What is climate impact?

Climate impacts are the actual consequences of climate change. The changes in long-term climate trends and extreme weather events can directly affect all stages of the energy value chain of the electricity system, which includes generation, transmission and distribution, and demand.

Tropical Cyclone Idai had devastating impacts on Africa in 2019. It was one of the strongest known cyclones on the east coast of Africa, hitting Mozambique, Madagascar, Malawi and Zimbabwe with strong winds, severe flooding and destructive landfall. Over 900 people died due to the storm, which was the greatest loss of life in a southern hemisphere tropical cyclone in the last 100 years (WMO, 2020).

Many climate experts believe that Tropical Cyclone Idai was intensified by climate change. Warmer air and sea-surface temperatures made more energy available for cyclones and more rain was released (BBC, 2019; The Telegraph, 2019). An El Niño drought, exacerbated by climate change, had continued for months before Idai hit, making the earth unable to absorb water quickly and susceptible to flash flooding. (Oxfam International, 2019). Rising sea levels intensified the impact of storm surges on coastal regions, raising the probability of inland flooding in low-lying cities. For instance, Beira, a coastal city of Mozambique, was severely devastated by Idai (WMO, 2019; The Telegraph, 2019).

Entire parts of the electrical energy value chain, including hydropower generation, were also affected by Tropical Cyclone Idai on several levels:

  • Generation: Due to flooding and excessive debris, two major hydropower plants in Malawi were damaged and went offline, reducing Malawi’s hydropower capacity by more than 80% (Centre for Disaster Philanthropy, 2019; The Watchers, 2019). It caused widespread disruptions in electricity supply for several days (ReliefWeb, 2019).
  • Transmission and distribution: The transmission lines from Mozambique to South Africa were damaged by the cyclone, and created a loss of 1 100 MW of power. It forced Eskom, South Africa’s electricity utility, to implement load-shedding to prevent putting more demand on the grid. At the height of the crisis, South Africans had their power interrupted twelve times in a four-day period (CFR, 2019).
  • Demand: Due to the interrupted electricity supply from the central grids after Tropical Cyclone Idai, electricity demand patterns in South Africa were markedly changed. Demand for diesel jumped as the disruption resulted in the use of back-up generators (CFR, 2019).

The number of intense tropical cyclones at the level of Idai is likely to increase in the future while the total number of tropical cyclones will decline (WMO, 2019). In 2019 in the South Indian Ocean basin 13 cyclones out of 18 reached hurricane intensity, equalling the largest number on record (WMO, 2020). The projected increase in frequency of high-intensity tropical cyclones requires African countries to be prepared for future climate impacts on their electricity systems. 

Sources: WMO (2019), WMO (2020); BBC (2019), The Telegraph (2019), Oxfam International (2019), Centre for Disaster Philanthropy (2019), The Watchers (2019), CFR (2019), ReliefWeb (2019).

Hydropower plants which generally have a long lifespan, ranging from 50 to 100 years, are likely to be impacted by climate change (ADB, 2013; Ebinger and Vergara, 2011; IHA, 2019; Burillo, 2018; WMO, 2017; US EIA, 2019). Rising temperatures will affect hydropower generation by increasing evaporation losses. Changes in precipiation will also alter potential, generation output, peak level and seasonal variations of hydropower. Increasingly erratic precipitation patterns such as the increasing number of dry days may arouse concerns over interrupted hydropower generation due to water shortages. Extreme weather events such as cyclones, floods, and land slides also damage hydropower assets and disrupt electricity supply. For instance, an increased sediment load after floods or landslides caused by storms can reduce the efficiency of hydropower generation and abrade turbines.

An assessment of future climate impacts is often challenging due to the complexity of the climate system and the range of models which often provide different results. For Africa, it is often compounded by a lack of historical observation data to verify those models. To address this, an assessment based on a thorough analysis of various models and data sources, and a comparison across these modeling outcomes, is needed.

