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The Groundwater Ubiquity Score (GUS) is widely used to indicate the relative leachability of pesticides based on the soil half-life and the adsorption partition coefficient. In this manuscript, we derive mathematically the Theoretical Groundwater Ubiquity Score (TGUS) that, based on considerations of the preferential movement of pesticides to groundwater and a first-order pesticide degradation model, leads to a similar function as the GUS model. In the preferential flow model, movement to groundwater is fast, and the adsorption partition coefficient is thus not used for calculating the travel time to the groundwater (as it is in the advective-dispersive equation) but rather only determines the distribution of the pesticide between the water and soil phases. Both the GUS and TGUS models well predict the groundwater contamination of the originally studied pesticides for rainfall event(s) that caused pesticide leaching from 30 days after application. The theoretically derived Groundwater Ubiquity Score (TGUS) shows, in accordance with experimental evidence, that for leaching events shortly after spraying, the mass lost to (and resulting concentration in) groundwater is inversely related to the adsorption partition coefficient and not necessarily to the GUS index. [ABSTRACT FROM AUTHOR]

Finding effective ecosystem services (ESS) management practices to counteract land degradation and poverty is becoming increasingly urgent in the Ethiopian highlands, where livelihood security is strongly dependent on local ESS, particularly those provided by water and soil. In this paper, we test the effects of widely implemented soil and water conservation (SWC) interventions on storm flow and sediment concentration in the Debre Mawi watershed (representative of watersheds in the upper Blue Nile basin and Ethiopian highlands). The SWC interventions were tested with a Parameter Efficient Distributed (PED) model. The PED model simulates saturation excess runoff from degraded and saturated valley bottoms, and base and interflow from hillsides. The model was calibrated with observed runoff and sediment data in a 95-ha subcatchment. We found that the PED model simulated the discharge and soil loss well by decreasing the proportion of degraded lands due to installing SWC practices. The results show that four years after the implementation of SWC practices, the infiltration of rainwater was improved in 53% of the degraded lands. Thus, installing SWC practices on hillsides where infiltration is limited is most beneficial and will result in greater water availability during the dry phase, especially in locations where volcanic dikes block the lateral flow. [ABSTRACT FROM AUTHOR]

Global food production faces challenges in balancing the need for increased yields with environmental sustainability. This study presents a six-year field experiment in the North China Plain, demonstrating the benefits of diversifying traditional cereal monoculture (wheat–maize) with cash crops (sweet potato) and legumes (peanut and soybean). The diversified rotations increase equivalent yield by up to 38%, reduce N2O emissions by 39%, and improve the system's greenhouse gas balance by 88%. Furthermore, including legumes in crop rotations stimulates soil microbial activities, increases soil organic carbon stocks by 8%, and enhances soil health (indexed with the selected soil physiochemical and biological properties) by 45%. The large-scale adoption of diversified cropping systems in the North China Plain could increase cereal production by 32% when wheat–maize follows alternative crops in rotation and farmer income by 20% while benefiting the environment. This study provides an example of sustainable food production practices, emphasizing the significance of crop diversification for long-term agricultural resilience and soil health. Food production systems need to balance yield and sustainability. Here, the authors conduct 6 years long crop diversification field experiments in the North China Plain, showing that diversifying cereal monocultures with cash crops and legumes cand improve yield and reduce GHG emissions. [ABSTRACT FROM AUTHOR]

The absence of a basin-wide apportionment agreement on using the Nile River equitably has been a long-standing source of disagreement among Nile riparian states. This study introduces a new approach that the riparian states can consider that quantifies the Nile River's apportionment. The approach includes (1) developing a basin-wide database of indicators representative of the United Nations Watercourse Convention (UNWC) relevant factors and circumstances, (2) developing an ensemble of indicator weighting scenarios using various weighting methods, and (3) developing six water-sharing methods to obtain a range of apportionments for Egypt, Sudan, Ethiopia and the group of the White Nile Equatorial States for each weighting scenarios. The results illustrate a relatively narrow range of country-level water apportionments, even though some individual factor weights vary from 3% to 26%. Considering the entire Nile River, the water apportionment for Ethiopia ranges from 32% to 38%, Sudan and South Sudan from 25% to 33%, Egypt from 26% to 35%, and the Equatorial States from 5% to 7%. We trust that the six proposed equitable water-sharing methods may aid in fostering basin-wide negotiations toward a mutual agreement and address the dispute over water sharing. [ABSTRACT FROM AUTHOR]

The highlands serve as water towers for the blue water in the surrounding area, with often insufficient rainfall for rainfed crops. The population is growing in the highlands, changing the hydrology and blue and green water availability. One of the changes that affect the highlands of Ethiopia is the rapidly expanding areas of small patches of eucalyptus on farmers fields. This manuscript aims to sort through the limited available literature and develop a water balance model as a starting point to discuss how hydrology is affected by increased acreage of eucalyptus in the highlands. We find some evidence in the literature that patches of eucalyptus during the dry phase may withdraw water from the subsoil up to twice the rate of evapotranspiration when the soil water is not limited. Since saturation excess generates surface runoff in the subhumid and humid highlands, water withdrawn during the dry phase should be made up before the area with eucalyptus becomes hydraulically active. The amount of water that can be removed from storage by eucalyptus is greater in areas with a long dry monsoon phase than in temperate climates for the same increase in trees. We also found, as expected, that the eucalyptus water balance model, as developed in this paper, was not valid for areas in semi-arid and arid regions. Soil crusting and water repellency might induce infiltration excess runoff. A tentative implication is that since most blue water is produced in the areas with the highest rainfall, eucalyptus in subhumid and humid monsoon regions will affect the blue water supply downstream but not the plant available green water although shading will decrease yield in the immediate surroundings of the eucalyptus trees. [ABSTRACT FROM AUTHOR]

Excess sediment and nutrient losses from intensifying agriculture degrade water quality and boost plant growth. The relationship between circulation patterns, spatial water quality degradation, and water hyacinth infestation is not adequately studied. The objective of this study is, therefore, to investigate the effect of lake circulation patterns on sediment and nutrient distribution and its implication on the spread of water hyacinth in a tropical lake. This study was carried out in Lake Tana, the largest freshwater lake in Ethiopia, where sediment and nutrient concentrations are increasing, and water hyacinths have become a challenge since 2011. The lake circulation pattern was simulated by the Delft3D model based on a bathymetry survey, discharge, and meteorological forcings. To predict the transport path of sediments and dissolved nutrients, an inert tracer was released in the four main river inlets of the lake. Observed lake water level measurements were used to validate the model. Our results show that the lake circulation pattern could explain the transport path of sediment and nutrients and the location of the water hyacinths found in the northeast of the lake. Sediments and nutrients from the largest river, Gilgel Abay, in the southeast of Lake Tana, flow through the two outlets nearby with little sediment deposition due to the relatively short retention time. The phosphorus-rich sediments of the 24 h at 105 °C remaining three main rivers joining the lake at the north and east are transported to the northeast. Thus, the management and control of water hyacinths should focus on the northern and eastern catchment areas of Lake Tana. [ABSTRACT FROM AUTHOR]

