities
Los Angeles, which was founded by the Spaniards in the 18th
century, contained only 1 600 people in 1848. The population was half Spanish
and half indigenous peoples and it was twice the size of San Franciscos.
In the 1850s, when San Francisco became one of the largest cities of the United
States, with more than 50 thousand people and one of the busiest ports in the
world, Los Angeles remained a torpid little town. Too far from the gold fields,
sitting on an arid plain, and lacking a port and a railroad, it did not possess
the conditions for rapid growth.
In the 1860s, Mormons started growing fruits and other
vegetables in the area. Later, agriculture was firmly established by Quakers and
German farmers. Groundwater was easily accessible and abundant; artesian
pressure threw it 2 to 3 metres into the air. In 1867, when a rail road
line was established, the city began to grow.
Californias Sierra Nevada mountain range blocks moist air
coming from the ocean and annual precipitation may vary from 2 400 millimetres
on the western slopes to 300 millimetres or less on the east. Rivers flowing
west are substantial; those on the east are small, except for the Owens River.
The Owens River arises southeast of Yosemite, flows west and south into the
Owens Valley, then into highly saline Owens Lake. The region contained a rich
ecosystem; shrimp and flies provided food for millions of waterfowl. In the
1860s, the Paiute Indians were practicing irrigation learned from the Spaniards.
By the 1870s, settlers had displaced them, taking over the farms and irrigation
systems. By the end of the century, 15 to 20 thousand hectares was under
When the water supply in Los Angeles became insufficient, one of
the first alternative sources to be considered was the Owens River. It was
almost 400 kilometres away, but it could provide water for I million people - at
least that was what the founders of the Los Angeles City Water Company thought
at the time. In 1880, however, an expensive engineering project of this type was
not possible, and the idea was not acted upon. By 1900, the population had
reached 100 thousand, and the artesian pressure of the aquifer supplying their
water continued to drop. In 1904, the municipal government took over the
citys water company and the LA Department of Water and Power (LADWP) was
created. One of its first tasks was to try to secure water rights in the Owens
Valley and construct an aqueduct to the city.
City officials also wanted to use excess water from the Owens
Valley to irrigate land in the San Fernando Valley. The words of Theodore
Roosevelt give us an idea of the ideology of the times: It is a hundred,
or a thousandfold more important to state that this water is more valuable to
the people of Los Angeles than to the Owens Valley.
The aqueduct took 6 years to build, up to 6 thousand workers
were involved in the enterprise, and it was 360 kilometres long, of which 80
kilometres was in tunnels. More than 190 kilometres of railroad track and 800
kilometres of roads and trails had to be constructed. Up to 380 kilometres of
telephone lines and 210 kilometres of power transmission lines were installed.
It was a huge undertaking for the time.
During the next 20 years, however, no water from Owens Valley
went to Los Angeles. It was all used for irrigation in the San Fernando Valley.
From fewer than 1 400 hectares in 1913, the area of irrigated land increased to
35 thousand hectares in 1918. In the 1920s, a drought necessitated the
construction of several complementary reservoirs.
In the early 1920s, Los Angeles began to use water from Owens
Valley. It was then that the problems began. The city managed to buy most of the
remaining water rights, depriving local farmers of the vital resource. At the
same time, the drought was becoming serious. In 1923, total rainfall was 250
millimetres; in 1924, 150 millimetres; in 1925, 175 millimetres. In addition,
the citys population had grown beyond all expectations over the last
decade to 1.2 million. The increased need for water forced Los Angeles
authorities to continue buying water rights. The conflict between the city and
the farmers became nasty and violent. In 1924, at the height of the drought, the
farmers remaining in the Owens Valley flooded their land to stop water from
entering the aqueduct. By 1927, terrorist actions had started; large pipes and
sections of the aqueduct were dynamited. Roadblocks, car searches, and
floodlights transformed the valley into a giant penitentiary.
