AFRICA
7. OVERALL CONCLUSIONS AND RECOMMENDATIONS
7. OVERALL CONCLUSIONS AND
are not uniform across the region. The identified hotspot areas of warming were the Western Cape and KwaZulu-Natal.
7.2 Summary of Changes Evident in Hydrological Responses over Southern Africa
The ACRUmodel was used to simulated streamflows and various other hydrological responses and drivers for the period 1950 - 1999. In this analysis, all human impacts were eliminated from simulations. Two periods of data, viz. 1980 - 1999 and 1950 - 1969 were extracted and split-sample analyses performed on the various hydrological responses and drivers. Analyses were conducted on reference potential evaporation, soil water content, median, lowest and highest accumulated streamflows in 10 years, ranges between high and low streamflows, baseflows, timing and concentration of streamflows and irrigation water demand.
The winter rainfall region emerged through all the analyses as an area experiencing increased flow parameters in the later period. Increases in the later period were observed in median annual accumulated streamflows, lowest summer accumulated streamflows in 10 years, lowest winter accumulated streamflows in 10 years and concentration of summer flows. Decreases in the later period, however, were observed in the winter range between the lowest and highest flows in 10 years.
The southeastern Free State, the area which feeds the Caledon River Basin, exhibits decreases in the later period in almost every analysis of hydrological responses conducted, be it in medians, extremes or ranges, and the decreases noted are substantial.
The east coast of southern Africa, in particular that of KwaZulu-Natal, showed marked increases in the upper end of the streamflow distribution. Increases in the later period in the annual highest accumulated streamflows in 10 years were evident, as were increases in the summer highest accumulated streamflows in 10 years. The range between the lowest and highest flows in 10 years for summer in the later period had also increased in this region.
The changes seen in streamflow were relatively large, and often the later period experienced more than twice the streamflows of the earlier period. These results however, may be an artefact of the two relatively short periods used in the split-sample analysis, for which the trends observed may not necessarily have statistical significance.
The extent to which the trends over the past 50 years are directly related to climate change is not clear. However, some trends are very marked over significantly large parts of Primary Catchments, with the hotspots of change being the winter rainfall region, KwaZulu-Natal and the southeastern Free State.
7.3 Summary of Changes in Rainfall Regimes
The substantial changes evident in hydrological responses prompted an exploration of changes in rainfall patterns. Daily rainfall values for each of the I 946 Quaternary Catchments were extracted from the AeR Umodel rainfall files for the periods 1980 - 1999 and 1950 - 1969. A split-sample analysis was perfonned, and the results displayed as a ratio. The changes evident in rainfall vary from unsubstantial increases or decreases to significant increase and decreases. The winter rainfall region of southern Africa seems to be experiencing more rainfall in the 1980 - 1999 period compared with the 1950 - 1969 period. Itis experiencing an increased median annual, lowest annual rainfall in 10 years, an increase in summer median and lowest summer rainfall in 10 years. The lowest winter rainfall in 10 years in the winter rainfall region is increasing, however, the highest winter rainfall in 10 years is decreasing, as is the number of events above thresholds of 10 mm and 25 mm.
The area of the southeastern Free State which feeds the Caledon River Basin, consistently indicates a decrease in rainfall in the later period for almost all rainfall parameters analysed. The Limpopo and North-West provinces, along the borders of South Africa with Botswana and Zimbabwe, stretching into the Northern Cape, represents another area consistently showing a decrease in rainfall in the later period for the various parameters analysed. The changes evident in daily rainfall varied spatially across the country, with hotspot areas in the Western Cape, southeastern Free State, Limpopo and North-West Provinces being identified.
7.4 Are Changes in Climate Already Evident over Southern Africa at a Regional Scale?
Changes in southern Africa's temperature, hydrology and rainfall have been shown in Chapters 3, 5 and 6. These changes, however, are not consistent spatially within the region, nor in direction and magnitude of change. However, hotspots or clusters of substantial change have been detected.
The Western Cape region is viewed as a definite hotspot of change. In almost every temperature parameter analysis performed warming was observed. Streamflows in the Western Cape are increasing, in particular low flow. The rainfall regime in the Western Cape has also been shown to be increasing. Another hotspot of detected change is KwaZulu-Natal, where strong increases in temperatures are evident, along with increases in the upper ends of the streamflow distribution. Increases in rainfall were also evident in this region.
In rainfall and hydrological detection studies, a hotspot showing substantial decreasing trends was the southeastern Free State. The Limpopo and North-West provinces were also identified as areas showing marked decreases in rainfall and hydrological responses.
From the analyses conducted in this study, it has become clear that South Africa's temperature and rainfall, as well as hydrological responses, have changed over the recent past in certain identifiable hotspots, viz. the Western Cape and KwaZulu-Natal.
These detected changes in climate need to be considered in all future water resources planning.
7.5 Recommendations Regarding the Rainfall Monitoring Network in South Africa
For each Quaternary Catchment the "best" representative rainfall station of that catchment was selected in this study from a more comprehensive and up-to-date database than that used in a previous selection of stations. The selection was based on a number of possible influences on the quality of the rainfall stations' records. The
rainfall stations selected to 'drive' each Quaternary Catchment generally had a long reliable and high quality record of daily rainfall.
However, an analysis of the rainfall network highlighted that low rainfall station reliability existed in the Western Cape and Drakensberg mountain areas and in the northernmost parts of South Africa. As a considerable portion of southern Africa's water resources have their origin in such high lying areas where the rainfall, and thus runoff, gradients are at their steepest and the strong curvilinear relationship between rainfall and runoff is at the high end of the curve, it is crucial that the reliability of the rainfall network in these areas be improved.
The rainfall stations selected in this study need to be highlighted in terms of the monitoring network in South Africa and should, if at all possible be, retained as high quality rainfall stations, as they are crucial in the region's future climate change detection and hydrological studies.
7.6 Recommendations for Future Climate Change Detection Studies in Southern Africa
Future research in detection studies in southern Africa should focus first on using the results of detected changes in climate parameters from this and other studies to convince roleplayers in national, regional and local governments and water resources managers that climate change has become a reality already, and can no longer be ignored.
Hydrological detection studies in future need to consider the impacts which actual catchment conditions, including present (and projected) land uses, dams, irrigated areas, inter-basin transfers and return flows, have had on the hydrological regime, and whether changes in the catchments hydrological responses, over and above these anthropogenic impacts, are present which can be attributed to changes in climate.
An in-depth examination of actual rainfall records from high quality rainfall stations, which have a homogeneous record of at least 50 years, needs to be undertaken. Water is crucial to human existence; hence, it is essential that changes in rainfall regimes are