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Scientific findings indicated there is climate change that affects given hydrology and, hence, water availability worldwide. To quantify its impact on a specific catchment scale, since spatial and temporal variability of climate change impact, this study was carried out at Ribb catchment, Lake Tana basin, Ethiopia. The catchment hydrology was represented by the Soil and Water Analysis Tool (SWAT) through using historical observed data. Regional Climate Model (RCM) projection data set for Nile Basin studies at Representative Concentration Pathway (RCPs) (RCP4.5 and RCP8.5) were used for future streamflow generation on three-time horizons; 2020s (2011–2040), 2050s (2041–2070), and 2080s (2071–2098). A baseline period (1976–2005) was used as a reference. SWAT was calibrated (R2 = 0.83 and NSE = 0.74) and validated (R2 = 0.72 and NSE = 0.71). The analysis was done based on the changes from the baseline period to the 2080s. Temperature showed an increasing trend but rainfall is decreasing. The mean annual streamflow could potentially reduce from 42.78 m3/s to 40.24 m3/s and from 42.78 m3/s to 37.58 m3/s based on RCP4.5 and RCP8.5 scenarios, respectively. On a monthly time scale, decreases in streamflow were found from March to August whereas there was a slight increase from September to February. Concerning individual months, June flows were found to have maximum impact in both scenarios (63.3% at RCP8.5 and 55.45% at RCP4.5 scenarios). The least impacted month was August based on the RCP8.5 scenario which is decreased by 6.64% and April based on the RCP4.5 scenario which is reduced by 1.21%. Looking at total volume, July showed a maximum decrease in both scenarios which is reduced by 21.08 m3/s at the RCP4.5 scenario and 51.22 m3/s at the RCP8.5 scenario. The maximum increase was found in October with 10.31 m3/s and 11.26 m3/s at RCP4.5 and RCP8.5 scenarios respectively. The future streamflow of Ribb River has decreased annually and monthly due to increasing temperature and reduction of rainfall. HIGHLIGHTS The research was done using the current RCP scenarios.; The research work focuses on future climate change impacts of the streamflow.; It is done on the different time horizons are predicted the climate change impact on the hydrology of a given catchment for a long period (up to 2100).; It used direct observed data to the stations to calibrate the model.

Soil erosion poses a global threat to soil loss, agricultural land deterioration, and crop yield decreases. This paper accounts to establish sustainable land planning, and methods for evaluating soil erosion rates are needed. The study was conducted based on the system complex analysis to prioritize soil erosion in Ribb watershed to improve soil and water conservation planning. Several geographical-environmental factors affecting soil erosion (land use, soil, slope, SPI, TWI, river Proximity, curvature, aspect) considered to assess potential soil erosion risk. The information levels were focused on expert experience, and the dynamic decision-making process built a network framework. The weights for each layer were computed by R Studio fuzzy AHP package. The map of soil erosion susceptibility was developed by combining layers in a platform based on their weights and means of erosion-related incidents in regional surveys. Hence, the soil erosion map's overall results showed very high, high, moderate, low, and very low vulnerability to erosion with areal coverage of 13.4 %, 27.93 %, 32.74 %, 17.42 %, and 8.5 %, respectively. The susceptibility map demonstrates that high soil erosion sensitive areas with Fuzzy and AHP respectively cover 11.05 % and 15.75 %. The study indicates that priority should be given to high and very high erosion-prone areas in Rib watershed to adapt to climate change and control sedimentation problems in the Rib reservoir and Lake Tana.

Soil loss is a continuous ecological problem. The loss of top fertile soil by erosion creates severe limitations to sustainable agricultural land use, which lead to reduced soil productivity and food insecurity. Soil loss is not affect only agriculture but also causes streams, lakes, dams, and reservoir sedimentation. Efforts should be focused to decrease risks of high erosion rates. This requires erosion prone area identification for urgent conservation plan. Techniques to know the spatial variability of erosion severity is essential for improving landuse management. The Revised Universal Soil Loss Equation (RUSLE) model with ArcGIS and Multi Criteria Evaluation (MCE) technique were used to estimate the annual soil loss rate and to identify high erosion risk areas in Gilegel beles watershed with a size of 770 km2, to prioritize area for conservation planning. land use land cover, soil map, digital elevation model (30m resolution), and twenty five years rainfall data at nine rain gage stations across the watershed were used to estimate soil loss in RUSLE model. The result showed that annual soil loss of the watershed ranges from 0 to 511.2ton/ha/yr with average of 28.68 ton /ha/ yr. Spatially 10.4% and 13.2% of the watershed was extremely sever and high soil erosion respectively. However, the remaining 46.4% and 30.03% of the area lies within low to moderate level. Our study revealed the most extensive soil loss rates were estimated in steep slopes, bare lands, crop land and biological degraded areas were aggravated soil loss problem. Finally, the combined models were effective for soil erosion estimation in small watersheds, so the outcome verified that integrated land management practices have needed to apply effective soil erosion control techniques like agroforestry, grass strips reduce runoff velocity and allow for infiltration, provide sediment trapping, erosion control blankets, dust control and percolation ditches for erosion prone areas and managing the inter catchment can be the best solution.