When the crisis continued, the head of the LADWP, William
Mulholland, decided to enlarge an existing dam in the nearby San Francisquito
Canyon. In 1928, the storage capacity of the San Francis dam was increased to 4
million cubic metres. The work was no sooner finished than the dam started to
leak. Soon after, it collapsed. A wave, 60 to 70 metres high, hit 160 men
sleeping downstream in a construction camp and 75 families were killed in San
Francisquito Canyon. Where the canyon opens onto the plain, the wave was still
25 metres high and engulfed the village of Castaic Junction. The death toll was
Finally, a new dam in Long Valley, on the Owens River, was
built. By the 1930s, the farming and ranching community of Owens Valley ceased
to exist. The last rancher left in the 1950s. Later, several other megaprojects
were built, the Colorado was tamed, and two giant aqueducts were
constructed to transfer water from the Colorado Valley to the California valleys
and Los Angeles.
In the 1950s and 1960s, large hydroprojects continued to be
constructed. The largest one, in the Central Valley, was proposed to supply Los
Angeles. However, the real purpose was to increase the value of desert land and
the wealth of a few speculators. The Central Valley project is depicted in the
film Chinatown. As soon as the project was approved, the value of the land
increased severalfold. Not a single drop of the water from the Central Valley
aqueduct reached Los Angeles. It was used to supply inexpensive irrigation water
to farmers. However, despite the dams and aqueducts, overpumping of the
valleys aquifers did not stop. Groundwater levels continued to drop and
soon new megaprojects were being discussed.
A similar situation had developed on the coastal plains next to
the metropolitan area of Los Angeles. In this area, more imaginative approaches
were being considered to increase water availability. Instead of investing huge
sums of money in distant projects, Los Angeles and Orange counties preferred
better management of nearby water resources, especially by increasing recharge
into the aquifer by artificial means. Today, in Orange County, groundwater
recharge through the bed of the Santa Ana River satisfies 70% of the needs of
its 3 million inhabitants. In Los Angeles, a similar solution has been
implemented in the Los Angeles River. Neighbouring cities of southern
California, such as San Diego, do not have available groundwater and depend
almost exclusively on imported water.
Water has been, and still is, a key issue in the urbanization of
southern California. However, as difficult as it seems, it is only one aspect of
a much larger issue: the development model that has been applied in that region.
Water scarcity, poor air quality (see also Chapter 8), soil degradation, and
ecosystem destruction have made southern California a veritable urban nightmare.
Drastic measures will be needed to begin the healing process. If Los Angeles is
to survive, a sustainable and long-term development strategy is needed; and this
will require a profound rethinking of southern Californias future.
Calcutta: a matter of survival
Calcutta, on one of the branches of the Ganga delta, the Hooghly
River, is strategically located 130 kilometres from the mouth of this river in
the Bay of Bengal in an area of commercial transshipment from sea to river and
land. Although a village named Calcutta existed in the area in the 16th century,
it was not until the end of the 17th century that the English East India Company
established the trading post that was going to become the current megalopolis.
This post was in direct competition with the upstream river port of Hooghly,
controlled by the Mughals. The site of Calcutta was also selected because it was
downstream of the Dutch and French settlements and protected by the Hooghly
River to the west and three brackish lakes on the east. However, the site was
far from ideal from a physical point of view. It is on a low, hot, humid
floodplain no more than 10 metres above sea level. Calcuttas environment
is subtropical, with average temperatures of about 22°C and rainfall in
excess of 1 500 millimetres per year, concentrated in a relatively short period
of 4 months (June to September).
The trading post grew relatively quickly, as merchants arrived
from nearby Satgaon and the Mughal emperor decreed freedom of trade in 1717,
which encouraged many tradesmen to move to the city. By 1706, the population was
already over 10 thousand; in 1752, it reached 115 thousand; and in 1822, it was
300 thousand, becoming one of the largest cities in India. By the beginning of
the 20th century, the city contained 1 million people and 10 million in 1975. In
1991, its population was estimated to be 15 million, and it is expected to
exceed 20 million before the end of this decade.
