Hazard areas land cover change between 1986 and 2010 in Sao Paulo City, Brazil

Abstract

Vegetation provides natural protection to soil, avoiding severe mass movements and regulating the flooding cycle of the drainage. The replacement of natural vegetation for urban areas takes population to risk situation. This hazard is increased in Megacities context, once the population density is very high and the low income population is exposed to slums and precarious settlements. Sao Paulo City is a great example for this process, where the prices of real estate nearby transportation system quickly increased in the last 5 years, accelerating the urban sprawl in risk areas. This work aims to assess the land cover changes at hazard areas in Sao Paulo city and relate this process with the expansion of the public transportation system. LANDSAT TM 5 scenes for the years 1986 and 2010 were classified using SVM algorithm. The hazard areas were defined based on the geotechnical map. The land cover change was evaluated for the whole study area, as well as focused on the hazardous areas such as flash flood and landslide. The results showed significant loss of vegetation in Sao Paulo City, and a large increase of the urban occupation at hazard areas. Findings from this study quantified loss of 43% for vegetation areas, 88% for bare soil areas, and 66% for pasture as consequences of uncontrolled urbanization process. Understanding land cover changes is important to subside urban planning, and avoid hazard areas occupation. Mainly considering the increasing projection for population, it is important to map and preview future occupation at hazard areas and also understand the factors that contribute to it. The subway system, rail system and roads expansion had a high contribution to this process. Therefore, this paper is relevant; because it points that transportation projects must consider the consequences over urban expansion and hazard areas occupation. This information, must be consider in relocation projects, once the hazard area population must not be relocated to places with lack of urban infrastructure.