Study region: Robit-Bata watershed, Upper Blue Nile basin, Ethiopia. Study focus: Stable isotopes of water (Oxygen-18 and Deuterium) were used as tracers to estimate the contribution of groundwater in shallow hillslope aquifers to streamflow in the Robit-Bata watershed. To assess the spatiotemporal variability of shallow groundwater and develop a hydrograph separation technique, we collected rainfall, shallow groundwater, and streamflow samples and analyzed their δ18O and δ2H isotopic compositions. The local meteoric water line (LMWL) and local evaporative line (LEL) of the study area were determined and compared with the global meteoric water line (GMWL). A standard unweighted two-component isotope-based hydrograph separation model was used to determine the percentage contribution of shallow groundwater to streamflow. New hydrological insights for the region: The LMWL (δ2H = 8.63·δ18O + 18.2) mostly showed heavy isotopic enrichment relative to GMWL, and the LEL (δ2H = 5.45·δ18O + 6.96) indicated isotopic enrichment compared to Ethiopian lakes. Shallow groundwater responded rapidly to rainfall, with good spatial correlation depending on topographic positions of wells. Pre-event water contributed 90% when the watershed reached maximum storage. This finding gives insight towards the predominant runoff generation process and has significant implications for sustainable dry season irrigation expansion in the area as the sub-surface flow drains out of the watershed from October onwards reducing water tables in the shallow wells.

The largest freshwater lake in Ethiopia, Lake Tana, has faced ecological disaster due to water hyacinth (Eichhornia crassipes) infestation. The water hyacinth is a threat not only to the ecology but also to the socioeconomic development of the region and cultural value of the lake, which is registered as a UNESCO reserve. This study aims to map the spatiotemporal dynamics of the water hyacinth using high-resolution PlanetScope satellite images and assesses the major environmental variables that relate to the weed spatial coverage dynamics for the period August 2017 to July 2018. The plausible environmental factors studied affecting the weed dynamics include lake level, water and air temperature, and turbidity. Water temperature and turbidity were estimated from the moderate resolution imaging spectroradiometer (MODIS) satellite image and the water level was estimated using Jason-1 altimetry data while the air temperature was obtained from the nearby meteorological station at Bahir Dar station. The results indicated that water hyacinth coverage was increasing at a rate of 14 ha/day from August to November of 2017. On the other hand, the coverage reduced at a rate of 6 ha/day from December 2017 to June 2018. However, the length of shoreline infestation increased significantly from 4.3 km in August 2017 to 23.4 km in April 2018. Lake level and night-time water temperatures were strongly correlated with water hyacinth spatial coverage (p < 0.05). A drop in the lake water level resulted in a considerable reduction of the infested area, which is also related to decreasing nutrient levels in the water. The water hyacinth expansion dynamics could be altered by treating the nutrient-rich runoff with best management practices along the wetland and in the lake watershed landscape.

Study region: Eastern Nile River Basin (Ethiopia, Sudan and Egypt). Study focus: This study aims to understand the future water development perspective in the Eastern Nile region by considering the current water use situation and proposed reservoirs in the upper Blue Nile (Abbay) River basin in Ethiopia using a simulation approach. The study was carried out by using a monthly time step and historical ensemble time series data as representative of possible near future scenarios. Series of existing and proposed cascaded water development projects in the upper Blue Nile were considered in the study. New hydrological insights for the region: The results indicated an overall energy gain in the Eastern Nile region increases by 258%. The upstream country Ethiopia can generate as much as 38200 GWh/year of Energy while the energy production in Sudan increases by 39%. The cascaded developments integrated with existing water resources systems have a performance efficiency of above 92%. This study was an indicative analysis of the potential benefit of upstream Nile development without significantly affecting existing development in the Nile Basin. Further scientific analysis in this direction would help the Nile countries to reach a water use agreement. Keywords: Eastern Nile, Water resource modeling, Blue Nile cascades, Renaissance Dam

Low flow analysis provides crucial information for the planning and design water resource development, risk assessment and environmental flow management. Understanding the low flow regimes and evaluating the magnitudes for incorporating in water resources management is vital for the countries like Ethiopia where demand for water is increasing. However, there were hardly enough studies in understanding the trends of low flow and frequency analysis. Therefore, this study focuses on evaluation of the trends in low flows and regional low flow analysis in the Blue Nile Basin, Ethiopia. In order to carry out the study, 15 river sub-basins in the Blue Nile Basin were selected based on the long term data availability and presence of quality of data. The 3-day sustained low flow (3d-slf), the 7-day sustained low flow (7d-slf) and the 14-day sustained low flow (14d-slf) models were used to extract the data from the daily time series stream data obtained from MoWIE. Trends in low flow were analyzed separately by using Mann-Kendall (MK) trend test. Low flow frequency analysis was used to estimate the long term low flow quantiles. In addition, regional analysis for estimating the quantiles for ungaged catchments was also developed based on the regional growth curve and catchment characteristic of drainage basins. The results indicated that 3d-slf, 7d-slf and 14d-slf models of low flow series indicated no significant difference for each station at 95% CI. Out of the 15 selected stations, 12 of stations have indicated decreasing; two stations indicated increasing and remaining one station with no trend. Mainly decreasing trend was associated with the land cover and climate change which results in increasing runoff and evapotranspiration respectively. Weibull distribution—GEV and LGN was found best fit based on the L-Moment Ratio Diagram (L-MRD). Hence quantile estimations have indicated diminishing magnitudes of low flow quintiles for 2 - 500 years return periods. Regional low frequency analysis has provided a very good relationship between discharge and catchment characteristics with an R2 of 0.72. Where area (A) and rainfall (R) followed by slope were found sensitive to compute in developing the regional region equations between mean low flows and the physiographic data. This study indicated that there needs to be a new water management scenario and adaptation mechanism of climate change and land use land cover dynamics for utilizing water resource in the Blue Nile Basin.