The metropolitan area is principally confined to two strips, 5
to 8 kilometres wide, on both sides of the river. The Salt Lake project, which
reclaimed the lowlands on the northeast fringe of the city, was followed by
other local projects allowing lateral expansion of the urban conglomerate.
Throughout most of its history, the city obtained water from
wells and the Hooghly River, which in 1947 was supplying 75% of the required
water. This stream provided fresh water during the rainy season and brackish
water during the dry period. However, contamination of the river from urban
sources has become so acute that, today, the water is unusable for most
purposes. However, many riverine neighbourhoods still use it directly. Since
construction of the Farakka barrage in the Ganges, a substantial volume of water
is obtained from this surface source. The rest comes from about 200 large wells,
some of which were drilled during colonial times.
Although the city needs an estimated 3 million cubic metres of
water per day (assuming a low per-capita consumption of 200 litres per day), the
actual supply is about half that amount. This deficit has pushed many citizens
to drill or excavate their own wells, adding to the strain on groundwater
Unfortunately, no attempts have been made to develop a
comprehensive plan to manage the groundwater resources of the city. In fact,
even the detailed underground structure of the aquifers is unclear. The major
water-bearing horizons are sandy (coarse and medium) with occasional gravel. In
the north of the city, these layers are found at a depth of between 46 and 137
metres, dipping toward the south, where they lie between 187 and 274 metres
below the surface. In the Calcutta region, these layers are covered by a
confining clay layer, which disappears about 50 kilometres north of the city.
The quality of the groundwater is medium to poor. It has a
relatively high lime content and total dissolved solids (TDS) values between 500
and 2 000 ppm (hard water). The salinity increases toward the south and east
because of the proximity of the Bay of Bengal, and it may become too hard for
drinking. In the north and west, the problem is less noticeable. It also has a
relatively high iron content, which together with the lime causes corrosion in
well tubing and screens and in industrial equipment.
Recharge to the aquifer does not seem to occur under the urban
area, fortunately, because of the presence of the impenetrable clay layer. It is
believed that it takes place by infiltration in the sandy deposits located near
the surface toward the north and west of the city. It is essential to identify
and protect these areas to prevent contamination that could irreversibly harm
the underground reservoir.
The city contains about 700 kilometres of sewers and about the
same length of surface drains. Domestic and human wastes are improperly disposed
of in all areas where there are no sewers, contaminating the river. As
mentioned, contamination of the groundwater is less likely. However, there are
indications that the Farakka barrage is receiving an excessive volume of wastes
(urban and agricultural). The Ganga River basin receives practically untreated
wastes from a population of 300 million and nearly 1 million square kilometres
of active agricultural land. This will affect the quality of the water and
increase treatment costs.
For some time, Calcutta has been one of the least healthy cities
in the world because of the mismatch between population growth and investment in
infrastructure. Calcutta is probably one the first urban nightmares of the Third
World, one of the largest cities without the resources it needs to maintain the
influx of people. Although degradation of Calcuttas environment has been
somewhat slowed recently, the situation remains precarious. Considerable
investment and intelligent and imaginative planning will be necessary to
transform the city into a liveable place for the majority of its population.
Cairo: the desert megacity
Cairo developed in a fragile environment. With an average annual
rainfall of barely 20 millimetres, it depends almost exclusively on water from
the Nile River, which crosses the city in an approximate south-north direction.
The Nile valley is relatively narrow, seldom more than 20 kilometres wide, and
frequently less than 5 kilometres. The valley has developed as the floodplain of
the river, and these flatlands have been the site of development of an ancient
agricultural civilization that has occupied the region continuously from the
time of the Pharaohs (2 to 3 thousand years BC).
