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While the availability of "big data" on biophysical parameters through citizen science and/or from public/private sources is expected to help in addressing data scarcity issues, there is little understanding of whether and/or how such data will improve watershed simulations. This research aimed to evaluate whether improvements in resolutions of Digital Elevation Model (DEM) and soil data will enhance streamflow and sediment yield simulations and thereby improve soil and water management decisions. The study was conducted in two different-sized watersheds (Anjeni and Gilgel Abay with ~ 1 km 2 and ~ 1655 km 2 area, respectively) in the Upper Blue Nile basin in Ethiopia. Effects of DEM and soil data resolutions on streamflow and sediment yield were evaluated using the Soil and Water Assessment Tool (SWAT). The results showed that the effect of DEM and soil data resolution on streamflow and sediment yield simulation was scale dependent finer resolution DEM and soil datasets improved streamflow and sediment yield simulations in the smaller Anjeni watershed, whereas DEM resolution had no effect in the bigger Gilgel Abay watershed. Small watersheds are often used to understand watershed processes, and thus the use of finer-resolution spatial data for watershed simulations could result in better results. Findings from the smaller Anjeni watershed suggested that the combined use of finer resolution DEM and soil data could potentially improve sediment yield simulations although the lack of observed sediment yield data did not allow verification of this at the larger Gilgel Abay watershed., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Soil erosion is the predominant agent affecting ecosystem services in the Ethiopian highlands. However, land management interventions aimed at controlling erosion in the region are hampered, mainly by a lack of watershed-based appropriate management practices and anticipated climate changes. This study examined the effectiveness of different land use changes and management scenarios in decreasing runoff and sediment loss under current and future climates in the drought-prone humid watershed of the Ethiopian highlands. We employed a modeling approach integrating observed data at watershed and plot scales with Soil and Water Assessment Tool. In the first step, we evaluated the impact of land use changes between 2006 and 2017 on runoff and sediment loss. Then, we developed five land use and management scenarios based on watershed land capabilities and selected land management practices. Model parameters were modified based on runoff and sediment loss results obtained from experimental plots of biophysical and agronomical land management practices in the watershed. The runoff and sediment loss were simulated under current (2014-2019) and future climates (the 2050s) for each land use and management scenario. Results revealed that land use changes (mainly an increase in Acacia decurrens plantations by 206%) alone between 2006 and 2017 reduced runoff by 31% and sediment loss by 45%. Under the current climate, the five land use and management scenarios reduced runoff by 71-95% and sediment loss by 75-96% compared to the baseline scenario. Under the future climate (2050s), these scenarios decreased runoff by 48-90% and sediment loss by 54-91%. However, their effectiveness was slightly decreased (5-23%) as a result of increases in rainfall (10-46%) and mean temperature (1.7-1.9 °C) in the 2050s. The scenario of improving vegetation cover through forage production and plantations in appropriate areas plus best land management practices was the most effective and climate-resilient of the five scenarios. This study suggests that evaluating the impact of land use and management practices under future climate change shows promise for guiding effective and sustainable interventions to adapt to climate change., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Soil erosion significantly affects agricultural production. Soil and Water Conservation (SWC) measures have been constructed to reduce soil loss. However, the impact of SWC measures on physicochemical soil properties has rarely been investigated in most parts of Ethiopia. Therefore, this study was designed to evaluate the effects of SWC measures on selected soil physicochemical properties in the Jibgedel watershed, West Gojjam zone, Ethiopia. The study also assessed the farmers' perception of the benefits and impacts of SWC measures. Composite and core soil samples were taken at a depth of 0 to 20 cm from four farmlands with SWC measures (soil bund, stone bund, and soil bund with sesbania tree) and without SWC measures in three replications. Results have shown that employing SWC measures in the farmland significantly improved most of the physicochemical properties of the soil compared to farmland without SWC measures. Bulk density from soil bund with and without sesbania trees was significantly lower than stone bund and untreated farmland. Soil organic carbon, total nitrogen, electrical conductivity, and available phosphorus from soil bund with sesbania tree were significantly higher than other treatments. The result also revealed that most farmers perceived that the implemented SWC measures improved soil fertility and crop yield. SWC measures are easier to adopt for integrated watershed management when farmers are well-versed in them., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

