Interannual variability of NDVI in northwest Mexico. Associated climatic mechanisms and ecological implications

Abstract

The relation between the Normalized Difference Vegetation Index (NDVI) interannual variability, precipitation and atmospheric circulation at 700 mbar in northwest Mexico is analyzed during the warm and cold phases of the El Niño Southern Oscillation (ENSO). A conditional probability test was conducted between this phenomenon and NDVI values. It was found that the negative ENSO phase is associated with drought conditions with a delay of 4–6 months related to the start of event, while the positive phase is related to high NDVI values during the driest season in the region. Clustering the NDVI values by terciles, it was determined that summers with high NDVI values are related to an intensification of the Mexican summer monsoon; while, in dry summers, the flow is characterized by the presence of an enhanced ridge of high-pressure aloft over most of the national territory. In winters with high NDVI values, a very intense low-pressure trough induces a meridional flow with penetration of humid air associated with frontal activity. This circulation pattern is common during the ENSO warm phase. Winters with low NDVI are associated atmospheric circulation patterns typical of the so-called Pacific North American (PNA) type. Based on the bio-seasonality and precipitation modulation in northwest Mexico due to the ENSO, it is concluded that the delay of a few months observed in NDVI values with respect to precipitation inputs supports the Seed Hydration Memory (SHM) concept. The ecological implications of this phenomenon for the region are also discussed.