Powering through uncertainty. Assessing the impact of climate change on hydropower generation: A case study of Kariba South Hydropower Station, Kariba subbasin, Zimbabwe.

Abstract

The Intergovernmental Panel on Climate Change (IPCC) AR5 highlights that climate change already impacts water resources, leading to extreme precipitation, floods, cyclones, decreased runoff in water-stressed regions, and expanding drought areas. These effects are evident in the Zambezi River Basin, Africa's fourth-largest river system. This study assesses the impact of climate change on the hydropower generation capacity of the Kariba South Hydropower Station (KSHS) in Zimbabwe's Kariba Subbasin over the past three decades. As hydropower remains Zimbabwe's primary renewable electricity source, with KSHS currently contributing 185 MW to the national grid, understanding climate-induced hydrological changes is crucial for the energy security of Zimbabwe. The research examines historical trends in precipitation, temperature, river flow, and effective live storage from 1990 to 2019 using data from the Meteorological Services Department of Zimbabwe (MSD) and the Zambezi River Authority (ZRA). Data analysis was conducted using XLSTAT version 2024.4. Preliminary findings indicate a slight increase in annual mean maximum temperature at both Binga and Kariba stations over the study period. The annual mean minimum temperature exhibited a slight increase from 1990 to 1998 at Binga and from 1990 to 1997 at Kariba, followed by a slight decrease from 1999 to 2019 at Binga and from 1998 to 2019 at Kariba. However, these temperature trends were not statistically significant. Precipitation trends varied across the stations, with Binga slightly experiencing increasing annual and seasonal total rainfall, while Kariba exhibited a decreasing trend. However, neither trend was statistically significant. River flow patterns at three gauging stations along the Zambezi River also revealed notable variations. Chavuma Gauging Station recorded a decline in discharge from 1990 to 1997, followed by an increasing trend from 1998 to 2019. Similarly, flow at the Victoria Falls Gauging Station declined from 1990 to 1997 but increased afterward. In contrast, the Ngonye Hydro Gauging Station exhibited a consistent decline in discharge across the study period, 2005-2019. These river flow changes directly impact water availability into Lake Kariba's inflows, influencing the hydropower generation capacity at KSHS. These findings highlight Zimbabwe's hydropower sector's vulnerability to climate change, emphasizing the need for adaptive strategies to enhance energy security. The study provides critical insights for policymakers and energy planners to develop climate-resilient hydropower infrastructure in the Middle Zambezi River Basin.