Essayas K. Ayana

California Department of Water Resources

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 Dig...

Climate change and increasing demands are stressing water allocation. In many places, water reallocation and expensive water development actions are being undertaken with more likely to be stimulated by climate change. Here we examine reallocation and development actions between and within municipal, agricultural, and energy industry users in a wat...

This study is to establish a new approach to estimate river salinity of semi‐arid agricultural watershed and identify drivers by using hydrologic modeling and machine learning. We augmented the limitations of the Soil and Water Assessment Tool (SWAT) to model salinity by coupling with eXtreme Gradient Boosting (XGBoost), a decision‐tree‐based ensem...

Ethiopia has the largest livestock population in Africa with 35 million tropical livestock units. The livestock system relies on natural open grazing which is affected by frequent droughts. However, little research exists that studies the suitability of the biophysical environment for fodder production and the risks due to climate change. The main...

The spatial and temporal scale of rainfall datasets is crucial in modeling hydrological processes. Recently, open-access satellite precipitation products with improved resolution have evolved as a potential alternative to sparsely distributed ground-based observations, which sometimes fail to capture the spatial variability of rainfall. However, th...

The spatial and temporal scale of rainfall datasets is crucial in modeling hydrological processes. Recently, open-access satellite precipitation products with improved resolution have evolved as a potential alternative to sparsely distributed ground-based observations, which sometimes fail to capture the spatial variability of rainfall. However, th...

The largest freshwater lake in Ethiopia, Lake Tana, has faced ecological disaster due to water hyacinth (Eichhornia crassipes) infestation. The water hyacinth is a threat not only to the ecology but also to the socioeconomic development of the region and cultural value of the lake, which is registered as a UNESCO reserve. This study aims to map the...

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 instrumen...

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 us...

Comprehensive spatially referenced soil data are a crucial input in predicting biophysical and hydrological landscape processes. In most developing countries, these detailed soil data are not yet available. The objective of this study was, therefore, to evaluate the detail needed in soil resource inventories to predict the hydrologic response of wa...

Freshwater makes up only 2.5 percent of the world’s water. More than half is channeled to man-made uses (Uitto, 2001). Freshwater sources are experiencing declines in quality and biodiversity far greater than those in the most affected terrestrial ecosystems (Dudgeon et al., 2006). Considerable effort has been made to understand processes that dete...

Study region Upper Blue Nile, Ethiopia Study focus The recent availability of high-resolution soil data offers a better representation of spatially varying hydrologic parameters and could help in building accurate models. Despite the release of the AfSIS 250 m resolution soil data in 2015, its benefits in improving streamflow prediction accuracy i...

Sudan constitutes the largest land area of the Nile river basin. Despite the large landmass in the basin, the average annual rainfall contribution is very small (about 254mm). Agricultural water withdrawal constitutes 97% of the total water withdrawal in Sudan. Sudan has the largest area (about 9.5 million hectares) under cereal production in the N...

The authors wish to make the following correction to their paper [1]: The second author’s name should be changed from “Yihun Dile Taddele” to “Yihun Taddele Dile”[...]

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 wate...

The Upper Blue Nile basin is considered as the lifeline for ∼250 million people and contributes ∼50 Gm³/year of water to the Nile River. Poor land management practices in the Ethiopian highlands have caused a significant amount of soil erosion, thereby threatening the productivity of the Ethiopian agricultural system, degrading the health of the aq...

This study assessed the impact of climate change on water availability and variability in two subbasins in the upper Blue Nile basin of Ethiopia. Downscaled future climate data from HadCM3 of A2 (medium-high) and B2 (medium-low) emission scenarios were compared to the observed climate data for a baseline period (1961–1990). The emission scenario re...

Watershed responses are affected by the watershed characteristics and rainfall events. The characteristics of soil layers are among the fundamental characteristics of a watershed and they are input to hydrologic modeling similar to topography and land use/cover. Although the roles of soils have been perceived, there are limited studies that quantif...

This study assessed the impact of climate change on water availability and variability in two subbasins in the Upper Blue Nile Basin of Ethiopia. Downscaled future climate data from HadCM3 of A2 (medium-high) and B2 (medium-low) emission scenarios were compared to the observed climate data for a baseline period (1961 to 1990). The emission scenario...

