Omo River Research Articles

Dam Reoperation to Mitigate Changing Climate Extremes in the Omo River Basin, Ethiopia

Dam Reoperation to Mitigate Changing Climate Extremes in the Omo River Basin, Ethiopia

Hydrological responses projection to the potential impact of climate change under CMIP6 models scenarios in Omo River Basin, Ethiopia

Climate change has a negative impact on the basin's hydrological processes and water resources. In this study, the projected impacts of climate change on hydrological processes in the Omo River Basin was evaluated under two Shared Socioeconomic Pathways (SSP245 and SSP585) scenarios. The latest Coupled Model Inter-comparison Project (CMIP6) climate model dataset of precipitation and temperature were used to assess the anticipated climate impact in the basin. The SWAT model was used to simulate the effects of climate change throughout the baseline (1990–2019), near (2031–2060), and far future (2071–2100) periods. The basin's predicted stream flow will increase annually and monthly in June, July, August, and September (JJAS) under both scenarios except decrease in the months of March, April, and May (MAM) under the SSP245 scenario. The basin mean annual and seasonal (JJAS and MAM) surface runoff will increase under the SSP585 scenarios; however, it decreases under the SSP245 scenario. The basin's mean annual and seasonal groundwater will increase in the near and far future under both scenarios except decline in MAM under SSP245 scenario. Likewise, the water yield will decrease in MAM under the SSP245 scenario, nevertheless, increases in annual and seasonal under both scenarios. The potential evapotranspiration increases with temperature over the basin in all circumstances. There will be significant spatial variations in the basin's water balance components in the future. The results of this study will be essential for managing water resources in the future, creating plans for coping with climate change, and reducing the basin's risk of flooding and water scarcity.

Validating the Skills of Satellite Rainfall Products and Spatiotemporal Rainfall Variability Analysis over Omo River Basin in Ethiopia

Recently created long-term and regionally dispersed satellite-based rainfall estimates have emerged as crucial sources of rainfall data to assess rainfall's spatial and temporal variability, particularly for data-scarce locations. <i>Objective (the general)</i>: The purpose of this paper is to assess the skills of nine selected satellite rainfall estimates i.e., (ARC 2.0, TRMM 3B42, CHIRPS v. 2.0, TAMSAT 3.1, CMORPH v. 1.0 adj., PERSIANN CDR and DNRT, and MSWEP v. 2.2) and understand Spatio-temporal variability of rainfall over the Omo River basin using the best performing product. <i>Method</i>: The validation analysis was done by using a point-to-grid-based comparison test at different temporal accumulations. MSWEP was selected as the best product to analyze the long-term trend and variability of rainfall over the Omo-River basin from 1990-2017. The coefficients of variation (CV) and the standardization rainfall anomalies index (SRAI) were used to examine rainfall variability, while the Mann-Kendall (MK) and Sen slope estimators were used to examine the trend and magnitude of rainfall patterns. <i>Results</i>: The overall statistical, categorical, and volumetric validation index results show that the MSWEP is the best performing rainfall product followed by CHRIPS, 3B42, and TAMSAT according to their order of appearance than the remaining products (i.e., ARC, RFE, PER CDR, PER DNRT, and CMORPH). The CV result with the relatively highest monthly variability (CV > 30%) was observed in some southern, northern, southeastern, and central parts of the study area. In general, the overall annual CV shows almost no variation in the entire basin except in the lower part because of the region's prevalent topographic variances, which ranged from 3455 to 352 m.a.s.l. In addition, the highest seasonal positive and negative anomalies are observed in each season in the entire basin. These abnormalities can result in significant floods and droughts that unquestionably influence the basin and its resources. <i>Conclusion</i>: In general, the basin has an increasing trend in the southern portions and a declining trend in the central to northern tip parts of the basin, as can be observed from the annual average MK trend tests. The basin has experienced a greeter variation but is not significant except in some parts of the basin.

Integration of geospatial analysis, frequency ratio, and analytical hierarchy process for landslide susceptibility assessment in the maze catchment, omo valley, southern Ethiopia

This investigation was conducted in southern Ethiopia's Maze watershed in the Omo River Valley. Frequency ratio (FR) and analytic hierarchy process (AHP) techniques were used to assess landslide susceptibility in the region. Identifying causative components and landslide inventory data achieved the goal. Remote sensing and on-site investigations found 793 landslide polygons. To assess vulnerability, the landslide inventory information is categorized into two groups: the training dataset (70%) and the validation dataset (30%). This study examined “slope, aspect, curvature, lithology, land use and cover, normalized vegetation index, and proximity to fault lines, rivers, and distance to road as landslide controlling factors”. The spatial analysis capabilities in Arc GIS were used to overlay the weights of all landslide-causing components to create the susceptibility map. A final landslide susceptibility map is produced using FR and AHP methods and categorized as “very low,” “low,” “moderate,” “high,” and “very high.” The frequency ratio method divides the region into susceptibility classes by frequency. The very low, low, medium, high, and very high susceptibility groups cover 25%, 20%, 18%, and 19% of the territory. The analytical hierarchical process technique shows that 3%, 7%, 26%, 36%, and 28% of the area are very low, low, medium, moderate, and very high landslide susceptibility. The receiver operating characteristic curve was employed to validate the area-underlayer susceptibility maps. The success rates were determined using the FR and AHP approaches, resulting in AUC numbers of 0.873 and 0.87. Similarly, the prediction rates were determined to be 0.81 and 0.80. The landslide susceptibility maps will significantly influence land resource allocation.

