Water-Energy-Food Nexus assessments at river basin scale make sense in particular if hydropower is an important source of energy in a given region. The Blue Nile Basin is a major source for Water in the Nile river basin. It provides around 65 % of the flow of the Nile entering Egypt, and occupies a mere 10% of the total basin area. The Blue Nile water is primarily used for irrigation, hydropower, and domestic supply in Ethiopia, Sudan, and Egypt. Climate variability and long-term climate and socio-economic changes pose a growing challenge to the provision of water, energy, and food security within the Blue Nile Basin as well as downstream. Thus, the scientifically sound quantification of available natural resources sustaining water, energy, and food security, and the development of different future scenarios can be helpful for decision-makers in the region. We suggest a new method of WEF Nexus accounting based on quantification of Nexus indicators derived mainly from public domain data. As observed data on water and land resources in the Blue Nile Basin are scarce, this study uses diverse remote sensing-based data sources to derive essential environmental information validated by using ground data, where possible. This includes land cover data, different precipitation products, actual evapotranspiration, net primary productivity (NPP), among others. Furthermore, several data analysis and modeling tools, such as WA+, various hydrological models, RiverWare, CropWat, etc., are employed to quantify the natural resources availability, variability, and productivity as a basis for a comprehensive WEF accounting based on selected indicators which were developed by a team of experts and scientists. The currently constructed Grand Ethiopian Renaissance Dam (GERD) as well as other planned hydropower and irrigation schemes are also considered for the future scenarios. The result is a comprehensive WEF Nexus accounting estimating water availability and uses with a focus on irrigation as the dominant water user, productivities (based on NPP and derived yield estimates), water use efficiency, energy production from hydropower and estimation of security levels compared to the required current and future demands. Finally, the derived nexus indicators are put into context of selected SDG target indicators.

Droughts are a recurrent phenomenon in water abundant tropical countries worldwide and are expected to become more frequent in the future. However, drought risk in tropical catchments is poorly understood and usually not adequately incorporated in water management strategies. Thus, methodologies to evaluate spatial and seasonal drought risk in data scarce tropical catchments are urgently needed. We combined hazard and vulnerability related information to assess drought risk in the test basin, the rural Muriaé basin in southeast tropical Brazil. Hazard indicates the cumulative frequency of drought anomalies, while vulnerability represents the potential of a drought to cause damages in the socioeconomic system. We simulated subcatchment discharges with a hydrological model (SWAT) to evaluate spatially distributed hydrological drought hazard and combined this information with precipitation and vegetation based indices to define the cumulative frequency of drought occurrence for each grid cell (0.1°). We tested the sensitivity of different climate and catchment related model input variables against low flow events and simulated artificial drought risk scenarios. To assess vulnerability, we reclassified and weighted globally and regionally available gridded socioeconomic data. Vulnerability in the downstream area was found to be stronger which coincided with a higher hydrological and vegetation based hazard. The drought risk map clearly identified the downstream area of the Muriaé basin as being exposed to a stronger drought risk compared to the upstream areas. Only limited hydrological drought sensitivity of the system against changes in land cover type and temperature was shown in the model results while geology and soils turned out to play a larger role for low flows. The drought scenarios showed that low flows were more severely affected than high flows by climatic changes such as decreased precipitation. In can be concluded that our risk assessment methodology offers a holistic, science based and innovative solution to inform regional planning and water management institutions dealing with the control of drought disasters in tropical rural areas. Such drought risk evaluation frameworks and spatial information are urgently needed in tropical regions worldwide.