The regions economy was (and still is, to a large extent)
based on the use of the river waters and sediments for irrigation and
fertilization. Since the construction of the Aswan High Dam in 1960, the level
of the river has been stable, and flooding no longer occurs. Although the Nile
still provides water, the supply of nutrients and sediments has been
significantly reduced, and Egyptian farmers are increasingly dependent on
The Nile widens significantly about 100 kilometres from the
Mediterranean Sea. In this area, the riverbed separates into two main canals
(the Rosetta and Damietta canals) and many more smaller canals forming a
delta-shaped alluvial region. The city of Cairo was established a few kilometres
upstream from the widening portion of the valley. This site was repeatedly
selected as an urban centre: the Giza pyramids were built (2500-2700 BC) to the
west of the river; later, the city of On was founded as a commercial and
religious centre for the worship of Ra to the east, where Masr Gadid or New
Cairo now stands. Although there were Persian and Roman forts (Babylon) on the
site of Old Cairo, the city did not gain importance until the arrival of the
Arabs in the 7th century, when the town of Fustat was founded, gradually
extending to Askar and Katai. Almost three centuries later, the town of al
Qahira was founded in a neighbouring site and, under Saladin, the four locales
were united into a larger city.
The city has grown considerably since then. In 1991, there were
nearly 14 million people living permanently in the metropolitan area, which
extends 80 kilometres, north-south, from al-Matariyah to al-Maadi, and
more than 15 kilometres on each side of the river, particularly toward the
Cairo has been built on a plain that lies over alluvial
silt-clay deposits about 10 metres thick. Under these deposits is a 60-metre
thick, water-bearing sandy formation, which, in turn, covers Mesozoic limestones
outcropping toward the south of the urban region.
For centuries, the Nile has been (and continues to be) the main
source of water for the people of Egypt and upstream nations. Its waters are
abundant and, since construction of the Aswan Dam, shortages do not occur. Wells
are used by more distant and isolated communities. Currently, water from the
river is treated in three plants, which supply only a portion of the 3 million
cubic metres per day needed by the large metropolitan population. More than 3
million people in Cairo have no access to the urban water-supply system, and
must buy their water from the carriers (or obtain it directly from the river or
shallow wells). The number of households not connected to the system is likely
to increase as the population increases. By the end of the century, as many as 5
million people will not be served by the citys water-distribution network.
Before 1980, wastewater and sewage flowed regularly in the
lowlying streets of the city. In the early 1980s, the system was gradually
reconstructed, but at the end of the decade more than I million cubic metres of
untreated raw sewage was still entering the river; slightly less than half of
the total 2 million cubic metres of wastewater per day was treated. The disposal
of untreated sewage into natural systems is causing the spread of waterborne
diseases, especially diarrhea, and increasing the risk of cholera and typhoid.
Filtration plants are inadequate to process the increasingly polluted Nile
The gravity of the issue has pushed national authorities and
international agencies into solving some of the most pressing problems. In 1980,
an overhaul of the old system was started (Bedding 1989). The sewers were
clogged with dust, dirt, and garbage. As much as 43 thousand tonnes of muck,
untreated industrial wastes, and other substances and residues were removed from
57 kilometres of sewers over a 6-year period.
A new system is currently under construction, but will not be
finished until well into the next decade (perhaps 2005). Digging in Cairo is an
archaeological endeavour. No one knows exactly what is buried under the streets
and buildings of the city. Old pipes, graves, ancient buildings, buried tunnels,
and walls require careful excavation, which has to be carried out laterally at a
depth of more than 25 metres below ground level. This work is partly completed,
and when the system is finished, 25 cubic metres per second will be moved toward
a treatment plant that will be built 15 kilometres from the city. The plan also
includes a large 5 metre diameter tunnel to collect the sewage for later
treatment, a pumping station, and effluent canals.
