Abstract:
Reliable estimates of daily, monthly and seasonal
soil moisture are useful in a variety of disciplines. The availability of continuous in situ soil moisture observations in
southern Africa barely exists; hence, process-based simulation model outputs are a valuable source of climate information, needed for guiding farming practices and policy interventions at various spatio-temporal scales. The aim of this
study is to evaluate soil moisture outputs from simulated and
satellite-based soil moisture products, and to compare modelled soil moisture across different landscapes. The simulation model consists of a global circulation model known
as the conformal-cubic atmospheric model (CCAM), coupled with the CSIRO Atmosphere Biosphere Land Exchange
model (CABLE). The satellite-based soil moisture data products include satellite observations from the European Space
Agency (ESA) and satellite-observation-based model estimates from the Global Land Evaporation Amsterdam Model
(GLEAM). The evaluation is done for both the surface (0–
10 cm) and root zone (10–100 cm) using in situ soil moisture
measurements collected from two study sites. The results indicate that both the simulation- and satellite-derived models
produce outputs that are higher in magnitude range compared
to in situ soil moisture observations at the two study sites,
especially at the surface. The correlation coefficient ranges
from 0.7 to 0.8 (at the root zone) and 0.7 to 0.9 (at the surface), suggesting that models mostly are in an acceptable
phase agreement at the surface than at the root zone, and this
was further confirmed by the root mean squared error and the
standard deviation values. The models mostly show a bias
towards overestimation of the observed soil moisture at both
the surface and root zone, with the CCAM-CABLE showing
the least bias. An analysis evaluating phase agreement using
the cross-wavelet analysis has shown that, despite the models’ outputs being in phase with the in situ observations, there
are time lags in some instances. An analysis of soil moisture
mutual information (MI) between CCAM-CABLE and the
GLEAM models has successfully revealed that both the simulation and model estimates have a high MI at the root zone
as opposed to the surface. The MI mostly ranges between 0.5
and 1.5 at both the surface and root zone. The MI is predominantly high for low-lying relative to high-lying areas.
