Análise de risco de desastres por inundação: cenários temporais para a cidade de Governador Valadares (MG)

Abstract

Brazilian cities have been affected by disasters related to floods, and this has been causing high amounts of losses and damages. Given this, the general objective of this thesis is to understand the construction of the risk of disaster by flood, considering geographic, social and environmental elements, which vary in time and space. The geographical area chosen for methodological application is the urban area of Governador Valadares (MG). To achieve the proposed objective, a methodology was developed considering three time scenarios (the years 2000, 2010 and 2018). The first methodological procedure was to make the census sectors compatible, in order to make it possible to compare the flood risk scenarios over the years. Subsequently, the flood hazard mapping and the urbanized areas mapping were elaborated. In order to understand the vulnerabilities of the exposed population, social vulnerability mappings were carried out for different methodological proposals (representation by area, spline interpolation and ordinary kriging). A methodology was also used to project social vulnerability data for 2018. Considering the maps of danger, urbanized area and social vulnerability, the mapping of disaster risk by flooding was formulated for different temporal scenarios, through the method of representation by area, spline and ordinary kriging. As it is a methodological proposal, the result of the year 2018 (the most recent year) was considered for the validation of social vulnerability, based on verification in the field, using the Kappa statistic and the absolute mean error method. It was found that all methodological proposals are valid for studies of social vulnerability, but ordinary kriging showed better values in the validations. The methodological proposals for the 2018 disaster risk scenarios were validated considering the 6.5 meter flood quota, made available by the Geological Survey of Brazil (CPRM). It was found that the ordinary kriging method showed better results, since it was closer to the 6.5 meter flood quota of (CPRM). Thus, it was found that the urban area has 11,69% of its surface with high susceptibility to flooding; 7,44% of its area is affected by high flood risk, and from 2003 to 2018 it presented a growth rate of 24,71% for a very dense urbanization class. It was evident that there was a reduction in social vulnerability classes in some places in the city, but this reduction did not occur significantly in the vicinity of the Doce River, places of exposure to flooding. The flood disaster risk scenarios, on the other hand, showed an increase in the very high and high degrees of risk for the analyzed scenarios. Finally, it is clear that even in the face of all recorded floods, the areas close to the Doce River continued to be occupied. Thus, the hypothesis of this research is confirmed that the risks of disaster by flood which are being built upon, because if these areas were not occupied, the flooding process of the Doce River would happen naturally, without reaching people.