Review article : a systematic review and future prospects of flood vulnerability indices

Despite the increasing body of research on flood vulnerability, a review of the methods used in the construction of vulnerability indices is still missing. Here, we address this gap by providing a state-of-art account on flood vulnerability indices, highlighting worldwide trends and future research directions. A total of 95 peer-reviewed articles published between 2002–2019 were systematically analyzed. An exponential rise in research effort is demonstrated, with 80 % of the articles being published since 2015. The majority of these studies (62.1 %) focused on the neighborhood followed by the city scale (14.7 %). Min–max normalization (30.5 %), equal weighting (24.2 %), and linear aggregation (80.0 %) were the most common methods. With regard to the indicators used, a focus was given to socioeconomic aspects (e.g., population density, illiteracy rate, and gender), whilst components associated with the citizen’s coping and adaptive capacity were slightly covered. Gaps in current research include a lack of sensitivity and uncertainty analyses (present in only 9.5 % and 3.2 % of papers, respectively), inadequate or inexistent validation of the results (present in 13.7 % of the studies), lack of transparency regarding the rationale for weighting and indicator selection, and use of static approaches, disregarding temporal dynamics. We discuss the challenges associated with these findings for the assessment of flood vulnerability and provide a research agenda for attending to these gaps. Overall, we argue that future research should be more theoretically grounded while, at the same time, considering validation and the dynamic aspects of vulnerability

Effects of different normalization, aggregation, and classification methods on the construction of flood vulnerability indexes

Index-based approaches are widely employed for measuring flood vulnerability. Nevertheless, the uncertainties in the index construction are rarely considered. Here, we conducted a sensitivity analysis of a flood vulnerability index in the Maquiné Basin, Southern Brazil, considering distinct normalization, aggregation, classification methods, and their effects on the model outputs. The robustness of the results was investigated by considering Spearman’s correlations, the shift in the vulnerability rank, and spatial analysis of different normalization techniques (min-max, z-scores, distance to target, and raking) and aggregation methods (linear and geometric). The final outputs were classified into vulnerability classes using natural breaks, equal interval, quantiles, and standard deviation methods. The performance of each classification method was evaluated by spatial analysis and the Akaike’s information criterion (AIC). The results presented low sensitivity regarding the normalization step. Conversely, the geometric aggregation method produced substantial differences on the spatial vulnerability and tended to underestimate the vulnerability where indicators with low values compensated for high values. Additionally, the classification of the vulnerability into different classes led to overly sensitive outputs. Thus, given the AIC performance, the natural breaks method was most suitable. The obtained results can support decision-makers in reducing uncertainty and increasing the quality of flood vulnerability assessments

To which extent are socio-hydrology studies truly integrative? The case of natural hazards and disaster research

Given the recent developments in socio-hydrology and its potential contributions to disaster risk reduction (DRR), we conducted a systematic literature review of socio-hydrological studies aiming to identify persisting gaps and discuss tractable approaches for tackling them. A total of 44 articles that address natural hazards or disasters were reviewed in detail. Our results indicated that: (i) most of the studies addressed floods, whereas few applications were applied to droughts and compound or multi-hazard events; (ii) none of the reviewed articles investigated interactions across temporal and spatial scales; (iii) there is a wide range of understandings of what “social” means in socio-hydrology; (iv) quantitative approaches were used more often in comparison with mixed and qualitative approaches; (v) monodisciplinary studies prevailed over multi- or interdisciplinary ones; and (vi) one-third of the articles involved stakeholder participation. In summary, we observed a fragmentation in the field, with a multitude of social and physical components, methods, and data sources being used. Based on these findings, we point out potential ways of tackling the identified challenges to advance socio-hydrology, including studying multiple hazards in a joint framework and exploiting new methods for integrating results from qualitative and quantitative analyses to leverage the strengths of different fields of knowledge. Addressing these challenges will improve our understanding of human–water interactions to support DRR

