From : Allafrica.com
9 October 2012
A NEW study has established that the Zambezi River Basin along with its existing and future large hydropower dams are ill-prepared for climate change. The report indicates that hydropower projects around the Zambezi are poorly evaluated for the risks from natural hydrological variability, which is very high in that area, much less the risks posed by climate change.
Overall, Africa’s fourth-largest river will experience worse droughts and more extreme floods, concludes the International Rivers report titled “A Risky Climate for Southern African Hydro: Assessing Hydrological Risks and Consequences for Zambezi River Basin Dams”, released on September 19.
International Rivers is a global non-governmental organisation that has worked to protect rivers and the rights of communities that have depended on them since 1985.
“Dams being proposed and built now will be negatively affected, yet energy planning in the basin is not taking serious steps to address these huge hydrological uncertainties,” said Dr Richard Beilfuss, author of the report.
“The result could be dams that are uneconomic, disruptive to the energy sector, and possibly even dangerous.”
Currently, 13 000 megawatts of new large-dam hydro is proposed for the Zambezi and its tributaries. Two large dams are already built along the 3 540km-long river — the Kariba Dam, providing power to Zimbabwe; and Zambia and the Cahora Bassa in Mozambique.
What the report findings mean is that the future of long-term clean power production at Kariba is under threat, if nothing is done now to prepare the 750MW hydropower plant for changing climatic conditions.
Moreso, the report strangles Zimbabwe’s efforts of developing a huge 800MW hydropower station at the Batoka Gorge by 2020. The report says the designs for Batoka, and another large dam proposed for the Zambezi in Mozambique (Mphanda Nkuwa dam) are based on historical hydrological records and have not been evaluated for the risks associated with reduced flows and more extreme flood and drought cycles.
Under future climate scenarios, it said, “these dams are unlikely to deliver expected services over their lifetimes”.
“More frequent extreme floods threaten the stability and safe operation of large dams.”
Peoples’ lives are endangered by dams “under-designed” for larger floods while Zambezi’s big dams have also greatly changed the hydrological conditions most important for maintaining downstream livelihoods and biodiversity.
“The ecological goods and services provided by the Zambezi, which are key to enabling societies to adapt to climate change, are under grave threat. These services are not being properly valued in planning for large dams in the basin,” the study said.
The report’s key findings describe a region that is drawing closer to a hydrological disaster: The Intergovernmental Panel on Climate Change says the Zambezi Basin exhibits the worst potential effects of climate change among 11 major sub-Saharan African river basins, and will experience the most substantial reduction in rainfall and run-off.
Warming in this basin will be significant, estimated in the region 0,3-0,6 degrees Celsius within the next century while evaporation rates are expected to be higher.
Because large reservoirs experience more water evaporation than natural rivers, big dams could worsen local water deficits and increase the risk of shortfalls in power generation, the report showed.
More than 11 percent of the mean annual flow of the Zambezi evaporates from large reservoirs associated with hydropower dams.
The IPCC estimates that rainfall across the basin will decline by up to 15 percent, as seasons also shift. The Zambezi run-off is expected to decrease by 26 percent to 40 percent by 2050. Unsustainable dam development in the Zambezi had also undermined the ecological balance. Dr Beilfuss said the value of the ecosystem services threatened by hydropower development in the Zambezi River system was astonishing.
A recent economic valuation study had shown that the annual total value of river-dependent ecosystem services in the Zambezi delta is between US$930 million and US$1,6 billion. Agriculture, fisheries, livestock, tourism and domestic water supply will all be affected.
“Cumulatively, the economic value of water for downstream ecosystem services exceeds the value of water for strict hydropower production, even without valuation of biodiversity and cultural uses of the river system,” said Dr Beilfuss.
“Successful adaptation in a highly vulnerable region such as the Zambezi River Basin requires a major shift in thinking, planning and designing water investments for the future.
“An alternative pathway, focused on climate-smart investments that explicitly factor in financial financial risk and the ecological functions and the values of river systems, is urgently needed.”
The report proffers a variety of proposals that governments wishing to exploit the Zambezi may pursue to limit ecological damage and prepare for climate change.
It stated that reducing the economic risks of climate change in hydro-dependent systems must address current as well as planned infrastructure. Firstly, the report recommends that governments assess hydropower in the context of comprehensive basin-wide planning.
This means 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, water for domestic use, agriculture, industry and other services”.
“Community and ecosystem-based adaptation approaches that integrate the use of biodiversity and ecosystem services into an overall strategy aimed at empowering people to adapt to climate change must be central to any comprehensive planning efforts,” it said.
Secondly, governments must incorporate climate change scenarios into dam design because “the major implication of climate for dams and reservoirs was that the future is uncertain and could no longer be assumed to mirror the past”.
The report said the Southern African Power Pool must be diversified to reduce hydropower dependency by creating a diverse energy supply, critical for climate change adaptation in water-stressed regions. The SAPP is 60 percent dependent on hydropower for all its energy needs. Dr Beilfuss stressed the need for the development of strong institutional capacity for water resources management.
“This may be the single most important factor in the successful adaptation of existing hydropower systems to cope with climate change . . . ,” he said.
It would also be important for governments to prioritise investments that increase climate resilience as well as ensuring that monitoring and evaluation systems support adaptive management. The Zambezi River Basin is the largest in Southern Africa with total drainage area of approximately 1,4 million square kilometres.
The basin currently has nearly 5 000MW of installed generation capacity. It also has one of the most variable climates of any major river basin in the world, with an extreme range of conditions across the catchment. Average annual rainfall ranges between 550mm and 1 600mm.