Soil erosion decreases soil fertility of the uplands and causes siltation of lakes and reservoirs; the lakes and reservoirs in tropical monsoonal African highlands are especially affected by sedimentation. Efforts in reducing loads by designing management practices are hampered by lack of quantitative data on the relationship of erosion in the watersheds and sediment accumulation on flood plains, lakes and reservoirs. The objective of this study is to develop a prototype quantitative method for estimating sediment budget for tropical monsoon lakes with limited observational data. Four watersheds in the Lake Tana basin were selected for this study. The Parameter Efficient Distributed (PED) model that has shown to perform well in the Ethiopian highlands is used to overcome the data limitations and recreate the missing sediment fluxes. PED model parameters are calibrated using daily discharge data and the occasionally collected sediment concentration when establishing the sediment rating curves for the major rivers. The calibrated model parameters are then used to predict the sediment budget for the 1994-2009 period. Sediment retained in the lake is determined from two bathymetric surveys taken 20 years apart whereas the sediment leaving the lake is calculated based on measured discharge and observed sediment concentrations. Results show that annually on average 34 t/ha/year of sediment is removed from the gauged part of the Lake Tana watersheds. Depending on the up-scaling method from the gauged to the ungauged part, 21 to 32 t/ha/year (equivalent to 24-38 Mt/year) is transported from the upland watersheds of which 46% to 65% is retained in the flood plains and 93% to 96% is trapped on the flood plains and in the lake. Thus, only 4-7% of all sediment produced in the watersheds leaves the Lake Tana Basin.

Agricultural intensification to meet the food needs of the rapidly growing population in developing countries affects water quality. In regions such as the Lake Tana basin, knowledge is lacking on measures to reduce non-point source pollutants in humid tropical monsoon climates. The aim of this paper was, therefore, to develop a non-point model that can predict the placement of practices to reduce the transport of sediment and phosphorus (P) in a (sub) humid watershed. In order to achieve the objective, hydrometeorological, sediment, and P data were collected in the watershed since 2014. The parameter efficient semi-distributed watershed model (PED-WM) was calibrated and validated in the Ethiopian highlands to simulate runoff and associated sediments generated through saturation excess. The P module added to PED-WM was used to predict dissolved (DP) and particulate P (PP) loads aside from discharge and sediment loads of the 700 ha of the Awramba watershed of Lake Tana basin. The PED-WM modules were evaluated using the statistical model performance measuring techniques. The model parameter based prediction of source areas for the non-point source sediment and P was also evaluated spatially and compared with the Topographic Wetness Index (TWI) of the watershed. The water balance component of the non-point source model performed well in predicting discharge, sediment, DP, and PP with NSE of 0.7, 0.65, 0.65, and 0.63, respectively. In addition, the predicted discharge followed the hydrograph with insignificant deviation from its pattern due to seasonality. The model predicted a sediment yield of 28.2 t ha−1 year−1 and P yield of 9.2 kg ha−1 year−1 from Awrmaba. Furthermore, non-point source areas contributed to 2.7 kg ha−1 year−1 (29%) of DP at the outlet. The main runoff and sediment source areas identified using PED-WM were the periodically saturated runoff areas. These saturated areas were also the main source for DP and PP transport in the catchment. Using the PED-WM with the P module enables the identification of the source areas as well as the prediction of P and sediment loading which yields valuable information for watershed management and placement of best management practices.

Rapid population growth and agricultural intensification have been directly associated with land degradation and with visible deterioration in water quality in the Ethiopian lakes. Assessing the extent and origin of pollution is cumbersome because of the lack of measurements for water quality parameters. This paper reports on the dissolved phosphorus (DP) concentrations in Lake Tana and its tributaries during 3 years from 2010 to 2012 and the four rainy months in 2014. Concentrations in the headwaters, at the gaging station, at the river mouth, near shore (littoral), and in the open lake (pelagic) were measured for the four major rivers. DP concentration in the rivers was on the average 0·32 mg l−1, and DP in the lake was much lower with an average concentration of 0·10 mg l−1. Temporally, DP concentrations were greater in the rainy phase of the monsoon than in the dry phase from November through March. Moreover, an upward trend in DP concentrations is coinciding with the area expansion of water hyacinths in the lake. Copyright © 2017 John Wiley & Sons, Ltd.

Optimizing the use of irrigation water is of vital importance in conserving land and water resources as well as maximizing crop yield utilizing available water. Evaluating an irrigation system performance should measure and show the effectiveness of existing irrigation practice, provide remedial measures if necessary, as well as determining the impacts of the factors which affect the performance parameters. This study attempted to evaluate and assess the performance of Quashni irrigation scheme using internal and external performance indicators. Two irrigation seasons in the 2018 (February–May) and 2018/2019 (October–January) were carried out. Primary data, e.g. soil moisture before and after irrigation, discharge measurements, irrigation depth and soil physical properties, were collected. Secondary data, e.g. meteorological data and irrigated area per crops, were also collected. CROPWAT 8.0 computer model was used to calculate the CWR. The conveyance and application efficiency of the scheme was estimated as 71.8% and 51.2% respectively, which led to an overall scheme efficiency of 36.8%. RWS and RIS of the scheme were 1.24 and 1.12, respectively. Irrigation ratio of Quashni irrigation scheme was found to be 0.84, which implies that 16% of the command area could not be provided with irrigation coverage. In general, the evaluation and assessment indicated a low performance of the Quashni irrigation scheme.

