Tropical (dry Winter and humid Summer)
Semi-arid Tropical (Tending to dry due to the irregularity of the action of the masses of air)
Coastal (Influenced by the Marine Tropical Mass)
Brazil, due to its continental dimensions, possesses a very wide climatic diversification, influenced by its geographical configuration, its significant coastal extension, its relief and the dynamics of the masses of air on its territory. This last factor assumes great importance, because it acts directly on the temperatures and the pluviometric indexes in the different areas of the country.
The masses of air, especially those that occur more directly in Brazil, are, according to the Statistical Annual of Brazil (of the IBGE), the Equatorial air mass, that is divided in Continental Equatorial and Atlantic Equatorial; the Tropical air mass, also divided in Continental Tropical and Atlantic Tropical; and the Polar Atlantic air mass. All these air masses provides the climatic differentiations in Brazil.
In this sense, are noticed in the country climates varying from very humid and hot climates, coming of the Equatorial air masses, as it is the case of great part of the Amazon area; to very strong semi-arid climates, as those native of the hinterlands of the northeastern Brazil. The climate of a given area is conditioned by several factors, among them are: temperature, rains, atmospheric humidity, winds and atmospheric pressure - which, in turn, are conditioned by factors such as altitude, latitude, relief characteristics, vegetation and continentality.
In agreement with Arthur Strahler's climatic classification, five major climates prevail in Brazil:
Great variations in temperature occur within Brazil. The following map illustrates average temperatures. As can be seen, the North Area and part of the interior of the Northeast region experience annual medium temperatures above 25oC, while in the South Area of the country and part of the Southeast the annual medium temperatures are below 20oC.
- humid equatorial climate caused by the convergence of the trade winds - this includes Amazônia;
- tropical climate alternately humid and dry - this includes the greater part of the central area of the country and the coast of the middle-north;
- tropical climate tending to be dry due to the irregularity of the action of the masses of air - this includes the hinterlands of northeastern Brazil and the medium valley of the river São Francisco;
- coastal humid climate exposed to the marine tropical masses - this includes narrow strips of the coast - east and northeast.
- humid subtropical climate of the oriental and subtropical coasts, dominated mainly by marine tropical mass - this includes the South Area of Brazil.
Above 25ºC Between 20ºC and 25ºC Below 20ºC Annual Averages of Temperature MapAs shown by data gathered by FIBGE, absolute maximum temperatures above 40oC are observed in interior lowlands of the Northeast Area; in the depressions, valleys and lowlands of the Southeast; in the Pantanal and lowered areas of the Middle-West; and in the central depressions and in the valley of the river Uruguay, in the South Area. Absolute minimum temperatures, with frequent negative values, are observed in the mountainous summits of the southeast and in a large part of the South Area, where they are accompanied by frosts and snow.Source: Atlas Escolar Melhoramentos
The following table shows the maximum and minimum air temperatures at the Brazilian state capitals:
|RO||Porto Velho (4)||34.8||15.0|
|AC||Rio Branco (4)||35.6||-|
|MA||São Luís (1)||32.8||20.6|
|PB||João Pessoa (5)||31.2||19.0|
|MG||Belo Horizonte (3)||32.3||10.0|
|RJ||Rio de Janeiro||-||-|
|SP||São Paulo (5)||33.9||4.4|
|RS||Porto Alegre (5)||37.2||-0.2|
|MS||Campo Grande (4)||35.3||4.1|
Notes: (1) referring data for 1989; (2) referring data for 1990; (3) referring data for 1991; (4) referring data for 1992; and (5) referring data for 1993.
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For a more detailed characterization, select the area of interest.
The North area of Brazil embraces a great part of the Amazon Basin, representing the largest extension of hot and humid forest on the planet. The area is cut, of an end to the other, by Ecuador and is characterized by low altitudes (0 to 200 m). There are four main systems of atmospheric circulation that act in the area, they are: system of winds of Northeast (NE) to East (E) of the Atlantic South and Açores, subtropical anticyclones, generally stable in nature; system of winds of West (W) of the mass equatorial continental (mEc); system of winds of North (N) of the Convergence Intertropical (CIT); and system of winds of South (S) of the Polar anticyclone. These last three systems are responsible for variability of the climate and for the rains in the area.