Nitrate is globally the most widespread and widely studied groundwater contaminant. However, few studies have been conducted in sub-Saharan Africa, where the leaching potential is enhanced during the rainy monsoon phase. The few monitoring studies found concentrations over drinking water standards of 10 mg N-NO3− L−1 in the groundwater, the primary water supply in rural communities. Studies on nitrate movement are limited to the volcanic Ethiopian highlands. Therefore, this study aimed to evaluate the transport and fate of nitrate in groundwater and identify processes that control the concentrations. Water table height, nitrate, chloride, ammonium, reduced iron, and three other groundwater constituents were determined monthly in the groundwater in over 30 wells in two contrasting volcanic watersheds over two years in the Ethiopian highlands. The first watershed was Dangishta, with lava intrusion dikes that blocked the subsurface flow in the valley bottom. The water table remained within 3 m of the surface. The second watershed without volcanic barriers was Robit Bata. The water table dropped rapidly within three months of the end of the rain phase and disappeared except near faults. The average nitrate concentration in both watersheds was between 4 and 5 mg N-NO3− L−1. Hydrogeology influenced the transport and fate of nitrogen. In Dangishta, water was blocked by volcanic lava intrusion dikes, and residence time in the aquifer was larger than in Robit Bata. Consequently, nitrate remained high (in several wells, 10 mg N-NO3− L−1) and decreased slowly due to denitrification. In Robit Bata, the water residence time was lower, and peak concentrations were only observed in the month after fertilizer application; otherwise, it was near an average of 4 mg N-NO3− L−1. Nitrate concentrations were predicted using a multiple linear regression model. Hydrology explained the nitrate concentrations in Robit Bata. In Dangishta, biogeochemistry was also significant. [ABSTRACT FROM AUTHOR]

Engineered carbon‐based nanoparticles are increasingly used for environmental, industrial, and medical purposes. Thus, understanding their interaction with and transport through materials is important. We examine the impact of nanoparticle hydrophobicity and porous medium surface area on the transport of carbon nanoparticles through sand‐packed columns under saturated and unsaturated conditions. The fluorescent carbon nanoparticles (FCNs) used in this study, synthesized from citric acid and ethanolamine, exhibit synthesis‐temperature‐dependent hydrophobicity. To quantify the impact of hydrophobicity on retention, we use FCNs synthesized at four temperatures: 190°C (FCN190), 210°C (FCN210), 230°C (FCN230), and 250°C (FCN250). Several observations are noted. First, the more hydrophobic particles (FCN230 and FCN250) attain lower outlet concentrations and mass recovery than more hydrophilic particles (FCN190 and FCN210). For instance, while 77% of the FCN190 was recovered after passing through a fine‐sand‐packed column, only 23% of the FCN250 was recovered. Second, sand surface area significantly impacts FCN recovery. A 17‐fold increase in sand surface area yields a 30% decrease in the recovery of FCN210. Third, no significant difference in the mass recovery of the FCNs was observed between the unsaturated and saturated conditions, which is attributed to the small size of the FCNs relative to the water film thickness surrounding sand grains. Fourth, the particle transport model in HYDRUS‐1D successfully simulated FCN transport, showing approximately a tenfold increase in the attachment coefficient for hydrophobic FCNs. In summary, through experiments and modeling, we show that hydrophobicity is a major factor impacting FCN transport. Key Points: The synthesis‐temperature‐dependent hydrophobicity reduces the transport of fluorescent carbon nanoparticles through sand‐packed columnsA two‐kinetic sites transport model describes the transport of fluorescent carbon nanoparticles in porous mediaFluorescent carbon nanoparticles are not trapped in the meniscus under unsaturated conditions at the tested moisture contents [ABSTRACT FROM AUTHOR]

This study employed geomorphometric analysis to characterize the four major watersheds (Gilgel Abay, Gumara, Rib, and Megech) of Lake Tana sub-basin, Ethiopia, and prioritize the watersheds for the implementation of SWC practices using GIS and remote sensing techniques. Also, the study analyzed streamflow and sediment data recorded at the outlets of each watershed to associate the geomorphometric prioritization result with recordings of the watersheds. Geomorphometric analysis results indicated that the Rib watershed is the most susceptible watershed for soil erosion and should be prioritized for the implementation of SWC practices. The analysis of streamflow and suspended sediment concentration suggest that the Rib watershed had the second maximum sediment yield (14.3 t ha−1 yr−1) compared to the other three watersheds. This is because of the low streamflow response of the watershed compared with the Gumara watershed which had the highest sediment yield (18.9 t ha−1 yr−1). [ABSTRACT FROM AUTHOR]

Agricultural intensification in sub-Saharan African countries has significantly increased pesticide applications. Information on pesticide residues and their transport in groundwater and streams is needed to properly manage and reduce any harm to the ecosystem and environment. This information is lacking in the volcanic soils of Ethiopian highlands. Therefore, this study was conducted to assess pesticide concentrations in ground and surface water and their risk to humans and aquatic life. The 9 km2 rural watershed Robit Bata in the Lake Tana Basin was selected. Crops were grown under rainfed and irrigated conditions. Pesticide use was assessed, and groundwater samples were collected from eight wells and surface water samples at the outlet twice in the rain phase and once in the dry phase. Samples were analyzed for chlorpyrifos, dimethoate, (α and β) endosulfan, profenofos, NO 3 − , and pH. Chlorpyrifos and endosulfan, which are strongly adsorbed and slowly degrading pesticides, were found in nearly all surface and groundwater samples, with maximum concentrations in surface water of 8 µg L−1 for chlorpyrifos and 3 µg L−1 endosulfan. Maximum groundwater concentrations were only slightly lower. The weakly adsorbed and fast degrading pesticides, dimethoate, and profenofos were detected only in the rain phase after spraying in the groundwater, indicating preferential transport to groundwater at depths of up to 9 m. The average concentration was 0.38 μg L−1 for dimethoate in surface waters and 1.24 μg L−1 in groundwater. Profenofos was not detected in surface water. In the groundwater, the average concentration was 0.05 μg L−1. Surface water concentrations of chlorpyrifos and endosulfan were highly toxic to fish. The World Health Organization banned these pesticides worldwide. It should be phased out for use in Ethiopia to safeguard the ecological health of Lake Tana, which is rich in biodiversity and endemic fish species. [ABSTRACT FROM AUTHOR]

With the increasing consumer awareness and knowledge about safe and healthy food, it is imperative to develop 'green' crops with reduced fertilizer application for quality food production, environmental protection and sustainable agricultural development. This study systematically evaluated and compared the water footprint (WF) including WFblue, WFgreen and WFgrey of eight crops including wheat, maize, rice, sweet potato, soybean, millet, mung bean and sorghum under green and traditional cultivation in the Huang-Huai-Hai farming region. The data came from 252 onsite questionnaires conducted in 2018 for land under green and traditional cultivation by 19 green planting companies and farming cooperatives with green food production certification authorized by the government of China. The results revealed that, compared to traditional cultivation, green cultivation under reduced N fertilizer application (1) decreased crop yields by 3–13%; (2) reduced the average WFtotal by 29% to 1168 m3 t−1 and average WFgrey by 57% to 419 m3 t−1 with no significant differences in WFblue and WFgreen; (3) decreased the WFtotal of maize by 55%, rice by 41%, wheat by 27%, mung bean by 31%, sorghum by 24%, sweet potato by 19%, millet by 17% and soybean by 17%. The WFgrey proportion of WFtotal under green cultivation ranged from 27–57% and contributed the most to the decline in WFtotal. This study offers insight into the impact of green cultivation on water requirements and pollution relative to traditional cultivation. Precision N fertilizer application and improved N use efficiencies on-farm are important pathways to sustainable agricultural development. [ABSTRACT FROM AUTHOR]