The main focus on three watersheds in the upper Blue Nile. The study used the Representative concentration pathway (RCP) climate model scenarios with 50 km resolution. The CORDEX-Africa model output of RCP2.6 and RCP8.5 scenarios were used. The Parameter Efficient Semi Distributed Water Balance model (PED-WM) was calibrated and validated to project the climate change impacts on the stream flow events. The future climate projection results were presented by dividing in to three future time horizons of 2030s (2021–2040), 2060s (2051–2070) and 2090s (2081–2100). The bias corrected maximum and minimum temperature increases in all months and seasons in the selected watersheds. The change in magnitude in RCP8.5 emission was higher than RCP2.6 scenario. The study resulted considerable average monthly, seasonal and annual precipitation change variability in magnitude and direction. In 2030s, the average annual Stream flow projection decreases up to −32.18% for RCP2.6 and up to −19.44% for RCP8.5 scenarios. In 2060s also the average annual stream flow decreases by −12.3% and −32.18% for RCP2.6 and RCP8.5 emission scenarios, respectively. Similarly, in 2090 s, the average annual Stream flow change decreases by −20.67 and −51.78% for RCP2.6 and RCP8.5 respectively. For the future time horizon, the maximum Stream flow changes in wide range from (−56.4 to 81.1%) and minimum flow from (−61.72 to 8.17%) in both RCP2.6 and RCP8.5.

This study focused on developing rule curves for multi-purpose cascade reservoirs operation to optimize the available water for hydropower production, irrigation development, water supply, and environmental flow in Blue Nile Basin using HEC-ResSim reservoir simulation model. The model tried to represent the physical behavior of cascade reservoirs in the basin with its high speed hydraulic computations for flows through control structures, and hydrologic routing to represent the lag and attenuation of flows through the main and tributaries of the river based on the current projects operation, and future likely development projects implementation period. Therefore, the management of multi-purpose cascade reservoirs is complex due to conflicting interests between these objectives. Thus, the optimal operation of cascade reservoirs is important to address trade-offs between multiple objectives to achieve the water management goals. From the simulation of cascade reservoirs operation, Hydropower power guide curve operation rule was selected to optimize the basin’s available water.

Understanding soil moisture at a small scale is beneficial for predicting productivity and management of both rained and irrigated agriculture in mostly smallholder communities. This study aims to accurately represent micro-watershed scale soil moisture using the optimization capability of SWAT (SUFI2) model and soil information derived from Sentinel 2 A level 1 C satellite images with OPtical TRApezoid Model (OPTRAM) and MNDWI. The study was carried in the 700 ha Awramba watershed in the Upper Blue Nile, Ethiopia. Calibration and validation of SWAT were performed using in-situ stream flow data to enable the accurate simulation of water balance components such as soil moisture. The spectral water index was evaluated using MNDWI from the green band (560 nm) and short wave infrared band (2190 nm). The Results were evaluated based on the runoff response n and soil moisture fit to measured values. The runoff fit against the measured data using Nash Sutcliffe Efficiency (NSE) and R2 criteria is 0.7 is and 0.75, respectively. The simulated daily soil moisture against the in-situ constant soil moisture provided NSE = 0.51, R2 = 0.77, RMSE = 0.19 and PBIAS = −0.242. The simulation results indicate that validation of SWAT, OPTRA M and MNDWI models with in situ soil moisture data leads to acceptable accuracy with 0.0027 cm3 cm−3, 0.0022 cm3 cm−3 and 0.034 cm3 cm−3 standard errors, respectively. Furthermore, Sentinel 2A imagery is found to have a higher potential to simulate soil moisture compared to TDR data. The overall study indicates satellite-based soil moisture provides an encouraging pathway to setting up soil moisture-based prediction for smallholder agriculture in Ethiopia.

The estimation of crop water demand and understanding groundwater use is an essential component for managing water effectively. Groundwater is the main source of irrigation in Dangila. However, there is a lack of information in the study area on amount of irrigated land, irrigation water use and demand, groundwater recharge. Consequently, the objective of this study is to determine the groundwater recharge and its potential for dry season irrigation. The study was conducted in Brante watershed of 5678 ha located in Dangila woreda, Ethiopia. Water table data from twenty-five wells and discharge data at the outlet of the watershed used to assess recharge amount in 2017. To calculate irrigation water demand, CROPWAT model was used. Questionnaires were undertaken to assess groundwater use. A KOMPSAT-2 image was used to map shallow groundwater irrigated vegetables in February 2017. From the soil water balance method, the annual groundwater recharge was 17,717,690 m3 which is 15.8% of annual rainfall, and recharge amount of 14,853,339 m3 was obtained using water table fluctuation method. From satellite image classification the area coverage of dry season irrigated vegetables (onion, tomato, pepper) below the main road was 4.02 ha. From CROPWAT result, seasonal irrigation water demand for onion, Tomato, and pepper was 333,314, and 261 mm respectively. However, the questioners result indicates that farmers apply in average 20% more water than crop water demand. In the watershed 60,150 m3, 62,750 m3 and 41,603 m3 of water was abstracted for irrigation, domestic and livestock use respectively. The ratio of groundwater use to groundwater recharge at the watershed scale was found to be only 1%. This study indicates that the current use of groundwater was sustainable. For better improvement of household livelihood irrigation can be further expand using ground water. Future work should be performed to determine if the method outlined in this research could be used to accurately estimate available water potential.

The increasing population has put an immense pressure on our natural resources leading to water pollution and land degradation. The need for new agricultural areas, urbanization and industrial development have been responsible for resources degradation and pollution. Eutrophication can be resulted due to substantial driven enrichment of seasonal cycle of nutrients like phosphorus and nitrogen. So, this study is aimed at evaluating the (1) spatial and temporal dynamics of eutrophication on Lake Tana, (2) linkage between eutrophication and water hyacinth infested area (3) lake-land linkage of nutrients and water hyacinth infestation. To evaluate the dynamics of eutrophication, the samples were taken from 143 points at 0.5 m depth of the lake in August (2016), December (2016) and March (2017). To see the lake-land linkage of nutrients, two major nutrients (P and N) were collected at the major tributary rivers. The trophic status index of TP, SDD and Chl-s was determined by adopting Carlson’s model by using spatial analyst tool of ArcGIS. The result of this study showed that the trophic status index of the lake is shifting from mesotrophic to eutrophic condition. The growth of the invasive weed in the northeastern part of the lake is caused by the spatial distribution of nutrient and eutrophication as well as the depth, wind direction and the extent of large floodplain. This study will help to manage and control the pollution of Lake Tana and the expansion of water hyacinth.