In terms of land use and climate, the world is changing at an unprecedented rate and these changes have a significant influence on our water resources. This study was conducted to examine the individual and combined potential impacts of land use and climate change on the water balance of the Baro basin in Ethiopia for the baseline period (1985-2002) and near-future period (2023-2040) using the Soil and Water Assessment Tool (SWAT). The plausible land use scenarios considering current (CUR), business as usual (BAU), and further expansion of altitudinal forest and watershed management practices (CON), as well as climate change scenarios from regional climate model outputs (RCMs) under two representative concentration pathways (RCP4.5 and RCP8.5) for the 2023-2040 time frame, were used as inputs to the models. The monthly calibrated and validated SWAT model produced an acceptable result, which was then used for water balance simulations. Findings show that forest decreased from 54.5% to 48.9% and 41.2% while agricultural land increased from 21.8% to 29.7% and 39.8% under the CUR and BAU land use change scenarios, respectively. The results from the ensemble mean showed an increase in maximum and minimum temperatures and a decrease in rainfall under the RCP4.5 and RCP8.5 climate change scenarios, which in turn resulted in an increase in evapotranspiration (ET) and a decrease in water availability. Climate change outweighed the impact of land-use change, thus indicating an increase in annual ET by up to 12% and a decrease of 42% in surface runoff (SURQ) under the RCP8.5 scenario. The BAU land use scenario projection triggers a respective increase of 18% in annual SURQ and reduction of ET by 2%. However, under the CON land use scenario, SURQ decreased by 24%. The study concluded that future land use and climate change will further challenge the basin's water supply capacity to meet the increased water demand. Understanding the changes in the basin's water balance is critical for mitigation and adaptation options. As a result, this study proposes restoration efforts and climate-resilient water management strategies that can increase the resilience of the river basin., Competing Interests: The authors declare no conflict of interest., (© 2023 Published by Elsevier Ltd.)

This study was conducted to evaluate the effectiveness of best management practices (BMPs) to reduce soil erosion in Gumara watershed of the Abbay (Upper Blue Nile) Basin using the Soil and Water Assessment Tool (SWAT) model. The model was calibrated (1995-2002) and validated (2003-2007) using the SWAT-CUP based on observed streamflow and sediment yield data at the watershed outlet. The study evaluated four individual BMP Scenarios; namely, filter strips (FS), stone/soil bunds (SSB), grassed waterways (GW) and reforestation of croplands (RC), and three blended BMP Scenarios, which combines individual BMPS of FS and RC (FS & RC), GW and RC (GW & RC), and SSB and GW (SSB & GW). Mean annual sediment yield at the baseline conditions was estimated at 19.7 t ha -1 yr -1 , which was reduced by 13.7, 30.5, 16.2 and 25.9% in the FS, SSB, GW, and RC Scenarios, respectively at the watershed scale. The highest reduction efficiency of 34% was achieved through the implementations of the SSB & GW Scenario. The GW & RC, and FS & RC Scenarios reduced the baseline sediment yield by 32% and 29.9%, respectively. The study therefore concluded that the combined Scenarios mainly SSB & GW, and GW & RC can be applied to reduce the high soil erosion in the Gumera watershed, and similar agro-ecological watersheds in Ethiopia. In cases where applying the combined scenarios is not possible, the SSB Scenario can yield significant soil erosion reduction.

Evaluating runoff and sediment responses to human activities and climate variability is crucial for prioritizing erosion hotspots and implementing appropriate land management interventions. This study evaluated the separate and combined impacts of soil and water conservation (SWC) practices, land use/land cover, and climate variability, on runoff and sediment yield (SY) using two approaches in drought-prone watersheds of northwestern Ethiopia. In the first (paired watershed) approach, runoff and SY outputs of Kecha (treated) and Laguna (untreated) watersheds were compared. In the second approach, we compared data before and after the implementation of SWC practices in the Kecha watershed. The Soil and Water Assessment Tool (SWAT) model was adopted for both untreated and treated watersheds and used to evaluate runoff and SY responses in the two approaches. Paired watershed approach results revealed that the SWC practices reduced the surface runoff in Kecha by about 28-36% and SY by about 51-68% as compared to those in Laguna. Similarly, compared with the baseline data at Kecha, the SWC practices reduced the surface runoff and SY by about 40% and 43%, respectively, corresponding to about 65-78% of the total changes brought by changes in land use/land cover and climate variability. Hence, combining the two approaches helped reasonably estimate the reduction of surface runoff and SY due to SWC practices by about 28-40% and about 43-68%, respectively, implying that SWC practices had a considerably greater effect on SY than surface runoff. The study further revealed that the untreated Laguna watershed, where >86% of the total area is categorized as the very high soil erosion severity class, should be an immediate conservation priority. The findings of this study will be vital to devise future alternative land management scenarios in these watersheds and similar agro-ecological areas elsewhere., Competing Interests: Declaration of competing interest The author(s) declare that have no any conflict of interest., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