This section shows results from an assessment of climate impacts on African hydropower generation. It involves estimating future annual and monthly capacity factors for 64 hydropower plants in 13 African countries between 2020 and 2099, and comparing the projected results with the values of the baseline period from 2010 to 2019.

The geographical scope of the assessment covers Nile basin countries (Egypt, Ethiopia, Kenya, Sudan and Uganda), Congo and Zambezi basin countries (the Democratic Republic of Congo, Malawi, Mozambique, Tanzania, Zambia and Zimbabwe), a North African country (Morocco) and a West African country (Ghana). The total installed hydropower capacity of the selected countries is over 21 000 MW, accounting for about 63% of the total installed hydropower capacity in Africa (over 36 000 MW) (International Hydropower & Dams, 2019).

The assessment covers over 18 000 MW of installed hydropower capacity in total, accounting for 80% of the total installed hydropower capacity of the 13 African countries, and around 50% of the entire continent. The full list of the assessed hydropower plants can be found in the Annex.

Share of selected hydropower plants in selected countries in terms of installed capacity


Share of selected countries in African hydropower in terms of installed capacity

  • To derive annual and monthly capacity factors per hydropower plant, the assessment developed a high-resolution global discharge map that combines monthly run-off data derived from 40 different ensembles of five General Circulation Models (GCM), four Global Hydrological Models (GHM), two Representative Concentration Pathways (RCP) (see Annex), a high-resolution (15” × 15”) area accumulation and drainage direction map from the HydroSHEDS project (ISIMIP Database; Gernaat et al., 2017; Lehner et al., 2008), and a low-resolution (0.5˚ x 0.5 ˚) map of monthly run-off.
  • The discharge maps were used to extract the design discharge and design load factors per hydropower plant (Gernaat, 2019). By ordering the discharge of a selected hydropower plant from the lowest to the highest month of discharge, a flow duration curve was generated. The value of the fourth-highest discharge month is called the design discharge and determines turbine capacity. The capacity factor is, by design, 100% for the four wettest months and less than 100% for the remaining eight drier months. Further information on the selected models and methodology is described in the Annex.
  • The assessment examined as many combinations of models as possible to enhance the reliability of results and minimise potential distortions by outliers. Since outliers are difficult to avoid due to the different assumptions within each model and the embedded uncertainty of climate and hydrological systems, the results present average annual and monthly capacity factors by aggregating and comparing outcomes from various GCMs, GHMs and RCPs.
  • The report assesses potential climate impacts using two different scenarios that lead to two different global average temperature outcomes: Below 2°C and Around 3°C. By comparing these two scenarios the report aims to present how greenhouse gas (GHG) concentrations are likely to impact hydropower capacity in Africa.
  • Both scenarios are based on the RCP of the Coupled Model Intercomparison Project Phase 5 (CMIP5) of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report. The RCPs show various representative GHG concentration trajectories and their impacts on the future climate (see Annex).
  • The Below 2°C scenario is based on the projections of the RCP 2.6 which assumes a radiative forcing value of around 2.6 W/m2 in the year 2100. Under the Below 2°C scenario the rise in global annual mean temperature stays below 2°C by 2100 compared to pre-industrial times (1850-1900). For the period 2080 to 2100, the global annual mean temperature increases by 1.6(±0.4) °C above the level of 1850-1900. The Below 2°C scenario assumes an early peak in global GHG emission trends followed by a drastic decline.
  • The Around 3°C scenario follows the trajectory of the RCP 6.0 which assumes a radiative forcing value of around 6.0 W/m2 in the year 2100. The Around 3°C scenario is associated with a rise by 2.8(±0.5) °C in global annual mean temperature for the period 2080 to 2100 compared to the pre-industrial level. The Around 3°C scenario is based on the assumption of stabilisation of total radiative forcing after 2100. Under the scenario global GHG emissions would peak during the latter half of the century and then decline.  

