Interannual Variability of Vegetation in the United States and its Relation to El Ni~ no/Southern Oscillation

The Normalized Di erence Vegetation Index (NDVI) is widely accepted as a good indicator for providing vegetation properties and associated changes for large scale geographic regions. Using multivariate time series data analysis methods based on Principal Component transform and Wavelet Decomposition, a sequence of 11-year monthly Advanced Very High Resolution Radiometer (AVHRR)-derived NDVI data from 1982 to 1992 is examined to study the vegetation and climate variation trends over the United States. We nd that one interannual NDVI variation signal over the United States, exhibits a strong relationship with the El Ni~ no/Southern Oscillation (ENSO) Index which is a measure of the phase and amplitude of the Southern Oscillations (SO). The corresponding spatial patterns of NDVI anomaly are also extracted for mapping the possible impacts of ENSO activity. The NDVI anomaly patterns approximately agree with the main documented precipitation and temperature anomaly patterns associated with ENSO, but also show additional patterns not related to ENSO. This study shows that ENSO activity e ects may have regionally signi cant e ects for vegetation in the United States.