Geography
Aridity and poverty in the Brazilian Northeast

Danilo Antón

The Brazilian northeast is the poorest region in the Brazilian subcontinent. Insufficient rains and a rough  has produced a tough human environment. Poverty and emigration are common. From Piauí to the hinterland of the Bahia state, the Northeast has a shared history of exploitation, poor practices of farming, slavery and frustrated rebellions. However, the main limitations of the area relate to the climatic and ecological environment.

I Climateⁱ

The Northeastern region of Brazil, possesses a hot and humid climate with a short dry season along the coast, and a hot and semiarid climate in the interior. Much of the region is a transition from the dry hinterland to the more humid coastal plains.

In the proximity of the ocean (up to about 50 to 100 km from the shoreline) annual precipitations exceed 1000 mm (i.e. Alagoas, Pernambuco, Paraiba, Rio Grande do Norte) reaching more than 2000 mm in some ocean-facing slopes.

As described earlier, rainfall in semi-arid areas varies from 800 mm per year to slightly below 400 mm in the driest zones of the sertão, The dry season occurs from July through September. Rainfall takes place in the Southern Summer (January through March). However, actual precipitations during the rainy season may be very irregular.

Mean monthly temperatures have small variations throughout the region, and they are more influenced by altitude than sun exposure. Annual medium temperature in the plains varies between 24 C^o (coast) and 26 C^o (interior).

Clouds and fogs can form in the highest areas even during the dry season, reducing sun exposure to less than 5 hours per day in the planalto (i.e. plateau), while the plain areas are subject to higher sun exposure, up to seven hours daily or more.

II) Geology and geomorphology

Northeastern Brazil geomorphology has developed on a very ancient shield bedrock, with cratonic (stable) geological behavior. Sedimentary basins formed along the eastern and northeastern edges of the region (Sergipe- Alagoas and Potiguar-Recife sedimentary basins), and in the Northwest and West, the large Parnaiba- Maranhão sedimentary basin and the nearby São Luis and Barreirinhas sedimentary basins, and the São Francisco sedimentary basin in the Southwest.

There are also several smaller sedimentary basins inland, within the shield region, of which the largest is the Araripe basin (approximately 15,000 km², 200 km long and about 100 km wide) which is located in the boundary of the states of Pernambuco, Piauí and Ceará..

Old erosion surfaces are found next to the water divides of the main hydrographic basins (i.e. between the Tocantins and the São Francisco, between the São Francisco and the northeastern basins) forming “chapadas” (plateaus)ⁱⁱ. Chapada soils are normally shallow and, because they have suffered long geological lixiviation, their fertility levels are low. Vegetation in drier chapadas is caatinga (see section 3), while more humid chapadas next to the coastal plain may possess other types of ecosystems (agreste).

Old chapadas are separated by erosion river valleys, often filled with alluvial deposits containing local aquifers that are normally used for water supply and irrigation.

Downstream, alluvial plains become wider until they merge with the coastal Tertiary and Quaternary formations (dunes, beach, lower valley alluvial and estuarine deposits)

III) Soils

In the interior of the Northeast region soils are shallow, particularly in the erosion surfaces and slopes. In the upper chapada flat areas fertility is low due to lengthy lixiviation. In the lower areas (alluvial valleys) soils are deeper and more fertile (more productive), but they may have salinity problems (often induced by inadequate irrigation management). However, due to their medium to high fertility and the persistent warm temperatures, if water resources (i.e. irrigation) are available, farming productivity can be very important.

Brazilian Northest; Biological environment

I) Caatinga

Caatinga (“white bush” in tupi language) occupies about 730,000 km² (7% do Brazil) and can be found in all northeastern states: Maranhão, Piauí, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Sergipe, Alagoas and Bahia (and North of Minas Gerais)

Caatinga is formed by cactus, bushes and small trees adapted to dry and hot conditions. The main adaptations of caatinga species are thorns, fleshy and/or small leaves, which also tend to fall during the dry season, and well developed root systems.

There are two types of caatinga the “Caatinga Hipoxerófila” typical of less extreme climate, as for instance the coastal “baixada” (slopes), and the hyper-xerophile caatinga, found in the driest regions, with thorny bushes and trees, and cactuses.

II) Agreste

Agreste is a transition zone between “caatinga” and tropical forest, including more and larger trees than in caatinga, but less than in the tropical forest. It is composed of trees, bushes and an undergrowth of herbaceous plants.

III) Cerrado

Cerrados (from the Spanish word “closed”) are a typical ecosystem of the Brazilian interior. In the Northeast they are found in the Western plateaus of the “sertão baiano”. They are composed of low canopy trees with a bushy and grassy undergrowth, producing a dense configuration difficult to penetrate.

IV) Tropical forest (mata umida)

The mata úmida or tropical forest, composed of trees with tall canopies, is found in coastal areas and in mountain valleys and lower slopes in the proximity of the sea.

In a large measure, these forests have been eliminated (logged, burned), often to make place for plantation activities. The present extension of “mata úmida” is today restricted to steep slopes and protected areas (which are not very extensive in Northeastern Brazil).
(to be continued)

i Source:Guia Internet Brasil, 1999

ii As defined by Aziz Nacif Absaber; Summit surfaces in Brazil, Revista Brasileira de Geociencias, 30 (3) 515-516; Sept. 2000.