This study aims to evaluate stream flow predication capability of three hydrological models including Parameter Efficient Semi-Distributed Watershed Model (PED-WM) model, Hydrologiska Byrans Vattenbalansavdelning (HBV) and Hydraulic Engineering Center-Hydrologic Modeling System (HEC-HMS) in range of sizes of watersheds, Upper Blue Nile Basin, Ethiopia. The model efficiency on daily time scale during calibration period for PED-W (NSE = 0.76, 0.81 and 0.57), HBV-IHMS (NSE = 0.68, 0.79 and 0.59) and HEC-HMS (NSE = 0.63, 0.68 and 0.48) were obtained for Anjeni, Gumara and Main Belles watersheds respectively. Similarly, for validation period PED-W (NSE = 0.6, 0.73 and 0.37), HBV-IHMS (NSE = 0.56, 0.79 and 0.55) and HECHMS (NSE = 0.52, 0.74 and 0.37) were obtained for Anjeni, Gumara and Main Belles watersheds respectively. Similarly, the model performances on monthly time steps were also varied among three hydrological models and the results better than the daily time scale. In PED-W, saturation excess is the main direct runoff process. The overall model performance indicated that PED-W model was better than the other two models. The result indicates that the models in the highlands of Ethiopia are dominantly dependent on the runoff mechanism dominantly on saturation excess runoff mechanism. Hence, there should be an approach to integrate climate region specific model in our water resource development system for predicting stream flow for ungagged catchments.

Anthropogenic landscape conversion from forest to agricultural land affects baseflow. Baseflow is a source of potable water and can be used for the irrigation of high value crops. Finding ways to increase base and inter flow (i.e., groundwater flow) is, therefore, essential for the improvement of the livelihood of rural inhabitants. Therefore, the objective is to investigate the effect of landscape interventions on stream discharge and, in particular, on groundwater flow. The Tikur-Wuha experimental watershed in the upper reaches of the Blue Nile was selected because discharge data were available before and after implementation of a suite of land management practices that, among others, enhanced the percolation of water to below the rootzone. The parameter efficient distributed (PED) model was used to separate overland flow from total flow. The groundwater flow index (GWFI), defined as the quotient of the annual groundwater flow to the total stream discharge at the outlet of the watershed, was calculated. Our analysis with the PED model showed that at similar annual rainfall amounts, more baseflow and less surface runoff was generated after the landscape intervention, which promoted deep infiltration of the rainwater. The decrease in surface runoff shortly after the implementation of the land management practices is similar to observations in other watersheds in the Ethiopian highlands.

The Soil Water Assessment Tool (SWAT) is employed throughout the world to simulate watershed processes. A limitation of this model is that locations of saturation excess overland flow in hilly and mountainous regions with an impermeable layer at shallow depth cannot be simulated realistically. The objective of this research is to overcome this limitation with minor changes in the original SWAT code. The new approach is called SWAT-with-impervious-layers (SWAT-wil). Adaptations consisted of redefining the hillslope length, restricting downward percolation from the root zone, and redefining hydrologic response units (HRUs) such that they are associated with the landscape position. Finally, input parameters were chosen such that overland flow from variable saturated areas (VSAs) corresponds to the variable source interpretation of the Soil Conservation Service (SCS) curve number runoff equation. We tested the model for the Town Brook watershed in the Catskill Mountains. The results showed that the discharge calculated with SWAT-wil agreed with observed outflow and results simulated with the original SWAT and SWAT-hillslope (SWAT-HS) models that had a surface aquifer that transferred water between groups of HRUs. The locations of the periodically saturated runoff areas were predicted by SWAT-wil at the right locations. Current users can utilize the SWAT-wil approach for catchments where VSA hydrology predominates.

Flow forecasting is used in activities requiring stream flow data such as irrigation development, water supply, and flood control and hydropower development. Real time flow forecasting with special interest to flooding is one of the most important applications of hydrology for decision making in water resources. In order to meet flood and flow forecasts using hydrological models may be used and subsequently be updated in accordance with residuals. Therefore in this study, different flood forecasting methods are evaluated for their potential of stream flow forecasting using Galway River Flow Forecasting and Modeling System (GFFMS) in Lake Tana basin, upper Blue Nile basin, Ethiopia. The areal rainfall and temperature data was used for the model input. Three forecast updating methods, i.e., autoregressive (AR), linear transfer function (LTF) and neuron network updating (NNU) methods were compared for stream flow forecasting, at one to six days lead time. The most sensitive parameters were fine-tuned first and modeled for a calibration period of 1994-2004 for three selected watersheds of the Tana basin. The results indicate that with the exception of the simple linear model, an acceptable result could be obtained using models embedded in the software. Artificial neural network model performed well for Gilgel Abay (NSE = 0.87) and Gumara (NSE = 0.9) watersheds but for Megech watershed, SMAR model (NSE = 0.78) gave a better forecast result. In capturing the peak flows LTF and NNU in forecast updating mode performed better for Gilgel Abay and Megech watersheds, respectively. The results of this study implied that GFFMS can be used as a useful tool to forecast peak stream flows for flood early warning in the upper Blue Nile basin.

