Development of a drought vulnerability index using MCDM and GIS: study case in São Paulo and Ceará, Brazil

Although climate change vulnerability research in general has increased over the last decade, Latin American countries have more directed more limited efforts toward vulnerability and its social aspects. To respond to this gap, the authors developed a method to quantify drought vulnerability, which is key climate risk in Brazil. The iSECA model uses MCDM techniques to calculate vulnerability indexes by applying weighting schemes to indicators that represent climatological, social, economic, and water management factors. GIS software was used to classify and to map vulnerability. The model output is a drought vulnerability index, displayed through maps and graphs, including a vulnerability triangle and frequency curves. The results provide a clear understanding for water managers and non-specialists and can serve as an indispensable tool for water management in drought-prone regions. A sensitivity analysis confirms the model's robustness. iSECA was applied to Ceará and São Paulo, two states with distinct climatological and socio-economic contexts. The application demonstrated how the model works well across different spatial scales within these different contexts. The study found that in São Paulo more than 30 million people are living with very high vulnerability to drought primarily due to water management characteristics. However, in Fortaleza, Ceará, the climatic factors are the most critical. Even the state’s robust interbasin water infrastructure system does not significantly reduce the drought risk. The ability to identify vulnerability hotspots and the underlying characteristics that influence the rankings provides the necessary input of policy decisions.