Alagamentos e inundações na cidade de União - PI: uma análise espacial de fatores de risco por meio de análise multicritério e geoprocessamento

Abstract

In Brazil, the risk of urban pluvial flooding and river flooding is a widespread problem in many cities, particularly where land occupation has expanded without planning, reducing permeable surface area, and where heavy rainfall has exceeded the capacity of the existing drainage system. In União, in the state of Piauí, this type of event has already caused economic and social damage as well as harm to public health; as an example, the flood that occurred in the city in 2009 left more than 100 families homeless (Cidade Verde, 2009). It was this scenario that motivated the research, whose main objective was to spatially analyze the risk factors for urban pluvial and river flooding in the consolidated urban area of the municipality from three fronts: the physical susceptibility of the territory, the exposure of the population and urban structures, and the socioeconomic vulnerability of those who occupy these areas. To this end, a Geographic Information System (GIS) gathered and integrated spatial, urban, and socioeconomic data from government agencies, forming the basis of a multicriteria analysis conducted using the analytic hierarchy process (AHP) method. In the Susceptibility component, the physical attributes of the terrain were addressed, such as slope, elevation, distance to urban drainage and to the Parnaíba River, and land use and cover, all related to the soil's propensity for water accumulation. In the Exposure component, the presence of population, buildings, and sensitive urban facilities were weighted, expressing the elements that could be affected in the event of flooding. Vulnerability, in turn, incorporated socioeconomic variables such as income, age group, education, and household density, linked to the population's differing conditions to face, respond to, and recover from the impacts caused by hydrological events. After being weighted through pairwise judgment, the three components were combined into a single risk factors map, which classifies the consolidated urban area of União by risk level. The results showed that the areas classified as high and very high risk coincided with the locations where real hydrological events were recorded between 2008 and 2021. This correspondence indicates that the AHP approach, applied to the Susceptibility, Exposure, and Vulnerability components, was able to adequately represent the most critical areas of the consolidated urban zone of União-PI. As a final product, the risk factors map serves as a reference for public authorities to plan mitigation measures and reduce the effects of these events on the population, the economy, and the environment.