ALBERT

Description: The choice of the base period, intentionally chosen or not, as a reference for assessing future changes of any projected variable can play an important role for the resulting statement. In regional climate impact studies, well-established or arbitrarily chosen baselines are often used without being questioned. Here we investigated the effects of different baseline periods on the interpretation of discharge simulations from eight river basins in the period 1960-2099. The simulations were forced by four bias-adjusted and downscaled Global Climate Models under two radiative forcing scenarios (RCP 2.6 and RCP 8.5). To systematically evaluate how far the choice of different baselines impacts the simulation results, we developed a similarity index that compares two time series of projected changes. The results show that 25% of the analysed simulations are sensitive to the choice of the baseline period under RCP 2.6 and 32% under RCP 8.5. In extreme cases, change signals of two time series show opposite trends. This has serious consequences for key messages drawn from a basin-scale climate impact study. To address this problem, an algorithm was developed to identify flexible baseline periods for each simulation individually, which better represent the statistical properties of a given historical period.

Description: Semi-arid regions are known for erratic precipitation patterns with significant effects on the hydrological cycle and water resources availability. High temporal and spatial variation in precipitation causes large variability in runoff over short durations. Due to low soil water storage capacity, base flow is often missing and rivers fall dry for long periods. Because of its climatic characteristics, the semi-arid north-eastern region of Brazil is prone to droughts. To counter these, reservoirs were built to ensure water supply during dry months. This paper describes problems and solutions when calibrating and validating the eco-hydrological model SWIM for semi-arid regions on the example of the Pajeú watershed in north-eastern Brazil. The model was calibrated to river discharge data before the year 1983, with no or little effects of water management, applying a simple and an enhanced approach. Uncertainties result mainly from the meteorological data and observed river discharges. After model calibration water management was included in the simulations. Observed and simulated reservoir volumes and river discharges are compared. The calibrated and validated models were used to simulate the impacts of climate change on hydrological processes and water resources management using data of two representative concentration pathways (RCP) and five earth system models (ESM). The differences in changes in natural and managed mean discharges are negligible (〈 5%) under RCP8.5 but notable (〉 5%) under RCP2.6 for the ESM ensemble mean. In semi-arid catchments, the enhanced approach should be preferred, because in addition to discharge, a second variable, here evapotranspiration, is considered for model validation.

Description: Global hydro-climatic trends are ambiguous, challenging the management of water resources. This challenge is addressed in the current study by investigating the impacts of hydro-climatic trends and upstream water management on hydropower generation at the Bagré dam. Modified Mann–Kendall trend test, Standard Normal Homogeneity Test and Pettit test were applied to some selected hydro-climatic variables for the trend and the change year detection, whereas the relationship between upstream dam management, hydro-climatic variables and hydropower were assessed through the Spearman correlation. The results revealed an annual positive trend for all hydro-climatic variables except for water level, lake evaporation and outflow. The break years observed in hydropower generation (2002) and inflow (2006) were mainly due to the construction of the Ziga dam in 2000 and its management change in 2005, respectively. The study also showed that hydropower generation declines each May (−30.36 MWh) and June (−16.82 MWh) due to the significant increase in irrigation withdrawals (1.94 hm3 in May and 0.67 hm3 in June). The results of this study highlighted the non-linearity in the relationship between hydropower generation and hydro-climatic variables as none of the correlation coefficients (apart from turbine) are very strong (〉0.8). As many human activities occurred in the basin, further research should be focused on the use of semi-distributed models to assess the impacts of water-use and land-use change on hydropower generation.

Description: To feed the growing population, achieve the Sustainable Development Goals, and fulfil the commitments of the Paris Agreement, West African countries need to invest in agricultural development and renewable energy, among other sectors. Irrigated agriculture, feeding millions of people, and hydropower, generating clean electricity, depend on water availability and compete for the resource. In the Volta basin, the planned 105 000 ha of irrigated land in Burkina Faso and Ghana could feed hundreds of thousands of people. However, irrigation in the dry season depends on upstream dams that change the river’s flow regime from intermittent to permanent, and at the same time irrigation water is no longer available for hydropower generation. Using an integrated eco-hydrological and water management model, we investigated the water demand and supply of three planned irrigation projects and the impacts of the planned Pwalugu multi-purpose dam on the hydropower potentials and water availability in the entire Volta basin. We found that future irrigation withdrawals would reduce the hydropower potential in the Volta basin by 79 GWh a−1 and the operation of Pwalugu by another 86 GWh a−1. Hence, Pwalugu contributes only about 101 GWh a−1 of its potential of 187 GWh a−1. Under climate change simulations, using an ensemble of eight bias-adjusted and downscaled GCMs, irrigation demand surprisingly did not increase. The higher evaporation losses due to higher temperatures were compensated by increasing precipitation while favouring hydropower generation. However, water availability at the irrigation site in Burkina Faso is clearly at its limit, while capacity in Ghana is not yet exhausted. Due to hydro-climatic differences in the Volta basin, the cost of irrigating one hectare of land in terms of lost hydropower potential follows a north-south gradient from the hot and dry north to the humid south. Nevertheless, food production should have priority over hydropower, which can be compensated by other renewables energies.