With regard to temperatures, the climate is hot, with annual medium temperatures ranging from 24o to 26oC.
Regarding the pluviosity, there is not a homogeneity as it occur with the temperature. In the mouth of the river Amazonas, in the coast of Pará and in the western section of the area, the total annual pluviometric index exceeds 3,000 mm in general. In the direction NO-SE, of Roraima to east of Pará there is less rain, with annual totals in the order of 1,500 to 1,700 mm.
The rainy period of the area occurs in summer & autumn, the exception being Roraima and of the north part of Amazonas, where the maximum pluviometric indexes occurs in winter, due to influence of the climatic conditions of the Northern Hemisphere.
The climatic characterization of the Northeast area is a little complex, and the four systems of circulation that influence the region are denominated Systems of Disturbed Currents of South, North, East and West.
The System of disturbed currents of South is represented by the polar masses that reach the area in the spring-summer, acts in the coastal areas until the south of Bahia, bringing frontal and back-frontals rains. In the winter the polar masses reach even the coast of Pernambuco, while the hinterlands regions remain under the influence of the tropical mass.
The system of disturbed currents of North, represented by Convergence Intertropical (CIT), produces rain from the summer to the autumn even in Pernambuco, in the vicinity of the Raso da Catarina. On the other hand, the currents of the East are more frequent in the winter and they usually produce abundant rains in the coastal regions, rarely reaching the scarps of the Plateau of Borborema (800 m) and of Chapada Diamantina (1,200 m).
Finally, the system of currents of the West, brought by the lines of Tropical Instability (IT), occur from the end of spring to the beginning of autumn, rarely reaching the states of Piauí and Maranhão.
Thermal temperatures are high, with annual averages between 20oC and 28oC, maximums of around 40oC having been observed in the south of Maranhão and Piauí. The months of winter, mainly June and July, produce minimum temperatures between 12oC and 16oC in the coastal regions - much lower in the plateau regions where temperatures of 1oC have been recorded in Chapada Diamantina after the passage of a polar front.
The pluviosity of the area is complex and is source of concern: its annual totals vary from 2,000 mm to values even lower than 500 mm, as verified in the Raso da Catarina, between Bahia and Pernambuco, and in the depression of Patos in Paraíba. In a general way, the annual medium precipitation in the northeast area is lower than 1,000 mm - in the city of Cabaceiras, interior of Paraíba, was observed the smallest annual pluviometric index registered in Brazil, 278 mm/year. Besides it in the interior of this area the rainy period is usually of just two months in the year, sometimes not coming in some years, causing then the denominated regional droughts.
The latitudinal position where is Tropic of Capricorn, the very uneven topography and the influence of the systems of disturbed circulation are factors that influence a lot the climatology of the Southeast, that is quite diversified in relation to the temperature.
The annual medium temperature ranges from 20oC, as verified in the border between São Paulo and Paraná, to 24oC, in the north of Minas Gerais, while in the elevated areas of the Serra do Espinhaço, Serra da Mantiqueira and Serra do Mar, the average medium temperature can be inferior to 18oC, due to the conjugated effect of the latitude with the frequency of the polar currents.
In the summer, mainly in the month of January, the normal average temperatures range from 30oC to 32oC in the valleys of the rivers São Francisco and Jequitinhonha, in the Zona da Mata (Zone of the Forest) of Minas Gerais, in the coastal lowlands and to west of the state of São Paulo.
In the winter, the normal average temperatures range from 6oC to 20oC, with minimum absolute from -4o to 8oC, the lowest temperatures being registered in the highest elevations. Vast areas of Minas Gerais and São Paulo register occurrences of frosts, after the passage of the polar fronts.
As far as the incidence of rain is concerned, there are two areas with heavy precipitation: one following the coast and the Serra do Mar, where the rains are precipitated by the southerly currents; and the other of the west of Minas Gerais to the Municipal district of Rio de Janeiro, where the rains are brought by the Westerly system. The annual precipitation total in these areas is in excess of 1,500 mm. In the Serra da Mantiqueira these indexes surpass 1,750 mm, and at the summit of Itatiaia, 2,340 mm.
