Posted on December 12, 2008
Researchers of the University of Pretoria (UP), the Agricultural Research Council (ARC) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia have collaborated to predict the climate of southern Africa, in a future world where green house gas concentrations gradually increase to more than double their natural levels. Should the current rate of greenhouse gas emissions persist, concentrations would reach double the natural levels by 2050. The research has been conducted by making use of a global circulation model of the CSIRO – the only model of its kind developed in the Southern Hemisphere. The climate simulation experiment was performed at high spatial resolution over southern Africa - on a powerful computer system at the UP. The study was lead by Dr. Francois Engelbrecht of UP, and was funded by the Water Research Commission (WRC).
The results of the study have recently been published in the “International Journal of Climatology“. The full reference is:
Engelbrecht F.A., McGregor J.L. and Engelbrecht C.J. (2008). Dynamics of the conformal-cubic atmospheric model projected climate-change signal over southern Africa. International Journal of Climatology. DOI: 10/1002/joc.1742.
The study shows that the southwestern Cape is highly vulnerable when it comes to future climate change. It is projected that this region may lose as much as 30 % of its annual rainfall, due to the southward displacement of cold fronts in the future climate. Over the largest part of eastern South Africa, a shorter but wetter summer rainfall season may be expected. However, because of drier conditions during spring and late summer, this region may also be expected to become generally drier. Limpopo Province is vulnerable in particular – here a decrease of up to 20 % in the yearly rainfall is projected.
Figure 1 (top panel) shows the projected rise in June maximum temperatures over southern Africa, in a world where greenhouse gas concentrations have risen to more than double their natural levels. Over large portions of South Africa maximum temperature is projected to rise with more than 3 or even 4° C – the regional outcome of Global Warming. The change in June rainfall, expressed as a percentage, is shown in the lower panel. The southwestern Cape is projected to lose as much as 40 % of its June rainfall, as a result of the southern displacement of cold fronts – also evident from the Figure.
Figure 1: Change in June maximum temperature (top, °C) and June rainfall (bottom, expressed as a percentage) relative to present-day values.
It is expected that Global Warming will lead to not only changes in the average rainfall patterns, but that the Earth will also experience more extreme weather events. The research team is at present busy with follow-up work, in order to determine how the distribution and frequency of occurrence of floods and droughts over southern Africa will change as a consequence of Global Warming. According to the model projection it may be expected that Tropical Cyclones will make landfall over northern Mozambique more often than in the past, with an associated increase in catastrophic flood events over this region. More intense convective rainfall events (thunder storms) are also likely to occur over eastern South Africa in summer of the future climate. Thus, in the midst of generally drier conditions over southern Africa, more flood events can be expected to occur over certain regions.
The researchers point out that there are numerous uncertainties when it comes to model projections of future rainfall patterns. For example, there exists uncertainty regarding the rate at which greenhouse gas concentrations will increase. On top of this, no computer model is capable of completely describing all the complexities of the land-ocean-atmosphere system. However, despite these uncertainties, consensus exists among most main-stream researchers that certain global changes, such as the southward displacement of the westerly wind belt and cold fronts, can be expected. The study performed at UP is the first to describe what the effect of these global changes may be within the regional context of southern Africa. The researchers point out that more studies of this nature should be performed, so that greater insight can be gained in the range of possible outcomes of climate change over southern Africa.
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