The first point to make is that the science now supports the main point being made that carbon dioxide and methane gas emissions have increased exponentially in the past century and continue to increase in a manner that is of great concern. This will result in global warming and will have consequences – what they will be and the extent of the changes is almost impossible to predict, but the models that have been developed point to rising sea levels and increased rainfall with greater variation from one season to another.
I think we can all sense that changes are taking place. Here in Zimbabwe the seasons are changing – our rains seem to come a bit later and be less predictable. In Windhoek where our workshop was located, they had 1000 mm of rain in 2012 and just 200 mm in 2013. Watching the weather daily on satellite imagery it seems to me that Botswana has been getting much more rain than usual.
Whither the ITCZ?
For southern Africa the changes are expected to influence the intensity and seasonal movements of a weather system we call the “Inter Tropical Convergence Zone”. I have known for all my life that if this sits over Zimbabwe, it can rain for many days and bring down the rivers in flood – sometimes it can do a lot of damage. Its absence means drought – in 1992 we had a season when it hardly rained at all and the suffering was terrible.
In preparation for the workshop I asked a good friend, Professor Euan Nisbet from London University, to send me some “stuff” and also read up what was available from other sources. Euan is a Zimbabwean and is now probably one of the top scientists on atmospheric changes in the world.
My conclusions are a bit amateurish but I drew from my reading that in this part of the world the ITCZ would shift to the north while higher ocean temperatures would raise overall precipitation and lead to more variation in rainfall from one season to another; hence the changes in annual rainfall in Windhoek for example. These changes will affect everyone and therefore we all have a stake in trying to mitigate the problem and manage the outcomes.
I just have a passion for the Zambezi River and the Zambezi basin – the river may not be the largest river in the world, but it is big and clean and traverses the whole continent, rising in Zambia, then running down to the Caprivi Strip and hence to Mozambique and the Indian Ocean. Looking at the river and the likely impact on it of Global Warming I came up with this possible scenario.
85 per cent of the water in the river comes from a region of Africa that is going to see much more rainfall, in addition, more extreme wet seasons. We can assume therefore that the volume of water in the river will be greater – not just the quantum but also the variations. I can recall the 1000 year flood of the river when the Kariba Dam was being built – it was something else and nearly destroyed the dam. The dam was designed in the early 50’s and completed by 1958. Designed for a river with a known and predictable flow; what happens if that changes?
Where the river runs through Zambia it has a lengthy flat section north of Kazungula. This section is navigable for quite large vessels and when the river floods in summer, the water rises and overflows the banks and floods very considerable areas of land on either side. This creates the flood plains that characterize much of this part of Zambia and the flood plains north of the Chobe River. These flood pains are covered in reeds and grass and gradually drain back into the main River through drainage channels that are maintained by the local Hippo population.
As a result the annual flooding of the Zambezi is extended from January right through to May and the silt from the upper reaches of the river basin is deposited in these vast wetlands then at the Victoria Falls, the water is clean and silt free – most unusual for an African River.
The Kariba Dam was designed for a certain river flow; it’s a vast stretch of water – perhaps 350 kilometers long and 50 kilometers wide. We already know that we cannot operate the full spill capacity through the wall as this might destabilize the foundations and cause vibrations in the wall. Should upper river flooding increase significantly, this might become a threat to the dam itself.
We are right now expanding the hydro power generation capacity from 1400 megawatts to 2000 and this will help as we can then release more water through the turbines, but this may not be enough. The key to this problem may be to expand the capacity created by nature upriver in the natural flood plains in Zambia and Caprivi. This could be achieved by installing flood barrages on the river with gates that can be raised and lowered to manage the river flow below them.
However this would depend on the protection we give to the resident Hippo who must keep the drainage channels open and flowing. In areas such as Caprivi we know that the Hippo populations are under threat from poaching and this needs further research and investigation.
We must, as a regional priority, develop our hydro electricity generation capacity. We must build the Batoko Gorge Dam and then look into river flow generation through low profile barrages on the river itself. We must develop the giant Inga scheme outside Kinshasa on the Congo River. This could generate 100 000 megawatts – enough to supply the total needs of all southern African States to the end of the century.
South Africa (the biggest polluter in the region) must stop building coal fired power stations, close down its older units and draw power from the hydro electric schemes to the north. To help with mitigation, all southern African States must take effective actions to protect forest areas and to prevent and manage wild fires.
If we were to adopt such strategies I am certain that the major developed nations would respond with financial facilities and support on a large scale. Access to clean, sustainable energy at a low cost would in turn lay the foundations of future growth and development. It would turn a problem into new opportunities.Post published in: Opinions & Analysis