Part 3: Hydropower development and vulnerability in the Zambezi Basin

From source to sea, the Zambezi River Basin has significant hydropower development potential, and has long attracted investment interests (Hidrotecnica Portuguesa 1965, GPZ 1973, CRI Consortium 2001, Euroconsult and Mott Macdonald 2008, World Bank 2010, SWRSD Zambezi Joint Venture 2010, many others). The basinwide assessment of hydrological variability in the previous section, however, reveals that hydrological conditions in the Zambezi River system are extremely variable, with a high level of unpredictability and strong cyclical periods of severe drought (including two prolonged drought periods in past century) and extreme floods. The basin is characterized by low runoff efficiency, with significant fluctuations in runoff generated from small changes in rainfall. There also is considerable hydrological variability across the basin, ranging from high rainfall areas in the north to semi-arid to arid regions in the south/southwest.

The degree to which existing and planned hydropower developments have taken this variability into consideration is critical to understanding the long-term risk and uncertainty associated with hydropower production. Several engineering studies conducted during the 1970s argued that annual flows in the Zambezi system were increasing over time as a result of changes in land use and runoff patterns in the catchment (e.g., SWECO 1971, Balasubrahmanyam and Abou-Zeid 1982a), for example, and that the trends observed from the 1940s to 1970s would continue in perpetuity. These studies proposed rates of hydropower generation that far exceeded the Zambezi's potential when considered over the full 92-year flow record. This section examines current and proposed hydropower development in the Zambezi River Basin, and the hydrological assumptions upon which those developments are based. In the next section, we examine the impact of climate change on these patterns of hydrological variability, and the implications for hydropower in the basin.