Description: Hydropower is the world’s largest and most widely used renewable energy source. It is expected that climate and land use changes, as well as hydraulic engineering measures, will have profound impacts on future hydropower potential. In this study, the hydropower potential of the Bafing watershed was estimated for the near future (P1: 2035–2065) and the far future (P2: 2065–2095). For this purpose, the moderate scenario ssp 126 and the medium–high scenario ssp 370 were used to explore possible climate impacts. In three management scenarios, we tested the interaction of the existing Manantali Dam with two planned dams (Koukoutamba and Boureya) using an ecohydrological water management model. The results show that, under ssp 126, a 6% increase in annual river flow would result in a 3% increase in hydropower potential in the near future compared with the historical period of 1984–2014. In the far future, the annual river flow would decrease by 6%, resulting in an 8% decrease in hydropower potential. Under ssp 370, the hydropower potential would decrease by 0.7% and 14% in the near and far future, respectively. The investment in the planned dams has benefits, such as an increase in hydropower potential and improved flood protection. However, the dams will be negatively affected by climate change in the future (except in the near future (P1) under ssp 126), and their operation will result in hydropower potential losses of about 11% at the Manantali Dam. Therefore, to mitigate the effects of climate change and adjust the operation of the three dams, it is essential to develop new adaptation measures through an optimization program or an energy mix combining hydro, solar, and wind power.

Description: Land use and Land cover change (LULCC) is a major global problem, and projecting change is critical for policy decision-making. Understanding LULCCs at the watershed level is essential for transboundary river basin management. The present study aims to analyse the past and future LULCCs in two significant watersheds of the Senegal River basin (SRB) in West Africa: Bafing and Faleme. This study used Landsat images from 1986, 2006 and 2020 and the Random Forest classification method to analyze past LULCCs in these two watersheds. The results revealed: In Bafing, vegetation, settlement, agricultural areas and water increased, while the bareground decreased significantly between 1986-2020. In Faleme, two periods have different trends. Between 1986-2006, vegetation, settlement, agricultural areas and water increased, while bareground decreased. Between 2006-2020, settlement increased, while vegetation, agricul-tural areas, water and bareground decreased. To predict LULCCs in 2050 under business-as- usual assumptions, the Multilayer Perceptron and Marcov Chain model (MLP-MC) was used. The MLP-MC shows better results on Bafing than on Faleme but without questioning its application on the two watersheds. Bafing has seen a trend towards ”more people, more trees”, while Faleme has seen a trend towards ”more people, more deforestation”. These results contribute to develop appropriate land management policies and strategies to achieve or to maintain sustainable development in the SRB.

Description: 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.

Description: Burkina Faso has a high socio-economic dependency on agriculture, a sector which is strongly influenced by weather-related factors and increasingly challenged by the impacts of climate change. Currently, only limited information on climate risks and its impacts is available for the agricultural sector in the country. Therefore, this study aims to provide a comprehensive climate risk analysis including a thorough evaluation of four potential adaptation strategies that can guide local decision makers on adaptation planning and implementation in Burkina Faso. The impact assessment consists of several steps including climate projections based on two emissions scenarios (SSP3-RCP7.0 and SSP1-RCP2.6), hydro-logical modelling on water availability changes, modelling and comparison of future yields of four widely used crops (maize, sorghum, millet and cowpeas) and an assessment of livestock production under future climate conditions. Based on the projected climate change impacts on agricultural production, four different adapta-tion strategies ((1) Integrated soil fertility ma-nagement (ISFM), (2) irrigation, (3) improved seeds and (4) climate information services (CIS)) suggested and selected by different national stakeholders were analysed regarding their potential to risk mitigation, (cost-)effectiveness and suitability for local conditions. The analyses have been further complemented by expert- and literature-based assessments, semi-structured key informant interviews and two stakeholder work-shops. The results show that the mean daily temperature is on the rise and projected to increase further by 0.6°C (2030) up to 1.1°C (2090) under SSP1-RCP2.6 and by 0.5°C (2030) up to 3.6°C (2090) under SSP3-RCP7.0 in reference to 2004, dependent on future greenhouse gas emissions. Some un-certainty exists for annual precipitation projections, with slight increases until 2050 followed by a slight decrease under SSP1-RCP2.6 and continuous increase under SSP3-RCP7.0 with high year-to-year variability. Projected impacts of cli-mate change on yields vary between regions and show partly opposing trends. Some regions in the north show increasing yields (up to +30% in SSP1-RCP2.6 and up to +20% in SSP3-RCP7.0), while few regions in the south present decreasing yields (down to -30% in SSP1-RCP2.6 and down to -20% in SSP3-RCP7.0). Crop models show that the areas suitable for cowpeas will decrease in Burkina Faso under future climate change conditions while the suitability for maize, millet and sorghum will remain stable. Moreover, the potential to produce multiple crops will become more and more difficult, which limits farmers’ diversification options. Regarding the livestock sector, it seems very likely that the grazing potential will decrease under both climate change scenarios with higher decreases under SSP1-RCP2.6 than under SSP3-RCP7.0. All four adaptation strategies were found to be economically beneficial, can have a high potential for risk mitigation and entail different co-benefits. Particularly, ISFM can be highly recommended for smallholder farmers, resulting in very positive effects for societies and environment. Irrigation and improved seeds have a high potential to improve livelihoods especially in Northern Burkina Faso, but are also complex, costly and support-intensive adaptation strategies. Lastly, CIS can support farmers to make informed decisions and thereby reduce the impact of climate risks. Generally, a combination of different adaptation strategies can entail additional benefits and active stakeholder engagement as well as participatory approaches are needed to ensure the feasibility and long-term sustainability of adaptation strategies. The findings of this study can help to inform national and local adaptation and agricultural development planning and investments in order to strengthen the resilience of the agricultural sector and especially of smallholder farmers against a changing climate.