Overview of the scenarios: Below 2°C and Around 3°C


Below 2°C

Around 3°C

Representative Concentration Pathway

RCP 2.6

RCP 6.0

Targeted radiative forcing in the year 2100

2.6 W/m2

6.0 W/m2

CO2-equivalent concentrations (ppm)



Global temperature change



Likelihood of staying below a specific temperature level over the 21st century

Likely to stay below 2°C

More unlikely than likely to stay below 3°C

Source: IPCC (2014), Climate Change 2014 Synthesis Report, https://www.ipcc.ch/report/ar5/syr/.

Key results of the impact assessment

Africa, where today more than 600 million people are deprived of electricity, is expecting to add 20 million people to the electricity network every year from now to 2030. In addition, the fast-growing urban population and accelerated economic growth are expected to boost electricity demand. Sub-Saharan Africa (excluding South Africa) in particular is likely to see the fastest growth in electricity demand of any region worldwide, at an annual rate of 6.5% on average (IEA, 2019a). Large-scale deployment of renewable energy is considered to be a cost-effective path to meet the soaring demand for electricity while mitigating emissions from electricity generation.

Hydropower, which currently comprises the majority of installed renewable capacity in Africa, is expected to remain one of the largest renewable sources of electricity. In a scenario that assumes the fulfilment of climate and sustainable development goals, hydropower grows even further to more than 23% of electricity generation by 2040 in Africa, accounting for one-third of total electricity generation from renewables (IEA, 2019a). Given the increasing role of hydropower in Africa, the impacts of climate change on the future hydropower capacity factor need to be assessed in advance to ensure climate resilience of the electricity system.

From now until the end of the century, the mean hydropower capacity factor of selected hydropower plants will decrease due to climate change in both climate scenarios, when other conditions remain unchanged.

The mean capacity factor over the period from 2020 to 2059 is likely to decrease by more than 1% compared to the baseline level of 2010-19. The decrease in hydropower capacity factor is projected to continue in the latter 40 years of the century. Between 2060 and 2099, the mean hydropower capacity factor is projected to fall by around 3% compared to the baseline level of 2010‑19 in both scenarios. The projected decrease in hydropower generation from the selected African hydropower plants during 2020‑99 is expected to be around 130 TWh, equivalent to the total annual hydropower generation in Africa in 2017 (IEA 2019a).

Average hydropower capacity factor of selected African hydropower plants, 2020-2099, relative to the baseline level of 2010-2019


The decline in capacity factors is mainly driven by two elements: decreasing levels of peak monthly capacity during the wettest months, and a further decline in water flow during the driest months in a majority of the selected plants. Under both climate scenarios, peak monthly capacity levels of the baseline period will no longer be reached in most of the selected countries from 2060 onwards. Moreover, in the Democratic Republic of Congo, Malawi, Morocco, Mozambique, Zambia and Zimbabwe, lower water levels during the driest months may further decrease hydropower capacity factors. 

The projected decrease in the regional mean hydropower capacity factor may generate false impressions regarding future climate impacts on African hydropower. For instance, the projected 3% decrease in 2060‑99 compared to the baseline period may seem to be negligible at first glance, given that non-climate factors could have same or even higher impacts. Furthermore, this may prompt the conclusion that different levels of greenhouse gas (GHG) concentrations will not have decisive impacts on future hydropower capacity factors.

However, country-specific data show that climate change will have significant impacts on most African countries, although the patterns of change may vary from one country to the other. For example, the hydropower capacity factors in Morocco, Zambia, Zimbabwe, the Democratic Republic of Congo and Mozambique are projected to decline considerably, while the decrease would be offset by an increase in the hydropower capacity factors of the Nile basin countries, notably Egypt, Sudan and Kenya.

The graph with fractions by country also shows that these climate impacts will be largely affected by the level of GHG concentration. Between 2060 and 2099, for example, the decrease of the hydropower capacity factor in Morocco, Zambia and Zimbabwe in the Around 3°C scenario is projected to be 50% more than in the Below 2°C scenario. The larger decrease in these countries offsets the higher increase from the Nile basin countries under the Around 3°C scenario. This will eventually generate the same level of decline of approximately 3% in the regional mean hydropower capacity factor in both scenarios.

