•We analyzed future climate impacts on hydrological extremes in Upper Blue Nile Basin.•We used the wettest and driest CMIP5 projections as inputs to the CREST-SVAS model.•We studied the effectiveness ...of the dam operation to moderate extreme event severity.•GERD can reduce flood and drought intensity by adjusting seasonal water release.•Expected hydropower generation (15,000 GWh/year) can be met in a wet climate scenario.
Climate change poses a great threat to society through its effects on extreme hydrological events (floods and droughts) and the sustainable development. Coping with climate change requires a better awareness of the possible impacts to inform climate adaptation strategies. In this study, we investigated the climate projections from two contrasting GCMs (wet scenario from MIROC5 and dry scenario from CSIRO) and quantified the possible outcomes in terms of hydrological components of the Upper Blue Nile Basin (UBNB). These two climate projection scenarios show that the overall precipitation change in the early (2011–2040), mid (2041–2070), and late century (2071–2100) over the UBNB may vary from –18.3 % to + 13.6 % of the baseline annual precipitation of 1350 mm. The hydrological simulations over the basin from our study showed that evapotranspiration may vary between –13.7 % and + 12.1 % of the average annual total actual ET of 710 mm, and the flow at the basin outlet may range between –40.7 % and + 30.8 % of the mean annual total flow volume of 45 billion cubic meters. As a result, the wet projection exhibited more frequent floods while the dry projection showed severe droughts, specifically in the late century. We also examined the role of the Grand Ethiopian Renaissance Dam (GERD), designed for hydropower generation, in moderating these potential future climate hydrological extremes. Our findings indicate that GERD operations can help reduce downstream flood and drought severity by managing flow releases. Thus, this study illustrates the most possible extreme hydrological events in the UBNB due to climate change and demonstrates the degree to which GERD operations can help reduce the impact of these extremes downstream. The findings and data generated in this study will aid understanding the importance of sustainable water management and reservoir operation that caters to both hydropower generation, and recurring floods and droughts.
The low level of access, rising fuel costs, and increasing effects of climate change are reinvigorating the policy-makers’ interest in Africa in renewable energy sources such as hydropower. Ethiopia ...is among countries which have very low modern energy sources, but possesses one of the highest hydropower potential, next to Congo. The topographic feature and the availability of water in Ethiopia permit a large hydropower potential. However, as the available runoff in rivers has very high hydrological variability, tapping into this potential requires investment on storage to smooth out the temporal hydrological variability. In this chapter, first the behavior of this hydrological variability and implication of water resources development are discussed. Second, various documents and reports providing varying values of hydropower potential of Ethiopia and Abbay are summarized. To improve the existing understanding of sites, topographical and hydrological evaluation of 129 hydropower potential sites has been carried out. These sites were identified in previous studies having a total capacity of 13,845 MW. After evaluations, 91 possible sites with total potential of 12,148 MW from various tributary rivers were identified and mapped. Dabus sub-basin stands first among the 16 sub-basins with 13 hydropower potential sites and a total capacity of 3,524 MW, and similarly the other sub-basins are also ranked. The ranking of these sites has been carried out based on cost per kilowatt hour of the hydropower potential (HP) sites. Furthermore, the chapter discusses the benefits and trade-offs for four priority developments identified as Eastern Nile regional fast-track projects.
Prediction of seasonal precipitation can provide actionable information to guide management of various sectoral activities. For instance, it is often translated into hydrological forecasts for better ...water resources management. However, many studies assume homogeneity in precipitation across an entire study region, which may prove ineffective for operational and local-level decisions, particularly for locations with high spatial variability. This study proposes advancing local-level seasonal precipitation predictions by first conditioning on regional-level predictions, as defined through objective cluster analysis, for western Ethiopia. To our knowledge, this is the first study predicting seasonal precipitation at high resolution in this region, where lives and livelihoods are vulnerable to precipitation variability given the high reliance on rain-fed agriculture and limited water resources infrastructure. The combination of objective cluster analysis, spatially high-resolution prediction of seasonal precipitation, and a modeling structure spanning statistical and dynamical approaches makes clear advances in prediction skill and resolution, as compared with previous studies. The statistical model improves versus the non-clustered case or dynamical models for a number of specific clusters in northwestern Ethiopia, with clusters having regional average correlation and ranked probability skill score (RPSS) values of up to 0.5 and 33 %, respectively. The general skill (after bias correction) of the two best-performing dynamical models over the entire study region is superior to that of the statistical models, although the dynamical models issue predictions at a lower resolution and the raw predictions require bias correction to guarantee comparable skills.
