Comparative study of the 1982–1983 and 1997–1998 El Niño events over different types of vegetation in South America

Abstract

This work presents results which help to understand the behaviour of the Normalized Difference Vegetation Index (NDVI) anomalies over the South America continent during the two strongest El Niño events of the last century (1982–1983 and 1997–1998). The data used are parts of a long-term series (July 1981 to December 1999) of calibrated NDVI data derived from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA AVHRR) datasets. Special emphasis has been given to the analysis of the response of the major Brazilian vegetation types. This paper introduces an approach that enhances NDVI anomalies relative to the long-term climatology of the region. We find a negative NDVI anomaly for most of the region during the 1982–1983 event, whereas for the 1997–1998 event positive NDVI anomalies were observed over most regions. Only the ‘Nordeste’ region showed a similar vegetation response for both events. We identify three possible factors that may play a role in the different NDVI responses to the two El Niño events. Firstly, poor intercalibration of sensors may account for some, but not all of the differences. Secondly the response of the vegetation may depend upon the climate conditions prior to the El Niño events. Thirdly, the difference in the onset date and the duration of the mature phase of the two El Niño events, associated with very different Atlantic surface temperatures are shown to have dynamical consequences which may impact upon the vegetation.

Acknowledgments

This work was part of a cooperation between IRD (Institut de Recherche pour le Développement, France) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil), support number 910153/98-1. It was also partly financed under FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) support number 99/06045-7. Many thanks to Dr J. P. Duvel and Dr N. Hall for helpful comments and discussions.

Notes

^†Also at: IRD/LTHE Institut de Recherche pour le développement/Laboratoire d'Etude des Transferts en Hydrologie et Environnement, B.P. 53, Grenoble, France.

^†Also at: IRD/LTHE Institut de Recherche pour le développement/Laboratoire d'Etude des Transferts en Hydrologie et Environnement, B.P. 53, Grenoble, France.

Additional information

Notes on contributors

N. Dessay†

†Also at: IRD/LTHE Institut de Recherche pour le développement/Laboratoire d'Etude des Transferts en Hydrologie et Environnement, B.P. 53, Grenoble, France.

H. Laurent†

†Also at: IRD/LTHE Institut de Recherche pour le développement/Laboratoire d'Etude des Transferts en Hydrologie et Environnement, B.P. 53, Grenoble, France.