Phosphonate‐based herbicides are extensively used in agriculture. Glyphosate was long considered immobile in soils due to strong complexation with metal oxides, but detection in agricultural effluents and surface waters points to glyphosate mobilization and transport. In particular, mechanisms of glyphosate adsorption and subsequent mobility from runoff‐prone soils enriched in quartz have not been fully elucidated. Here we used theoretical and experimental approaches to gain new insights on the soil mobility of glyphosate and two other phosphonate herbicides, glufosinate and fosamine. Molecular modeling simulations of optimized adsorbate complexes of the phosphonate herbicides with quartz and montmorillonite revealed Ca‐enhanced interactions for all three herbicides at both mineral interfaces, weak binding of Na‐complexed phosphonate herbicides on quartz, and more favorable interactions for glufosinate and fosamine with Na‐montmorillonite than for glyphosate. We conducted adsorption and desorption experiments to evaluate the mobility of glyphosate on quartz‐enriched agricultural soils. Consistent with our theoretical findings, adsorption experiments conducted with CaCl2 resulted in greater than a twofold increase in glyphosate retention compared with experiments with NaCl. The desorption experiments revealed release of about 30–90% of the initially bound glyphosate into solution, whereby Ca in the desorption solution promoted glyphosate mobility compared with Na. Furthermore, in all conditions, the relative initial wetness of the agricultural soil was correlated positively with the enhanced glyphosate mobilization, consistent with field‐scale reports that herbicide applied to soils following rain events were prone to runoff. Core Ideas: ■Herbicide adsorption mechanisms on minerals depends on compound chemical structures.■Only diffuse layer suspension occurs with a lack of surface adsorption on Na‐quartz.■Glufosinate and fosamine have stronger binding than glyphosate on Na‐montmorillonite.■Ca‐complexed herbicides have enhanced adsorption on both montmorillonite and quartz.■Experimental data with quartz‐enriched agricultural soils are consistent with simulation results. [ABSTRACT FROM AUTHOR]

The importance of soils to society has gained increasing recognition over the past decade, with the potential to contribute to most of the United Nations' Sustainable Development Goals (SDGs). With unprecedented and growing demands for food, water and energy, there is an urgent need for a global effort to address the challenges of climate change and land degradation, whilst protecting soil as a natural resource. In this paper, we identify the contribution of soil science over the past decade to addressing gaps in our knowledge regarding major environmental challenges: climate change, food security, water security, urban development, and ecosystem functioning and biodiversity. Continuing to address knowledge gaps in soil science is essential for the achievement of the SDGs. However, with limited time and budget, it is also pertinent to identify effective methods of working that ensure the research carried out leads to real‐world impact. Here, we suggest three strategies for the next decade of soil science, comprising a greater implementation of research into policy, interdisciplinary partnerships to evaluate function trade‐offs and synergies between soils and other environmental domains, and integrating monitoring and modelling methods to ensure soil‐based policies can withstand the uncertainties of the future. Highlights: We highlight the contributions of soil science to five major environmental challenges since 2010.Researchers have contributed to recommendation reports, but work is rarely translated into policy.Interdisciplinary work should assess trade‐offs and synergies between soils and other domains.Integrating monitoring and modelling is key for robust and sustainable soils‐based policymaking. [ABSTRACT FROM AUTHOR]

Earth's water resources are critical for supporting livelihoods and food security but are being increasingly overexploited to support global agriculture. Diversifying cropping systems could potentially resolve unsustainable water use but trade‐offs with other aspects of sustainability and food security have not yet been assessed. We performed a detailed analysis of 31 different field crop rotations conducted during 1990–2019 in the North China Plain, to assess the potential impact of crop diversification on actual evapotranspiration (ETa), changes in regional groundwater table, grain yield, economic output, and water use efficiency (WUE) and to identify configurations that can achieve co‐benefits across multiple dimensions. We found that a combination of lowering the cropping index (i.e., harvest frequency), incorporating fallow periods, and introducing higher‐value crops into the currently dominant winter wheat–summer maize double cropping system can reduce growing season ETa by as much as 31%, mitigate groundwater decline by 19% or more, and increased economic output and economic WUE by more than 11% and 3%, respectively. We also found that multiple diversified wheat‐maize–based rotations—all with rotation lengths greater than 2 years—achieve co‐benefits across all evaluated dimensions. This study provides new empirical evidence of the opportunities for diversified crop rotations to balance the multiple objectives of food production, sustainable groundwater use, and farmer profitability. Extending this solution to other water‐stressed agricultural regions could be an effective strategy in achieving more sustainable food production system globally. [ABSTRACT FROM AUTHOR]

Agricultural production in the North China Plain with rainfall of less than 500 mm$yr-1 has been steadily increasing over the past 40 years, with the groundwater levels decreasing at a rate of over 1 m$yr-1. In this paper, it is demonstrated theoretically that the water level in the aquifer can be expressed as a function of agricultural production and the sum of water added as rainfall and imported from outside the basin. Therefore, the most effective measures to halt groundwater depletion are importing water, decreasing cropping intensity and growing less thirsty crops. Irrigation improvements, mulching and agronomic measures that could increase the yield per unit area have less of an impact on solving the declining groundwater levels. [ABSTRACT FROM AUTHOR]

Evapotranspiration (ET) is the major component of the hydrology cycle. Satellites provide a convenient way for gathering information to estimate regional ET. The most widely applied method for converting the instantaneous satellite measurement to daily scale assumes that evaporative fraction (EF), defined as the ratio of ET to the available energy, is constant during the daytime. However, this method was proved to underestimate the daily ET. This study implemented a theoretically improved EF algorithm to calculate daily ET with the decoupling factor method based on the Penman‐Monteith and McNaughton‐Jarvis equations. Seven improved algorithms were developed by assuming that various parameters remain constant during the day. The satellite‐based ET estimates were compared with seven local flux tower measurements in China. The results showed that: (a) The original ET method calculated the daily evaporation more accurately than the other algorithms. However, the good fit was based on two compensating inaccuracies. Compared to the flux tower measurement, the original ET method underestimated the daily EF by 26% and overestimated the daily net radiation by 30%. (b) Six of the seven proposed algorithms underpredicted the daily ET by 30%–60%, mainly due to the inaccurate daily net radiation. (c) The algorithm that assumed that the instantaneous decoupling parameter Ω∗ was equal to its daily value method calculated EF and ET with relative errors of 8% and 10% separately when the inaccurate estimated daily net radiation was replaced by the observed flux tower data. Plain Language Summary: The water that evaporates from the land surface sustains the hydrological cycle that replenishes the world's freshwater resources. Scientists and water managers are therefore interested in quantifying the water that evaporates each day. It is especially true for China that has one of the lowest water reserves in the world. Satellites that provide coverage of all the land surface would be ideal for recording evaporation if we could scale up the instantaneous satellite measurements to a daily scale. The current scale‐up methods available have not been widely tested. In this manuscript, we test the available methods and show how they can be improved for China. Key Points: This article improved satellite‐based daily evapotranspiration calculations for ChinaA decoupling parameter method was used in the daily evaporation fraction algorithm [ABSTRACT FROM AUTHOR]

Accelerated sediment concentration has become a pervasive feature in developing countries and has substantially impacted lake ecosystem functioning. Despite this, very few comprehensive studies have examined the changes in sedimentation over the time that agriculture intensified greatly with the increasing population. This study aims to fill this gap using historical and recent bathymetric surveys to determine sediment deposition and link these to watershed development. With its unique ecology, Lake Tana that was pristine less than 100 years ago, is one of these systems experiencing increasing sediment concentrations. A detailed bathymetric survey was conducted in late 2017 and compared with bathymetric surveys conducted in 1940, 1987, and 2006. The result shows that in the past 77 years, Lake Tana's depth decreased an average of 28 ± 11 cm, equivalent to nearly 0.9 ± 0.4 Tg (million tons). Sediment deposition was 2.8 ± 2.3 mm a−1 between 1940 and 1987, when the agricultural intensification started. It almost doubled to 5.0 ± 3.7 mm a−1 after that. Spatially, the sediment deposition was most significant in areas near the major river inlets where 2 to 10 km long peninsulas were formed. The increase in sediment deposition is primarily driven by newly formed valley bottom gullies formed after deforestation disturbed the hydrological equilibrium, and watershed outflow increased. [ABSTRACT FROM AUTHOR]

