• Energy Research

Abstract. Lake Victoria, the second largest freshwater lake in the world, is one of the major sources of the Nile River. The outlet to the Nile is controlled by two hydropower dams of which the allowed discharge is dictated by the Agreed Curve, an equation relating outflow to lake level. Some regional climate models project a decrease of precipitation and an increase of evaporation over Lake Victoria, with potential important implications for its water balance and resulting level. Yet, nothing is known about the potential consequences of climate change for the water balance of Lake Victoria. In this second part of a two-paper series, we feed a new water balance model for Lake Victoria presented in the first part with climate simulations available through the Coordinated Regional Climate Downscaling Experiment (CORDEX) Africa framework. Our results reveal that most regional climate models are not capable of giving a realistic representation of the water balance of Lake Victoria. Therefore we applied two bias correction methods, resulting in both cases in a closed water balance. Our results reveal that for two emission scenarios (RCP4.5 and 8.5), the decrease in precipitation over the lake and an increase in evaporation are compensated by an increase in basin precipitation leading to more inflow. The future lake level projections show that the outflow scenario and not the emission scenario is the main controlling factor of the future water level evolution. Moreover, inter-model uncertainties are larger than emission scenario uncertainties. The comparison of four different outflow scenarios for the future uncovers that the only sustainable outflow scenario is regulating outflow following the Agreed Curve. The associated outflow encompasses however large uncertainties ranging up to 177 %, which are important to take into account regarding future hydropower generation and water availability downstream.

AbstractTransformation pathways for the land sector in line with the Paris Agreement depend on the assumption of globally implemented greenhouse gas (GHG) emission pricing, and in some cases also on inclusive socio-economic development and sustainable land-use practices. In such pathways, the majority of GHG emission reductions in the land system is expected to come from low- and middle-income countries, which currently account for a large share of emissions from agriculture, forestry and other land use (AFOLU). However, in low- and middle-income countries the economic, financial and institutional barriers for such transformative changes are high. Here, we show that if sustainable development in the land sector remained highly unequal and limited to high-income countries only, global AFOLU emissions would remain substantial throughout the 21st century. Our model-based projections highlight that overcoming global inequality is critical for land-based mitigation in line with the Paris Agreement. While also a scenario purely based on either global GHG emission pricing or on inclusive socio-economic development would achieve the stringent emissions reductions required, only the latter ensures major co-benefits for other Sustainable Development Goals, especially in low- and middle-income regions.

Ethiopia, Sudan and Egypt are currently embroiled in a politically charged conflict that surrounds the soon-to-be-completed Grand Ethiopian Renaissance Dam (GERD), with Ethiopia’s energy objectives purportedly conflicting with the water needs in Sudan and Egypt. Here we show that the multiple political and environmental challenges that surround GERD could be mitigated by explicitly coupling its operation to variable solar and wind power, which would create an incentive for Ethiopia to retain a seasonality in the Blue Nile flow. We found that this could deliver fivefold benefits across the three countries: decarbonizing power generation in the Eastern Africa Power Pool; allowing compliance with Sudan’s environmental flow needs; optimizing GERD’s infrastructure use; harmonizing the yearly refilling schedules of GERD and Egypt’s High Aswan Dam; and supporting a strong diversification of Ethiopian power generation for domestic use and for Eastern Africa Power Pool exports. These results argue for an explicit integration of complementary hydro, solar and wind power strategies in GERD operation and Eastern Africa Power Pool expansion planning. The Grand Ethiopian Renaissance Dam will be hugely beneficial to Ethiopia, but has raised tensions with neighbouring countries that rely on flow from the Blue Nile. Sterl et al. present scenarios for dam operation coupled with solar and wind power generation that could mitigate some of these concerns.

Abstract Increasing renewable sources in the energy mix is essential to mitigate climate change, not least in countries where the energy demand is likely to rise over the coming decades to reduce or even skip durations of time where fossils dominate. For Africa, solar photovoltaic (PV) and inland wind energy, combined with hydropower, provide significant and untapped potentials, whereas trends and robustness measures need further investigation. This study aims to gain insight into distributed trends in solar PV and wind energy potentials over Africa. This study employs relevant metrics, including relative change, model agreement, robustness, bias, and absolute levels for every available model combination and two climate scenarios, with energy planning purposes in mind. The study finds that regional climate models were the primary control of spatio-temporal patterns over their driving global climate model. Solar PV potentials show more coherence between models, a lower bias and general high potentials in most African regions than wind potentials. Favourable locations for inland wind energy include mainly the regions of greater Sahara and the Horn region. For wind and solar potentials combined, scattered locations within Sahara stand out as the most favourable across scenarios and periods. The analysis of minimum energy potentials shows stable conditions despite low potentials in certain regions. The results demonstrate a potential for solar and wind power in most of the African regions and highlight why solar and wind power or synergies of energy mix should be considered for local energy planning and storage solutions.

AbstractClimate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change.