Ridge-tillage is an agricultural practice where crops are planted on elevated ridges, with furrows in-between. Ridge-tillage has been shown to significantly reduce erosion from croplands, but data on the presence of ridge-tillage is sparse and challenging to collect at the landscape scale. Thus, water quality models often do not account for ridge-t...

Given the increasing demand for water resources and the need for better management of regional water resources, it is essential to quantify the groundwater use by phreatophytes in tropical monsoon climates. Phreatophytes, like eucalyptus plantations are reported to be a groundwater sink and it could significantly affect the regional groundwater res...

Rapid population growth and agricultural intensification has been directly associated with land degradation and with visible deterioration in water quality in the Ethiopian lakes. Assessing the extent and the origin of pollution is cumbersome due to lack of measurements for water quality parameters. This paper reports on the dissolved phosphorus co...

Modeling sediment accumulation in constructed reservoirs is hampered by lack of historic sediment concentration data in developing countries. Existing models simulate sedimentconcentration using data generated from sediment rating curves usually defined as a power function of the form S = aQ b. This often results in residual errors that are not ide...

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) fr...

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...

There is a scientific knowledge gap in locating runoff producing areas and their spatial variation in the landscape of the Ethiopian highlands and the upper Blue Nile basin. Identification of these spatial variations and runoff generation mechanisms is needed for optimum implementation of conservation measures. In many cases poor performance of soi...

The water quality of Lake Tana has recently showed degradation with occurrence of first signs of eutrophication. Hence monitoring water quality of Lake Tana is paramount. This study presents current and historical water quality of lake using measurements and Landsat Images near entry of Gumera river. Statistical analysis of the measured water quali...

The Koga irrigation scheme is the first attempt of eleven major proposed large-scale irrigation schemes in Lake Tana sub-basin in the Upper Blue Nile Basin . The schemes are to provide water for small holder farmers. The completion of Koga scheme poses various challenges and provides important lessons in implementing and operating large-scale irrig...

Intensifying agriculture in Africa is degrading the water quality of rivers and lakes, thereby, threatening the sustainable use of water resources. In Lake Tana in the Ethiopian highlands, the first signs of eutrophication were recently observed. Since relatively little is known about the non-point source pollution in sub-Saharan Africa, the object...

Soil erosion decreases soil fertility of the uplands and causes siltation of lakes and reservoirs. However, very little data exists to quantify accurately the impact of sediment on lakes in tropical monsoonal areas in the African highlands. Lake Tana is one of these lakes in Ethiopia. The objective of this study is to quantify the sediment budget f...

Understanding functions of a watershed is important for implementing appropriate soil and water conservation measures and for planning and development of sustainable water resources use. Watershed storage is a significant part of a catchment water budget and its quantification provides a clue to understand the fundamental catchment hydrological pro...

In most developing countries , there is a lack of historical sediment data. In Ethiopia, over the past 40 years, sediment concentrations in rivers are periodically measured for determining sediment rating curves. But, no such historical data are available for lakes such as Lake Tana in Upper Blue Nile River basin , greatly hampering the ability to...

Soil and water conservation (SWC) measures introduced by the Ethiopian government in 2010, under the Growth and Transformation Program (GTP), have positively impacted watersheds in northern Ethiopia. Five years of field studies (2010-2014) in the Debre-Mawi watershed in northwestern Ethiopia found that different SWC measure need to be considered in...

Abstract: The effect of land use and topography on runoff and soil loss is evaluated in two small agricultural watersheds in the Debre Mawi watershed, in the sub-humid Ethiopian highlands. The first watershed has an area of 8.8 ha of which the majority (60%) is in grass cover and the reminder in cropland. The second watershed is 8.5 ha of which 72%...

Using measured runoff and sediment monitoring, the effectiveness of large scale soil and water conservation (SWC) implementations are analyzed from a five year (2010-2014) study, in the 95 ha Debre Mawi watershed and four nested sub-watersheds. Under the large scale government led SWC program, terraces with infiltration furrows were installed in 20...

Abstract: Intense rainfall-runoff events contribute large proportions of sediment to the total yield in (sub)-humid areas where rainfall is limited to a few months. Understanding the magnitude of sediment transported during intense events and how soil and water conservation (SWC) practices affect peak sediment transport is important for improving t...

In response to the continually increasing sediment concentrations in rivers and lakes, the Ethiopian government is leading an effort where farmers are installing soil and water conservation measures to increase infiltration and reduce erosion. This paper reports on findings from a four year study in the 95 ha Debre Mawi watershed where under the go...