Water resource development opens up opportunities for improving smallholder farmer livelihoods in sub-Saharan Africa; however, implementation of water resource interventions to ensure sustainability hinges on the availability of sufficient quantity and quality data for monitoring, analysis and planning. Such data is often acquired through instrumentation of water resources (e.g. stream flow monitoring) or the use of hydrological models. In sub-Saharan Africa, data scarcity has limited the ability to monitor and make appropriate decisions for water resource allocation and use. Data derived from remote sensing has been considered a viable option to fill this gap; however, there is limited research in the region that evaluate the quality of the remotely sensed based datasets. This study evaluated actual evapotranspiration (AET) estimates derived from Advanced Very High Resolution Radiometer (AVHRR AET) images and Moderate Resolution Imaging Spectrometer (MOD16 AET) images using estimates from a grid-based Soil and Water Assessment Tool (SWAT). The SWAT model was set up for the entire country of Ethiopia, and calibrated and validated using observed streamflow at several meso-scale watersheds in which satisfactory model performance was obtained. AET estimates from the calibrated and validated SWAT model were then used to evaluate remotely sensed based AET for three landscapes. The AVHRR AET better agreed with the SWAT-simulated AET than the MOD16 AET, although the AVHRR AET overestimated the SWAT-simulated AET in all of the landscapes. Both remotely sensed AET products showed better agreement with the SWAT-simulated AET over agriculture dominated landscapes compared to grassland and forest dominated landscapes. The findings of the study suggest that remotely sensed based AET may help to fine-tune hydrological models in agricultural landscapes in data-scarce regions to improve studies on the impacts of water management interventions aiming to ensure environmental sustainability while enhancing agricultural production, and household income and nutrition., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

Assessing the potential impacts of different land management practices helps to identify and implement sustainable watershed management measures. This study aims to assess a change in soil erosion rate under different land management practices in the Gilgel Abay watershed of the upper Blue Nile basin, Ethiopia. The Revised Universal Soil Loss Equation (RUSLE) model that was adapted to the Ethiopian highlands context was employed to estimate the rate of soil erosion. The impact of land management practices on soil erosion was estimated for three scenarios, which were baseline, intensive cultivation, and extensive cultivation scenarios. At the baseline scenario, the mean annual soil erosion was estimated at ~32.8 t ha -1 yr -1 , which is equivalent to a loss of ~13.66 Mt yr -1 from the entire watershed. While the rate of soil erosion reduced to ~11.3 t ha -1 yr -1 during the implementation of intensive cultivation management practice, which reduced the total soil loss in the watershed by 65%. On the other hand, under the extensive cultivation scenario, the mean annual soil erosion rate increased to ~34.4 t ha -1 yr -1 . The findings suggest that implementing agricultural intensification management practices can significantly reduce soil erosion in the watershed., (© 2020 Published by Elsevier Ltd.)

The Weather Research and Forecasting (WRF) model is one of the regional climate models for dynamically downscaling climate variables at finer spatial and temporal scales. The objective of this study was to evaluate the performance of WRF model for simulating temperature and rainfall over Lake Tana basin in Ethiopia. The WRF model was configured for six experimental setups using three land surface models (LSMs): Noah, RUC and TD; and two land use datasets: USGS and updated New Land Use (NLU). The performances of WRF configurations were assessed by comparing simulated and observed data from March to August 2015. The result showed that temperature and rainfall simulations were sensitive to LSM and land use data choice. The combination of NLU with RUC and TD produced very small cold bias (0.27 °C) and warm bias (0.20 °C) for 2m maximum temperature (Tmax) and 2m minimum temperature (Tmin), respectively. WRF model with RUC and NLU captured well the observed spatial and temporal variability of Tmax, while TD and NLU for Tmin. Moreover, rainfall simulation was better with NLU; especially NLU and Noah configuration produced the smallest mean bias (2.39 mm/day) and root mean square error (6.6 mm/day). All the WRF experiments overestimated light and heavy rainfall events. Overall, findings showed that the application of updated land use data substantially improved the WRF model performance in simulating temperature and rainfall. The study would provide valuable support for identifying suitable LSM and land use data that can accurately predict the climate variables in the Blue Nile basin., (© 2019 Published by Elsevier Ltd.)