Changes in hydropower capacity factor in the Around 3°C Scenario, 2020-2099, relative to the baseline period


Changes in hydropower capacity factor in the Below 2°C Scenario, 2020-2099, relative to the baseline period


The decline in the regional mean hydropower capacity factor means that the overall hydropower generation in Africa is likely to decrease. However, the impacts of climate change will be spread unevenly across the continent. For instance, Morocco in North Africa is likely to experience the largest drop in its hydropower capacity factor during the rest of the century, while East African countries around the Nile basin are likely to see an increase, benefiting from more frequent heavy rainfall. 

Changes in hydropower capacity factor in Congo and Zambezi Basins, 2020-2099, relative to the baseline 2010-2019


Changes in hydropower capacity factor in the Nile Basin, 2020-2099, relative to the baseline 2010-2019


Changes in hydropower capacity factor in Northern Africa (Morocco), 2020-2099, relative to the baseline 2010-2019


Changes in hydropower capacity factor in West Africa (Ghana), 2020-2099, relative to the baseline 2010-2019


The projected decrease in the capacity factor in the Congo and Zambezi Basins is alarming, given the significant role of hydropower in this subregion. Some countries already have difficulties in coping with the current level of dryness. For instance, the power supply in Zambia, where more than 80% of electricity comes from hydro (IEA, 2019b), has been significantly affected by declining water availability due to a shorter rainy season and more frequent droughts (Onishi, 2016). In February 2016, the water level of the Kariba Dam, one of the biggest electricity sources for Zambia and Zimbabwe, dropped to near-record lows, 12%, prompting blackouts, power rationing, and a slow-down of economic development in some places (IHA, 2017). The disruption occurred again in August 2019, and the Kariba station needed to cut output and impose daily blackouts (Bloomberg, 2019). The projected changes in rainfall patterns can severely threaten the electricity security of Zambia and Zimbabwe, given their heavy reliance on electricity supply from the Kariba station.

In the Below 2°C scenario, Central and Southern African countries around the Congo and Zambezi basin are likely to see decreases of 3% on average in hydropower capacity factors from 2020‑59. On the other hand, East African countries around the Nile basin such as Egypt, Ethiopia, Kenya, Sudan and Uganda, are projected to experience mild increases of over 1.5% during the same period on average. During the last 40 years of the century (2060‑99), countries in the Congo and Zambezi river basin are likely to see a continued decrease in the hydropower capacity factor to over 6.5%, while the Nile basin countries experience a further increase of over 2%. The spatial variations in hydropower capacity factors at a country level could be even larger, with a decrease of 10% in Morocco and Malawi, and an increase of almost 3% in Kenya.

In the Around 3°C scenario, the Congo and Zambezi basin countries could see a more significant decrease of over 7% on average during 2060‑99, while Nile basin countries are likely to see an increase of more than 7%. For instance, the hydropower capacity factors in Mozambique, Zambia and Zimbabwe are likely to fall by over 9% during 2060‑99, while those of Kenya and Uganda increase by over 12% and 7% respectively.

Change in hydropower capacity factors in Africa in the Around 3°C Scenario compared to the baseline


Change in hydropower capacity factors in Africa in the Below 2°C Scenario compared to the baseline


The projected geographical variations in hydropower capacity factors underline the importance of developing a tailored approach for each country based on the best available scientific assessments of climate impact. Indeed, the two subregions, the Congo and Zambezi river basin and the Nile basin, are attracting much of the focus for future hydropower development. In the coming decades, 13 GW and 28 GW of additional hydropower capacity is envisioned for the Zambezi basin and the Nile basin, respectively (Trace, 2019). For the reliable operation of these new hydropower plants, countries in the Congo and Zambezi river basins need to consider long-term measures to address the gradual but negative impact of climate change. Meanwhile, East African countries need to consider measures to manage the projected increase in heavy rainfall along with plans to exploit the potential increase in generation.

