Dams Threaten River Zambezi’s Prospect

Newton Sibanda in Grahamstown, South Africa
September 25, 2012

A report recently released by a US based not-for profit International Rivers has warned against further construction of dams on the Zambezi River due to climatic risks.

The study, by Dr. Richard Beilfuss, a well-respected hydrologist with 20 years’ experience on the Zambezi, warns that new and proposed dams are ill-prepared to withstand the shocks of a changing climate and that the result could be uneconomic dams that under-perform in the face of more extreme drought, and more dangerous dams that have not been designed to handle increasingly damaging floods.

The report finds that existing and proposed hydropower dams are not being properly evaluated for the risks from natural hydrological variability, which is extremely high in the Zambezi, much less the risks posed by climate change.

It notes that across the continent, African leaders are under pressure to grow their national economies, and to raise standards of living for their people, which translate into increased demands for energy.

Hydropower, the report notes, is generally being promoted as a source of large-scale energy capacity for the continent and numerous large dams are being built or under consideration.

The continent has experienced recurring drought in the past quarter century, which has become a leading contributor to power shortages in numerous hydro-dependent countries.

The report states that large hydropower schemes also harm the wealth of ecological services provided by river systems that sustain human livelihoods and freshwater biodiversity and that these impacts are being compounded by climate change.

It also notes that despite these concerns, 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.

This report presents an evaluation of the hydrological risk of hydro-dependent power systems in the face of climate change, using the Zambezi Basin as a case study.

“The future of the Zambezi Basin exemplifies the challenges faced by decision-makers weighing potential benefits of hydropower development against the risks of hydrological change,” the report reads.

The Zambezi River Basin is the largest in Southern Africa, and currently has approximately 5,000 MW of installed hydropower generation capacity, including the massive Kariba- whose reservoir is, by volume, the largest in the world, and Cahora Bassa dams.

An additional 13,000 MW of hydropower potential has been identified. According to the report, none of these projects, current or proposed, has seriously incorporated considerations of climate change into project design or operation.

The report says that the Zambezi River Basin has one of the most variable climates of any major river basin in the world, with an extreme range of conditions across the catchment and through time.

“The entire Zambezi River Basin is highly susceptible to extreme droughts, often multi-year droughts and floods that occur nearly every decade. Droughts have considerable impact on river flows and hydropower production in the basin.
For example, during the severe 1991/92 drought, reduced hydropower generation resulted in an estimated $102 million reduction in GDP, $36 million reduction in export earnings, and the loss of 3,000 jobs,” the report says.

“Extreme floods have resulted in considerable loss of life, social disruptions, and extensive economic damage. Hydropower operators and river basin managers face a chronic challenge of balancing trade-offs between maintaining high reservoir levels for maximum power production and ensuring adequate reservoir storage volume for incoming floods,” it says.

The report further says the natural variability of Zambezi River flows is highly modified by large dams, particularly Kariba and Cahora Bassa dams on the mainstem, as well as Itezhi-Tezhi and Kafue Gorge Upper dams on the Kafue River tributary.

It says Zambezi hydropower dams have profoundly altered the hydrological conditions that are most important for downstream livelihoods and biodiversity, especially the timing, magnitude, duration, and frequency of seasonal flood pulses.

The Intergovernmental Panel on Climate Change (IPCC) has categorized the Zambezi as the river basin exhibiting the “worst” potential effects of climate change among 11 major African basins, due to the resonating effect of increase in temperature and decrease in rainfall.

The report says these staggering climate change predictions, based on the average (not extreme case) of many climate models, have profound implications for future hydropower in the Zambezi River Basin.

The report notes that most hydropower projects are designed on the basis of recent climate history and the assumption that future hydrological patterns will follow historic patterns.

“However, this notion that hydrological systems will remain “stationary” in the future (and thereby predictable for the design and operation of hydropower schemes) is no longer valid. Under future climate scenarios, a hydropower station based on the past century’s record of flows is unlikely to deliver the expected services over its lifetime.

It is likely to be over-designed relative to expected future water balances and droughts, and under-designed relative to extreme inflow events,” it says.
The report notes that extreme flooding events, a natural feature of the Zambezi River system, have become more costly downstream since the construction of large dams, and will be exacerbated by climate change.

The financial and social impact of a major dam failure in the Zambezi River Basin would be nothing short of catastrophic, it says.

The report says the design and operation of the Batoka Gorge and Mphanda Nkuwa dams now under consideration for the Zambezi illuminate these concerns and that both dams are based on historical hydrological records and have not been evaluated for the risks associated with reduced mean annual flows and more extreme flood and drought cycles.

It says the wealth of ecological services provided by river systems that sustain life are rarely given much weight in the energy planning process and that the current course of dam building in Africa is not being evaluated with respect to the impact of dam-induced hydrological changes on the ability of rural populations to adapt to new flow regimes, much less on their ability to adapt to climate change’s impacts more generally.

“ Continued dependence on hydropower systems will exacerbate the economic impact of reduced ecosystem services already associated with river development.
The value of the ecosystem services threatened by hydropower development in the Zambezi
River system is astonishing. A recent economic valuation study estimates that the annual total value of river-dependent ecosystem services in the Zambezi Delta is between US$930 million and $1.6 billion,” the report says.

It recommends that planners need to carefully consider dams in the context of how climate change will shape water supply, and how future river flows must meet competing demands for power, conservation, and water for domestic use, agriculture, industry, and other services.

The report notes that while the Southern African Power Pool (SAPP) provides an excellent framework for diversifying power production and reducing dependency on hydropower, in practice, however, SAPP has emphasized large-scale coal and hydropower development to feed the regional grid, without serious consideration of climate change impacts and risks.

Other recommendations are that existing hydropower structures should be rehabilitated, refurbished, renovated, or upgraded prior to the construction of new hydropower facilities as adding new or more efficient turbines is almost always much lower impact than building new dams.