Análise multi-critério aplicada ao mapeamento da suscetibilidade a escorregamentos

This paper presents the application of a multi-criteria analysis (MCA) tool for landslide susceptibility assessment in Porto Alegre municipality, southern Brazil. A knowledge driven approach was used, aiming to ensure an optimal use of the available information. The landslide conditioning factors considered were slope, lithology, fl ow accumulation and distance from lineaments. Standardization of these factors was done through fuzzy membership functions, and evaluation of their relative importance for landslide predisposition was supported by the analytic hierarchy process (AHP), based on local expert knowledge. Finally, factors were integrated in a GIS environment using the weighted linear combination (WLC) method. For validation, an inventory, including 107 landslide points recorded between 2007 and 2013 was used. Results indicated that 8.2% (39.40 km²) of the study area are highly and very highly susceptible to landslides. An overall accuracy of 95% was found, with an area under the receiver operating characteristic (ROC) curve of 0.960. Therefore, the resulting map can be regarded as useful for monitoring landslide-prone areas. Based on the fi ndings, it is concluded that the proposed method is eff ective for susceptibility assessment since it yielded meaningful results and does not require extensive input data.Este estudo apresenta a aplicação de uma ferramenta de análise multi-critério para mapear a suscetibilidade a escorregamentos no município de Porto Alegre, sul do Brasil. Uma abordagem guiada pelo conhecimento de especialistas foi utilizada, com o intuito de otimizar a utilização das informações disponíveis. Os fatores condicionantes dos escorregamentos considerados foram declividade, litologia, acúmulo defl uxo e distância de lineamentos. A padronização desses fatores foi realizada por meio da aplicação de funções fuzzy e a importância relativa de cada um na predisposição do terreno a escorregamentos foi estabelecida com o apoio da técnica AHP (Analytic Hierarchy Process), com base no conhecimento de especialistas locais. Por fi m, a integração dos fatores em ambiente SIG se deu por meio do método denominado Combinação Linear Ponderada (WLC). Para validar os resultados, utilizou-se um mapa inventário contendo 107 cicatrizes de escorregamentos, registradas entre 2007 e 2013. Os resultados indicam que 8,2% (39,38 km²) da área de estudo possui uma suscetibilidade alta e muito alta a escorregamentos. A validação dos resultados obteve uma exatidão geral de 95%, com uma área abaixo da curva ROC (Receiver Operating Characteristic) de 0,960. Portanto, o mapa obtido pode ser considerado útil para monitorar as áreas propensas a esses processos. Com base nos resultados, conclui-se que o método proposto é efi caz para a avaliação da suscetibilidade, uma vez que os resultados obtidos são robustos e que não foi necessária uma quantidade extensa de dados de entrada

Multicriteria analysis applied to landslide susceptibility mapping: a case study in Cascata District, Porto Alegre, RS