One of the biggest challenges caused by climate change is the increased year-to-year variability in hydropower capacity factors. Increasing anomalies in climate patterns and more frequent extreme weather events are likely to make the capacity factors of African hydropower fluctuate more. In particular, most of the selected hydropower plants (30 out of 32) in Egypt, Ethiopia, Ghana, Morocco and Sudan are likely to experience an increasing magnitude of fluctuation in their capacity factors for the remainder of this century in both scenarios. In particular, during the latter 40 years of this century, these hydropower plants are projected to see a higher variability in capacity factors. The escalating variability in hydropower capacity factors and output can significantly damage reliable electricity supply in these countries.

Moreover, if global GHG concentration is not regulated effectively, the increasing variability will become a serious concern for electricity security. Under the Around 3°C scenario, the variability in hydropower capacity factors is likely to be more accentuated. Of the plants analysed, 85% present stronger fluctuations in hydropower capacity factors under the Around 3°C scenario than the Below 2°C scenario.

In particular, Morocco, Mozambique and Zambia are likely to see an increase of over 50% in inter-annual variability under the Around 3°C scenario, compared to the level of the Below 2°C scenario. Given the significant share of hydro in electricity generation in Mozambique and Zambia, the projected increase in variability with higher GHG concentrations may pose a considerable challenge to electricity supply in these countries.

Even the Nile Basin countries (notably, Egypt, Ethiopia, Kenya, Sudan and Uganda), are also likely to face an increase in inter-annual variability under the Around 3°C scenario. Although the Nile Basin countries may benefit from a changing climate in terms of annual hydropower generation output, they will be unable to avoid the adverse impacts from increased inter-annual variability under the Around 3°C scenario.

Variability of hydropower capacity factors in Africa in the Around 3°C scenario, 2020-2099


Variability of hydropower capacity factors in Africa in the Below 2°C scenario, 2020-2099


Many African countries such as the Democratic Republic of Congo, Ethiopia, Ghana, Mozambique and Tanzania are already experiencing frequent electricity outages due to poor maintenance regimes and aging infrastructure. In 2018, therefore, 40 TWh of electricity was generated from back-up generation capacity in sub-Saharan Africa (IEA, 2019a). However, most of the current back-up generators in Africa are relying on diesel fuel, which would contribute to a further increase in GHG emissions. To meet the climate and sustainable development goals while ensuring reliable electricity supply, African countries need to ensure access to other low-carbon back-up options.

Expanded interconnections can be a low-carbon option to address the increasing variability in hydropower generation. An interconnected network provides access to diverse and complementary markets. A country where hydropower generation drops or soars unexpectedly due to the increasing variability, may consider electricity import or export through an interconnected network. By allowing trades among countries, expanded interconnections can contribute to addressing the issues resulted from increasing spatial variations in climate impacts.

In Africa, most countries are already participating in regional power pools. For instance, in Ethiopia, which is a member of the Eastern Africa Power Pool (EAPP), cross-border interconnections with neighbouring countries are rapidly expanding, making Ethiopia a power hub for East Africa. Given the immense untapped potential and the projected increase in hydropower output in Ethiopia, hydropower is likely to take a greater share of future traded electricity in East Africa over the rest of this century.

Diversification of renewable energy sources in the electricity mix can also help to maintain reliable and sustainable electricity services. For instance, Morocco, which may well see a considerable increase in variability in hydropower capacity factors, has committed to diversifying its renewable energy sources. The government announced a target in 2015 to increase renewable generation capacity to 52% of the total installed power capacity by 2030, led by a significant increase in installed capacities of solar and wind. With the initiative of the government, the share of wind significantly increased from 3% in 2010 to 9% in 2017 while the share of hydropower in electricity generation fell rapidly from 15% to 5% for the same period (IEA, 2019b). The efforts to diversify renewable energy sources while lowering reliance on hydropower in Morocco are expected to reduce the vulnerability of the power sector to future climate impacts.