Effective watershed planning requires an understanding of the hydrology. In the humid tropical monsoon climates and especially in volcanic highland regions such as the Ethiopian Highlands, the understanding of watershed processes is incomplete. The objective is to better understand the hydrology of the volcanic regions in the humid highlands by linking the hillslope processes with the discharge at the outlet. The Ene-Chilala watershed was selected for this study. The infiltration rate, piezometric water levels and discharge from two nested sub watersheds and at the watershed outlet were measured during a four-year period. Infiltration rates on the hillsides exceeded the rainfall intensity most of the time. The excess rain recharged a perched hillside aquifer. Water flowed through the perched aquifer as interflow to rivers and outlet. In addition, saturation excess overland flow was generated in the valley bottoms. Perched water tables heights were predicted by summing up the recharge over the travel time from the watershed divide. Travel times ranged from a few days for piezometers close to the divide to 40 days near the outlet. River discharge was simulated by adding the interflow from the upland to overland flow from the saturated valley bottom lands. Overland flow accounted only for one-fourth of the total flow. There was good agreement between predicted and observed discharge during the rain phase therefore the hillslope hydrologically processes were successfully linked with the discharge at the outlet. [ABSTRACT FROM AUTHOR]

Land degradation in developing countries is exacerbating hardpan development that causes the formation of perched watertable, which in turn results in increased runoff and erosion. To reduce overland flow and erosion, percolation through the hardpan needs to be improved. One successful way to achieve this is ripping off the hardpan and plausibly liming. However, in the highlands of Ethiopia, there is little information available on these two techniques. The objectives of this study were, therefore, to determine the effects of ripping off degraded soils on runoff and erosion rates and whether liming would improve the effectiveness of ripping. A field study was conducted in the Anjeni watershed. Thirty‐two experimental runoff plots were installed across the watershed. Conventional tillage at 15 cm depth and ripping to 30, 45, and 60 cm depths were applied with and without lime amendments. Results showed that ripping to 60 cm depth resulted in a significant reduction of runoff. However, liming increased runoff response, on average by 10%. In contrast to the reduction in runoff amounts, an increase in ripping depth increased the amount of soil loss especially during the first storms at the beginning of the monsoon rainy season. Liming significantly decreased soil loss by up to 35%. Although plots with deep ripping plus liming had greater runoff production than other plots, soil loss was less. Overall, the findings suggest that deep ripping has promise but more research is needed before widely implemented. [ABSTRACT FROM AUTHOR]

Given the critical role of water in rural development, it is essential to quantify water use by various sectors. Reportedly, a significant water loss during the dry monsoon phase is by Eucalyptus trees in the Ethiopian highlands but few quantitative studies have been carried out. In our study in the Fogera plain near Lake Tana, consumptive water use of a small Eucalyptus patch was calculated from the fluctuating diurnal water table observations for two dry monsoon phases. During the dry monsoon phase in 2014, the groundwater table declined linearly at a rate of 2.6 cm d−1 and in 2015 the decline was 2.5 cm d−1. Daily fluctuations in groundwater were around 20 cm. Translating changing groundwater levels in precise evapotranspiration rates was cumbersome because of uncertainty in the value of drainable porosity. We concluded that the evapotranspiration over the small Eucalyptus patch was at a minimum 3.4 mm d−1 but more likely around 10 mm d−1 at the end of the dry phase. The 10 mm d−1 is twice the reference evaporation rate. This is in accordance with advection aridity approach where the actual evaporation of isolated patches with access to groundwater in dry environments can evaporate at twice the reference rate. The current and future extent of Eucalyptus patches and forests need, therefore, be considered in the management of the groundwater resource. [ABSTRACT FROM AUTHOR]

Feeding 9 billion people in 2050 will require sustainable development of all water resources, both surface and subsurface. Yet, little is known about the irrigation potential of hillside shallow aquifers in many highland settings in sub‐Saharan Africa that are being considered for providing irrigation water during the dry monsoon phase for smallholder farmers. Information on the shallow groundwater being available in space and time on sloping lands might aid in increasing food production in the dry monsoon phase. Therefore, the research objective of this work is to estimate potential groundwater storage as a potential source of irrigation water for hillside aquifers where lateral subsurface flow is dominant. The research was carried out in the Robit Bata experimental watershed in the Lake Tana basin which is typical of many undulating watersheds in the Ethiopian highlands. Farmers have excavated more than 300 hand dug wells for irrigation. We used 42 of these wells to monitor water table fluctuation from April 16, 2014 to December 2015. Precipitation and runoff data were recorded for the same period. The temporal groundwater storage was estimated using two methods: one based on the water balance with rainfall as input and baseflow and evaporative losses leaving the watershed as outputs; the second based on the observed rise and fall of water levels in wells. We found that maximum groundwater storage was at the end of the rain phase in September after which it decreased linearly until the middle of December due to short groundwater retention times. In the remaining part of the dry season period, only wells located close to faults contained water. Thus, without additional water sources, sloping lands can only be used for significant irrigation inputs during the first 3 months out of the 8 months long dry season. [ABSTRACT FROM AUTHOR]

Gullies that are expanding at alarming rate are responsible for the majority of soil losses in the (sub) humid highlands of Ethiopia. Few affordable and effective methods for gully erosion control are available in the highlands. The objective of the study was to develop cost-effective measures to halt gully expansion by determining stable-bank conditions under a variety of environmental situations using the Bank Stability and Toe Erosion Model (BSTEM). The study was carried out in the sub humid Debre Mawi watershed, located 30 km south of Lake Tana. Input data for the BSTEM model were collected using field surveys and soil sampling. After the BSTEM was tested on actual measured soil data, soil cohesion and internal friction angle were calibrated against observed gully bank retreat. Using the calibrated parameters, the model evaluated the stabilization of the existing gully bank under different scenarios in which groundwater table, bank angle and bank height, tension crack depth, vegetation, and toe protection were varied. Finally, the head-cut of the study gully was treated based on the model recommendation. The simulated results showed that a 5 m deep gully was stable under fully saturated conditions when the bank toe is protected, its upper surface is vegetated, and its bank angles do not exceed 45°. If the depth of the gully is less than 5 m or if its water table is deeper than 0.5 m, only regrading the gully bank to an angle of 45° can stabilize the gully. BSTEM showed to be an effective tool that can be used to evaluate gully control measures. [ABSTRACT FROM AUTHOR]

