Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hess-2016-685
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
16 Jan 2017
Review status
This discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa
Nobuhle P. Majozi1,2, Chris M. Mannaerts2, Abel Ramoelo1,5, Renaud Mathieu1,3, Alecia Nickless4, and Wouter Verhoef2 1Earth Observation Group, Natural Resources and Environment, Council for Scientific and Industrial Research, Pretoria, 0001, South Africa
2Department of Water Resources, Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, 75AA, the Netherlands
3Department of Geography, Geoinformatics and Meteorology, University of Pretoria, South Africa
4Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, OX2 6GG, United Kingdom
5University of Limpopo, Risk and Vulnerability Centre, Sovenga, 0727, South Africa
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 investigated, as well as how it is affected by atmospheric vapor pressure deficit (VPD), and net radiation. After filtering years with bad data (2004–2008), our results show an overall mean EBR of 0.93. Seasonal variations of EBR also showed summer (0.98) and spring (1.02) were closest to unity, with winter (0.70) having the least closure. Nocturnal surface energy closure was very low at 0.11, and this was linked to low friction velocity during night-time, with results showing an increase in closure with increase in friction velocity. The surface energy partitioning of this savanna ecosystem showed that sensible heat flux dominated the energy partitioning 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 the 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 characterized by a decrease in LE and increase in H during the wet season, and an increase of both fluxes during the dry season.

Citation: Majozi, N. P., Mannaerts, C. M., Ramoelo, A., Mathieu, R., Nickless, A., and Verhoef, W.: Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-685, in review, 2017.
Nobuhle P. Majozi et al.
Nobuhle P. Majozi et al.
Nobuhle P. Majozi et al.

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