Tipos de clima do estado do Rio de Janeiro


  • Lisia Maria Cavalcanti Bernardes


Rio de Janeiro, Geografia Física, Climatologia


            In the State of Rio de Janeiro, relief and altitude are the principal factors which cause the observed diversification of the climate as well as the distribution of the various types of climate, which is directly subordinated to them.

            The "Serra do Mar" isolates on the sea-side a hot, humid lowland where a rainy season in summer and a dry season in winter are observed; this lowland disappears to the West where the escarpment of the "Serra" comes close to the littoral and appears again to the northeast on the large plain surrounding the city of Campos.

            The referred lowland is limited to the west by the basin of the Rio Guandu and it is narrower to the north of Guanabara bay due to the proximity of the "Serra".

            To the east and northeast this lowland is broader, near Cabo Frio, where the coast changes in direction, and in the plain of the lower Paraíba valley, as well as in the lower Itabapoana river.

            This narrowing or broadening of the lowland exerts an important influence on the local variations of the climate of the region.

            This climatic type, hot and humid, with summer rains and a dry season in winter corresponds to the Aw classification of Koppen.

            The general aspects of the pluviometric regime of the coastal lowland in the State of Rio de Janeiro are explained, though, by the predominance of the thunder storms of local formation, during summer, which are due to the high increase in heat of the continental equatorial mass which appears in the region during that period.

            Besides this type of. rain, the ones provoked by the cold invasions also are observed but the rainfall which they cause is not abundant except when mountainous obstacles are encountered.

            The coastal lowland appears as a region where medium temperatures are regularly elevated and its variations from place to place are minor; annual medium temperatures oscillate between 22°.1 and 21°.9, if the region immediately at the base of the "serra" is excluded,

            January and February are the hotter months, the lower mediums occurring in July.

            The climate Aw, hot and humid, with a rainy season in summer and a dry season in winter, occupies, besides the coastal lowland, a vast area In the north of the State; this area has been profoundly dissected and lowered by erosion. It is distinguished, though, from the coastal region, in what concerns to rainfall, temperatura, wind and humidity, a fact that shows the influence of a greater distance from the littoral.

            Rainfall is somewhat more abundant, the dry season much more intense, summers are hotter and amplitude greater.

            The type of climate which is more humid, though milder, on account of the altitude, appears on the slope and over the higher altitudes of the "serra" and is characterized by relief rain even during the drier period. This type of rain is also found at the base of the "serra" where temperatures, nevertheless, remain relatively elevated.

            Bearing in mind these relief rains, a super-humid climate can be plotted at the base of the "Serra do Mar".

            This effect of relief rains is particularly noted in the zones where the mountains are closer to the coast. Thus, in the zone of Paratí, Angra dos Reis and Mangaratiba, as well as at the base of the "Serra da Estrela" and "Serra dos Orgãos", this fact occurs.

            In this region, the drier month appears with ‘60 mm. (type Af of Köppen) of rainfall, though rainfall is not regularly distributed during the year. With lesser intensity, this increase in rainfall also appears along the escarpment of the "serra", where the climate is also super-humid, (more than 2.000 mm. yearly) though the dry season did not disappear totally (type Am of Köppen).

            On the slope of the "Serra do Mar" which faces the Atlantic, as well as on the higher points of the same, i.e., on the higher levels of the plateau, close to the ridge line, a mesotermic, humid climate occurs.

            The principal features of the climate of the higher zone are the high indexes of rainfall and the mildness caused by altitude.

            There is not a dry season and the rains are not evenly distributed because the proportion between summer and winter totals is almost equal to the one which appears on the lowland.

            At less than 200 m. above sea-level the temperatura decreases to less than 18 degrees during the coldest month - July - thus causing the character of the climate to change to Cfa. Above 500 m. even summers are milder and either on the Atlantic slope or in the higher points of the "serra", a mesotermic climate with mild summers and cold winters appears, thus corresponding to the Cfb and Cwb classifications of Koppen.

            To the interior, beyond the higher points of the "serra", there appears the plateau, where a mesotermic climate occurs.

            On the plateau the dry-rainy season regime reappears, and is even more conspicuous because 'it is not exposed to the coastal influences.

            Rainfall also decreases to the interior. Temperatures, on the other hand, are increased due to the lowering of the altitude caused by the proximity of the Paraíba valley. The same type of climate (Cwa) appears again on the water divides of the left margin of the Paraíba, where altitude increases to 250-300 m., the contact of these conditions with the climate, hot, which is found along valleys and lowlands.

            The same fact is repeated at the "Serra da Mantiqueira", specially on the Itatiaia, the westernmost point of the State.

            The total rainfall in this regions is of more than 2.000 mm. and monthly medium temperatures decrease to 8.4 at the summit of the Itatiaia, the annual medium being of 11.5 degrees.

            As a conclusion, the author emphasizes the importance of the "Serra do Mar" when a classification of the climates of Rio de Janeiro is to be made. The "serra" really causes a different climate on its own zone as well as it has a definite influence on the characterization of the climate of other zones, as, for instance, the part of the coastal lowland immediately at the base of its slope or the plateau which is found to the interior.