Analysis of the NDVI Temporal Dynamics in Semi-arid Ecosystems: Brazilian Caatinga and African Western Sahel (Análise da Dinâmica Temporal do NDVI nos Ecossistemas Semi-áridos: Caatinga Brasileira e Sahel Ocidental Africano)

Os resultados indicaram que o efeito causado pelo evento El Nino, nos varios tipos de vegetacao na regiao semi-arida do Nordeste do Brasil, durante as duas ultimas decadas do seculo passado, apresentou diferentes padroes sazonais e interanuais dos tipos de vegetacao no Sahel africano. A amplitude sazonal na variacao do Indice de Vegetacao Diferenca Normalizada – NDVI, no Sahel Africano nao foi alterada pelo efeito climatico do El Nino, no entanto, na regiao semi-arida do Nordeste do Brasil, os tipos de vegetacao foram afetados durante os eventos El Nino. Alem disso, observou-se que o NDVI varia de acordo com as condicoes climaticas locais, apresentando uma lacuna temporal entre a ocorrencia de precipitacao e absorcao de agua disponivel na vegetacao. Esta informacao e importante para mostrar condicoes de contorno para os modelos climaticos e tambem para a previsao numerica de tempo. Palavras-chave: Vegetacao, Aridez . Satelite Analise da Dinâmica Temporal do NDVI nos Ecossistemas Semi-aridos: Caatinga Brasileira e Sahel Ocidental Africano ABSTRACT The results indicated that the effect caused by the El Nino event in the various types of vegetation in the semi-arid region of Northeast Brazil during the last two decades of the last century, presented a differing seasonal and interannual patterns from the vegetation types in the African Sahel. The seasonal amplitude of Normalized Difference Vegetation Index - NDVI variation in the African Sahel was not altered by the climatic effect of El Nino, however, in the semi-arid region of Northeast Brazil, the vegetation types were affected during the El Nino events. Furthermore, it was observed that the NDVI varies according to the local climatic conditions, presenting a temporal gap between the precipitation occurrence and water absorption available from the vegetation. This information is important to show contour conditions for climatic models and also for the weather numerical forecasting. Keywords: Vegetation, drought, satellite.