Recently there are signs of water quality impairment in Lake Tana, the largest fresh water in Ethiopia. The lake is the growth corridor of the government and supports millions of livelihood around. In order to sustain the benefit and maintain the ecosystem of the lake, the lake health has to be kept safe. Therefore monitoring and evaluation of the water quality of lake is very vital. This study focuses on current and previous trends water quality of the lake through measurements and Landsat Images near entry of Gumera River. Statistical analysis of the physical (Turbidity and STD and biological (Cha-a,) and chemical (DPC) water quality parameters were done. Linear and non-linear regression models between water quality parameter and reflectance of Landsat 7 ETM+ images were fitted based on band combinations. Pervious trend in turbidity was analyzed based on the regression models. The results showed that reflectance and turbidity satisfactorily result with an R2 ranging from 0.61 - 0.68. Form 1999-2014 the turbidity of the lake has indicated an increasing trend. Delta development near the entry of Gumera River has been enlarged by 48% because of an increase sediment inflow. The sign in the decreasing water quality of the lake was attributed to the non-point source sediment and nutrient inflow to the lake with high erosion rate from the watersheds. Measures to reduce the non-point source sediment and nutrient inflow by targeting the source areas (hot spots) in the agricultural watersheds need to be priority for stakeholders working on the soil and water conservation. Moreover, reducing the recession agriculture around the lake and wetland management could be crucial for improving lake water quality.

Information on sediment concentration in rivers is important for design of reservoirs and for environmental applications. Because of the scarcity of continuous sediment data, methods have been developed to predict sediment loads based on few discontinuous measurements. Traditionally, loads are being predicted using rating curves that relate sediment load to discharge. The relationship assumes inherently a unique relationship between concentration and discharge and therefore although performing satisfactorily in predicting loads, it may be less suitable for predicting concentration. This is especially true in the Blue Nile Basin of Ethiopia where concentrations decrease for a given discharge with the progression of the rainy monsoon phase. The objective of this paper is to improve the sediment concentration predictions throughout the monsoon period for the Ethiopian highlands with a modified rating type equation. To capture the observed sediment concentration pattern, we assume that the sediment concentration was at the transport limit early in the rainy season and then decreases linearly with effective rainfall towards source-limited concentration. The modified concentration rating curve was calibrated for the four main rivers in the Lake Tana basin where sediment concentrations affect fish production and tourism. Then the scalability of the rating type equation was checked in three 100 ha watersheds for which historic data were available. The results show that for predicting sediment concentrations, the (modified) concentration rating curve was more accurate than the (standard) load rating curve as expected. In addition loads were predicted more accurately for three of the four rivers. We expect that after more extensive testing over a wider geographical area, the proposed concentration rating curve will offer improved predictions of sediment concentrations in monsoonal climates.

Lake Tana in the Ethiopian highlands is showing the first signs of eutrophication. The origin of the non‐point source dissolved phosphorus loss is examined. The periodically saturated and reduced bottomlands are a main source of P. Maize grown mid‐slope provides only P during high flow events. Converting the bottom lands to buffer zones will decrease non‐point source pollution.

Minasny et al. (2020) proposed enhancing future global soil science research by examining the role of soils in global ecosystem functioning. They argued in particular that meaningful collaboration between high- and low-income countries is essential to generate new knowledge and facilitate capacity building. In this commentary, we provide an account of our experience with an effective cooperative research and training partnership between Cornell University and Bahir Dar University in Ethiopia. We note that, in addition to the willingness and commitment of the scientists to cooperate, support and flexibility of senior university administrators is essential for international cooperation to succeed. We illustrate these points describing our experience and show that these cooperative efforts are evolving incrementally and in many cases do not follow well-laid-out programs.

Water hyacinth originated from the Amazon Basin and has expanded to other parts of the world since the 1800s. In Ethiopia, the weed is affecting the socio-economic activities of the people whose livelihood is directly or indirectly dependent on Lake Tana. Still, the area covered by water hyacinth and the impact of water level fluctuation on the expansion of water hyacinth has not been known clearly. Therefore, the main objective of this study was to determine the spatiotemporal distribution of water hyacinth and relation with lake-level fluctuation. The area covered by water hyacinth was determined using monthly Sentinel-2 images, which were collected from November 2015 to December 2019. The impact of water level fluctuation on the expansion of water hyacinth was evaluated using hourly water level data converted to a monthly average to correlate with the area covered by the water hyacinth. In addition, MOD13Q1.006 data was used to evaluate the trend of the Normalized Difference Vegetation Index (NDVI) and its linkage with the weed. The maximum areas covered by water hyacinth were 278.3, 613.6, 1108.7, 2036.5, and 2504.5 ha in Feb 2015, October 2016, September 2017, December 2018, and in December 2019, respectively. Its areal coverage was declining from the north corridors and increasing in eastern shores of the lake. The lake-level fluctuation was observed in the range of 1.5 to 3.98 m in this study. The annual mean maximum spatial values of the NDVI were in the range of 0.27 and 0.47. The area covered by water hyacinth was increasing significantly (P &lt, 0.05) and positively correlated with the seasonal lake-level fluctuation. High water level enabled the expansion of the weed by extending its suitable habitat of shallow water to the flood plain. Based on the results of this study, lake-level fluctuations can have an adverse impact on the expansion of the weed.

The Blue Nile Basin, Ethiopia, whose inter-annual variability in local precipitation has resulted in droughts and floods that lead to economic and food insecurity, is the area of interest for our N...

This chapter evaluates the impact of climate change on mean and extremes state of hydrological variables in Megech watershed, Upper Blue Nile Basin, Ethiopia. Four global climate models (GCMs) with A1B and A2 scenarios were selected for analysis. Linear scaling bias correction was used to downscale GCM to the watershed scale. Soil and Water Assessment Tool (SWAT) was used to predict stream flow. SWAT predicted the daily stream flow with good performance (R2 = 0.69, NSE = 0.67, and RVE = − 15%) with observation. An increase in average annual temperature of 2.71°C and 4.8°C by 2050s and 2090s, respectively was found. Precipitation showed decreasing tendency for all GCMs except in the CNRM. The low flow indicated decreasing tendency unlike an increasing trend of the peak flow in future climate projection period. In general, there would be changes and variation in hydrometerological variables in the watershed. Hence, a new water management scenario should be implemented for sustainable utilization of the water resource in the region.

