Abstract
Understanding the linkages between between climatic and surface
properties that influence water uptake and loss by vegetation is
essential for understanding the impact of drought on dryland regions.
The Normalized Difference Vegetation Index (NDVI) is a common metric
used to identify vegetation condition across LULC types. Here we employ
empirical dynamic modeling (EDM) to forecast NDVI changes for savannas,
grasslands, and croplands across East Africa at a dekadal (10-day) time
scale using satellite-derived environmental forcing variables. The model
relies on state space reconstruction with lagged coordinate embedding of
multiple time series observations to recover the dynamic environmental
system that links vegetation dynamics to environmental forcing. We apply
convergent cross mapping based on Takens’ Theorem to detect the impact
of landcover on directional causal interactions and time delays between
driving (e.g. LST, rainfall) and response variables (NDVI). The model
brings to light that certain regions are highly consistent in their
trajectories and therefore easier to project while other regions are
more dispersive and thus more difficult to determine anomalies. In terms
of land cover, we are able to make projections with high accuracy for
grasslands out to 6 months ahead while croplands and savannas show
reduced forecast skill overall and prove less useful after 3 months. The
use of historical seasonal NDVI patterns to diagnose the manner by which
landcover and land use determine climate-land surface couplings provides
a means for defining critical areas of inquiry related to the impacts of
future change, particularly the expansion of agricultural areas. In
addition, the EDM approach provides a robust means for creating short
term vegetation forecasts across LULC types in East Africa. These
predictions can assist relief organizations in advising drought
management, declaring food security classifications and providing early
response to famine.