Description: Niger has a high socio-economic dependency on agriculture which is strongly influenced by weather-related factors and highly vulnerable to climate change. Currently, only limited information on climate risks and its impacts is available for the agricultural sector in the country. Therefore, this study aims to provide a comprehensive climate risk analysis including a thorough evaluation of four potential adaptation strategies that can guide local decision makers on adaptation planning and implementation in Niger: (1) agroforestry and farmer managed natural regeneration (FMNR) of trees, (2) integrated soil fertility management (ISFM), (3) irrigation and (4) improved fodder management for livestock. The impact assessment includes climate projections based on two future emissions scenarios (SSP3-RCP7.0 and SSP1-RCP2.6), hydrological modelling on water availability, modelling and comparison of future yields of four dominant crops (sorghum, millet, maize and cowpeas) and an as-sessment of livestock production under future climate conditions. Based on the projected climate change impacts on agricultural production, the four adaptation strategies suggested by different national stakeholders were analysed regarding their potential to risk mitigation, cost-effectiveness and suitability for local conditions. The analyses have been complemented by expert- and literature-based assessments, semi-structured interviews and two stakeholder workshops. The results show that the mean daily temperature is projected to increase further in Niger, up to +1.3 °C (SSP1-RCP2.6) and +4.2 °C (SSP3-RCP7.0) by 2090, in reference to 2004. The mean annual precipitation sum is also projected to increase until 2050 under both emissions scenarios, with a slight decrease in the interannual variability. In the second half of the century, this trend in precipitation is likely to continue (SSP3-RCP7.0) or decrease slightly (SSP1-RCP2.6), while the year-to-year variability would increase. Greater annual rates of groundwater recharge due to increasing precipitation amounts and higher annual mean river discharge are expected until mid-century. Sorghum yields would decline in general, by 20-50% (SSP1-RCP2.6) or 40-75% (SSP3-RCP7.0) by 2090, compared to 2005. Crop models hinted at an increase in the suitability of sorghum and millet, and no significant change for maize and cowpeas in Niger under both emissions scenarios. In addition, the potential for multiple cropping would de-crease from mid-century, limiting farmers’ diversification options. Regarding the livestock sector, the grazing potential is likely to decrease in the south and increase in the central regions of Niger, under SSP1-RCP2.6, while it is expected to increase in the whole country under SSP3-RCP7.0. All four adaptation strategies were found to be economically beneficial, risk-independent, with a medium to high risk mitigation potential, and can bring about various co-benefits. FMNR practice can be highly recommended, as the upscaling potential is high and the climate resilience of local livelihoods will be strengthened. ISFM can help to improve water use efficiency and benefit from positive environmental and social outcomes. Irrigation has a medium potential to improve livelihoods of smallholder farmers but is also a support-intensive adaptation strategy that needs to be carefully implemented in order to avoid overexploitation of local water resources. Lastly, improved fodder management, especially al-falfa production, contributes to building up resilience of livestock farming systems and affects women and youth employment positively. Gener-ally, a combination of different adaptation strategies can yield additional benefits and active stake-holder engagement as well as participatory ap-proaches are needed to ensure the feasibility and sustainability of adaptation strategies. The findings of this study can help to inform national and local adaptation as well as development planning and investments in order to strengthen the climate resilience of the Nigerien agricultural sector and especially of smallholder farmers.