Hydrological modeling in Ethiopia is limited by the availability of climate data. Substituting satellite based for ground-based meteorological data could resolve this limitation. This study evaluates the applicability of bias corrected CFSR meteorological data for hydrological modeling in the upper Blue Nile basin for three different sized watersheds: Anjeni (1.13 km2), Gilgel Abay (1656 km2) and Belles (3474 km2). The Soil and Water Assessment Tool (SWAT) was used for simulating of the stream flow with ground-based and CFSR climate data. The observed and predicted discharge agreed well using the ground-based climate data (0.75

This chapter presents a local-scale investigation of the potential association of climate change to increasing extreme meteorological variables over the Lake Tana subbasin of Blue Nile basin, Ethiopia using observed and projected maximum daily temperature and precipitation variables over the near future. The results are generally consistent with Intergovernmental Panel for Climate Change (IPCC) and other reports that both temperature and precipitation extreme events will likely increase in the Tana subbasin since 2020s. The increase in extreme precipitation will likely aggravate already recurring flood disasters in the flood plain areas of Dembia, Fogera, and Bahir Dar towns which are located in the vicinity of the lake. In addition, the overall potential evapotranspiration demand increase from the catchments may result in increased irrigation water demand from the Lake complicating water management decisions in the subbasin. Although the interplay between the increased precipitation and temperature events is complicated to discern, the study suggests future adaptive measures in the area of water resource planning, design and management shall consider regular revision of design guidelines of water infrastructures, roads, bridges and culverts, and update water management decision support systems in light of the climate change.

This chapter evaluates flood inundation area in Fogera-Dera floodplain under future climate change in Lake Tana basin. Downscaling of the Global Climate Model (GCM) to watershed level was done by Linear Scaling (LS) bias correction method. Parameter-efficient semidistributed watershed (PED-W) model was used to simulate streamflow under baseline and future climate projections. Two-dimensional (2D) BASEMENT hydrodynamic model was used for flood inundation area evaluation. Calibration and validation of PED-W indicated very good agreement with R2 = 0.77 and NSE = 0.76 and R2 = 0.77 and NSE = 0.76, respectively, on daily basis. Inundation area increased from 36.76 to 38.4, 41.91, and 46.36 km2 in RCP 2.6 and 40.12, 44.15, and 48.21 km2 in RCP 8.5 for 2020s, 2050s, and 2080s, respectively. Flooding in Dera-Fogera areas would be aggravated under future climate change. Flood monitoring and management systems have to be developed taking into consideration climate change scenarios.

This study presents modeling runoff and sediment with management scenarios for watershed management and resource erosion in Koga watershed using AnnAGNPS model. Calibration of the model was carried from 1988–2001 and validation from 2002–2007. The result of sensitivity analysis indicated that the CN was the most sensitive parameter to runoff and peak runoff rate whereas LS and K-factor were for sediment yield following RF, and these parameters were subjected to calibration. For model calibration, R2 of 0.69, 0.35, 0.55; NSE of 0.69, −0.38, 0.55; RSR of 0.54, 1.14, 0.67; and PBIAS of 0.07%, −80.56% and 4.09% were obtained for surface runoff, peak runoff rate, and sediment load, respectively. Similarly validation results indicated an R2 of 0.76, 0.54, 0.62; NSE of 0.76, 0.38, 0.62; RSR of 0.43, 0.71, 0.56, and PBIAS of 2.31%, −36.58% and 5.68% for surface runoff, peak runoff rate, and sediment load, respectively. Where the model efficiency was rated at the range of fair to excellent for three of the outputs of the model for both calibration and validation period. Only 21.5% of the area was able to generate the 78.8% of total soil erosion, with higher than tolerable limit. Hence converting of 21.5% of highest eroding cropland cells either to forest or grassland would reduce soil erosion, sediment yield and load significantly. Ultimately it would help to reduce the sedimentation in Koga dam which could result in reduction of storage capacity.

This study aims at developing a model that can generate synthetic hourly rainfall data from the existing daily rainfall data of Awash river basin. Fifteen minutes rainfall data collected from national meteorological agency for 13 active stations and daily data collected from 54 stations were considered. Stochastic rainfall disaggregation and Hyetos temporal precipitation model was tested using the available fifteen minutes data. Three regions with close climate condition and rainfall pattern were identified and tested to be homogeneous in the stochastic method. Both methods are tested by using statistical comparison of variance, skew-ness, probability of dry period, and Lag-1 ACF. The result of the stochastic method showed very good performance in preserving the probability of zero rainfall and the daily rainfall total. But it has limitation in disaggregating rainfall magnitudes with high return period. Statistical comparison of Hyetos model indicated very good agreement with the original data. Especially the daily total statistical properties were well preserved. The comparison of the two methods showed that Hyetos is better in preserving the statistical property. Generally the methods are capable in preserving statistical properties and the daily total rainfall depth. Therefore, Hyetos model is pertinent for only temporal disaggregation, whereas the stochastic method is applicable for both spatial and temporal disaggregation in the basin.