While hydrological science has made great strides forward during the last 50 years with the advance of computing power and availability of satellite images, much is unknown about the sustainable development of water for irrigation, domestic use, and livestock consumption for millions of households in the developing world. Specifically, quantification of shallow underground water resources for irrigation in highland regions remains challenging. The objective is to better understand the hydrology of highland watersheds with sloping hillside aquifers. Therefore, we present a subsurface flow model for hillside aquifers with recharge that varied from day to day. Recharge to the aquifer was estimated by the Thornthwaite Mather procedure. A characteristic time was identified for travel time of water flowing from the upper part of the hillside to the river or well. Using the method of characteristics, we found that the height of shallow groundwater level can be predicted by determining the total recharge over the characteristic time divided by drainable porosity. We apply the model to farmer‐dug wells in the Ethiopian highlands using observed rainfall, potential evaporation, and a fitted travel time. We find that the model performs well with maximum water table heights being determined by the soil surface and minimum heights by the presence or absence of volcanic dikes downhill. Our application shows that unless the water is ponded behind a natural or artificial barrier, hillslope aquifers are unable to provide a continuous source of water during the long, dry season. This clearly limits any irrigation development in the highlands from shallow sloping groundwater. Plain Language Summary: The population in the Ethiopian highlands, similar to other developing countries, is rapidly increasing. In order to have enough food during the year, most families grow their food crops during the rainy season. More food can be grown by irrigation during the dry season. We mathematically tested and observed data of eight wells as to whether shallow aquifers on the sloping lands can store sufficient water during the rainy season so it can be used for irrigation after the rains have stopped. We found that groundwater on sloping soils is only available during the whole year when volcanic‐derived subsurface barriers prevent flow downslope. Key Points: A novel parsimonious model was developed for shallow hillslope groundwater tablesShallow groundwater depth in wells can be predicted from the recharge and the drainable porosityHillslope aquifers cannot supply water for irrigation at end of the dry monsoon phase unless a downhill obstruction to flow is present [ABSTRACT FROM AUTHOR]

Sustainable development in degraded landscapes in the humid tropics requires effective soil and water management practices. Coupled hydrological‐erosion models have been used to understand and predict the underlying processes at watershed scale and the effect of human interventions. One prominent tool is the parameter‐efficient distributed (PED) model, which improves on other models by considering a saturation‐excess runoff generation driving erosion and sediment transport in humid climates. This model has been widely applied at different scales for the humid monsoonal climate of the Ethiopian Highlands, with good success in estimating discharge and sediment concentrations. However, previous studies performed manual calibration of the involved parameters without reporting sensitivity analyses or assessing equifinality. The aim of this article is to provide a multiobjective global sensitivity analysis of the PED model using automatic random sampling implemented in the SAFE Toolbox. We find that relative parameter sensitivity depends greatly on the purpose of model application and the outcomes used for its evaluation. Five of the 13 PED model parameters are insensitive for improving model performance. Additionally, associating behavioural parameter values with a clear physical meaning provides slightly better results and helps interpretation. Lastly, good performance in one module does not translate directly into good performance in the other module. We interpret these results in terms of the represented hydrological and erosion processes and recommend field data to inform model calibration and validation, potentially improving land degradation understanding and prediction and supporting decision‐making for soil and water conservation strategies in degraded humid landscapes. [ABSTRACT FROM AUTHOR]

Abstract Soil degradation and associated soil erosion is a daunting socio-economic challenge for smallholder farmers that cause environmental harm in the developing regions of the world. This is especially true in the Ethiopian highlands where soil degradation and soil erosion significantly impact the productivity of land and water. In this study, GIS-based classic RUSLE model supported with multi-criteria evaluation (MCE) analysis was used to map erosion hotspot areas in the sub-humid Ethiopian highlands. RUSLE model results indicated that annual average soil loss in the study area reaches up to 288 t ha−1. In the majority (83%) of the study area predicted soil loss ranges between 0 and 40 t ha−1, whereas 13% of the study area has soil loss of 40–100 t ha−1 and the remaining 4% is in excess of 100 t ha−1. Seventy-two percent of upper Gilgel Abbay watershed was found moderately sensitive to erosion. The classic RUSLE predicted lower erosion rates mainly in the bottomlands because does not consider soil erosion by gullies. On the other hand, the MCE analysis integrated with field survey indicated that the potential location of gullies is the saturated bottomlands. The locations of bottomland gullies also coincided with important hydrologic parameters such as higher soil wetness and stream power index values. The implication is that in addition to RUSLE criteria such as gullies, topographic wetness index (TWI) and stream power index (SPI) should be considered in erosion risk mapping studies in the sub-humid Ethiopian highlands, where soil saturation plays an important role in the formation and expansion of gullies. [ABSTRACT FROM AUTHOR]

Core Ideas: A simple multiregion model predicts herbicide transport well using tracer data.A chloride tracer is used to characterize the preferential flow paths.A surface layer in the model distributes water and solutes to the preferential pathways. Simulation of preferential flow remains a challenge despite being a recognized phenomenon. With short‐interval data, we adapted and tested the preferential flow model (PFM) to simulate the vertical transport of herbicides to lower soil layers. The PFM divides the soil profile into a top distribution zone and a conveyance zone below. The distribution zone acts as a reservoir, with an exponential loss of solutes to the conveyance zone. In the conveyance zone, water and solutes move as convective–dispersive flow through multiple flow paths—preferential and matrix—to shallow groundwater. Our field experiment was performed on a structured Hudson silty clay loam soil (a fine, illitic, mesic Glossaquic Hapludalf) that exhibits preferential flow. The site was instrumented with a variety of soil water samplers placed at depths of 60 cm to monitor the volume and quality of the leachate. Agronomic application of atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] and 2,4‐D [2‐(2,4‐dichlorophenoxy)acetic acid] was used, followed by 75 cm of controlled and natural rainfall over 100 d. In addition, Cl− was applied as a conservative tracer. All samplers monitored during this period showed a fast breakthrough of solutes consistent with the occurrence of preferential flow, with two groups of breakthrough curves observed. By fitting the Cl− breakthrough curve for each group, PFM input parameters were estimated including water velocity in preferential flow paths and the fraction of water moving through each flow path. With two additional parameters for herbicide adsorption and degradation rates, the model successfully simulated the extent of preferential flow of herbicides. [ABSTRACT FROM AUTHOR]

Uncertainty in hydrological modeling is of significant concern due to its effects on prediction and subsequent application in watershed management. Similar to other distributed hydrological models, model uncertainty is an issue in applying the Soil and Water Assessment Tool (SWAT). Previous research has shown how SWAT predictions are affected by uncertainty in parameter estimation and input data resolution. Nevertheless, little information is available on how parameter uncertainty and output uncertainty are affected by input data of varying complexity. In this study, SWAT-Hillslope (SWAT-HS), a modified version of SWAT capable of predicting saturation-excess runoff, was applied to assess the effects of input data with varying degrees of complexity on parameter uncertainty and output uncertainty. Four digital elevation model (DEM) resolutions (1, 3, 10 and 30 m) were tested for their ability to predict streamflow and saturated areas. In a second analysis, three soil maps and three land use maps were used to build nine SWAT-HS setups from simple to complex (fewer to more soil types/land use classes), which were then compared to study the effect of input data complexity on model prediction/output uncertainty. The case study was the Town Brook watershed in the upper reaches of the West Branch Delaware River in the Catskill region, New York, USA. Results show that DEM resolution did not impact parameter uncertainty or affect the simulation of streamflow at the watershed outlet but significantly affected the spatial pattern of saturated areas, with 10m being the most appropriate grid size to use for our application. The comparison of nine model setups revealed that input data complexity did not affect parameter uncertainty. Model setups using intermediate soil/land use specifications were slightly better than the ones using simple information, while the most complex setup did not show any improvement from the intermediate ones. We conclude that improving input resolution and complexity may not necessarily improve model performance or reduce parameter and output uncertainty, but using multiple temporal and spatial observations can aid in finding the appropriate parameter sets and in reducing prediction/ output uncertainty. [ABSTRACT FROM AUTHOR]