•A groundwater (GW) model is developed using MODFLOW-NWT in the Gilgel-Abay Catchment.•Data scarcity is dealt with citizen science initiative, and one-way CREST coupling.•Model simulates 39 years of ...hydraulic head at a monthly scale and 500 m resolution.•Calibration, validation and global model comparisons produce acceptable results.•The model findings will be helpful for future local-scale model developments in Ethiopia.
Groundwater (GW) is the main source of domestic water supply in Ethiopia (85%), however, despite widespread acknowledgement of its potential for resource-based development and climate change adaptation, the sector is still quite under-investigated. This is mainly due to the scarcity of in situ data, which are essential to building robust impact models. To address this, we developed a fine-resolution (500 m) GW model using MODFLOW-NWT, focusing on the Gilgel-Abay Catchment located in the Upper Blue Nile basin, fed with daily distributed input forcings of recharge and streamflow simulated by the Coupled Routing and Excess Storage (CREST) hydrological model. The model was calibrated against instantaneous observation records of GW table for 38 historical wells, and validated at selected sites using time series data collected from the Citizen Science Initiative (PIRE CSI), and the Innovation Lab for Small Scale Irrigation (ILSSI) project. An RMSE of 14.4 m (1.8% of range) was achieved for calibration and same for validation was 18.21 m and 15.76 m at the PIRE CSI and ILSSI sites, respectively. The findings of this research indicate substantial physical GW resource availability in the Gilgel-Abay region. Moreover, we expect the model to have multiscale future applications. These include obtaining dynamically downscaled boundary conditions for a local-scale GW model, to be developed in the next phase of our research. Further, an upscaled version of this model to encompass the entire Tana Basin would be developed to simulate lake-aquifer interactions. Finally, the approach of this research combining different types of datasets (e.g., reanalysis products, satellite data, citizen science data, etc.) is adaptable to other global data-scarce regions. Moreover, the method overcomes specific challenges associated to in situ data scarcity, limited knowledge on GW resources availability in the area, interaction with complex boundary conditions, and sensitivity under meteorological boundary forcings.
Recently water resources reanalysis (WRR) global streamflow products are emerging from high- resolution global models as a means to provide long and consistent global streamflow products for ...assessment of global challenge such as climate change. Like any other products, the newly developed global streamflow products have limitations accurately represent the dynamics of local streamflow hydrographs. There is a need to locally evaluate and apply correction factors for better representation and make use of the data. This research focuses on the evaluation and correction of the bias embedded in the global streamflow product (WRR, 0.25°) developed by WaterGAP3 hydrological model in the upper Blue Nile basin part of Ethiopia. Three spatiotemporal dynamical bias correction schemes (temporal-spatial variable, temporal-spatial constant and spatial variable) tested in twelve watersheds of the basin. The temporal-spatial variable dynamical bias correction scheme significantly improves the streamflow estimation. The Nash-Sutcliffe coefficient (NSCE) improves by 30% and bias decreases by 19% for the twelve streamflow gauging stations applying leave one out cross-validation approach in turn. Therefore, the temporal-spatial variable scheme is applicable and can use as one method for the bias correction to use the global data for local applications in the upper Blue Nile basin.
The demand for water-energy (WE) should be addressed with their sustainable supply in the long-term planning. The total energy demand was estimated to be around 14,000000 and 53,000000 MWh for 2030 ...and 2050 years respectively. These years' predicted water demand was 0.4 and 0.7 billion-cubic-meter. Based on the estimated energy and water demand, sustainable supply through WE management were determined. In 2030 and 2050 the water supply-demand balance index is around 1, showed water demand will be met for respective years, whereas the energy supply-balance after the intervention become around 0.9 and 0.7. The study results clearly predicted future WE demand of Addis Ababa city and have been put their quantified supply suggestion.
