In relation to water resources, indexes can be created to express the multiple dimensions involved with it to aid the planning and management of basins. In this regard, the Water Poverty Index is globally used, but one of its criticisms includes the subjectivity associated with how the sub-indexes are weighted. Therefore, in this study, we applied principal component analysis (PCA) to determine the sub-indexes’ weight: resource, access, capacity, use, and environment of the Seridó river basin. This new index with PCA presents an average range with broader values compared to methodologies without, allowing clear identification of the disparities among the cities and the possibility to better prioritize investments concerning water poverty reduction. Our results show that this approach makes it possible to qualitatively identify geographical locations that have greater water poverty compared to others. Additionally, with this approach, it can be determined whether water poverty is caused due to natural characteristics or deficits in water infrastructure investment, providing insight into social fragilities as well. Overall, the presented hierarchical tool in this study has a high value to improve the planning of water resource uses.

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The traditional methodologies to determine hydrologic drought use standardized drought indexes, which do not express a drought's severity in terms of the volume deficit and do not consider water demand as a component of its calculation. To overcome these disadvantages, this work presents a method for the assessment of hydrological drought that determines the volume of water below its demand. A drought can be characterized by its duration, severity and magnitude, using the Threshold Level Method. Complementarily, the method for the assessment of hydrological drought developed by Araújo and Bronstert (2016) was used to compare the characteristics of drought events in the same reservoirs. For this purpose, the droughts that occurred between 1997 and 2015 were studied in two reservoirs in the Piranhas-Açu River basin (Brazil). For both methodologies, the results showed that the reservoir with a higher storage capacity is more efficient and, thus, less susceptible to drought than the smaller. It was found that the basic difference between the two approaches is the time analysis of drought events: while the Threshold Level Method makes it possible to study what occurred in the past to diagnose and plan the use of water in the future, the other method enables the assessment of current conditions to anticipate the start of a hydrologic drought. It is suggested that the two methodologies presented can be used simultaneously by water resource managers to enable a more comprehensive analysis of drought events in the basin.

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Doutor -Empresa de Pesquisa Agropecuária do Rio Grande do Norte. RESUMO:Os resultados dos estudos de delimitação de áreas homogêneas de precipitação têm sido utilizados no planejamento das atividades econômicas, possibilitando o uso mais eficiente e racional dos recursos hídricos e também em regiões com dados de precipitação escassos. O objetivo desta pesquisa é determinar áreas homogêneas em termos do regime de precipitação no estado do Rio Grande do Norte. Foram utilizadas duas técnicas de agrupamento: a hierárquica de Ward e a não hierárquica de k-means. Verificou-se que a precipitação anual média e os índices PCP e PCD foi o conjunto de variáveis mais adequado para determinar os quatro grupos homogêneos. O grupo identificado na região leste do estado é caracterizado como a região de maior precipitação anual, melhor distribuição desta precipitação e concentração de mesma no mês de maio. Se dirigindo para o oeste do estado foi identificada uma região com período de maior precipitação adiantado para o início de maio, menor precipitação anual e uma maior concentração da precipitação. Na região central do estado o grupo identificado é caracterizado por apresentar uma elevada concentração da precipitação e um adiantamento das chuvas para o período do mês de abril, além de ser a região com menor precipitação anual. Na região oeste do estado as chuvas são adiantadas para o final de março, a região apresenta a pior distribuição da precipitação no estado e as precipitações anuais nesta região são mais elevadas do que na região central. Palavras-chave:Análise de agrupamento; Áreas homogêneas; Índices de variabilidade. THE USE OF PCP AND PCD INDICES TO DETERMINING PRECIPITATION HOMOGENEOUS AREAS ABSTRACT:The results of studies of delimitation of homogeneous areas of precipitation have been used in the planning of economic activities, enabling more efficient and rational use of water resources and also in regions with scarce rainfall data. The objective of the research is to determine homogeneous areas in terms of the precipitation regime of Rio Grande do Norte State (Brazil), from the cluster analysis and techniques: hierarchical (Ward) and non-hierarchical (k-means). It was found that the average annual precipitation and PCP and PCD indices were the most appropriate set of variables for determining the four homogeneous groups. The hierarchical and non-hierarchical techniques showed similar results, with only 5 seasons differ. The four homogenous groups identified have the following characteristics. The group identified in the eastern region of the state is characterized as the region of highest annual rainfall, better distribution of this precipitation and concentration of the precipitation in the month of May. In the region more the western state was identified a region that has the rainy season advance to the beginning of May, the lower annual rainfall and a higher concentration of precipitation. The central region of the state is characterized by having a high concentration of precipitation and an advance of rainfall...