The massive hydropower dams built on the Zambezi River, the largest river system in Southern Africa, not only supply power to major economies in the region but also help mitigate annual floods. But as electricity demands grow and rising global temperatures affect rainfall patterns, the dams will be unable to meet energy needs or control floods, warns a new study.
The study, A Risky Climate for Southern African Hydro, was conducted for the NGO, International Rivers by Richard Beilfuss, a hydrologist and environmentalist who teaches at the University of Wisconsin-Madison College of Engineering in the US and the University of Eduardo Mondlane in Mozambique. Beilfuss says the region - and the rest of Africa as well - must reconsider the construction of massive hydropower dams and rethink their use as a flood management tool, especially as floods are expected to worsen with climate change.
"Large dams are being built or proposed, typically without analysis of the risks from hydrological variability that are already a hallmark of African weather patterns, much less the medium- and long-term impacts expected from climate change," Beilfuss noted in the report. "Likewise, ecosystem services are rarely given much weight in the energy-planning process.”
Extreme floods expected
The report uses the Zambezi basin as a case study to inform governments planning to establish new hydropower plants.
Assessing climate change impact studies conducted on the Zambezi River Basin, Beilfuss said the Zambezi is expected to experience "drier and more prolonged drought periods". Over the next century, rainfall is expected to decrease by between 10 and 15 percent over the basin, according to several studies cited by the Intergovernmental Panel on Climate Change. There will be a significant reduction in the amount of water flowing through the river system, affecting all eight countries it passes through. The water that feeds the river is expected to decrease by between 26 percent and 40 percent in another four decades, the study observed.
But when the rains do fall, they will be more intense, triggering more extreme floods.
No major dams are currently under construction on the Zambezi, Beilfuss told IRIN, but two large dams have been proposed: Batoka Dam on the Middle Zambezi and Mphanda Nkuwa Dam on the Lower Zambezi. “Batoka is politically and financially complex because it must be a joint project between Zambia and Zimbabwe,” Beilfus said. “Mphanda is entirely within Mozambique and is in very advanced stages of preparation with a timeline for construction."
There has been considerable opposition to Mphanda Nkuwa, which environmentalists warn could displace several thousand people. Much of the anxiety over its construction is fuelled by the experience of the Cahora Bassa Dam in Mozambique, which has been widely cited as an environmental catastrophe since its construction in the early 1970s by the former Portuguese colonial government.
"None of these projects, current or proposed, has seriously incorporated considerations of climate change into project design or operation," noted Beilfuss.
Guido Van Langenhove, who heads Namibia’s Hydrological Services Department, agreed with the concerns raised by Beilfuss and said, "Our dams cannot handle one-in-a-hundred-year [extreme] flood events. They cannot handle the sheer volume of water that might be involved. We have to even consider how to fortify our existing structures."
Recent floods and their impact on the existing dams offer a possible view of future disasters. In 2007, heavy rains over the Zambezi threatened the dam structure, forcing the authorities to open the sluice gates of the Cahora Bassa Dam, affecting up to half a million people [some displaced, but others had crops destroyed etc ].
|Large dams are being built or proposed, typically without analysis of the risks from hydrological variability that are already a hallmark of African weather patterns, much less the medium- and long-term impacts expected from climate change|
In a case study on the floods and cyclones that struck Mozambique that year, the Overseas Development Institute warned that the two biggest dams on the Zambezi, Cahora Bassa and Zambia’s Kariba, "do not have the spill-way capacity to cope with the very large floods that occur on the river every five to 10 years. At best, the dam operators can slow down the sudden rise in water levels by phasing the spillage of water over a period of a few days, which gives the people living downstream a little more time to evacuate their homes."
Hydrologists in Southern Africa have been calling for a reconsideration of dam planning for years. In 2001, Bryan Davies, an ecologist and a Zambezi river expert, conducted an assessment of the Cahora Bassa and told IRIN, "one of these days there will be a cyclonic event" that the full dams would be unable to cope with.
Part of the problem is that the Zambezi River Basin in Mozambique is a naturally occurring flood plain. In the past, human habitation patterns took flooding into account. When the waters subsided, people would move in to plant in the rich soils, and shift to higher ground when the floods returned, but since the construction of Cahora Bassa, communities have settled much closer to the river, making them more vulnerable, Davies warned.
Van Langenhove, the Namibian official, said people mistakenly believe that the construction of a dam means they will be safe from flooding, and so tend to settle close to dams. "Should an extreme event take place, there would be a huge disaster," he said.
Beilfuss suggested using hydropower dams to produce electricity only and not to store flood water. "Many hydropower projects are justified on the basis of providing flood control in addition to energy generation. However, allowing for flood storage means the reservoir must be drawn down to provide flood capture space at the very time that this water is most needed to supply energy".
The vast natural flood plains of the Zambezi should be allowed to flood while ensuring people do not settle in those areas, he said. "This will allow for regeneration of the floodplains systems for wildlife and fisheries and agriculture, and also will reduce the impact of extreme floods - which already occur in the basin as it is - on people and property.
"By removing people from flood-prone areas - in accordance with Mozambique and Zambia law, by the way - it becomes especially important to restore modest annual high flows in the basin so that people can secure their livelihoods from fisheries and agriculture," he told IRIN by email.
Beilfuss also suggested that countries in the region improve existing hydropower capacity rather than investing in new infrastructure. "Adding new or more efficient turbines is almost always much lower-impact than building new dams." Countries should also consider alternative sources of energy generation.
In 2011, the eight countries through which the Zambezi flows set up the Zambezi Watercourse Commission (ZAMCOM) to manage the river. Though still a new body, "ZAMCOM is a very important step forward for the integrated development and water conservation in the Zambezi River Basin,” Beifluss said. “In particular, the ZAMCOM structure offers the potential to strategically address river development, including hydropower, on a basin-wide level rather than a country-by-country level."
Américo José Ubisse, secretary general of the Mozambique Red Cross, has been involved in flood relief operations in Mozambique for many years. He told IRIN in an email that, in the past, issues related to the "environment, climate change and their future humanitarian consequences were deeply undermined... The added value that is coming with these scientific studies must been taken into consideration. Undermining [scientific studies]... can be a big mistake, not only for the future of economic investment but also for the future of humanitarian sustainability.”