Using MODIS data to study the relation between climatic spatial variability and vegetation phenology in northern high latitudes

In this study we investigated methods to identify phenological transition dates and the linkage between phenology and spatial climatic variation in North America between 30.5degreesN and 70degreesN utilizing Moderate-Resolution Imaging Spectro-radiometer (MODIS) data. The results show a clear trend in which vegetation greenup gradually migrated northward from 38degreesN to 70degreesN starting in late March, and dormancy spread southward from late September. The observed pattern in phenology was significantly associated with both mean annual temperature and incoming solar radiation. Spatial analysis revealed that the date of greenup advanced by roughly 2.4 days, while the onset of dormancy was delayed by 1.8 days, for each one-degree increase in mean annual temperature.