In short
- Mokolo River data from 1990–2020 shows declining rainfall and rising temperatures.
- Rainfall variability strongly drives river flow, producing extreme peaks and prolonged low-water periods.
- Climate pressures threaten water supply, agriculture, ecosystems and local livelihoods.
- Climate-resilient water management and ecosystem protection are essential to strengthen long-term water security.
HSRC researchers and collaborators recently published findings of three decades of rainfall, temperature and river flow data from Limpopo’s Mokolo River catchment. The findings show how declining rainfall and rising temperatures are reshaping water availability in semi-arid South Africa, offering crucial lessons for climate-resilient water management nationwide. Such a technical analysis provides important knowledge for thinking about the social and economic impact of climate change on people’s lives.
A crossing at the Mokolo River, where sandy banks, rocks, and patches are exposed during the dry season, Limpopo, 2024. Photo: HSRC, Prof. Fhumulani I. Mathiva
South Africa is a water-stressed nation. With an average annual rainfall of just 495 mm in 2022, less than half the global average of 1040 mm, according to The World Bank, the country faces a precarious water future. Yet the challenge is not simply scarcity, as South Africa has experienced devastating extremes, from the catastrophic 2015–2016 drought to the deadly 2022 KwaZulu-Natal floods that caused widespread displacement and destruction.
The government’s 2018 National Water and Sanitation Master Plan delivered a stark warning that, without decisive intervention, water demand could exceed supply by 2030. Climate change is expected to intensify this risk. According to the Intergovernmental Panel on Climate Change, southern Africa is projected to experience significant drying and greater hydrological variability under continued warming.
Understanding how climate variability affects water resources has become urgent. A recent collaborative study between the University of Limpopo and the HSRC examined 30 years of data from the catchment area of the Mokolo River, a tributary of the Limpopo River in Limpopo Province. Their analysis revealed how rainfall patterns, temperature changes, and river flows interact, and what these dynamics in this area mean for water security in a changing climate.
The area below this construction shows exposed sandy banks, rocks, and patches at the Mokolo River during the dry season, Limpopo, 2024. Photo: HSRC, Prof. Fhumulani I. Mathiva
Why catchments matter
Water catchments, areas of land where rainfall flows downhill into the same river, stream, dam or wetland, function as early warning systems for climate impacts. Rainfall drives streamflow, and when precipitation becomes erratic or declines, river flows respond immediately. For example, higher peaks in river flow generally occur after heavy rain, and lower flows occur during droughts. Tracking these patterns over time, researchers can identify emerging trends and anticipate future water availability challenges.
The Mokolo River catchment provides a critical case study. This semi-arid system supports domestic water use, agriculture, and industry across 8387 km² of Limpopo Province. The river rises in the Waterberg Mountains near Lephalale, and researchers analysed data from seven rainfall monitoring stations distributed across the catchment between 1990 and 2020.
A clear decline in rainfall
The Mokolo River catchment followed a distinct summer rainfall cycle, with most precipitation falling between October and March. Winter months brought very little rain, causing river levels to drop significantly outside the summer season.
But rainfall patterns showed troubling instability. Month-to-month and year-to-year variability was extremely high across all rainfall monitoring stations, so high that the fluctuations exceeded average rainfall totals themselves. This represents deeply unpredictable precipitation rather than stable seasonal patterns. February 1996 illustrated these extremes: several monitoring stations recorded their highest monthly totals for the entire 30-year period.
More concerning was the long-term trend. Across all seven rainfall monitoring stations, rainfall declined consistently over the study period, a statistically significant downward trajectory that researchers documented from 1990 to 2020.
Rivers under stress
River flow exhibited even greater volatility than rainfall. Monitoring stations recorded sharp swings between extremely low and high flows, with extended periods of minimal water punctuated by sudden peaks.
The highest recorded streamflow, 133.8 m3 per second, occurred in February 1996, coinciding precisely with that month’s exceptional rainfall. This timing confirms a direct rainfall-runoff relationship in the catchment. Conversely, 1992 and 1993 brought exceptionally low flows across all stations during a severe regional drought affecting southern Africa.
Streamflow trends varied across the catchment. One station (A4H010) showed a consistent downward trend, matching the overall rainfall decline. Other stations, however, displayed shifting patterns rather than steady directional change. Local factors, land-use practices, catchment topography and underlying geology explained these differences.
The temperature factor
Rising temperatures intensify water stress by increasing evaporation and plant water consumption, reducing the amount of water that reaches streams and rivers. The study confirmed an overall warming trend across the three decades.
However, researchers found no evidence that temperature changes directly altered river flow independently. Instead, their analysis confirmed that rainfall remained the primary driver of streamflow, though rising temperatures compound water stress by increasing losses before precipitation can replenish rivers and groundwater.
A system on the edge
The hydrological responses documented in this study reveal a river system highly sensitive to climate extremes. The dramatic oscillations between extremely low flows and sudden peaks demonstrate that the Mokolo River responds rapidly to rainfall events but provides minimal buffering during dry periods.
This volatility carries serious implications. Beyond flooding risks during extreme rainfall, researchers highlighted how persistently low river flows can trigger cascading problems. These include deteriorating water quality, ecosystem degradation and severe impacts on livelihoods dependent on the river. The Mokolo River catchment is a highly agriculturally active area where crop irrigation accounts for much of its water use. Game, livestock and subsistence farmers also rely on water from the catchment. The river is also the primary water source for the town of Lephalale, with the Mokolo Dam supplying water to a nearby power station and coal mines.
Implications for water management
Understanding how climate factors translate into hydrological responses, and how water in a landscape reacts when weather changes, helps explain climate variability’s impacts on local water availability. This knowledge is essential for effective adaptation planning.
A portable pump and hose system drawing water from the river, commonly used for irrigation, livestock watering, and temporary water supply during dry periods, Limpopo, 2024. Photo: HSRC, Prof. Fhumulani I. Mathiva
The Mokolo findings have significance beyond a single catchment. South Africa’s national water planning already acknowledges that business-as-usual approaches are unsustainable given projected supply-demand gaps. The Mokolo analysis demonstrates precisely how climate pressures manifest in real river systems, informing where adaptation investments should be prioritised.
As South Africa confronts both chronic water scarcity and increasing climate extremes, the Mokolo River Catchment offers both a warning and a roadmap. The data show unmistakably that climate pressures are already reshaping water availability in semi-arid regions. Researchers argued that adaptation must focus on integrated, climate-resilient water management, given the evidence of declining rainfall, rising temperatures and highly variable streamflow in the catchment. They emphasised strengthening water storage and supply infrastructure to buffer against prolonged low-flow periods and increasingly intense droughts.
At the same time, the study highlighted the need to protect and restore natural vegetation, soils and ecosystems around the catchment, which play a critical role in maintaining water quality, regulating flows and supporting biodiversity. Finally, the authors stressed that adaptive and collaborative governance, supported by proactive monitoring and flexible planning, is essential to manage growing uncertainty and competing water demands under future climate conditions.
Research contacts and acknowledgements
This Review article is based on the peer-reviewed journal article Variability and impacts of hydrometeorological variables on surface water resources in Mokolo river catchment, South Africa. The analysis was conducted by Dr Selelo Matimolane (former research specialist) and Mokgethwa Madubye (senior researcher) from the HSRC’s Equitable Education and Economies Division, and Prof. Fhumulani Mathivha from the University of Limpopo’s Department of Water and Sanitation. This Review article was written by HSRC science writer Jessie-Lee Smith and Matimolane.
For more information about this work, please contact Mokgethwa Madubye at mmadubye@hsrc.ac.za.
