Gauteng is becoming progressively warmer and drier as a result of global warming. Weather experts say a powerful high pressure belt over southern Africa caused by greenhouse gases in the atmosphere is responsible for this.
It is also pushing the winter cold front, which used to bring wave after wave of rain to the Western Cape, offshore.
Across the world, extreme climatic conditions such as the major floods in Britain and the United States, the extreme heatwaves in Europe last year and an increase in the incidence and strength of hurricanes off the American coast, all show that global warming is finally having the effect scientists have warned about for years.
And the bad news for the Western Cape in particular is that the province is to get progressively drier for many decades to come.
University of Pretoria meteorology scientist Francois Engelbrecht said the whole of the southern African region would be getting less and less rain as the effects of global warming increased.
“Industrialised countries are not doing enough to cut back on greenhouse gases and the effect on the southern African region and the Western Cape in particular will be devastating.”
“Even if industrial countries stopped producing greenhouse gases, it would take many a year to turn around the effects of global warming.”
“What we have established through our research is that a high pressure system has been formed over a large part of southern Africa, fed by hot air caused by greenhouse gases over the equator.”
“The hot air rises about 15km into the air above the equator. The air cannot escape into the atmosphere and is forced in a northerly and southerly direction. The air that is pushed southward towards South Africa is then diverted westward because of the rotation of the earth and is piled up as a huge subtropical high pressure belt over central South Africa.”
“This pressure belt that has been growing in strength because of the mass inflow of air that rises at the equator, is the key to climate changes in this country. The high pressure belt pushes the cold fronts further and further south during the winter season and that is why the Cape is getting less rain. In fact, in future that region may have to look at changing its agricultural products to handle the drier weather.”
But it is not only the Western Cape that will be getting less rain as the effects of global warming grow.
“During the summer months the high pressure system is broken up and pushed eastward. This means that areas such as the Free State, Mpumalanga and other summer rainfall areas will also be getting less rain and become drier.”
“This will cause a decrease of rainfall in the eastern half of the country and central interior, including Gauteng a summer rainfall region.”
“For Gauteng this means warmer conditions and a decrease in rainfall.”
“Ironically there is a belt across the Northern Cape and central parts of the Eastern Cape that has been getting wetter over the past 40 years (the period during which other areas have been getting drier).”
“However, this belt of wet weather will continue to be pushed westward as the high pressure belt continues to grow. Eventually the wet belt will be pushed out towards the Atlantic. By that time the cold fronts bringing rain will have been pushed even further to the south of the Cape.”
“Unless greenhouse gas emissions can be radically cut, we don’t see this scenario changing and there is very little chance that industrial countries will cut back emissions. It is going to get worse and the southern African sub-continent is going to get very dry,” said Engelbrecht.
University of Cape Town climatology professor Bruce Hewitson said global warming and its effects could no longer be denied by anyone.
“We no longer have a normal climate. The climate is in transition and one can expect an increase in the frequency of extreme weather events.”
“The occurrence of extreme weather events such as the flooding in the United Kingdom is indicative of global warming. Global warming adds energy to the earth and atmosphere and with more energy, weather events are more intense.”
Hewitson said global warming should not be identified by single events, but took place over many years.
He said the Western Cape had been getting drier over the past 50 years and the trend would continue well into the 21st century.
But this did not mean the province would become a desert. There would still be periods of good rain.
Referring to the effects of global warming, he said the oceans were on average rising by about 5mm a year, although there were places where the rise was much more substantial.
“I don’t believe the South African coastline is under particular threat, but estuaries would be under some threat.”