Abstract: Soil erosion, with significant contributions from gullies, is a serious problem in the Ethiopian highlands. The objective of this paper is to examine patterns of discharge and sediment transport in the Ethiopian highlands, and to provide an initial assessment of whether soil and water conservation practices (SWCP) can reduce sediment loads in watersheds with actively eroding gullies. The study was conducted in the 414‐ha Ene‐Chilala watershed with a unimodal sub‐humid monsoon climate and actively eroding gullies in the valley bottoms. In 2013 and 2014, the local community was mandated to install upland infiltration furrows and farmers voluntarily rehabilitated six gully heads and protected 16 m of eroding stream banks. Discharge and sediment concentration were measured in two upslope watersheds and at the outlet. Since median infiltration capacity in the uplands was always greater than the rainfall intensity, saturation excess and interflow were main runoff pathways. After 175 mm cumulative rainfall, the groundwater table reached the surface in the valley bottoms, restricting infiltration, and runoff was generated as saturation excess overland flow and flowed through active gullies out of the watershed. Upland rill erosion on ploughed land early in the rain phase, and gully erosion in saturated valley bottoms thereafter, were sources of sediment in the rivers. The mandated infiltration furrows installed on the contour overtopped and damaged cropland. The off‐contour furrows increased streamflow. Gully rehabilitation of an upland gully effectively reduced stream sediment concentration in the upland weir. However, there was little benefit at the watershed outlet since the stream picked up the unconsolidated sediment from the failing banks in the downstream porting of the watershed. Therefore, soil conservation programs that in addition to installing upland practices, rehabilitate the main sediment source (gullies) appear to be the most effective approach to reducing in‐stream suspended sediment concentrations. © 2018 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Grasses and trees are often used to stabilize gully banks. However, the effectiveness of such biological conservation measures has not been investigated for the Ethiopian highlands. This study investigates the reinforcement that plant roots may provide to strengthen gully banks in Ethiopia. The root systems of 26 indigenous and exotic plant species of 3 plant life forms (grasses, shrubs, and trees) were sampled, and root tensile strength and distribution were determined. The RipRoot model was used to quantify the additional cohesion derived from the plant roots. Among all tested roots, Eleusine floccifolia (grass), Tephrosia vogelii (tree), and Rosa abyssinica (shrub) had the strongest roots for each life form. The root volumetric ratio (root volume divided by soil volume) in the top 0.6 m of soil ranged from 0.03% to 0.46%. Roots of Digitaria abyssinica provided the maximum added cohesion (10.6 kPa) over this depth. For a given plant species, root volumetric ratio had a greater effect on additional cohesion than root tensile strength. Plant species with a fibrous root system provided greater additional cohesion values in the top 0.6 m (on average 3.4 vs. 1.7 kPa for tap root systems) and could potentially enhance gully bank stability for shallow gullies more than plants having a tap root system. To effectively rehabilitate larger gullies, plants should be integrated with other gully rehabilitation measures, such as regrading of gully banks and structural measures such as check dams to trap sediments, thereby reducing the effective gully bank height relative to rooting depth. [ABSTRACT FROM AUTHOR]

The control of soil moisture, vegetation type, and prior land use on soil health parameters of perennial grass cropping systems on marginal lands is not well known. A fallow wetness-prone marginal site in New York (USA) was converted to perennial grass bioenergy feedstock production. Quadruplicate treatments were fallow control, reed canarygrass (Phalaris arundinaceae L. Bellevue) with nitrogen (N) fertilizer (75 kg N ha−1), switchgrass (Panicum virgatum L. Shawnee), and switchgrass with N fertilizer (75 kg N ha−1). Based on periodic soil water measurements, permanent sampling locations were assigned to various wetness groups. Surface (0-15 cm) soil organic carbon (SOC), active carbon, wet aggregate stability, pH, total nitrogen (TN), root biomass, and harvested aboveground biomass were measured annually (2011-2014). Multi-year decreases in SOC, wet aggregate stability, and pH followed plowing in 2011. For all years, wettest soils had the greatest SOC and active carbon, while driest soils had the greatest wet aggregate stability and lowest pH. In 2014, wettest soils had significantly (p < 0.0001) greater SOC and TN than drier soils, and fallow soils had 14 to 20% greater SOC than soils of reed canarygrass + N, switchgrass, and switchgrass + N. Crop type and N fertilization did not result in significant differences in SOC, active carbon, or wet aggregate stability. Cumulative 3-year aboveground biomass yields of driest switchgrass + N soils (18.8 Mg ha−1) were 121% greater than the three wettest switchgrass (no N) treatments. Overall, soil moisture status must be accounted for when assessing soil dynamics during feedstock establishment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Land use changes in many landscapes result in gully formation, carving up agricultural land and playing a large role in filling up downstream reservoirs by connecting uplands with rivers. This includes the Ethiopian highlands. Our objective is to begin investigating the interaction of upland and gully erosion and to quantify the portion of eroded sediment originating from a gully to prioritize erosion control practices. For this purpose, a 5‐m deep valley bottom gully of the 13‐ha catchment in the Debre Mawi watershed in the subhumid Ethiopian highland near Lake Tana was selected. The upstream and downstream gully discharge and sediment concentrations were measured over a 2‐year period. The results show that the sediment concentration at the outlet was about 10 times greater than at the inlet. The sediment budget calculation showed that about over 90% of the sediment at the outlet originated from within the gully. Hysteresis analysis of the sediment concentration discharge relationship showed that sediment supply from the upland was limited, but sediment was always available to be eroded and transported in the gully because of bank failures and headcut retreat. Thus, to reduce sediment loads in rivers and consequent adverse downstream impacts, designing cost‐effective measures to treat gullies should be a priority in the subhumid Ethiopian highlands. [ABSTRACT FROM AUTHOR]

