Ph.D. (Geography) / South Africa is characterised by limited natural water resources and is water-stressed. The Upper Vaal Water Management Area (WMA) is part of the Vaal River system, which is deemed to be the ‘workhorse’ of South Africa as it is located in the economic heart of the country. The WMA supplies water to all of the major economic entities in the economic hub of the country and is fully exploited in terms of the water that it makes available. Owing to its prime importance in terms of the economic development of the country, the quality of the water in the Upper Vaal WMA is an important factor which needs to be investigated and monitored intensively. The degradation in the quality of the water in this region will in its turn reduce the availability of water in the Upper Vaal WMA and have widespread environmental, social, as well as economic consequences and impacts. The aim of this study is thus to quantify and predict future hydrological responses, in terms of water quality, towards land cover changes in the case of the Upper Vaal WMA for the period, July 2000 to June 2012. In so doing, model equations can be formulated and predictions can be made for future hydrological changes in terms of future concentrations of the selected water quality parameters linked to specific land cover change scenarios. The quality of the water in the Upper Vaal WMA varies significantly across all of the secondary and tertiary catchments and could, therefore, be described as being of a heterogeneous nature. Its quality as a whole is below average and in some cases, poor. The quality of the water in the secondary catchment of the Wilge River, on the other hand, is for the most part of an ideal to acceptable standard. However it has been degraded to a certain extent as it displays tolerable concentrations of phosphate, COD and Chlorophyll a and unacceptably high concentrations of nitrate. The Vaal River, Vaal River Barrage and the Mooi River catchments are significantly degraded owing to the mainly tolerable to unacceptably high concentrations of most of the selected water quality parameters that they contain.....

Global climate change is a naturally occurring phenomenon, influencing weather and climate patterns. However, the greatest cause for concern at present is the rate at which climate change is currently occurring. Natural shifts in climate take place over a period of many thousands of years, not in a matter of decades, which is what is occurring at present. In South Africa, climate change is projected to have different regional effects, which in turn could impact on the components of the terrestrial hydrological system, such as land use. The alteration of the catchment upstream of the estuaries could affect the quantity and quality of streamflows entering estuaries. This could impact negatively upon estuaries, thereby reducing the considerable biodiversity in estuaries and the ecosystems goods and services provided by estuaries which would reduce the significant revenue provided by these systems. The research undertaken in this project investigates the possible effects of climate change, and changes in upstream land use on freshwater inflows into estuarine ecosystems using a daily hydrological model. Owing to the regionality of climate change in South Africa 10 estuaries in different climatic regions were selected for this investigation. Climate output from five GCMs under the SRES A2 climate scenario for the present (1971 – 1990), intermediate (2046 – 2065) and distant future (2081 – 2100) periods was used as input for the selected climate input. Results of these simulations show that the eastern regions of South Africa may experience considerable increases in the occurrence of high intensity rainfall events into the future. This could influence the abiotic factors of the system which may impact upon the biotic components of estuaries, as these systems are physically controlled. In the western regions the difference of the magnitude of flows between present and projected future is minimal. However, projected increases in temperature could influence evaporation, thereby decreasing future flows into estuaries. This, in some instances, may result in systems turning hyper-saline, which could have far reaching implications, both ecologically and economically. Additionally, an investigation, as to the possible effects of irrigation and climate change combined on flows entering and breaching events of the Klein estuary, was undertaken. Hence, simulations including and excluding irrigation routines have been completed. Results from these simulations illustrate the detrimental effects of irrigation into the future periods, especially during 1 in 10 low flow years, when flows into the Klein estuary cease completely. Breaching event results illustrate that climate change could have a negative impact on this estuarine system as the number of events decreases into distant future period. The addition of agricultural abstractions decreases the number of breaching events markedly. Therefore, the link between the marine and terrestrial hydrological systems is lost which could, if this estuary is isolated from the ocean for an extended period of time, become extremely detrimental to the ecological integrity of the Klein estuary. This highlights the value and vulnerabilities of estuarine ecosystems in South Africa to future climate and upstream land use changes. