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Water Resources in the Brazilian
Hydrographic Regions
Water availability and use
For the purpose of water resources management and following
the spirit of the Water Law, Brazil has been divided into hydrographic
regions. A hydrographic region is a catchment or group of contiguous catchments
in which the principal river flows to the sea or into another country.
There are twelve Brazilian hydrographic regions (Figure 4), namely:
1) Amazon;
2) Tocantins;
3) Parnaíba;
4) São Francisco;
5) Paraná;
6) Paraguay;
7) Uruguay;
8) Coastal region of the North;
9) Coastal region of the Western Northeast;
10) Coastal region of the Eastern Northeast;
11) Coastal region of the Southeast, and
12) Coastal region of the South.
The annual mean discharge of Brazilian rivers is around
182,600 m3/sec. Taking into account the rivers that rise in the Amazon
region and discharge in neighboring countries, estimated at 89,000 m3/sec,
total water availability reaches the order of 272,000 m3/sec.
Figure 4
Brazilian Hydrographic Regions - Area, Population and Mean Discharge
Percentages in relation
to Country Totals. |
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Table 1 presents data on water availability and demand
in the hydrographic regions. Over 70% of surface water resources are in
the Amazon region, with 47% of the country’s land area. Water balance
data show Brazil’s great diversity, in hydrological terms. Discharges
vary from about 34 l/s/km2, in the Amazon Region and Coastal
Region of the North, to 4 l/s/km2 in the Coastal Region of
the Eastern Northeast, and São Francisco and Paraguay regions.
Similar to other countries, agriculture uses most of the water produced,
especially irrigation, at almost 63% of the total, as indicated in Figure
5. Domestic use follows (urban and rural, 18%), then industry (14%) and
finally livestock (5%).
Figure 5
Percentage Distribution of Water Demands in Brazil |
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Among large Brazilian rivers, only the Amazon and the Paraguay are predominantly
plains rivers and widely used for navigation. The São Francisco
and the Paraná are the main plateau rivers. Before analyzing the
summary of water availabilities and demands, the observations in Table
No.2 should be noted. There is, unfortunately, no database available divided
along the lines of the water resources management units, the catchments.
Therefore several of the maps shown in the following figures use different
divisions: states, power generation basins and others. The consistency
of results consequently suffered. Even so, the decision was taken to publish
these results as a first approximation. For the next edition, the National
Water Agency is in contact with the Brazilian Geographical and Statistics
Institute (IBGE) to seek an agreement to work with its new territorial
division.
Figure 6 shows per capita water availability by hydrographic
region: (average discharge divided by total population) using data from
the 2000 census, which arrived at almost 34,000 m3/inhab/year for Brazil.
As can be seen, this indicator varies considerably.
The most critical situation is observed in the Coastal Region of the Eastern
Northeastern, in the catchments of: the Capibaribe River, Pernambuco,
at 428m3/inhab/year; the Inhambupe River in Bahia and Sergipe, at 479
m3/inhab/year; and the Vaza Barris River, in Bahia, at 610m3/inhab/year.
On more aggregate levels, in the same region, numbers such as 740 m3/inhab/year
are observed for Pernambuco/East; 886 m3/inhab/year for Paraiba/East;
1024 m3/inhab/year for the Potiguar/East region in Rio Grande do Norte;
and 1,165m3/inhab/year in the Rio de Contas catchment in Bahia. Low availability,
associated, however with a high concentration of population, and this
situation is also found in the Tietê catchment, in the state of
São Paulo, at 810 m3/inhab/year, part of the Paraná hydrographic
region, in the Southeast of Brazil.
In contrast, in the Amazon hydrographic region, in the
north of Brazil, the highest per capita availability rates in the country
are found – 558,000 m3/inhab/year, and in the Coastal Region of
the North (Oiapoque, Amapari and Calçoene Rivers), the number is
1.7 million m3/inhab/year.
Methodological Considerations
The main source of information regarding water
resources availability and demand was the 1998 study “National
Water Resources Plan”, prepared by the Getulio Vargas Foundation
(FGV), for the Water Resources Secretariat of the Ministry of the
Environment, which accepted the hydrographic division used by the
Brazilian Electric Power Agency (ANEEL), with a few small changes,
especially in the São Francisco and Paraná regions.
On the other hand, the hydrographic division of Brazil was based
on the recent classification made by the IBGE with ten regions.
