Dynamics of MODIS Time Series for Ecological Applications in Southern Africa

Intra and inter-annual vegetation dynamics indicate important ecological processes. The first are the basis of phenological analysis and describe the vegetation state and seasonal development. Inter-annual observations can be used to monitor multi-year modification and conversion processes of the land surface. Time series of remotely sensed parameters are important to understand these annual and inter-annual vegetation dynamics. Remotely sensed parameters such as vegetation indices, describing the activity of chlorophyll active vegetation, are available on a daily basis. This study employs annual time series of the Enhanced Vegetation Index (EVI) of the MODIS instrument for South Africa. Four phenologically described vegetation types are distinguished, including non-modal, uni-modal with maximum in summer or winter and bimodal cycles. Temporal cross-correlation is used to analyze phenological shifts of the EVI for consecutive years. Furthermore, EVI time series are related to high spatial resolution precipitation rate estimates. Considerable shifts in EVI phenology are shown for the northern continental provinces Limpopo, North West Province, and northern Mpumalanga and partly for Kwazulu Natal on the eastern coast. These phenological shifts in time are spatially related to high biomass land cover units such as forested land. Notably small shifts are identified for winter rain environments in the Cape floristic region indicating a higher stability of the vegetation development. A near constant temporal lag of one to two months between precipitation and EVI for six years indicates the functionality of the natural ecosystems in South Africa and the dependence on rain onset for vegetation green-up.