It’s been a week, this Monday, March 18, that Zambians no longer have power for eight hours a day. The government took this rationing measure because drought, linked to climate change and the El Niño weather phenomenon, is affecting the flow of the gigantic Zambezi River and its tributaries, on which the main hydroelectric dams of this southern African country are located. .
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In Zambia, 80% of electricity is produced thanks to hydroelectric dams which are installed mainly on the Zambezi River and its tributary, the Kafue River. Because of the drought, “ the flow of these two rivers is at 30% of its normal level”, explains to RFI the country’s Minister of the Environment, Collins Nzovu.
The government therefore decided to ration energy. This is why Zambians have been experiencing power cuts for eight hours a day since Monday March 11. “Mainly at night, before 8 a.m.”, assures the minister. However, daily life and the economy are affected. “We must be able to hold out until the next rainy season”, justifies the minister. In this southern African country, the wet season normally extends from November to April but this year, the month of February in particular remained desperately dry.
Vulnerability to climate change
This situation risks becoming more and more frequent, warns Sebastian Sterl, specialist in clean energy in Africa, at the World Resources Institute (WRI), based in Ethiopia.
“ Due to climate change, the differences between extremely wet and extremely dry years will become more and more pronouncedexplains the researcher. Wet years will become even wetter, dry years will become even drier, and this can obviously have negative consequences for hydropower production. We are seeing it at the moment in Zambia “.
Many other African countries rely very heavily on hydropower and are therefore very vulnerable to droughts. This is the case, among others, of Lesotho, Mozambique and Zimbabwe, points out Sebastian Sterl. To reduce this vulnerability, certain states such as Ethiopia and Kenya have diversified their sources of electricity production by developing solar and wind power in particular.
The Kariba dam
At the heart of Zambia’s power generation is the Kariba Dam on the Zambezi River. This pharaonic construction which dates from the time of Independence gave birth to the artificial lake of the same name. A reservoir of 185 billion m3 in normal times, which is located on the border between Zimbabwe and present-day Zambia and 200 km downstream from the famous Victoria Falls.
Today managed by the Zambezi River Authority (ZRA in English for Zambezi River Authority), this dam is of capital importance in terms of hydroelectric production for both countries. The lake level is theoretically likely to vary artificially. The authorities can, depending on needs, decide to open the floodgates in order to regulate the level of the lake in the event of flooding, for example.
The ZRA provides very illuminating graphs regarding the flow rates of the Zambezi River which feeds the lake. The dark blue curve on the graph below shows very low flow in mid-March. 348 cubic meters per second over 2023-2024 compared to 960 m³ for the period 2022-2023.
A French expert working in dam engineering and construction comments: “There is a real problem there. We are normally in a humid period, and the flow rates are exceptionally low. We also note that last year’s flood was very weak. It is therefore entirely credible that we will be facing a problem until mid-2025, especially if the flood persists in not coming in the coming months.”
That being said, the graph also shows us two things. First of all, “late” floods can appear like at the end of April 2018 (red curve). And there are also years without flooding, this is particularly visible in 1996 and 2019 (gray and yellow curves).
The El Niño phenomenon could also worsen the situation. During his previous visit in 2016, he had already weighed concerns about filling of Lake Kariba and on the electricity production of the dam.
To examine the consequences of the drop in lake level on electricity production, it is necessary to look at the filling data provided by the ZRA. Last week the filling was less than 15%.
The dotted line at the bottom of the graph symbolizes the minimum operating coast. That is to say the level below which it will no longer be possible to produce electricity because, to put it simply, the water no longer has enough force to turn the turbines. This limit is 475.5 m. The authorities in charge of operating the dam can decide to reduce production (thus causing cuts), before reaching this level, precisely to keep enough water in the reservoir, time to see what happens.
The normal reservoir of the dam is 488.5, and we are therefore currently a little below 478. The expert consulted by RFI specifies: “the rating itself does not seem to be anything to worry about. The problem is the incoming flow rates which are not arriving even though it is the season. We should be on the way up and it’s not going up.”
