Spatial patterns of land surface phenology relative to monthly climate variations: US Great Plains

We extracted and mapped six land surface phenological metrics including: (1) the peak normalized difference vegetation index (NDVI), (2) peak date, (3) start of season (SOS), (4) end of season (EOS), (5) length of growing season (LOS), and (6) cumulative NDVI from 2000 to 2009 using Moderate-Resolution Imaging Spectroradiometer (MODIS) images covering the United States (US) Great Plains. Their patterns relative to monthly precipitation, maximum temperature, minimum temperature, and dew points were analyzed using multiple linear regression, stepwise selection, and geographically weighted regression (GWR) analysis. Both peak NDVI and cumulative NDVI had similar spatial patterns. Their values decreased along an east to west gradient. Peak date and SOS also showed compatible patterns. The southeastern Great Plains had the earliest SOS, peak date, and the longest LOS, given its warmer temperatures and greater precipitation. Dew points in March and October as well as the maximum temperature in April highly influenced the SOS, while dew point in August was found more influential for EOS and LOS. Precipitation in March and September also affected the total cumulative NDVI. The GWR models performed better than the OLS because the GWR utilized the spatial relationships between the different variables resulting from local level processes. The regression models predicted peak NDVI and cumulative NDVI better than the other phenological indices.