According to Intergovernmental Panel on Climate Change (IPCC) future projections, precipitation and temperature will increase over eastern Africa in the coming century. This chapter presents basin-level impact of climate change on sediment yield in Upper Gilgel Abay catchment, Blue Nile Basin, Ethiopia, by downscaling HadCM3 global climate model us...

According to Intergovernmental Panel on Climate Change (IPCC ) future projections , precipitation and temperature will increase over eastern Africa in the coming century. This chapter presents basin-level impact of climate change on stream flow in Upper Gilgel Abay catchment , Blue Nile basin, Ethiopia , by downscaling HadCM3 global climate model (...

According to Intergovernmental Panel on Climate Change (IPCC ) future projections , precipitation and temperature will increase over eastern Africa in the coming century. This chapter presents basin-level impact of climate change on stream flow in Upper Gilgel Abay catchment , Blue Nile basin, Ethiopia , by downscaling HadCM3 global climate model (...

Stream water quantity and quality are dependent on the physical characteristics of a catchment. The effect of physical catchment characteristics (PCCs) on river flow is not adequately investigated in the upper Blue Nile River Basin. We selected two adjacent watersheds, Ribb and Gumara, of comparable area but significantly different long-term mean a...

Investigation of hydrological processes in few watersheds of the Ethiopian highland indicated the dominance of saturation excess runoff processes. To generalize this in the highland, repeated investigation and replication is necessary. The main focus of this study is twofold 1) Investigating the hydrological response in the new experimental watersh...

The Sourcebook brings together key material from existing experience in the region, synthesizes and organizes this material and provides a basis for future thinking and doing to ensure that water is more productively and sustainably used across smallholder farming. The bottom line is water and food security for farmers in the context of environment...

The Sourcebook brings together key material from existing experience in the region, synthesizes and organizes this material and provides a basis for future thinking and doing to ensure that water is more productively and sustainably used across smallholder farming. The bottom line is water and food security for farmers in the context of environment...

D ebre Mawi is an agricultural watershed in the upper Blue Nile Basin. The slope ranges from 1% to 30% and the altitude varies from 2,195 m near the outlet to 2,308 m in the southeast. The area receives a mean annual rainfall of 1,240 mm with most of it concentrated between June and September (Dagnew et al., 2014). Smallholder farmers produce cerea...

As a response to the continuing increasing sediment concentrations in rivers and lakes in the Ethiopian highlands, the Ethiopian government is leading an effort where farmers are installing soil and water conservation practices to reduce erosion. This paper reports on a four year study in the 95 hectare Debre Mawi watershed, in the upper Blue Nile...

The effectiveness of water management interventions is hampered by the lack of knowledge about the spatial distribution of runoff and associated soil loss. A study was conducted in the 95-ha Debre Mawi watershed in the Upper Blue Nile basin to understand where and when runoff and erosion takes place on the landscape. During the rainy phase of the 2...

Future river discharge predictions seldom take into account the degrading landscape. The objective of this study was to investigate the relationship of river discharge and sediment concentrations, and the effect of changing landscape and climate on discharge and sediment transport in the Ethiopian Blue Nile basin. This study used past precipitation...

According to future projections, precipitation and temperature will increase over Eastern Africa in the coming century. This chapter presents basin-level impact of climate change over the Upper Gilgel Abay River catchment, Blue Nile basin, Ethiopia, by downscaling the Hadley Centre Coupled Model, version 3 (HadCM3) global climate model using the st...

Future river discharge predictions seldom take into account the degrading landscape. The objective of this study was to investigate the relationship of river discharge and sediment concentrations, and the effect of changing landscape and climate on discharge and sediment transport in the Ethiopian Blue Nile basin. This study used past precipitation...

The effectiveness of water management interventions is hampered by the lack of knowledge about the spatial distribution of runoff and associated soil loss. A study was conducted in the 95-ha Debre Mawi watershed in the Upper Blue Nile basin to understand where and when runoff and erosion takes place on the landscape. During the rainy phase of the 2...

A major challenge in constructing the storage characteristics for a lake is the inaccessibility to the shores due to operational limitation of survey campaigns. Lake bottom profiles are often extrapolated beyond the actual survey lines. The potential of satellite images to construct the storage characteristics of the shore areas is explored. Modera...