Abstract
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.
Highlights
Net solar radiation (Rn) reaching the Earth’s surface determines the amount of energy available for latent (LE), sensible (H), and soil (G) heat fluxes, and heat stored by the canopy, the ground, and energy storage terms by photosynthesis
We examined the surface energy balance partitioning into soil heat conduction, convection, and latent heat components and its energy balance closure using 15 years (2000–2014) of eddy covariance data from the Skukuza flux tower
In regions and locations where water availability is not a limiting factor, latent heat flux may take the highest portion of net radiation. This study investigated both surface energy balance closure and how this energy is partitioned into turbulent fluxes during the wet and dry seasons in a semi-arid savanna ecosystem in Skukuza using eddy covariance data from 2000 to 2014
Summary
Net solar radiation (Rn) reaching the Earth’s surface determines the amount of energy available for latent (LE), sensible (H), and soil (G) heat fluxes, and heat stored by the canopy, the ground, and energy storage terms by photosynthesis. Energy partitioning on the Earth’s surface is a function of interactions between biogeochemical cycling, plant physiology, the state of the atmospheric boundary layer, and Published by Copernicus Publications on behalf of the European Geosciences Union. Majozi et al.: Analysing surface energy balance closure and partitioning climate (Wilson et al, 2002). How the turbulent fluxes (H and LE) are partitioned in an ecosystem plays a critical role in determining the hydrological cycle, boundary layer development, weather, and climate (Falge et al, 2005). Understanding the partitioning of energy, the turbulent fluxes, is important for water resource management in (semi) arid regions, where reference evapotranspiration far exceeds precipitation
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