An investigation into the evidence of seasonal rainfall pattern shifts in the Western Cape, South Africa

Du Plessis, J. A. ; Schloms, B. (2017-12)

CITATION: Du Plessis, J. A. & Schloms, B. 2017. An investigation into the evidence of seasonal rainfall pattern shifts in the Western Cape, South Africa. Journal of the South African Institution of Civil Engineering, 59(4):47-55, doi:10.17159/2309-8775/2017/v59n4a5.

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ENGLISH ABSTRACT: Climate change is a highly contentious topic in the modern world. There is much evidence to indicate that climatic shifts and extreme weather anomalies are taking place globally, in some places more than others. This paper presents the findings on research to determine whether shifts in seasonal rainfall patterns are indeed already visible in historical rainfall data in the Western Cape of South Africa. The paper aims to provide some baseline information which can stimulate further research in this field. Different analytical methods were formulated to investigate the relationships between daily rainfall indices over a set timescale. Data was collected from the South African Weather Service (SAWS) in order to accumulate 20 rainfall stations, each with at least 100 years of historical daily rainfall data. Statistical analysis, linear trend line distributions, time lag comparisons, cumulative distributions, moving average plots and autocorrelation relationships were applied to the data. The results of the analysis indicated that (1) the rainfall season undergoes fluctuations of wetter and drier years (approximately 20-year cycles), (2) the South Coast region exhibits a shift towards a longer rainfall season, and in contrast the Mediterranean region is shifting to a shorter rainfall season when linear trend lines were analysed, and (3) the moving average plots showed only isolated seasonal shifts at the boundary months.

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