Browsing by Author "Kibii, Joshua Kiprotich"
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- ItemAssessment of seasonal and annual rainfall trends and variability in South Africa(Stellenbosch : Stellenbosch University, 2021-12) Kibii, Joshua Kiprotich; Du Plessis, Kobus J. A.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Weather variability, especially rainfall, receives significant global attention. The variability of rainfall distribution in time and space differs. Therefore, examining the trends and patterns of rainfall over South Africa, a water-scarce country, is important. A significant amount of research has been done both in South Africa and globally to find possible relationships between rainfall variability, seasonality, trends, and or climate change. This research was aimed at building on existing research of rainfall patterns in South Africa. The focus was on the use of non-parametric statistical analyses for trend analysis of recorded daily rainfall data (1900-2019), using 46 stations adequately distributed across South Africa. Absolute homogeneity tests were done and homogenous data characterised at monthly, seasonal and annual time steps. South Africa was divided into three rainfall regions: Summer, Winter and ‘All year’ rainfall regions. These regions were further categorised into eight climatic zones, based on SAWS climatic zones: North-Eastern Interior, KwaZulu-Natal, Western Interior, Central Interior, Southern Interior, North-Western Cape, South Western Cape and South Coast. Trend analysis was performed, and results indicated significant differences between daily, monthly, seasonal to annual time steps. The daily rainfall reflects insignificant trends. Monthly rainfall recorded statistically significant increasing trends in November, December, and January in the ‘All year’ and Summer rainfall regions and March, May, June and September recorded statistically significant decreasing trends in all three rainfall regions. The seasonal and annual trend analysis were performed for a long-term period of 120 years and three short-term periods of 40 years each. The short-term trends shift periodically within the three periods, resulting in only a few rainfall stations recording statistically significant long-term trends. The Summer rainfall region experienced alternating trends shifting across the three short-term periods towards an early or a late wet season with little change in mean annual rainfall. The Winter rainfall region had its main rainfall season becoming shorter, but wetter over the three short-term periods of analysis, while the ‘All year’ rainfall region experienced alternating shifts of dry and wet cycles with a slightly decreasing mean annual rainfall. In general, the seasonal rainfall trends of South Africa illustrated shorter, but more pronounced trends, progressively for the three short-term analysis periods. Only a marginal increase in annual rainfall was observed using the long-term analysis, while variability increased over the years, using the short-term analysis. The observed trends using non-parametric analysis do not have significant deviations from previous research outputs. However, the observed changes in rainfall were relatively low with a long-term increasing trend in annual rainfall of between 0.6 and1.0 mm during the analysis period of 120 years. This research, therefore, recommends that the use of projected rainfall (climate change) data in South Africa, should be well guided by considerations based on the observed rainfall data trends. Design and management decisions based on long-term rainfall projections due to climate change should be considered carefully, taking the design life of the infrastructure into consideration.