Brazil is a little larger than the Australia; almost half of South America falls within its borders. Extending from 5° N to 34° S, it is broadest at about 7° S, the greater part of the country lying within the tropics. Unlike most other South American countries, it does not include any part of the Andes Mountains, so no area of the country has permanent snowfields.
The highest areas within Brazil just fail to reach 3,000 m/10,000 ft and there are no large areas above 1,800 m/6,000 ft.
The two largest physical regions of the country are the Amazon basin and the Brazilian plateau. The Amazon basin occupies the whole north and centre of the country and is everywhere below 300 m/1,000 ft; it has the climate of an equatorial lowland with few differences from place to place.
The Brazilian plateau lies to the south and east of the Amazon basin and is highest near the Atlantic coast. Most of the plateau has an average height of 600-900 m/2,000-3,000 ft, and it decreases in height northwards and westwards towards the basins of the Amazon and Paraguay rivers.
From Recife in the north to Porto Alegre in the south, the Atlantic coastlands of Brazil are narrow and are overlooked by the hills forming the high edge of the plateau. Only around the mouth of the Amazon in the north are there extensive lowlands on the Atlantic coast.
This geography makes for a simple division of the country into four climatic regions: the Amazon basin, the Brazilian plateau, the coastlands within the tropics and the southern states of Paraná, and Rio Grande do Sul and Santa Catarina. This last division is distinctive because it is outside the tropics and has a temperate climate similar to that of Uruguay, but modified by the greater height of the interior.
The Amazon Basin
Temperatures are typically tropical in all months with average midday temperatures in the range 27° C/80° F -32° C/90° F. Frost is unknown, although in the southern parts of the region occasional cold spells, lasting a day or two and known as friagem, cause night temperatures to fall below 10° C/50° F.
These spells are most uncomfortable for the local inhabitants, who then stay indoors and light fires. They are most likely to occur at the time of low sun between May and September. They are caused by invasions of cold air, originating from Antarctica and the southern oceans, which track northwards across Argentina and Paraguay into central Brazil.
Excessively high temperatures are almost unknown in the Amazon basin; daytime temperatures of 38° C/100° F are very rare. The high humidity and the monotony of the temperature from day to day make this area unpleasant for those unfamiliar with, or unacclimatized to, the hot, wet tropics, but conditions are not physically dangerous.
Belém at the mouth of the Amazon is the wettest place and the heaviest rainfall comes in the months January to May, but all months have many days with rain.
Sena Madureira in the extreme southwest of the region is nearer the Andes and so wetter. Being farther south, it has a greater concentration of rain in the period of high sun from December to March and a distinct drier season at the time of low sun. Hours of sunshine a day range from three to four in the wetter months to seven to eight in the drier season.
The Brazilian Plateau
With the exception of the northeast of this region, in the valley of the river São Francisco and the province of Ceará, annual rainfall is about 1,250 mm/50 in - 1,500 mm/60 in. There is a very distinct wet season at the time of high sun, with almost all the rain falling between October and April. The remaining months are almost dry.
The dry region in the northeast not only has a much lower average rainfall, with many places receiving less than 750 mm/30 in, but the rainfall is most unreliable from year to year. This district suffers many prolonged droughts, which cause great distress and damage to both agriculture and cattle rearing. Average conditions in this dry region are represented by the table for Iguatú.
The table for Goiás is representative of conditions in the area of the new capital of the country, Brasília, which has not been established long enough for reliable weather statistics to be collected. The tables for Goiás and the Paraná both show conditions over the wetter parts of this region.
There is not a great variation in average monthly temperatures around the year but during the drier months of low sun the daily range of temperature is greater because the nights are generally clear and the days sunnier. These months are the most comfortable because midday humidity is lower. The wet season has more cloud, higher humidity and higher night temperatures.
Average daily sunshine hours in this region range from five to six during the wetter months to as much as nine to ten during the dry season. Frost is virtually unknown except in some valleys in the extreme south or on the higher parts near the east coast.
The East Coast within the Tropics
Near the mouth of the Amazon all months are wet but rainfall is greater in the months December to May, as shown by the table for Belém. From about 3° S to Bahía at 14° S the wettest months are from May to August and the rest of the year is comparatively dry (see the table for Recife). This unusual regime of rainfall only applies to the coastal lowlands; inland on the plateau the rainfall is less and the wet season is the period of high sun.
South of Bahía, near Sao Paulo, the distribution of rainfall changes and the table for Rio de Janeiro shows that the wettest period is from November to April. Here some appreciable rainfall occurs in all months. Nowhere on this coast do maximum temperatures rise so high as to be uncomfortable, though the combination of warmth and humidity can be uncomfortable at night. Daytime heat is often tempered by the sea breeze.
Along this coast, from Recife southwards, cloudy and cool weather with some rain or drizzle may last for a few days at the period of low sun. As the tables show, temperatures never drop very low and frost is unknown on the coast but in the hills, behind Santos, occasional frosts may damage the valuable coffee crop.
Hours of sunshine on the coast are less round the year than at similar latitudes inland on the plateau. They average from five to six in the wetter season to six to seven in the drier months.
The Southern States of Brazil outside the Tropics
As the table for Porto Alegre shows, even on the coast there is a distinct cooler season when frost can be expected in the winter months. Here winter has a real significance and the difference between the seasons is determined by temperature rather than rainfall.
On the coast rainfall is well distributed throughout the year but the cooler months are also slightly wetter. This area is affected by travelling depressions which form in the disturbed region of the westerlies farther south, and by more frequent invasions of cold air from the Antarctic.
During the warmer summer months temperatures reach similar levels to those found farther north in the tropical regions of Brazil. This region has a generally healthy and pleasant climate with an average of eight to nine hours' sunshine a day in the summer months.
Inland where the land is higher, frosts are quite common in winter but snow is very rare. Inland the wettest months are during the summer, in contrast to the coastal district.