Brazil has a humid tropical and subtropical climate except for a drier area in the Northeast, sometimes called the drought quadrilateral or drought polygon, that extends from northern Bahia to the coast between Natal and São Luís; that zone receives about 15–30 inches (375–750 mm) of precipitation a year. Much of Brazil receives 40–70 inches (1,000–1,800 mm) annually, but precipitation often is much heavier in parts of the Amazon basin and the sea-facing rim of the Serra do Mar.

The central parts of the Brazilian Highlands receive most of their precipitation during the summer months (November to April), often in the form of torrential downpours. Storms and floods may strike the Northeast at that time, depending on weather patterns, but the region may also experience prolonged drought. These shifting conditions make life difficult in the sertão, the backlands of the Northeast, and are a major cause for migration out of the region. Summer temperatures are largely uniform. In January most of the lowlands average roughly 79 °F (26 °C), and the highlands are a few degrees cooler, depending on elevation. The coast of Rio Grande do Sul is also somewhat cooler, averaging around 73 °F (23 °C), whereas the Northeast backland’s drought quadrilateral, the hottest region of the country, averages some 84 °F (29 °C), with daytime temperatures exceeding 100 °F (38 °C). However, the Northeast’s low humidity makes the heat less oppressive than in Rio de Janeiro.

In the winter (May to October) the Brazilian Highlands are generally dry, and snow falls in only a few of the southernmost states. Regular frosts accompany winter air patterns from the south, and near-freezing temperatures can reach as far north as São Paulo. Cool, rainy weather may extend along the coast as far north as Recife and, in the west, to the Pantanal. Cool air occasionally spills over from the Paraguay lowlands into the western Amazon basin and may travel as far north as the Guyana border. Winter temperatures in the Amazon lowlands remain virtually unchanged from those of the summer months, but temperatures in the drought quadrilateral drop to about 79 °F (26 °C). Temperatures in the Brazilian Highlands average about 68 °F (20 °C) in the central and northern regions and are cooler toward the south: Curitiba, at an elevation of some 3,000 feet (900 metres), averages 57 °F (14 °C) in June and July. During those months the mean temperature at Porto Alegre is the same, but Rio de Janeiro is much hotter, averaging 73 °F (23 °C), partly because of the warm currents that bathe the entire Brazilian coast.

Soils

Brazil’s soils form a vast and intermixed pattern. A large band of nutrient-rich, deep reddish purple soil (terra roxa) lies in the Southeast and South between central Rio Grande do Sul and southern Minas Gerais, including large areas of Paraná and São Paulo states. That region contains Brazil’s most heavily farmed lands; however, terra roxa is not necessarily more productive than soils in other regions of the country. Soils in the Northeast also contain many nutrients, but agriculture is limited there because few fields are irrigated. Heavy rainfall has intensely leached many soils, leaving them with few nutrients but with an overabundance of insoluble iron and aluminum silicates. Laterites (soils dominated by iron oxides) and other infertile soils are especially prevalent in the Brazilian Highlands, where they can reach depths of as much as 90 feet (27 metres).

Amazonian soils are also leached but not as deeply. In the terra firme of the rainforest, dead organic matter quickly decays and is recycled. However, once the overlying forest canopy is destroyed—e.g., by clear-cutting or burning—that regenerative cycle is interrupted, and many nutrients and organic matter are lost. More fertile Amazonian soils, interspersed between the zones of leached soil, include várzea alluvial deposits and terra preta dos indios (“black earth of the Indians”), which has developed throughout Amazonia on the sites of prehistoric settlements.

Plant and animal life

Amazonia

The Amazon basin has the greatest variety of plant species on Earth and an abundance of animal life, in contrast to the scrublands that border it to the south and east. The Amazonian region includes vast areas of rainforest, widely dispersed grasslands, and mangrove swamps in the tidal flats of the delta. Individual plants of most species tend to be widely dispersed, so that blights and other natural threats cause them only limited damage. A typical acre (0.4 hectare) of Amazonian forest may contain 250 or more tree species (in contrast, an acre of woods in the northeastern United States might have only a dozen species).

