Brazil's slums grow at a fast pace and occupy 106,000 hectares

Data from MapBiomas show that for every 100 hectares of shantytown, 15 were built in risk areas

In the last 37 years, urbanized areas in the country went from 1.2 million hectares to 3.7 million. In this period, informal areas totaled 106 thousand hectares - an expansion of approximately three times the area of the city of Belo Horizonte, in Minas Gerais. This data comes from the most recent MapBiomas survey on urbanized areas, based on the analysis of satellite images taken between 1985 and 2021.

Most of the urbanized area in slums is concentrated in the capital cities. Manaus is one of the highlights: the capital of Amazonas has the largest growth in the historical series, totaling about 10,000 ha in 2021. São Paulo (5,579 ha), Belém (5,450 ha), Rio de Janeiro (5,038 ha) and Salvador (4,793 ha) come next. All registered similar growth in informal areas, even though they have their own territorial characteristics.

The Amazon leads in the percentage of growth of informal occupations in the territory: 29.3% of the urban growth in this biome was in informal areas. The northern region has 13 of the 20 cities with the highest proportion of growth, with Belem among the top five on the list.

"The growth of the slums has a behavior similar to that of the urbanized areas, but in the 90's the informal areas accelerated their advance. The expansion of urbanization has impacts on the consumption of natural resources, on the quality of life and, in general, on urban sustainability, but when we talk about favelas, in addition, there is a very high chance of an increase in the occupation of risk areas by more vulnerable populations," explains Julio Cesar Predrassoli, one of the coordinators of MapBiomas' mapping of Urbanized Areas.

The satellite images allowed us to identify that urban occupation as a whole in risk areas increased 3 times between 1985 and 2021, and in informal areas this advance was even greater: 3.4 times. Of every 100 hectares of slum, 15 were built in risk areas.

Of the 887 cities with some urbanized area in risk areas, only 20 cities account for 36% of all the risk area occupied in the last 37 years. Salvador (BA), Ribeirão das Neves (MG), Jaboatão dos Guararapes (PE), São Paulo (SP), Recife (PE) and Belo Horizonte (MG) are the first six on the list.

The Cerrado leads the ranking of biomes with the largest increase in urbanized areas at risk with 382%, followed by Caatinga with 310%, Amazon with 303%, Atlantic Forest with 297%, Pampa with 193% and lastly the Pantanal with 187%. As the ranking is done by area and Petrópolis has a small urban extension, the city is not at the top of the list, but it is one of the most emblematic examples of the consequences of the occupation of risk areas that has been happening in the region since the 19th century.

The Cerrado was also the biome that lost the most native vegetation to urban expansion. Of the more than 558 thousand hectares of natural formations that were converted to urbanized areas between 1985 and 2021, 28% (156.5 thousand hectares) were in the Cerrado. In second place comes the Atlantic Forest (13008 thousand ha), followed by the Amazon (123 thousand ha), Caatinga (108 thousand ha), Pampa (40 thousand ha) and Pantanal (778 ha).

The survey also showed that the greatest expansion of urbanized areas occurred in areas of agricultural use. Between 1985 and 2021, the 2.5 million hectares that were urbanized were 67.8% agricultural use: 30.7% were pasture areas, 30.5% mosaics of use and 6.4% agriculture.

"Although agriculture and cattle raising have almost 70% growth in urban areas, it is the advance on native vegetation that draws our attention. Proportionally, some states have lost more than half of their natural cover to urbanized areas, affecting the natural ecosystems in which cities are inserted and contributing to a less efficient response to climate challenges," points out Mayumi Hirye, coordinator of MapBiomas' mapping of Urbanized Areas.

The total loss of natural formations to urban areas was 22.2% in 37 years. In Piauí, 68.4% (29,029 ha) of urbanization occurred over natural cover, forest and savanna formations total 26,421 hectares lost. In Amazonas, 59.9% (17,159 ha) of natural cover was lost, such as forests and flooded fields. Ceará lost 58.6% (53,845 ha), especially savannah formations. The loss in Mato Grosso was 51.2% (38,156 ha), savannah, grassland and forest formations totaling more than 36 thousand ha.

The states of São Paulo and Rio de Janeiro, located in the Atlantic Forest, have the two largest urbanized areas in the country and together they lost almost 38 thousand hectares of native vegetation: 26,655 ha and 10,982 ha, respectively.

The Pantanal and Pampa are the biomes with the largest proportion of native vegetation in both high and low density urban areas. In the Amazon, on the other hand, the greatest loss of native vegetation was observed in both density areas. "Low density areas comprise the expansion areas of cities, where the ecosystem services of vegetation could be incorporated into new, greener and more sustainable neighborhoods," warns Hirye. The highlight goes to the Atlantic Forest: there are about 730 thousand ha of native vegetation in low density urban areas.

The Atlantic Forest, which concentrates more than half of the urbanized areas (53%), is also the leader in the ranking of urban occupation of marginal strips (30 m) of water bodies by biome. In 2021, the biome corresponded to 67% of all urban occupation that pressures the margins of water bodies. In addition, 280 thousand hectares of the Atlantic Forest are low density urbanized areas.