Another problem affecting the city is the rise in the water
level in its aquifer, which creates problems during all tunneling operations and
for some city basements, and is threatening to cause flooding in low-lying
areas. Only a small proportion of the water recharging the aquifer is believed
to come from surface rainfall. Because groundwater levels are higher than the
Nile River, it is not a source for the aquifer. The most likely sources of
recharge seem to be the following:
· Leakage from the
· Leakage from the
· Uncontrolled disposal of
· The return flow of
The partial solution to the problem has been to pump water out
of the aquifer into the river. In 1979, nearly 300 thousand cubic metres per day
was transferred, but that was insufficient at that time. Additional pumping may
be necessary to bring groundwater down to manageable levels.
Cairo is drowning in its own population and wastes. The fragile
environment, the lack of precipitation, its dependence on a single water source
(which is also the disposal site), and the continuing growth of the city will
force the investment of large sums of money to keep the situation even partly
under control. The only final solution would be to put a halt to Cairos
growing population, something that would require a drastic review of the current
Egyptian development model.
Sao Paulo: giant of the Third World
Despite its relatively small area by Brazilian standards (245
thousand square kilometres), the State of Sao Paulo, with 33 million
inhabitants, contains about 23% of the countrys population at a density
that is among the highest in Latin America - almost 140 people per square
kilometre. The state also produces over 65% of the industrial output of the
country and is the largest agricultural producer; its sugarcane, coffee, and
citrus fruit plantations are the largest in Brazil and among the largest in the
world. Its cattle stock number nearly 12 million, and it is the biggest producer
of milk and dairy products.
The population is mainly urban (over 80%); 29 cities have
populations exceeding 100 thousand. The largest, the capital of the state, is
the city of Sao Paulo, with 17.5 million inhabitants in early 1990. The 37
municipalities forming the greater Sao Paulo metropolitan area hold 55% of the
population of the state and 15% of the total population of Brazil. The Sao Paulo
urban area alone produces more industrial goods than the rest of the country.
More jobs, by far, are created in Sao Paulo than in any other major city in
Brazil. It is not surprising, then, that the citys population has
increased through constant immigration from other areas of the country. If
current trends continue, greater Sao Paulo will hold 20 to 22 million people by
the year 2000 and 25 to 30 million by 2010.
Portuguese settlement in the Sao Paulo region began in 1532,
when Martin Alfonso de Souza founded the city of Sao Vicente on the Atlantic
coast about 400 kilometres south of the bay of Rio de Janeiro. In that part of
the country, the coastal area is a narrow plain at the foot of the Serra do Mar
escarpment, with little room for agricultural expansion. Therefore, a settlement
was needed in the interior, beyond the coastal mountains. The city of Sao Paulo
de Piratininga or Sao Paulo dos Campos (which was to become simply Sao Paulo)
was founded in 1554 on a hill between the Anhangabau and Tamanduatei rivers,
tributaries of the Tiete.
During the 17th and 18th centuries, the growth of Sao Paulo was
linked with its role as a centre for native workers for the sugarcane
plantations of the northeast and for mineral exploration in the hinterland. In
the 19th century, the city became a centre for coffee production, which would be
the main export of the region and the country for many decades. During the 20th
century, particularly during the last few decades, the citys industries
grew, producing both for national consumption and for export. Some of the most
important industrial activities include metallurgy, automobile manufacturing,
chemicals, textiles, and food.
The areas climate is humid subtropical; the average annual
temperature is 20°C, varying from an average low of 14°C in winter
(July) to an average high of 26°C in the summer (January). Sao Paulo is
among the most humid areas of Brazil. Average annual rainfall ranges from 1500
to 2000 millimetres, and can reach 3 000 millimetres in some neighbouring hilly
Although the city of Sao Paulo is in a high rainfall area, the
volume of available water is limited because of the proximity of the Serra do
Mar divide. All rivers are small, with small catchment basins, and many dams had
to be built to store the water required by this megacity. Unfortunately,
groundwater resources are not very abundant either. Sao Paulo is located on the
crystalline Brazilian shield with few hydro-geologically productive areas. The
main aquifers in the region are in the coarser sandy lenses of the Sao Paulo
formation and the thick mantle of weathered crystalline rocks. The wells in the
city are normally screened at a depth of 100 to 200 metres and can deliver 50 to
1 700 litres per minute.
