DESCRIPTION:
Vegetation seasonality assessment through remote sensing data is crucial to understand ecosystem responses to climatic
variations and human activities at large-scales. Whereas the study of the timing of phenological events showed significant
advances, their recurrence patterns at different periodicities has not been widely study, especially at global scale.
In this work, we describe vegetation oscillations by a novel quantitative approach based on the spectral analysis of
Normalized Difference Vegetation Index (NDVI) time series. A new set of global periodicity indicators permitted to
identify different seasonal patterns regarding the intra-annual cycles (the number, amplitude, and stability) and
to evaluate the existence of pluri-annual cycles, even in those regions with noisy or low NDVI. Most of vegetated
land surface (93.18%) showed one intra-annual cycle whereas double and triple cycles were found in 5.58% of the land
surface, mainly in tropical and arid regions along with agricultural areas. In only 1.24% of the pixels, the seasonality
was not statistically significant. The highest values of amplitude and stability were found at high latitudes in the northern
hemisphere whereas lowest values corresponded to tropical and arid regions, with the latter showing more pluri-annual cycles.
The indicator maps compiled in this work provide highly relevant and practical information to advance in assessing global
vegetation dynamics in the context of global change.