O objetivo deste estudo foi mapear, com o emprego de uma técnica de avaliação multicritério em ambiente SIG, a suscetibilidade a escorregamentos no bairro Cascata, Porto Alegre. As variáveis utilizadas foram: declividade, litologia, pedologia, uso do solo e cobertura vegetal. Após a padronização das variáveis, definiu-se a importância de cada uma na predisposição do terreno a escorregamentos com o apoio da técnica de avaliação multicritério AHP (Analytic Hierarchy Process). Os resultados indicam que 3,27% da área de estudo possuí alta suscetibilidade; 83,29% média; 11,98% baixa e 1,46% muito baixa. Verificou-se também que 70,12% da classe alta suscetibilidade já foi urbanizada, configurando-se em áreas prioritárias para a mitigação de riscos. Esse quadro tende a se agravar, uma vez que a expansão urbana é inevitável e contínua, e que à medida que a população cresce, ela modifica o território, potencializando a ocorrência desses desastres. Dessa forma, o mapa resultante constitui-se em subsídio importante para a tomada de decisão, possibilitando uma escolha mais racional na definição de estratégias de prevenção e intervenção do poder público. Isso demonstra que o geoprocessamento aliado a técnicas de avaliação multicritério, simplifica e torna ágil o mapeamento da suscetibilidade.This study aims to map, with the use of a multi-criteria analysis (MCA) technique in a GIS environment, the landslide susceptibility in the Cascata district, Porto Alegre, Brazil. Variables used were: slope, geology, soil, land use and vegetation cover. After the standardization of these variables, their importance for landslides predisposition was defined with the support of the multi-criteria technique AHP (Analytic Hierarchy Process). Results indicate that 3.27% of the study area has a high susceptibility; 83.29% moderate, 11.89% low and 1.46% very low. It was also found that 70.12% of the high susceptibility class has already been urbanized, and therefore, should be considered as priority for risk mitigation. This situation tends to worsen since urban sprawl is inevitable and continuous, and as the populations grow, it changes the territory, enhancing the occurrence of these disasters. Thus, the resulting map is an important tool for decision making, enabling a more rational definition of public strategies for landslides prevention and intervention. This demonstrates that GIS combined with MCA techniques simplifies and makes the susceptibility mapping faster. Keywords: landslides, GIS, susceptibility, MCA, AHP

Analysis of landslide conditioning factors in Porto Alegre municipality based on historical data

O município de Porto Alegre é altamente suscetível a movimentos de massa, os quais ocasionam perdas econômicas, sociais e ambientais. Com o intuito de mitigar esses impactos e compreender melhor esses processos torna-se necessário mapear as áreas afetadas pelos mesmos, uma vez que movimentos de massa recentes podem sugerir futuros padrões de instabilidade. Nesse sentido, este estudo teve por objetivo elaborar um inventário de movimentos de massa e analisar os fatores que contribuem para a sua ocorrência no município de Porto Alegre, Rio Grande do Sul. Para tanto, foram consultados relatórios de vistoria do Programa de Áreas de Risco (PAR) de Porto Alegre, de 2007 a 2013. Posterior mente, analisou-se a distribuição espacial e temporal desses registros, bem como a sua relação com os principais fatores condicionantes, por meio da aplicação de técnicas de geoprocessamento. Ao total, foram registradas 132 ocorrências de movimentos de massa, das quais 114 correspondem a escorregamentos e 18 a quedas de blocos. Além disso, mapearam-se 84 locais com predisposição à ocorrência de escorregamentos e 31 à quedas de blocos. No caso dos escorregamentos, os fatores condicionantes mais relevantes na área de estudo foram declividade, geologia e distância de lineamentos. Além disso, a ação antrópica foi o principal agente defl agrador. O inventário elaborado permite indicar os locais onde é necessário realizar mapeamentos detalhados, como por exemplo, análises de suscetibilidade e risco, constituindo num subsidio importante para tomadores de decisão.Porto Alegre municipality is highly susceptible to mass movements, which cause economic, social and environmental losses. In order to mitigate these impacts and better understand these processes, it is necessary to map the areas affected by them, since recent mass movements may indicate future patterns of instability. In this sense, this study aimed to analyze the factors that contribute to mass movements occurrence by preparing an inventory map of these events in Porto Alegre municipality, Rio Grande do Sul. For this, survey reports elaborated by the Porto Alegre Risk Areas Program (PAR) between 2007 and 2013 were consulted. Subsequently, we analyzed the spatial and temporal distribution of these records, as well as their relationship with the main conditioning factors, through geoprocessing techniques. In total, 132 occurrences were mapped, of which 114 correspond to landslides and 18 to rock falls. In addition, 84 sites with predisposition to landslide occurrence and 31 to rock falls were mapped. For landslides, the most significant conditioning factors were slope, geology and distance to lineaments. Moreover, anthropic activity was the main triggering factor. The inventory elaborated allows indicating places where detailed mappings, such as susceptibility and risk analysis, are required, constituting an important tool for decision makers