The Hawizeh marsh, a unique wetland which is part of the Mesopotamian marshes, is recognized as a wetland of international importance. The marsh has been shrinking and there has been little research into its degradation. This study aims to reconstruct historical water regimes in the contributing basins (Tigris and Karkheh river Basins, TKRB) to investigate factors that have affected the wellbeing of the marsh. The Soil and Water Assessment Tool (SWAT) was used for this study. The model was calibrated and validated using nine river gauging stations. Results indicated that inflows to the marsh decreased by 65% and 80% in the '90s and 2000s, respectively, compared to the '80s. The reductions in streamflow were caused by decrease in precipitation and water abstraction. The annual precipitation decreased by 14% and 38% in the '90s and 2000s, respectively, compared to the '80s. Highest water abstraction was seen in Karkheh dam which caused a reduction of 45% in the annual streamflows. Average annual evaporative losses from Tharthar lake (2700km 2 ) were very high (2260hm 3 [cubic hectometer]). Although the Hawizeh marsh has been shrinking for the last three decades, recent satellite images (2013) have shown that the marsh has been reviving, mainly due to increased precipitation from 2011 to 2013. The revival of the marsh is promising; however, if the planned dams on TKRB are implemented, the future of the marsh remains uncertain. The sustainability of the Hawizeh marsh will require integrated water resources management among the riparian countries to rehabilitate and maintain this unique wetland., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Water harvesting systems have improved productivity in various regions in sub-Saharan Africa. Similarly, they can help retain water in landscapes, build resilience against droughts and dry spells, and thereby contribute to sustainable agricultural intensification. However, there is no strong empirical evidence that shows the effects of intensification of water harvesting on upstream-downstream social-ecological systems at a landscape scale. In this paper we develop a decision support system (DSS) for locating and sizing water harvesting ponds in a hydrological model, which enables assessments of water harvesting intensification on upstream-downstream ecosystem services in meso-scale watersheds. The DSS was used with the Soil and Water Assessment Tool (SWAT) for a case-study area located in the Lake Tana basin, Ethiopia. We found that supplementary irrigation in combination with nutrient application increased simulated teff (Eragrostis tef, staple crop in Ethiopia) production up to three times, compared to the current practice. Moreover, after supplemental irrigation of teff, the excess water was used for dry season onion production of 7.66 t/ha (median). Water harvesting, therefore, can play an important role in increasing local- to regional-scale food security through increased and more stable food production and generation of extra income from the sale of cash crops. The annual total irrigation water consumption was ~4%-30% of the annual water yield from the entire watershed. In general, water harvesting resulted in a reduction in peak flows and an increase in low flows. Water harvesting substantially reduced sediment yield leaving the watershed. The beneficiaries of water harvesting ponds may benefit from increases in agricultural production. The downstream social-ecological systems may benefit from reduced food prices, reduced flooding damages, and reduced sediment influxes, as well as enhancements in low flows and water quality. The benefits of water harvesting warrant economic feasibility studies and detailed analyses of its ecological impacts., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Climate change is likely to have severe effects on water availability in Ethiopia. The aim of the present study was to assess the impact of climate change on the Gilgel Abay River, Upper Blue Nile Basin. The Statistical Downscaling Tool (SDSM) was used to downscale the HadCM3 (Hadley centre Climate Model 3) Global Circulation Model (GCM) scenario data into finer scale resolution. The Soil and Water Assessment Tool (SWAT) was set up, calibrated, and validated. SDSM downscaled climate outputs were used as an input to the SWAT model. The climate projection analysis was done by dividing the period 2010-2100 into three time windows with each 30 years of data. The period 1990-2001 was taken as the baseline period against which comparison was made. Results showed that annual mean precipitation may decrease in the first 30-year period but increase in the following two 30-year periods. The decrease in mean monthly precipitation may be as much as about -30% during 2010-2040 but the increase may be more than +30% in 2070-2100. The impact of climate change may cause a decrease in mean monthly flow volume between -40% to -50% during 2010-2040 but may increase by more than the double during 2070-2100. Climate change appears to have negligible effect on low flow conditions of the river. Seasonal mean flow volume, however, may increase by more than the double and +30% to +40% for the Belg (small rainy season) and Kiremit (main rainy season) periods, respectively. Overall, it appears that climate change will result in an annual increase in flow volume for the Gilgel Abay River. The increase in flow is likely to have considerable importance for local small scale irrigation activities. Moreover, it will help harnessing a significant amount of water for ongoing dam projects in the Gilgel Abay River Basin.