Abstract: Predicting the impact of urbanization on the hydrology of peri‐urban catchments remains a challenge. Using data from nine streamflow gauges installed in a small Portuguese catchment, this study investigates the streamflow responses over a 3‐year period. The catchment comprises unique nested sub‐catchments, characterized by varying proportions of non‐urban land‐use (17–97%) and impermeable surfaces (6–36%), distances between the urban areas and the stream network and storm drainage systems (piped versus dispersed) and overlying distinct lithologies consisting of sandstone and limestone. The results show that in the peri‐urban catchment (39% urban and 22% impervious surfaces) most water infiltrated and annual storm runoff varied between 9% and 13% of rainfall. In urban sub‐catchments (≈50% urban), 29% of rainfall became storm runoff on sandstone and 17% on limestone. In sub‐catchments with more than 80% forest, storm runoff coefficients were averaged 6% independent of the lithology. Sub‐catchments with storm runoff drainage systems and downslope urban areas had shorter response times (<20 min) than dispersed urban sub‐catchments, in which part of the runoff infiltrated, and the response time was up to 1 h. Baseflow contributed between 25–33% upstream and 37–38% downstream of the sandstone total runoff, but was less than 5% in limestone areas independent of location. Hydrological impacts of urbanization may be minimized in planning through disconnecting the urban areas from the stream network, thereby enabling runoff from impervious areas to infiltrate into the soil in downstream forest patches before reaching the stream. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Worldwide, soil erosion has greatly decreased agricultural productivity and continues unabatedly despite decades of developing sustainability and soil conservation strategies. Current strategies need integrated interdisciplinary perspectives to develop more effective measures, especially in degrading mountainous landscapes where rising sediment concentrations persist. By comparing spatio‐temporal field observations and community perceptions with the Geographic Information System (GIS)‐based universal soil loss equation (USLE), this study critically examined theorized erosion patterns (by USLE) in a degraded landscape (Shanko Bahir, Ethiopia) to improve soil conservation strategy development. Daily hydro‐sedimentological data (showing 792 mm of rainfall leading to 3·2 Mg ha−1 y−1 of sediment yield) revealed mild but variable erosion patterns in 2012. Overlooking hydrology hindered the USLE's suitability for conservation planning. For instance, the median infiltration rate (33 mm h−1) was rarely exceeded (3·5% of events), meaning runoff‐induced erosion risk were not well predicted spatio‐temporally by the USLE R‐factor. Conversely, heterogeneous local perspectives explicitly considered accumulated runoff, saturation (“the water at the top level rests on the bottom”), fertility, and gullies as drivers of erosion (“black soil breaks and forms gorges”). Additionally, they designated steeper mono‐cropped lands as at risk (incidentally also highlighted by USLE). Observational evidence showed steeper midslope areas decreasing in topsoil depth by 14 mm, flatter downslope areas by 0·8 mm, and the mild upslope areas increasing 2 mm. Operationalizing effective soil conservation strategies will require expanding beyond (USLE‐based) technical knowledge to incorporate local stakeholders and consider the main hydrological processes causing erosion in sub‐humid mountainous landscapes: saturated pathways, downslope saturation, subsurface flow, and gully formation. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Uncertainty in hydrological and water quality modelling is of significant concern due to its effects on prediction and subsequent application in watershed management. Similar to other distributed hydrological models, model uncertainty is an issue in applying the Soil and Water Assessment Tool (SWAT). Previous research has shown how SWAT predictions are affected by uncertainty in parameter estimation and input data resolution. Nevertheless, little information is available on how parameter uncertainty and output uncertainty are affected by input data of varying complexity. In this study, SWAT-Hillslope (SWAT-HS), a modified version of SWAT capable of predicting saturation excess runoff was applied to assess the effects of input data with varying degrees of complexity on parameter uncertainty and output uncertainty. Four digital elevation model (DEM) resolutions (1, 3, 10 and 30 m) were tested for their ability to predict streamflow and saturated areas. In a second analysis, three soil maps and three land use maps were used to build nine SWAT-HS setups from simple to complex (fewer to more soil types/ land use classes), which were then compared to study the effect of input data complexity on model prediction/output uncertainty. The case study was the Town Brook watershed in the upper reaches of the West Branch Delaware River in the Catskill Region, New York, USA. Results show that DEM resolution did not impact parameter uncertainty or affect the simulation of streamflow at the watershed outlet but significantly affected the spatial pattern of saturated areas, with 10 m being the most appropriate grid size to use for our application. The comparison of nine model setups revealed that input data complexity did not affect parameter uncertainty. Model setups using intermediate soil/land use specifications were slightly better than the ones using simple information, while the most complex setup did not show any improvement from the intermediate ones. We conclude that increasing spatial input details may not necessarily improve model performance or reduce parameter and output uncertainty, but using multiple temporal and spatial observations can aid in finding the appropriate parameter sets and in reducing prediction/output uncertainty. [ABSTRACT FROM AUTHOR]

Purpose: 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. Materials and methods: 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. Results and discussion: 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 year and P yield of 9.2 kg ha year from Awrmaba. Furthermore, non-point source areas contributed to 2.7 kg ha year (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. Conclusions: 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. [ABSTRACT FROM AUTHOR]

Land use and management affects runoff and soil loss from a catchment. The present study investigated the effects of land use on runoff and suspended sediment concentration and yield in the northwestern Ethiopia. We selected two small catchments: cultivated land and grassland dominated catchments within the 95 ha Debre Mawi catchment. Hydrometric and sediment concentration data were collected for five years (i.e., 2010–2014). Significant ( p < 0.05) differences in daily, monthly and annual runoff, as well as suspended sediment concentrations were observed between cultivated land and grassland dominated catchments. The greater runoff, suspended sediment concentration and yield in the cultivated catchment could be attributed to repeated tillage and low soil organic matter. Repeated tillage in the cultivated land lead to soil disturbance and the low organic matter lead to aggregate instability, both of which consequently increase the detachment of soil particles and transport by generated runoff. Our results support that land management practices that involve lower soil disturbance and increase ground cover on degraded highland areas such as the Ethiopian highlands could help reduce runoff and soil loss. [ABSTRACT FROM AUTHOR]

Communities on islands with mass-tourism, like Santorini, rely on vast quantities of water to develop the local economy. Today's inhabitants of Santorini have largely abandoned the traditional cisterns that were used to sustain the island's pre-modern civilizations in favor of water obtained from desalinization, ship deliveries, and well withdrawals. In June 2016, Cornell University researchers worked with the Water and Sewage Authority of Thera (DEYATH) to assess the viability of improving sustainability and water efficiency by restoring traditional rainwater harvesting and storage cisterns. The team surveyed five cisterns, held meetings with water authority staff and mayoral leadership, conducted interviews with local tourism stakeholders, and coordinated with GlobalWater Partnership-Mediterranean. One conclusion was that cisterns could be rehabilitated as decentralized storage reservoirs and integrated into the island's centralized water systems, or alternatively, serve as educational and cultural spaces used to communicate the importance of water to residents and tourists. The research findings highlight how multi-stakeholder partnerships could assist local authorities with developing new water management initiatives to foster more sustainable models of tourism development. [ABSTRACT FROM AUTHOR]

Quantifying components of soil water balance in farmland of the middle reaches of Heihe River Basin is essential for efficiently scheduling and allocating limited water resources for irrigation in this arid region. A soil water balance model based on empirical assumptions in the vadose zone of farmland was developed and simulation results were compared/validated with results by the numerical model HYDRUS-1D. Results showed a good coherence between the simulated results of the water balance models and the HYDRUS-1D model in soil water storage, evapotranspiration, deep percolation and groundwater recharge, which indicated that the water balance model was suitable for simulating soil water movement in the study area. Considering the spatial distribution of cropping patterns, groundwater depth and agricultural management, ArcGIS was applied for the pre-/post-processing of the water balance model to quantify the spatial distribution of components of soil water balance in the major cropland in middle reaches of Heihe River Basin. Then, distributions of components of soil water balance in the major cropland under different water-saving irrigation practices during the growing season were predicted and discussed. Simulation results demonstrated that evapotranspiration of the main crops would be more prominently influenced by irrigation quota under deep groundwater depth than that under shallow groundwater depth. Groundwater recharge would increase with the increase of irrigation quota and decrease with the increase of groundwater depth. In general, when groundwater depth reached 3 m, groundwater recharge from root zone was negligible for spring wheat. While when it reached 6 m, groundwater recharge was negligible for maize. Water-saving irrigation practices would help to reduce groundwater recharge with a slight decrease of crop water consumption. [ABSTRACT FROM AUTHOR]

