Characterising the response of vegetation cover to water limitation in
Africa using geostationary satellites
Abstract
Hydrological interactions between vegetation, soil, and topography are
complex, and heterogeneous in semi-arid landscapes. This along with data
scarcity poses challenges for large-scale modelling of vegetation-water
interactions. Here, we exploit metrics derived from daily Meteosat data
over Africa at ca. 5 km spatial resolution for ecohydrological analysis.
Their spatial patterns are based on Fractional Vegetation Cover (FVC)
time series and emphasise limiting conditions of the seasonal wet to dry
transition: the minimum and maximum FVC of temporal record, the FVC
decay rate and the FVC integral over the decay period. We investigate
the relevance of these metrics for large scale ecohydrological studies
by assessing their co-variation with soil moisture, and with
topographic, soil, and vegetation factors. Consistent with our initial
hypothesis, FVC minimum and maximum increase with soil moisture, while
the FVC integral and decay rate peak at intermediate soil moisture. We
find evidence for the relevance of topographic moisture variations in
arid regions, which, counter-intuitively, is detectable in the maximum
but not in the minimum FVC. We find no clear evidence for wide-spread
occurrence of the “inverse texture effect”’ on FVC. The FVC integral
over the decay period correlates with independent data sets of plant
water storage capacity or rooting depth while correlations increase with
aridity. In arid regions, the FVC decay rate decreases with canopy
height and tree cover fraction as expected for ecosystems with a more
conservative water-use strategy. Thus, our observation-based products
have large potential for better understanding complex vegetation–water
interactions from regional to continental scales.