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Stellenbosch University (2021)

Assessment of seasonal and annual rainfall trends and variability in South Africa

Kibii, Joshua Kiprotich

Titre : Assessment of seasonal and annual rainfall trends and variability in South Africa

Auteur :

Université de soutenance : Stellenbosch University

Grade : Master Civil Engineering 2021

Résumé partiel
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

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