The Upper Blue Nile (UBN) basin is less-explored in terms of drought studies as compared to other parts of Ethiopia and lacks a basin-specific drought monitoring system. This study compares six ...drought indices: Standardized Precipitation Index (SPI), Standardized Precipitation Evaporation Index (SPEI), Evapotranspiration Deficit Index (ETDI), Soil Moisture Deficit Index (SMDI), Aggregate Drought Index (ADI), and Standardized Runoff-discharge Index (SRI), and evaluates their performance with respect to identifying historic drought events in the UBN basin. The indices were calculated using monthly time series of observed precipitation, average temperature, river discharge, and modeled evapotranspiration and soil moisture from 1970 to 2010. The Pearson’s correlation coefficients between the six drought indices were analyzed. SPI and SPEI at 3-month aggregate period showed high correlation with ETDI and SMDI (r > 0.62), while SPI and SPEI at 12-month aggregate period correlate better with SRI. The performance of the six drought indices in identifying historic droughts: 1973–1974, 1983–1984, 1994–1995, and 2003–2004 was analyzed using data obtained from Emergency Events Database (EM-DAT) and previous studies. When drought onset dates indicated by the six drought indices are compared with that in the EM-DAT. SPI, and SPEI showed early onsets of drought events, except 2003–2004 drought for which the onset date was unavailable in EM-DAT. Similarly, ETDI, SMDI and SRI-3 showed early onset for two drought events and late onsets in one-drought event. In contrast, ADI showed late onsets for two drought events and early onset for one drought event. None of the six drought indices could individually identify the onsets of all the selected historic drought events; however, they may identify the onsets when combined by considering several input variables at different aggregate periods.
An extensive evaluation of nine global-scale high-resolution satellite-based rainfall (SBR) products is performed using aminimum of 6 years (within the period of 2000–13) of reference rainfall data ...derived from rain gauge networks in nine mountainous regions across the globe. The SBR products are compared to a recently released global reanalysis dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF). The study areas include the eastern Italian Alps, the Swiss Alps, the western Black Sea of Turkey, the French Cévennes, the Peruvian Andes, the Colombian Andes, the Himalayas over Nepal, the Blue Nile in East Africa, Taiwan, and the U.S. Rocky Mountains. Evaluation is performed at annual, monthly, and daily time scales and 0.25° spatial resolution. The SBR datasets are based on the following retrieval algorithms: Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis (TMPA), the NOAA/Climate Prediction Center morphing technique (CMORPH), Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks (PERSIANN), and Global Satellite Mapping of Precipitation (GSMaP). SBR products are categorized into those that include gauge adjustment versus unadjusted. Results show that performance of SBR is highly dependent on the rainfall variability. Many SBR products usually underestimate wet season and overestimate dry season precipitation. The performance of gauge adjustment to the SBR products varies by region and depends greatly on the representativeness of the rain gauge network.
•This study compares hydrological performance of multi satellite precipitation products in the upper Blue Nile basin.•Grid based, fully distributed hydrological model CREST is calibrated using ...in-situ observed rainfall data.•Performance results indicate that the MSWEP precipitation shows consistently higher results.•MSWEP precipitation product can be a priori alternative source of data for various water resources applications.•This by no means undermines the potential benefits of the rest satellite products for different watersheds and time scale.
Ethiopia, upper Blue Nile.
This study evaluates hydrological performance of multiple globally available precipitation products in the data scarce region of the upper Blue Nile basin over multi-scales (1656–199,812 km2) focusing on multi-year (2000–2012) for daily simulation. Grid based, fully distributed hydrological model Coupled Routing and Excess STorage (CREST) is calibrated using in-situ observed rainfall data. The evaluation compares five precipitation products of gauge adjusted Climate Prediction Center Morphing Technique (CMORPH), Tropical Rainfall Measuring Mission (TRMM) Multi-Satellite Precipitation Analysis 3B42 version 7 (TMPA), ERA-Interim (ERAI), Global Precipitation Climatology Centre (GPCC) and Multi-Source Weighted Ensemble Precipitation (MSWEP).
Performance results indicate that the MSWEP precipitation shows consistently better performance than from the rest of precipitation products. This global precipitation product can be a priori alternative source of data for various water resources applications in the upper Blue Nile basin for its predictive ability and the length of data availability which the product has an advantage over the satellite products. However, the product needs improvement to estimate the total annual flow volume of the observed flow for the three nested watersheds to perform close to the gauged rainfall. This by no means undermines the potential benefits of the rest products for different watersheds and time scale.
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