Groundwater resource development for various uses is increasing in the Lake Tana basin, as surface water became limited in quantity and quality. Assessment of the groundwater potential (GWP) in the basin is crucial for sustainable use of water resources. This study aims at assessing the GWP in the basin using remote sensing and GIS-based Multi Criteria Decision Analysis (MCDA). Seven factors (lithology, lineaments, drainage density, rainfall, slope, land use/land cover and soils) that affect groundwater distribution were considered. Analytical Hierarchy Process (AHP) approach were used to compute each layer weight. Thematic weighted layers were overlaid in ArcGIS to identify GWP are-as in the basin. The result indicated that, 15% (1765 km2) classified as “very high”, 26.5% (3151 km2) as “high”, 31% (3592 km2) as “medium”, and 27.5% (3224 km2) were classified as “low” GWP zones in the basin. The GWP map was validated using observed borehole and springs data in the basin, and it indicated that 76% of agreement. It was found that GWP was highly sensitive to lithology and rainfall with mean variation index of 2.7% and 2.0%, respectively. High GWP is available at the southern and eastern side of the Lake Tana.

This chapter discusses an extraction method of hourly maximum rainfall from daily maximum rainfall data in part of Upper Blue Nile basin. A regional growth curve with site-specific quantiles of hourly maximum rainfall is also developed. The extracting method was developed using four hourly and 162 daily recording stations in the basin. Regionalization was carried out by clustering analysis with an input of latitude, longitude, elevation, and mean annual rainfall. The grouped stations were evaluated with discordant measure. Regional homogeneity of the stations was tested by heterogeneity measures using daily maximum rainfall of 62 stations. The dimensionless ratio of hourly maximum rainfall to daily maximum rainfall (rmax) that was modeled with a specific probability distribution was used as an approach to extract hourly maximum rainfall. The Upper Blue Nile basin was grouped in two clusters and it was found that Pearson type III and Generalized Extreme Value distributions are best representatives for the dimensionless ratio rmax of each region with a heterogeneity measure (H1) of 0.88 and 0.77, respectively. The extracted hourly maximum rainfall was also fitted with Pearson type III and Generalized Logistic distributions and quintiles were finally estimated for each region.

Under the auspices of the UN Millennium Development Goals, access to safe drinking water in the developing world, including the Ethiopian highlands, has improved greatly. However, in many cases, it is not known how safe the water is. With the intensification of agriculture and increasing applications of fertilizers, high levels of nitrate are a concern. The objective of this study is to assess the nitrate levels in drinking water supply systems. To assess nitrate levels, we sampled 213 water supply points in a 4880 km2 area in the northwest Ethiopian highlands. The results show that the average concentration was below the World Health Organization (WHO) health standard of 10 mg N-NO3/L. The average concentration in wells was 3.3 mg N-NO3/L and in springs was 1.8 mg N-NO3/L. Only in three wells, that were in agricultural cropped areas, was the WHO standard exceeded. Wells in the agricultural fields had an average nitrate concentration of 3.6 mg N-NO3/L, which was almost twice that on grazing land and four times that in upland wells. Spatially, the groundwater nitrate concentrations were greater in the moderately sloped parts of the study area where agriculture was intensive and denitrification limited. Thus, although current nitrate levels are safe, in the future, the nitrate concentration could exceed the WHO health standard when fertilizer use increases.

In Ethiopia the population is rapidly expanding. As a consequence the landscape is rapidly changing. Eucalyptus plantations are increasing and irrigation projects are implemented. The hydrological effects of the changing landscape on river (low) flows have not been well documented and therefore the amount of water available in the future might be over optimistic. The objective of this paper is to establish how low flows have been impacted by new developments in irrigation and by landscape change. For this paper, we choose the Gilgel Abay in the headwaters of the upper Blue Nile basin, since it has both good quality discharge data and it is located in the Tana Beles growth corridor. Numerical and statistical means were used to analyze the 25 years of available low flow data. We found a statistically significant decreasing trend (P < 0.00001) of low flow in the Gilgel Abay. From 1980’s to 1990’s the low flow decreased by 25% and from 1990’s to 2000’s the low flow was reduced by 46%. The deterministic analysis with the Parameter Efficient Distributed (PED) model supported the statistical findings and indicated that in the middle of the nineteen nineties, after irrigation projects and eucalyptus plantations increased greatly, the low flows decreased more rapidly.

Water hyacinth is a well-known invasive weed in lakes across the world and harms the aquatic environment. Since 2011, the weed has invaded Lake Tana substantially posing a challenge to the ecosystem services of the lake. The major factors which affect the growth of the weed are phosphorus, nitrogen, temperature, pH, salinity, and lake depth. Understanding and investigating the hotspot areas is vital to predict the areas for proper planning of interventions. The main objective of this study is therefore to predict the hotspot areas of the water hyacinth over the surface of the lake using the geographical information system (GIS)-based multi-criteria evaluation (MCE) technique. The main parameters used in the multi-criteria analysis were total phosphorus (&gt, 0.08 mg L&minus, 1), total nitrogen (&gt, 1.1 mg L&minus, 1), temperature (&lt, 26.2 &deg, C), pH (&lt, 8.6), salinity (&lt, 0.011%), and depth (&lt, 6 m). These parameters were collected from 143 sampling sites on the lake in August, December (2016), and March (2017). Fuzzy overlay spatial analysis was used to overlay the different parameters to obtain the final prediction map of water hyacinth infestation areas. The results indicated that 24,969 ha (8.1%), 21,568.7 ha (7.1%), and 24,036 ha (7.9%) of the lake are susceptible to invasion by the water hyacinth in August, December, and March, respectively. At the maximum historical lake level, 30,728.4 ha will be the potential susceptible area for water hyacinth growth and expansion at the end of the rainy season in August. According to the result of this study, the north and northeastern parts of the lake are highly susceptible for invasion. Hence, water hyacinth management and control plans shall mainly focus on the north and northeastern part of Lake Tana and upstream contributing watersheds.