In its early days, the citys water supply was brought from
several surface sources and springs by water carts of doubtful sanitary
condition (Avelima 1990). In 1877, when the citys population was about 50
thousand, the private Companhia Cantareira de Esgotos was created to manage the
water supply and sanitation. Ten years later, as a result of popular
dissatisfaction with this company, the government took it over, forming the
Reparticao de Agua e Esgotos (RAE). In 1897, the water from the Tiete River
already showed signs of contamination and, in 1914, a typhoid epidemic broke out
in the poor neighbourhoods of the city.
Originally, all of Sao Paulos water drained toward the
Parana basin. In 1920, however, a reservoir was built in the upper Pinheiro
basin (the Billings reservoir) to take advantage of the elevation of the Serra
do Mar to produce hydroelectric power and water was pumped into it from the
Pinheiro River. At that time, this river was not contaminated, because the
expanding city had not yet reached its banks. Since then, however, it has become
an open sewer, containing highly contaminated urban wastewaters and
storm runoff, which are being pumped into the Billings reservoir.
Instead of discontinuing use of the reservoir for the
citys water supply, it has been divided in two parts one that receives
water from the Pinheiro and a smaller section from which water is taken to
supply the large suburb of San Andre (with over 1 million inhabitants) and other
urban and suburban neighbourhoods. The two sections are separated by a
relatively permeable earth dam; however, the water supply is kept at
a higher level than the contaminated water to restrict flow into it.
Unfortunately, the Billings reservoir also probably receives polluted water from
urban areas encroaching on its basin. Close monitoring of the situation is
necessary to prevent the obvious hazards.
The upper course of the Tiete River, near and downstream from
Sao Paulo, has also become highly contaminated. Its waters are used to irrigate
vegetable farms, which supply Sao Paulo, then continue downstream through the
Paulista hinterland, where they supply several communities of the
interior. Several attempts to improve this situation have failed, and to correct
it now would require a huge capital investment that is not readily available.
In 1973, water management in the area was consolidated under a
new body, the Companhia de Saneamento Basico do Estado de Sao Paulo (SABESP).
SABESP has made improvements from an organizational point of view. However, the
growth of the metropolitan area has been faster than the expansion of water and
sanitation services and, as a result, such services in many urban and suburban
areas are inadequate. In a number of communities and in many industrial plants,
groundwater is used; as many as 30% of the homes in greater Sao Paulo obtain
their water from wells.
The main water supply for the city and neighbouring
municipalities is delivered from a complex network of reservoirs in many small
tributaries in the upper basin of the Tiete River, including the Billings
reservoir in the upper Pinheiro basin. A complex system of pipes, tunnels, and
storage tanks has been constructed to bring water into Sao Paulo. In 1990, total
water consumption in the greater Sao Paulo area was 50 to 55 cubic metres per
second. By the year 2000, it is expected to reach 65 to 70 cubic metres per
second; by 2010, 80 to 85 cubic metres per second - exceeding the ultimate
capacity of the citys systems.
These estimates are for water obtained from surface sources and
do not include private wells. Some groundwater is obtained for municipal use
from aquifers contained in the Sao Paulo formation and in the weathered mantle
of a crystalline complex. By far, the main users of groundwater (slightly more
than one-third) are industries, which consume 20 to 25 cubic metres per second.
Sao Paulo will face a difficult future unless plans are made to
manage its water resources more carefully. Although its environment was suitable
to satisfy the needs of a small or medium-sized city, it is inadequate to
provide water to a megalopolis of nearly 20 million