Hardpan is a major cause of land degradation that affects agricultural productivity in developing countries. However, relatively, little is known about the interaction of land degradation and hardpans. The objective of this study was, therefore, to investigate soil degradation and the formation of hardpans in crop/livestock-mixed rainfed agriculture systems and to assess how changes in soil properties are related to the conversion of land from forest to agriculture. Two watersheds (Anjeni and Debre Mewi) were selected in the humid Ethiopian highlands. For both watersheds, 0-45 cm soil penetration resistance (SPR, n = 180) and soil physical properties (particle size, soil organic matter, pH, base ions, cation exchange capacity, silica content, bulk density and moisture content) were determined at 15 cm depth increments for three land uses: cultivated, pasture and forest. SPR of agricultural fields was significantly greater than that of forest lands. Dense layers with a critical SPR threshold of ≥2000 kPa were observed in the cultivated and pasture lands starting at a depth of 15-30 cm but did not occur in the undisturbed forest land. Compared with the original forest soils, agricultural fields were lower in organic matter, cation exchange capacity, and exchangeable base cations; more acidic; had a higher bulk density and more fine particles (clay and silt); and contained less soluble silica. Overall, our findings suggest that soil physical and chemical properties in agricultural lands are deteriorated, causing disintegration of soil aggregates, resulting in greater sediment concentration in infiltration water that clogged up macro-pores, thereby disconnecting deep flow paths found in original forest soils. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In many parts of the world, watershed management practices have been extremely effective. However, implementation of soil and water conservation technologies in the humid African highlands, while beneficial in the short term, were remarkably unsuccessful in the long term. Insights from community knowledge perspectives have revealed that alternative methods are needed. Although conservation practices are designed to conserve water in semi-arid areas, safely draining excess water is needed in humid areas. The objective of this paper is to review current watershed management approaches used in humid regions as exemplified by those used in Ethiopian highlands and then based on these findings propose more effective practices. Although current government sponsored practices primarily protect the hillsides, direct run-off is generated from areas that become saturated on valley bottoms near rivers and on specific parts of the hillsides with degraded soils (or with highly permeable surface soils) and with perched water tables on slowly permeable horizons at shallow depths. In these areas, direct run-off is increasing with deforestation and the soil degradation, demanding additional drainage ways that evolve in the form of gullies. Therefore, watershed management interventions for erosion control should prioritize revegetation of degraded areas, increasing sustainable infiltration, and rehabilitating gullies situated at saturated bottomlands. [ABSTRACT FROM AUTHOR]

Landscape response to drivers of change is more visible and noticeable in deltas and floodplains than in upstream. Here, we address the changes of Lake Tana basin by investigating the delta development of Gumara River and sediment deposition in the Fogera floodplain over a 58-year period when agricultural land expanded, agriculture intensified, and flooding of the alluvial plain became more frequent. Old maps show that delta formation before the 1950s was minimal, indicating that the sediment contributed by the rivers to the lake was small. However, during the last 58 years, the delta has expanded continuously. When considering the same lake level (2·68 m) from 1984 to 2014, the delta has expanded an average of 5 ha annually, and by considering different lake levels and corresponding delta areas, the delta increased in height an average of 3 cm annually. While the growth of the delta was approximately linear, the sediment concentration in the river doubled in the last 30 years, indicating more efficient sediment trapping in the floodplain as a result of higher lake levels, rising river beds, and farmers intervening with the course of the river near the shore. Unless effective river restoration and catchment-based treatment measures are put in place, the capacity of the rivers will further reduce and aggravate the flooding of the floodplain, causing more sediment deposition in the river channel and on the floodplain. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Controlling soil erosion is important for maintaining land productivity and reducing sedimentation of reservoirs in the Ethiopian highlands. To gain insights on sediment loss patterns, magnitude of peak sediment events, and their contribution to annual loads, hydrometric and sediment concentration data were collected for five years (2010 - 2014) from the 95-ha Debre Mawi and four nested catchments (located 30 km south of Lake Tana). Soil and water conservation practices (SWCPs) consisting of soil bunds with 50-cm-deep furrows were implemented in the third year, which made it possible to examine the effects of SWCPs on peak sediment loads. The results show that a 10-min event causes soil loss of up to 11·4 Mg ha−1, which is 22% of the annual sediment yield. Thirty to seventy-five percent (up to 30 Mg ha−1day−1) of the sediment yield was contributed by the greatest daily flow in each year. The contribution increases to 86% for the two largest daily flows. SWCP interventions reduced sediment loss by half but did not affect the relative contribution of peak events to annual loads. Because of gully erosion, peak sediment loads at the outlet of the entire catchment were greater (up to 30 Mg ha−1day−1) as compared to the nested catchments without gullies (0·5 to 8 Mg ha−1day−1). Consequently, to reduce sediment loss, conservation measures should be designed to decrease runoff during large storms. This can be attained by deepening furrows on unsaturated hillsides and reducing the entrainment of unconsolidated sediment from failed gully banks. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Groundwater levels are declining at unsustainable levels in many areas of the world. To secure this resource for future generation, well-documented groundwater level observations are needed to derive recharge rates and sustainable withdrawal amounts. Although groundwater is routinely monitored in most of the world, relatively little information is available in sub-Saharan Africa including the Ethiopian highlands where groundwater irrigation could greatly increase food security. To obtain sustainable withdrawal rates for the wet Ethiopian highlands, we selected the Fogera plain in the Lake Tana basin with a sub-humid climate. Weekly groundwater levels were measured in 32 abandoned shallow wells over a 2-year period in 2014 and 2015. Our observations showed that in the 2 years, the groundwater level reached the surface during the rainy monsoon phase around first week of August. At the end of the dry monsoon phase in May, the average groundwater table was at 4 m depth. The amount of water removed by evaporation during the dry phase was 850 mm year−1. This is replenished through recharge during the wet phase. Rain in excess of the recharge and evaporation is stored on the surface or converted to overland flow. The groundwater flowed slowly towards the lake, but water passing the lakeshore was not a significant term in the water balance of the plain. Irrigation from groundwater seems to be sustainable especially when rivers flood periodically. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Long-term erosion monitoring data in the Ethiopian highlands are only available from the Soil Conservation Research Program (SCRP) watersheds including the Anjeni watershed. The 113 ha Anjeni watershed was established in 1984 and fanya juu terraces were installed in 1986. Runoff and erosion data are available from three different plot sizes and at the watershed outlet. The objective of this study was to investigate how erosion processes and sediment rating parameters vary with plot size and the progression of the rainy monsoon phase. We analyzed runoff and sediment loss data from 40 plots and the watershed outlet. The dataset included erosion data from 24 newly constructed plots (3 m length) during the rainy monsoon phase of 2012 and 2013, and 16 long-term plots (with 12, 16, 22, and 24% slopes and 3, 15 and 30 m lengths) and the watershed outlet during the period between 1986 to 1990. Sediment concentration ( C) was fitted to runoff ( Q) using a power regression equation ( C = aQ b). Sediment concentration and yield increased with increasing plot length from 3 m to 15 m, but sediment yield decreased as plot length increased to 30 m.The coefficients ( a and b) were affected by plot size and the progression of the rainy monsoon phase. As plot size increases, the a value increased, while the b value decreased. Greater a values were observed during the beginning of the monsoon phase, while values of b were greater towards the end of the monsoon phase. Overall findings suggest that erosion from cultivated fields is primarily controlled by transport limitations at the beginning of the monsoon phase, while towards the end of the monsoon phase, as surface covers emerge, sediment availability will be reduced, and thus sediment source would be a limitation. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the northern highlands of Ethiopia, gully erosion is severe. Despite many efforts to implement gully prevention measures, controlling gully erosion remains a challenge. The objective is to better understand the regional gully erosion processes and to prevent gully head retreat. The study was conducted in the Ene-Chilala catchment in the sub-humid headwaters of the Birr River located southwest of Bahir Dar, Ethiopia. Twelve gully heads were monitored during the 2014 and 2015 rainy monsoon phase. We measured gully head morphology and retreat length, soil shear strength, ground water table levels, and catchment physical characteristics. Two active gully head cuts were treated in 2014 and an additional three head cuts in 2015 by regrading their slope to 45° and covering them with stone riprap. These treatments halted the gully head advance. The untreated gullies were actively eroding due to groundwater at shallow depths. The largest head retreat was 22.5 m, of which about half occurred in August of the first year when the surrounding soil was fully saturated. Lowering both the water table and protecting the gully heads can play a key role in reducing gully expansion and soil loss due to gully erosion in the Ethiopian highlands. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]