Abstract:
Flux towers provide essential terrestrial climate,
water, and radiation budget information needed for environmental
monitoring and evaluation of climate change impacts
on ecosystems and society in general. They are also intended
for calibration and validation of satellite-based Earth observation
and monitoring efforts, such as assessment of evapotranspiration
from land and vegetation surfaces using surface
energy balance approaches.
In this paper, 15 years of Skukuza eddy covariance data,
i.e. from 2000 to 2014, were analysed for surface energy balance
closure (EBC) and partitioning. The surface energy balance
closure was evaluated using the ordinary least squares
regression (OLS) of turbulent energy fluxes (sensible (H) and
latent heat (LE)) against available energy (net radiation (Rn)
less soil heat (G)), and the energy balance ratio (EBR). Partitioning
of the surface energy during the wet and dry seasons
was also investigated, as well as how it is affected by atmospheric
vapour pressure deficit (VPD), and net radiation.
After filtering years with low-quality data (2004–2008),
our results show an overall mean EBR of 0.93. Seasonal
variations of EBR also showed the wet season with 1.17
and spring (1.02) being closest to unity, with the dry season
(0.70) having the highest imbalance. Nocturnal surface
energy closure was very low at 0.26, and this was linked to low friction velocity during night-time, with results showing
an increase in closure with increase in friction velocity.
The energy partition analysis showed that sensible heat
flux is the dominant portion of net radiation, especially between
March and October, followed by latent heat flux, and
lastly the soil heat flux, and during the wet season where latent
heat flux dominated sensible heat flux. An increase in net
radiation was characterized by an increase in both LE and H,
with LE showing a higher rate of increase than H in the wet
season, and the reverse happening during the dry season. An
increase in VPD is correlated with a decrease in LE and increase
in H during the wet season, and an increase in both
fluxes during the dry season.
