Spatial shifts of seasonal vegetation cycles in Europe over time

Seasonal cycles of vegetation functioning are changing as a consequence of climate change. For example, a widespread greening of the northern hemisphere is observed, with an earlier start of the growing season and a later end of the growing season in some regions. However, in other regions, the growing season is actually ending earlier due to water limitations or more frequent extremes.

In this study, we focus on Europe and calculate seasonal cycles of vegetation indices at each grid cell during a past time period, and determine where most similar seasonal cycles are observed during a more recent time period. This way, we examine how the seasonal vegetation cycle at grid cells has shifted in space over the past decades by analyzing satellite-derived Leaf Area Index (LAI) data. The spatial shift is calculated for each grid cell as the difference between the locations with (i) most similar seasonal cycles during 2010-2018 and (ii) most similar seasonal cycles during 1982-1989. Similarity is assessed based on the RMSE between the seasonal cycles. First results show a widespread eastward and northward shift of seasonal cycles across Europe. The variability of determined shifts is high across regions. Calculations of spatial shifts using MODIS LAI data during more recent time periods are used to validate the long-term results. Finally, we compare the determined spatial shifts to respective trends in hydro-meteorological conditions. 

Our detection of large-scale shifts in seasonal vegetation cycles can help to better understand vegetation response and adaptation to global change, and thereby improve the prediction of future shifts.