Differences in Land Surface Phenology and Primary Productivity in the Western United States during El Niño and La Niña Events from 2000-2012

Timing of plant life cycle events (phenology) and annual plant productivity represent key interactions between the atmosphere and the biosphere, with implications and feedbacks for climate and ecosystem functions. The El Niño-Southern Oscillation (ENSO) system is the dominant source of interannual climate variability in the western United States, with important effects on temperature, precipitation, and drought. We examine the connection between ENSO and terrestrial vegetation dynamics using the enhanced vegetation index and net primary production (NPP) from MODIS, along with the 2006 National Land Cover Dataset and EPA Level 2 Ecoregions. El Niño events are associated with significant increases in NPP throughout the western U.S., and with an earlier start of the growing season in much of the Pacific Northwest and parts of the Southwest (though the overall association of ENSO with land surface phenology is complex and spatially heterogeneous). The correlation between total annual production and the Southern Oscillation Index is highest in mid- to late-winter prior to the growing season, suggesting some predictive power in advance of the growing season.