A Risky Climate for Southern African Hydro

Dr. Richard Beilfuss
Wednesday, September 19, 2012

Report assesses hydrological risks for Zambezi River Basin dams

This in-depth study of the hydrological risks to hydropower dams on the Zambezi River gives an early warning about what Southern Africa could be facing as it contemplates plans for more large hydropower dams in a time of climate change.

Currently, 13,000 megawatts of new large-dam hydro is proposed for the Zambezi and its tributaries. 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.

Overall, Africa’s fourth-largest river will experience worse droughts and more extreme floods. 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. The result could be dams that are uneconomic, disruptive to the energy sector, and possibly even dangerous.

The report’s key findings describe a region moving toward the edge of a hydrological precipice:

  • 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 runoff, according to the International Panel on Climate Change.

  • The basin is likely to experience significant warming and higher evaporation rates in the next century. Because large reservoirs evaporate more water than natural rivers, big dams could worsen local water deficits and increase the risk of shortfalls in power generation.

  • The designs for two of the bigger dam projects proposed for the Zambezi – Batoka Gorge and Mphanda Nkuwa dams – 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, these dams are unlikely to deliver expected services over their lifetimes.

  • More frequent extreme floods threaten the stability and safe operation of large dams. If dams are “under-designed” for larger floods, the result could be serious safety risks to millions of people living in the basin.

  • The Zambezi's large dams have profoundly altered 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 report recommends a series of steps to address the coming storm of hydrological changes, including changes to how dams are planned and operated.