This classification is more detailed than the one in the FGV study
of the coastal region of the country, while the opposite occurs
in the other regions.
The hydrographic subregions used by FGV were thus employed, following
IBGE classifications, to maintain the characteristics of the Tocantins,
São Francisco, Paraná, Uruguay and Southern Coastal
Regions. For this reason, in the figures containing information
by hydrographic region, the spatial variation of the indicator can
be seen, within the IBGE region, by means of the change in color
(For instance, figure 6, in the Paraná basin).
These procedures required adjustments and simplifications in some
areas and are being improved.
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Figure 6
Mean Discharge per Inhabitant in the Brazilian Hydrographic Regions
in the year 2000 |
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BRAZIL 33.900 M3/INHAB/YEAR |
Figure 7 shows population density per hydrographic region, expressed in
terms of inhab/km2. The average demographic density in the
country, approximately 20 inhab/km2, ranging from 1.9 inhab/km2
in the Amazon region and 0.6 inhab/km2 in the Coastal Region
of the North; to 126 inhab/km2 in the Coastal Region of the
Southeast; or 385 inhab/km2 in the Tietê catchment, part
of the Paraná Region; and 773 inhab/km2 in the Macaé
catchment, in the Coastal Region of the Southeast.
The problem of lack of water for human use occurs in the Brazilian hydrographic
regions with high population densities and average to low discharges.
The greatest availability of water for human uses found in areas with
high discharges and with low population density. This is particularly
true of the Amazon Region and Coastal Region of the North, and northwest
sector of the Tocantins Region, as shown in Figure 8, with an average
discharge in L/s.km2. These are regions with few water use
conflicts, with some cases of pollution close to the urban centers of
these regions. In the case of the Amazon hydrographic region, besides
its high natural availability, water inflow brought by rivers draining
areas of neighboring countries within the Amazon Region is also important.
Figure 7
Demographic Density in the Hydrographic Regions of Brazil |
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| BRAZIL 20 hab/KM2 |
Figure 8
Mean Discharge in the Brazilian Hydrographic Regions |
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| BRAZIL 21 L/s.km2 |
There are regions in Brazil where, despite the high natural
availability of water, their intense and disorganized settlement has generated
problems of water disputes, mainly due to scarcity of water of the required
quality. The South and Southeast Coastal hydrographic regions fit into
this category.
At the other extreme, there are regions with little
natural water availability, such as the coastal hydrographic regions of
the Eastern Northeast, the Parnaíba, the São Francisco and
the Paraguay. In those regions there is usually an association between
low rainfall and high evaporation levels.
This picture of low natural availability of water, associated
with higher population densities, leads to conflicts over water use, as
in the hydrographic coastal regions of the Eastern Northeast, and in part
of the Parnaíba and São Francisco hydrographic regions.
In these regions, the lack of regular rainfall, not only throughout the
year but also in multi-annual periods, further worsens the dispute over
water and the regions’ social problems. It is, however, in the semi-arid
areas of these regions that drought hits hardest and water means survival.
In the regions with naturally low discharge, but also
sparsely occupied, such as the plains of the Paraguay hydrographic region
(Pantanal), there are few recorded cases of water use conflicts. In the
case of this region, due to its low declivity, low availability is compensated
by the accumulation of water in the watercourses and lakes draining from
the headwaters of the rivers in the Pantanal. The range of landscapes
and wealth of local fauna and flora, make this a region of great ecological
interest for the country.
In other hydrographic regions of the country, such as
the Paraná and Uruguay catchments, the upper courses of the Tocantins
and São Francisco rivers, as well as in part of the coastal hydrographic
regions of the Southeast and South, water use conflicts are essentially
about pollution, limiting possible options for its use, or arise because
of the excessive use of water for irrigation.
In Figure 8 there may be some inconsistencies in the
data presented, such as the variations in discharges in regions such as
the Tocantins, the São Francisco and the Amazon (at the border
between the states of Amazonas and Pará).
In Brazil, the volume of subterranean water has been
estimated at 112,000 km3. Estimates indicate that there are
approximately 300,000 wells being used, and over 10,000 more are bored
every year. Cities such as: Ribeirão Preto (SP), Mossoró
and Natal (RN), Maceió (AL), the metropolitan region of Recife
(PE), and Barreiras (BA) depend wholly or partly on subterranean water
for their supply. In Maranhão more than 70% of the towns are supplied
by underground water. In Piauí this is over 80%.
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