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Avaliação da suscetibilidade, exposição e vulnerabilidade aos ravinamentos na cidade de Nacala em Moçambique
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Esta tese avaliou suscetibilidade, exposição e vulnerabilidade aos ravinamentos na Cidade de Nacala em Moçambique. O levantamento das principais ocorrências permitiu a elaboração dum perfil de risco da cidade de Nacala. A análise da ocupação territorial conduziu a avaliação da exposição, e a vulnerabilidade social foi avaliada mediante a análise das caraterísticas da população em dois bairros amostrais.
A avaliação da suscetibilidade aos ravinamentos foi baseada no método de Valor Informativo considerando o inventário completo das cabeceiras (modelo 1), metade das cabeceiras separadas em grupo A e grupo B e procedendo a validação independente cruzada (modelos 2 e 3) e o inventário completo de canais erosivos (modelo 4). O mapa de suscetibilidade final para a área de estudo (modelo 5) resulta da combinação da suscetibilidade à ocorrência de cabeceiras erosivas com a suscetibilidade de desenvolvimento de canais erosivos. A validação dos 4 modelos do Valor Informativo resultou em área abaixo das curvas de sucesso relativamente elevadas, entre 0,800 (modelo 4) e 0,851 (modelo 3). No entanto, a capacidade preditiva dos modelos validados de modo independente apresenta resultados mais modestos e mais realistas, avaliados pelas taxas de predição dos modelos 2 e 3 (0,663 e 0,777, respetivamente). A análise da relação entre a distribuição espacial das cabeceiras e ravinas na cidade de Nacala e dos seus fatores condicionantes mostrou que esta não é aleatória. O modelo 5 evidencia que os bairros mais antigos na envolvente do núcleo central da cidade são mais suscetíveis a erosão por ravinamento, em comparação com os bairros criados mais recentemente e considerados de expansão.
O crescimento urbano recente da cidade de Nacala tem resultado num incremento da exposição, caracterizado pela ocupação de áreas perigosas para fins habitacionais. Este facto regista-se com mais incidência nos bairros mais antigos que envolvem o núcleo central da cidade, sendo menos marcado em bairros mais recentes.
Por último, a análise comparada de dois bairros amostrais mostrou que as famílias com indicadores de vulnerabilidade social mais baixos residem no bairro com maior exposição ao risco de ravinamento, o que tenderá a agravar a sua condição de vulnerabilidade. Contudo, não é seguro que esta situação se verifique em toda a cidade de Nacala, sendo necessário o alargamento da análise aos restantes bairros da cidade, de modo a confirmar uma eventual segregação territorial, onde os mais vulneráveis social e economicamente ocupam as áreas mais perigosas do território na cidade de Nacala.
This thesis assessed susceptibility, exposure, and vulnerability to gully erosion in the City of Nacala in Mozambique. The survey of the main events allowed the elaboration of a risk profile for the city of Nacala. The analysis of territorial occupation led to the assessment of exposure, and social vulnerability was assessed by analysing the characteristics of the population in two neighbourhoods. The assessment of susceptibility to gully erosion was based on the Informative Value method considering the complete gully head inventory (model 1), half of the gully heads separated into group A and group B and proceeding with cross-independent validation (models 2 and 3) and the complete inventory of gully channels (model 4). The final susceptibility map for the study area (model 5) results from the combination of the susceptibility to the occurrence of gully head and the susceptibility to the development of gully channels. The validation of the four Informative Value models resulted in an area under the success curve relatively high ranging from 0.800 (model 4) to 0.851 (model 3). However, the predictive capacity of independently validated models shows more modest and more realistic results, assessed by the prediction rates of models 2 and 3 (0.663 and 0.777, respectively). Model 5 shows that the older neighbourhoods along the central core of the city are more susceptible to gully erosion than those neighbourhoods recently created and in expansion. The recent urban expansion of Nacala city has resulted in an increase in exposure, promoted by the occupation of dangerous areas for housing purposes. This fact is registered with greater incidence in the older neighborhoods that involve the central core of the city and is less marked in more recent neighborhoods. Lastly, the comparative analysis of two sample neighborhoods showed that families with lower social vulnerability indicators live in the neighborhoods with the greatest exposure to the risk of gully erosion, which will tend to aggravate their condition of vulnerability. However, it is not certain that this situation will occur in the entire city of Nacala, and it is necessary to extend the analysis to the rest of the city, in order to confirm an eventual territorial segregation, where the most socially and economically vulnerable occupy the most dangerous areas of the territory in the city of Nacala.
This thesis assessed susceptibility, exposure, and vulnerability to gully erosion in the City of Nacala in Mozambique. The survey of the main events allowed the elaboration of a risk profile for the city of Nacala. The analysis of territorial occupation led to the assessment of exposure, and social vulnerability was assessed by analysing the characteristics of the population in two neighbourhoods. The assessment of susceptibility to gully erosion was based on the Informative Value method considering the complete gully head inventory (model 1), half of the gully heads separated into group A and group B and proceeding with cross-independent validation (models 2 and 3) and the complete inventory of gully channels (model 4). The final susceptibility map for the study area (model 5) results from the combination of the susceptibility to the occurrence of gully head and the susceptibility to the development of gully channels. The validation of the four Informative Value models resulted in an area under the success curve relatively high ranging from 0.800 (model 4) to 0.851 (model 3). However, the predictive capacity of independently validated models shows more modest and more realistic results, assessed by the prediction rates of models 2 and 3 (0.663 and 0.777, respectively). Model 5 shows that the older neighbourhoods along the central core of the city are more susceptible to gully erosion than those neighbourhoods recently created and in expansion. The recent urban expansion of Nacala city has resulted in an increase in exposure, promoted by the occupation of dangerous areas for housing purposes. This fact is registered with greater incidence in the older neighborhoods that involve the central core of the city and is less marked in more recent neighborhoods. Lastly, the comparative analysis of two sample neighborhoods showed that families with lower social vulnerability indicators live in the neighborhoods with the greatest exposure to the risk of gully erosion, which will tend to aggravate their condition of vulnerability. However, it is not certain that this situation will occur in the entire city of Nacala, and it is necessary to extend the analysis to the rest of the city, in order to confirm an eventual territorial segregation, where the most socially and economically vulnerable occupy the most dangerous areas of the territory in the city of Nacala.
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ravinamento suscetibilidade exposição vulnerabilidade social Nacala gullies susceptibility exposure social vulnerability