The crowns of giant Amazonian trees form a virtually closed canopy above several lower canopy layers, all of which combine to allow no more than 10 percent of the sun’s rays to reach the ground below. As a result, more plant and animal life is found in the canopy layers than on the ground. The tallest trees may rise to 150–200 feet (45–60 metres) and are festooned with a wide variety of epiphytes, bromeliads, and lianas, while their branches teem with animal life, including insects, snakes, tree frogs, numerous types of monkeys, and a bewildering variety of birds. Several hundred bird species nest in the immediate vicinity of the main Amazon channel, and alligators, anacondas, boa constrictors, capybaras, and several smaller reptiles and mammals are found along the riverbanks. In the waters are manatees, freshwater dolphins, and some 1,500 identified species of fish, including many types of piranhas (not all of them flesh-eating), electric eels, and some 450 species of catfish. There may also be hundreds of unidentified species.

The Amazon is also home to the world’s largest freshwater turtle, the yellow-headed sideneck (Podocnemis), which weighs an average of 150 pounds (70 kg) and is extinct everywhere else except on the island of Madagascar. The turtles, once a mainstay of local Indians’ diets, are now endangered, but they continue to be hunted illegally for their meat.

Conservation and ecology

Dozens of parks, biological reserves, and other protected areas have been established in Brazil’s vast wildernesses, many of which remain pristine; however, state and federal governments have not adequately maintained many parklands, and some have been modified to allow for new highways or other construction projects. In addition, pollution has degraded Brazil’s rivers, threatening the water supplies of most of the population, and ecological disasters are common: in 2000 alone there were major oil spills in Rio de Janeiro’s Guanabara Bay and in the Iguaçu River. The Brazilian government’s environmental agencies regularly fine manufacturers and mining companies for failing to provide adequate environmental safeguards, but the fines are often small and oversight lax. São Paulo and some other cities have dangerous levels of smog, mainly because of motor vehicle emissions; in response, the government has promoted the use of fuels containing ethanol and pollution-control policies to improve air quality. In the late 20th century Curitiba, one of Brazil’s larger cities, rapidly decreased local air pollution and traffic congestion by developing an innovative busing system and other programs.

Brazil’s first conservation law, issued in 1797, prohibited the burning or destruction of forests. The country’s first national parks were created in the late 1930s. From the mid-20th century, Brazilian and international environmental organizations have pressured the national government to curb damage to the Amazon rainforest, the Pantanal, and other ecosystems in Brazil. The government has become increasingly willing to address environmental issues, although widespread destruction has continued. The chief Brazilian environmental agency (Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis, or IBAMA) was created in 1989 in an attempt to reform Brazil’s conservation system. IBAMA, which operates under the Ministry of the Environment, oversees the use of renewable resources, enforces federal environmental laws, and coordinates the efforts of various agencies. However, IBAMA has had limited funding and personnel: in the late 20th century it employed only one staff member for every 110 square miles (290 square km) of federally protected land. In 1992 Rio de Janeiro hosted the United Nations Conference on the Environment and Development (the Earth Summit), and a few years afterward Brazil and the major developed countries of the world issued a joint plan for the protection of the rainforest. (See also Amazon River: Ecological concerns.)

Many state and national parks are located near urban centres, but most of the newer national parks lie in remote areas, particularly at the headwaters of Amazon tributaries and adjacent to biological reserves or Indian reservations; they are not intended for any great number of visitors. Among the more popular national parks are Itatiaia, Iguaçu, and Serra dos Órgãos, all of which were created in the 1930s. The larger national parks, which range in size from roughly 2,170 to 8,770 square miles (5,620 to 22,700 square km), include Neblina Peak (1979), Jaú (1980), Amazônia (Tapajós; 1974), Serra do Divisor (1989), Pacaás Novos (1979), and Cape Orange (1980), all in the North, and Xingu (1961) and Araguaia (on Bananal Island; 1959), both in the Central-West. In the mid-1980s the United Nations Educational, Scientific and Cultural Organization (UNESCO) designated Iguaçu Falls a World Heritage site, followed by Serra da Capivara National Park in 1991 and two coastal regions in 1999, including the Serra do Mar in the Southeast and the Discovery Coast of Bahia state.