Characterizing Climate Controls on Vegetation Seasonality in the North American Southwest

Thursday, 18 December 2014
Meredith Anne Fish, Pennsylvania State University Main Campus, University Park, PA, United States, Benjamin Cook, NASA Goddard Institute for Space Studies, New York, NY, United States, Jason E Smerdon, LDEO of Columbia University, Palisades, NY, United States, Richard Seager, Lamont Doherty Earth Obs, Palisades, NY, United States and Park Williams, Lamont -Doherty Earth Observatory, Palisades, NY, United States
The North American Southwest, which extends from Colorado to southern Mexico and California to eastern Texas, encompasses a diversity of climates, elevations, and ecosystems. This region is expected to experience significant climatic change, and associated impacts, in the coming decades. To better understand the spatiotemporal variability of vegetation in the Southwest and the expected climatic controls on timing and spatial extend of vegetation growth, we compared GIMMS normalized difference vegetation index (NDVI, 1981-2011) against temperature and precipitation data. Spatial variations in vegetation seasonality and the timing of peak NDVI are linked to spatial variability in the precipitation regimes across the Southwest. Regions with spring NDVI peaks are dominated by winter precipitation, while late summer and fall peaks are in regions with significant summer precipitation driven by the North American Monsoon. Inter-annual variability in peak NDVI is positively correlated with precipitation and negatively correlated with temperature, with the largest correlation coefficients at one-month lags. The only significant long-term trends in NDVI are for northern Mexico, where agricultural productivity has been increasing over the last 30 years.