In the Serra do Mar, in São Paulo, it rains on the average more than 3,600 mm. Near Paranapiacaba and Itapanhaú maximum rainfall was measured at 4, 457.8 mm, in one year. In the valleys of the rivers Jequitinhonha and Doce the smallest annual pluviometric indexes are recorded at around 900 mm.
The maximum pluviometric index of the Southeast area usually occurs in January and the minimum in July, while the dry period is usually concentrated in winter, lasting six months, in the case of the valleys of the rivers Jequitinhonha and São Francisco, to as much as two months in the Serra do Mar e Serra da Mantiqueira.
The South region is located below the Tropic of Capricorn, in a temperate zone. It is influenced by the system of disturbed circulation of the South, which produces the rains, mainly in the summer. It is also influenced by the system of disturbed circulation of theWest, that brings rains and storms, sometimes hail, producing winds with bursts of 60 to 90 km/h.
Regarding temperatures: the winter is cold and the summer is hot. The annual medium temperatures range from 14oC to 22oC, and in places with altitudes above 1,100 m, drops to approximately 10oC.
In the summer, mainly in January, in the valleys of the rivers Paranapanema, Paraná and Ibicuí-Jacuí, the medium temperature is in excess of 24oC, and the medium temperature of the river Uruguay surpasses 26oC. The average maximum temperature stays around 24oC to 27oC on the elevated surfaces of the plateau and, in the lowest areas, between 30oC and 32oC.
In the winter, mainly in July, the medium temperature stays relatively low, oscillating between 10oC and 15oC, except for the valleys of the rivers Paranapanema and Paraná, besides the coast of Paraná and Santa Catarina, where the averages are approximately 15oC to 18oC. The average maximum temperature is also low, around 20oC to 24oC, in the big valleys and in the coast, and 16oC to 20oC in the plateau region. The average minimum temperature varies from 6oC to 12oC, and the thermometer frequently registers temperatures near 0oC, sometimes even reaching negative indexes, accompanied by frost and snow, in consequence of the invasion of polar masses.
The annual medium pluviosity oscillates from 1,250 to 2,000 mm, except along the coast of Paraná and west of Santa Catarina, where the values are in excess of 2,000 mm, and in the north of Paraná and in a small coastal area of Santa Catarina, which have lower recordings down to 1,250 mm. The maximum pluviometric indexes occur in the winter and the minimum in the summer throughout almost the whole area.
Three systems of circulation occur in the Middle-West region: the system of disturbed currents of the West, represented by unstable events during the summer; system of disturbed currents of the North, represented by Convergence Intertropical (CIT), that produces rains in the summer, autumn and winter in the north of the region; and the system of disturbed currents of the South, represented by the polar fronts, invading the area in the winter with great frequency, producing rains of one to three days duration.
In the north and south extremes of the region, the annual medium temperature is 22oC and in the Chapadas it varies from 20oC to 22oC. In the spring & summer, temperatures are commonly high, the average of the hottest month varying from 24oC to 26oC. The average of the maximum temperatures of September (hotter month) oscillates between 30oC and 36oC.
The winter is an interesting season - low temperatures occurring quite frequently. This is caused by the polar invasion, that produces the cold weather which is very common at this time of the year. The medium temperature of the coldest month oscillates between 15oC and 24oC, and the average of the minimum temperatures ranges from 8oC to 18oC. Minimum temperatures are sometimes negative.
The characterization of the pluviosity of the region is almost exclusively due to the system of atmospheric circulation. The annual medium pluviosity varies from 2,000 to 3,000 mm in the north of Mato Grosso, to 1,250 mm in the Pantanal mato-grossense.
In spite of this inequality, the region is well provided with rain. Its seasonality is typically tropical, with maximum in the summer and minimum in the winter. More than 70% of the total rain that is accumulated during the year falls from November to March. The winter is excessively dry, because the rains are very rare.
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