Atmosphere-vegetation interactions over South Africa

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dc.contributor.advisorHewitson, Bruceen_ZA
dc.contributor.authorShannon, Debbie Anneen_ZA
dc.date.accessioned2016-10-10T14:56:04Z
dc.date.available2016-10-10T14:56:04Z
dc.date.issued1997en_ZA
dc.descriptionBibliography: pages 107-118.en_ZA
dc.description.abstractThis study examines the sensitivity of the atmospheric circulation to vegetation change over South Africa in the context of the portended global warming. This is achieved using a vegetation model driven by climate change information and subsequently incorporated within a general circulation model (GCM). The stand-alone vegetation model is driven using precipitation, temperature and relative humidity derived from downscaling using artificial neural networks. The vegetation model is then run with perturbed precipitation, temperature and relative humidity from downscaled model data from lxCO₂ and 2xCO₂ GCM simulations. The resultant vegetation perturbation response to climate change is then examined and incorporated into the GCM in order to ascertain the atmospheric sensitivity to vegetation changes. The off-line results of the vegetation model indicate a moderate degree of sensitivity of the vegetation to perturbations in precipitation, temperature and relative humidity. The general trend in response to the CO₂ climate is a westwards and altitudinal shift of lowland vegetation over the eastern part of the country, and a southwards and eastwards shift of the more dryland vegetation in the west. These shifts are in accordance with expected responses, since lowland vegetation responds more to temperature changes and the dryland vegetation to precipitation changes. Nonetheless, the use of the model provides a physically justifiable scenario on which to base the GCM studies, and at a finer resolution than otherwise available. A GCM simulation with the perturbed vegetation was then performed using sea surface temperature boundary conditions for 1980 and compared to an identical GCM run without the perturbation. 1980 was chosen since this year does not represent either a strong El Niño or La Niña year. The atmospheric sensitivity to the vegetation perturbation has been examined in terms of climatic variables such as temperature, precipitation, pressure, specific humidity, horizontal divergence, and sensible and latent heat fluxes. The results show that the atmosphere is quite sensitive to relatively small vegetation changes. Atmospheric response to vegetation perturbations indicates greater sensitivity over the NW and SE regions of southern Africa. The perturbation indicates a reduction in precipitation over the SE interior, related to less moisture feeding in over the interior from the SE Indian Ocean. Wind speed changes over the adjacent ocean were also evident, and are probably related to the changes in the South Atlantic and Indian high pressures. A southwards extension of the Hadley Cell was also suggested, as well as changes in sensible and latent heat fluxes, relating to precipitation and temperature changes. It is suggested that changes may be in response to the general drying out of the country and the associated increase in aridity. This research forms the preliminary investigation for further work incorporating the atmospheric perturbation response back into driving the vegetation model in order to examine the direction of the feedback -- whether this is positive or negative in the longer term. Thus, this study has demonstrated that the atmosphere is significantly sensitive to vegetation changes over South Africa and reinforces the need for improved land surface parameterization schemes and vegetation models in general circulation models.en_ZA
dc.identifier.apacitationShannon, D. A. (1997). <i>Atmosphere-vegetation interactions over South Africa</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Environmental and Geographical Science. Retrieved from http://hdl.handle.net/11427/22109en_ZA
dc.identifier.chicagocitationShannon, Debbie Anne. <i>"Atmosphere-vegetation interactions over South Africa."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Environmental and Geographical Science, 1997. http://hdl.handle.net/11427/22109en_ZA
dc.identifier.citationShannon, D. 1997. Atmosphere-vegetation interactions over South Africa. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Shannon, Debbie Anne AB - This study examines the sensitivity of the atmospheric circulation to vegetation change over South Africa in the context of the portended global warming. This is achieved using a vegetation model driven by climate change information and subsequently incorporated within a general circulation model (GCM). The stand-alone vegetation model is driven using precipitation, temperature and relative humidity derived from downscaling using artificial neural networks. The vegetation model is then run with perturbed precipitation, temperature and relative humidity from downscaled model data from lxCO₂ and 2xCO₂ GCM simulations. The resultant vegetation perturbation response to climate change is then examined and incorporated into the GCM in order to ascertain the atmospheric sensitivity to vegetation changes. The off-line results of the vegetation model indicate a moderate degree of sensitivity of the vegetation to perturbations in precipitation, temperature and relative humidity. The general trend in response to the CO₂ climate is a westwards and altitudinal shift of lowland vegetation over the eastern part of the country, and a southwards and eastwards shift of the more dryland vegetation in the west. These shifts are in accordance with expected responses, since lowland vegetation responds more to temperature changes and the dryland vegetation to precipitation changes. Nonetheless, the use of the model provides a physically justifiable scenario on which to base the GCM studies, and at a finer resolution than otherwise available. A GCM simulation with the perturbed vegetation was then performed using sea surface temperature boundary conditions for 1980 and compared to an identical GCM run without the perturbation. 1980 was chosen since this year does not represent either a strong El Niño or La Niña year. The atmospheric sensitivity to the vegetation perturbation has been examined in terms of climatic variables such as temperature, precipitation, pressure, specific humidity, horizontal divergence, and sensible and latent heat fluxes. The results show that the atmosphere is quite sensitive to relatively small vegetation changes. Atmospheric response to vegetation perturbations indicates greater sensitivity over the NW and SE regions of southern Africa. The perturbation indicates a reduction in precipitation over the SE interior, related to less moisture feeding in over the interior from the SE Indian Ocean. Wind speed changes over the adjacent ocean were also evident, and are probably related to the changes in the South Atlantic and Indian high pressures. A southwards extension of the Hadley Cell was also suggested, as well as changes in sensible and latent heat fluxes, relating to precipitation and temperature changes. It is suggested that changes may be in response to the general drying out of the country and the associated increase in aridity. This research forms the preliminary investigation for further work incorporating the atmospheric perturbation response back into driving the vegetation model in order to examine the direction of the feedback -- whether this is positive or negative in the longer term. Thus, this study has demonstrated that the atmosphere is significantly sensitive to vegetation changes over South Africa and reinforces the need for improved land surface parameterization schemes and vegetation models in general circulation models. DA - 1997 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1997 T1 - Atmosphere-vegetation interactions over South Africa TI - Atmosphere-vegetation interactions over South Africa UR - http://hdl.handle.net/11427/22109 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/22109
dc.identifier.vancouvercitationShannon DA. Atmosphere-vegetation interactions over South Africa. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Environmental and Geographical Science, 1997 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/22109en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Environmental and Geographical Scienceen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherEnvironmental and Geographical Scienceen_ZA
dc.titleAtmosphere-vegetation interactions over South Africaen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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