Turning off the lights at Kariba

Lake Kariba is the pride of Zimbabwe, an enduring symbol of engineering triumph. The vast man-made reservoir straddling the banks of Zambia and Zimbabwe was built on the Zambezi River. The dam and six floodgates were built between 1955 and 1959 primarily for hydropower generation. However, the El Niño event of 2023 raises concerns about its potential impact on an already struggling source of regional and domestic hydroelectric power.

Lake Kariba's water levels have been dwindling in recent years due to a combination of factors, including reduced rainfall. The most recent El Niño event of 2023/24 exacerbated this problem. During El Niño events, the region typically experiences decreased rainfall and elevated temperatures, leading to higher evaporation rates. This has resulted in a further reduction in the lake's water levels, potentially impacting water availability for irrigation, electricity generation, and domestic use.

According to a report released by the Zambezi River Authority (ZRA) on September 2, 2024, the current Kariba Dam level stands at 476.7 metres ASL (above sea level). The minimum operating level of the dam wall is 475.5 metres ASL. This gives a balance of 1.20 metres.

In terms of water volumes, the current volume is 5.37 billion cubic metres, meaning there is 8.3% of live storage available for power generation. This time last year, that figure was 479.21 metres - 16.89 billion cubic metres - equating to 26.08% of live storage.

Zimbabwe drew 215 MW from Kariba out of a total power generation of 1258 MW on Monday September 2, the day the ZRA report was released. The rest of Zimbabwe’s power generation that day came from Hwange (1004 MW) and 39 MW from Independent Power Providers (hydroelectric and solar generation from private companies who generate their own power and feed surplus back into our national grid).

The graphic released by the ZRA (above) is a stark visual representation that shows whilst there is still plenty of water in the dam, it is “dead storage” and water for power generation at Kariba Dam is almost depleted.

The Kariba Lake is designed to operate between levels 475.50m and 488.50m (with 0.70m freeboard) for hydropower generation.

Zambia's power utility ZESCO has warned that it will shut down its power station at Kariba on September 14. Zambians now get just 3 hours of electricity per day, "on a rotational basis".

It is unclear why Zambia is currently drawing less water than Zimbabwe and also unclear why Zambia would shut down before Zimbabwe. Maybe Zambia has used more water in the last year or maybe it is their allocation

The ZRA is responsible for the environmental management of the Zambezi River as well as all the infrastructure developments on that stretch of water, including the Kariba Dam.

Zambia is shutting down its hydroelectric power generation from Kariba on 14 September. There has been no official word yet from Zimbabwe on timing but judging by those levels, public opinion from engineers is that it looks as if it may be under two months from now.

Are there any ways to mitigate the impact of El Niño when it comes to power generation in Zimbabwe? As climate change continues to influence weather patterns, the importance of adapting and implementing sustainable alternative energy resources practices becomes increasingly evident. It is clear that both public and private sectors have a role to play; just what and to what extent remain to be seen.