The impact of climate change on hydrological predictions, with specific reference to 24-hour rainfall intensities in the Western Cape

Van Wageningen, Andries (2006-03)

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2006.


The climate of the world varies from one decade to another, and a changing climate is natural and expected. However there is a well-founded concern that the unprecedented human industrial development activities of the past two centuries (and mainly the last century) have caused changes over and above natural variation. Climate change is the natural cycle through which the earth and its atmosphere are going to accommodate the change in the amount of energy received from the sun. There are various indicators that can be monitored to measure and verify possible climatic changes. This thesis will firstly emphasize what the possible effects of climate change could be on amongst others, the coastal zone, biodiversity and water resources. If the impact of climate change on the above mentioned processes are monitored, and changing trends can be identified, these processes could in fact be seen as climate change indicators. This is of major importance to us, to be able to accurately identify whether climatic changes are experienced in any given area and to attempt to quantify it. Engineering hydrologists are, amongst other duties, responsible for the determination of peak discharges to be able to size conduits to safely convey the stormwater for given recurrence interval events. All hydrological predictions are indirectly or directly based on historical data. Empirical formulas and deterministic methods were developed and calibrated from known historical data. Statistical predictions are directly based on actual data. The question that arises is whether the historical data still provides an accurate basis from which possible future events can be predicted? This thesis strives to find an answer to this question and will also try to advise hydrologists on how they should interpret historical data in the future, taking climate change into consideration. The methodology that will be followed will be to compare the percentage of occurrence of 24-hour rainfall events of different magnitudes, for historical- as well as predicted rainfall, for five different rainfall stations in the Western Cape. A detailed analysis of measured data at a rainfall station, with 42 years of useable data, will also be performed, to verify whether any measurable trends have already been experienced. Conclusions shall be drawn as to possible trends, and recommendations will be made as to how hydrologists could allow for the possible changing rainfall patterns.

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