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Climate detection studies point to changes in global surface temperature and rainfall patterns over the past 100 years, resulting from anthropogenic influences. Studies on the analysis of rainfall patterns [1950 – 1999] in southern Africa’s summer rainfall areas show an increase in the duration of late summer dry spells, and this change is in line with expected effects of global warming. Observations of surface temperature increases are consistent with climate projections from General Circulation Models (GCMs), as well as with overall changes in climate over the past century. As such, the alterations in climate conditions have a potential to significantly impact agro-ecosystems. The changes in these climatic patterns are projected to result in a cascade of changes in crop responses, and their associated crop yield-limiting factors through altering water available for agriculture, as well as yield-reduction factors by increasing pest/disease/weed prevalence, both of which may lead to agricultural production being affected severely. The objective of this study is to explore effects of scenarios of climate change on agrohydrological responses in the Limpopo Catchment, with an emphasis on the development and application of statistical modelling and analysis techniques. The algorithms of temperature based life cycle stages of the Chilo partellus Spotted Stem Borer, those for agricultural water use and production indicators, and for net above-ground primary production (an option in the ACRU model) as a surrogate for the estimation of agricultural production. At the time that these analyses were conducted, the downscaled daily time step climate projections of the ECHAM5/MPI-OM GCM, considered to indicate projections that are midway between the extremes from other GCMs for southern Africa, were the only scenarios available at a high spatial resolution which had been configured for South Africa. Further, the statistical analysis techniques conducted in the dissertation include quantitative uncertainty analyses on the temperature and precipitation projections from multiple GCMs (the output of which subsequently became available), as well as validation analyses of various algorithms by comparing results obtained from the GCM’s present climate scenarios with those from historically obtained climates from the same time period. The uncertainty analyses suggest that there is an acceptable consistency in the GCMs’ climate projections in the Limpopo Catchment, with an overall high confidence in the changes in mean annual temperature and precipitation projections when using the outputs of the multiple GCMs analysed. However, the means of monthly projections indicated varied confidence levels in the GCMs’ output, more so for precipitation than for temperature projections. Findings from the Validation analyses of the ECHAM5/MPI-OM GCM’s present climate scenario estimations of agricultural production and the agricultural yield-reduction (Chilo partellus) factor against those from observed baseline climate conditions for the same time period indicated a positive linear relationship and a high spatial correlation. This suggests that the ECHAM5/MPI-OM GCM’s present climate scenario is relatively robust when compared with output from observed climate conditions. ECHAM5/MPI-OM GCM projections show that agricultural production in future might increase by over half in the southern and eastern parts of the Limpopo Catchment compared to that under present climate conditions. Findings from the projections of the yield-limiting factor representing water available for agriculture over the Catchment suggest increases in the agricultural water productivity indicator under future climate conditions, with pronounced increases likely in the eastern and southern periphery. On the other hand, the agricultural water use indicator maintained high crop water use over most of the Catchment under all climate scenarios, both present and future. These positive effects might be due to this particular GCM projecting wetter future climate conditions than other GCMs do. Similar increases were projected for the yield-reduction factor, viz. the development of Chilo partellus over the growing season. These results suggest an increase in the C. partellus development, and thus prevalence, over the growing season in the Catchment, and this correlates spatially with the projected rise in agricultural production. The projected positive effects on agricultural production are thus likely to be reduced by the prevalence in agricultural yield-reduction factors and restricted by agricultural yield-limiting factors. The techniques used in this study, particularly the temperature based development models for the agricultural yield-reduction factor and the agricultural water use/water productivity indicators, could be used in future climate impact assessments with availability of outputs from more and updated GCMs, and in adaptation studies. This information can be instrumental in local and national policy guidance and planning. Keywords: Climate projections (scenarios), agricultural production, agricultural yield-reduction (Chilo partellus) and -limiting factors, uncertainty analysis, validation analysis. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.