An Isotope Mass Balance Analysis of Evaporative Loss From Lake Turkana, Kenya Using δ18O and δD of Natural Waters

AbstractMeasurements of oxygen and hydrogen stable isotope ratios (δ18O and δD) in meteoric waters provide insight to overlapping effects of evaporation, precipitation, and mixing on basin scale hydrology. This study of waters collected between 2016 and 2021 in the Turkana Basin, northern Kenya, uses δ18O and δD to understand water balance in Lake Turkana, a large, low‐latitude, alkaline desert lake. The Omo River, a major river system in the Ethiopian Highlands, is historically understood to provide approximately 90% of the water input to Lake Turkana. Discharge of the Omo is prohibitively difficult to measure, but stable isotope ratios in the lake may provide a meaningful method for monitoring the lake's response to changes in input. Precipitation in the Turkana Basin is low (<200 mm/year) with negligible rainfall on the lake's surface, and all water loss from the lake is evaporative. We compare new measurements with previous data from the region and records of lake height and precipitation from the same time period. We show that a Bayesian approach to modeling evaporation using atmospheric conditions and river δ18O and δD yields results consistent with published water balance models. Continued sampling of lake and meteoric waters in the Turkana Basin will be a useful way to monitor the lake's response to regional and global climate change.

The prioritisation of development projects and devaluation of cultural heritage: the case of material culture in Wolaita, southern Ethiopia

This study looks at the prioritisation of development projects and the consequential devaluation of cultural heritage in the case of the Kawo Amado Kella defensive wall in Wolaita, southern Ethiopia. The study region has several cultural, natural and combined world heritage sites, although the location is practically unknown on a regional and national level. The area is one of Ethiopia’s most culturally rich regions, and the wall was discovered at an ancient location near the Omo River. The Wolaita people live in the Omo River basin and have a rich cultural heritage and over time the defensive wall has suffered from various man-made and natural forces. This study focussed on the maintenance and conservation challenges of the Kawo Amado Kella defensive wall and used a qualitative ethnographic research approach with purposive sampling to understand the significance of the wall on a regional and national level as well as internationally. The results of the research are presented in this article.

Heavy metal levels and human health risk implications associated with fish consumption from the lower Omo river (Lotic) and Omo delta lake (Lentic), Ethiopia.

This study is the first to determine the levels of heavy metals in commercially important fish species, namely Lates niloticus and Oreochromis niloticus and the potential human health risks associated with their consumption. A total of 120 fish samples were collected from the lower Omo river and Omo delta, with 60 samples from each water source. The fish tissue samples (liver and muscle) were analyzed using a flame atomic absorption spectrometer for nine heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn). The human health risk assessment tools used were the target hazard quotient (THQ), the hazard index (HI), and the target cancer risk (TCR). The mean levels of heavy metals detected in the liver and muscle of L. niloticus from the lower Omo river generally occurred in the order Fe > Zn > Pb> Cu > Mn> Cr > Co > Ni and Pb > Cu > Mn > Co > Ni, respectively. The mean levels of metals in the muscle and liver tissues of O. niloticus were in the order Fe > Pb > Zn > Mn > Cu > Cr > Co > Ni and Pb > Zn > Mn > Fe > Cu > Co > Ni, respectively. Similarly, the mean levels of heavy metals detected in the liver and muscle of L. niloticus from Omo delta occurred in the order Fe > Zn > Pb > Cu > Mn > Cr > Co > Ni and Fe > Pb > Zn > Mn > Cu > Co > Cr > Ni, respectively. The mean levels in the muscle and liver tissues of O. niloticus from the Omo delta were in the order Fe > Pb > Zn > Mn > Cu > Cr > Co > Ni and Pb > Fe > Zn > Mn > Co > Cu > Ni, respectively. The study revealed that the THQ values were below 1, indicating that consumption of L. niloticus and O. niloticus from the studied sites does not pose a potential non-carcinogenic health risk. Although the TCR values for Pb in this study were within the tolerable range, it's mean concentration in the muscle and liver tissues of both fish species from the two water bodies exceeded the permissible limit established by FAO/WHO. This is a warning sign for early intervention, and it emphasizes the need for regular monitoring of freshwater fish. Therefore, it is imperative to investigate the pollution levels and human health risks of heavy metals in fish tissues from lower Omo river and Omo delta for environmental and public health concerns.

Evaluating Water Quality of Lower Omo River and the Ethiopian part of Lake Turkana, Southern Ethiopia

Evaluating Water Quality of Lower Omo River and the Ethiopian part of Lake Turkana, Southern Ethiopia

Heavy Metal Contamination in Omo River, Ethiopia: Environmental and Human Health Risks.

The Omo River flows through the town of Omorate, where domestic, municipal, and industrial wastes from the town and its surroundings, including agrochemicals, are discharged into the river. The present study was conducted to determine the levels of heavy metals and associated environmental and human health impacts from the Lower Omo River freshwater ecosystem (water and sediment) of the Lower Omo River. The mean concentrations of heavy metals detected in the river water were 0.439 mg/l for (Mn), 0.1 (Zn), 0.168 (Cu), 0.393 (Cr), 0.318 (Pb), 0.007 (Ni), 8.926 (Fe), and 0.06 (Co).The order for the mean concentrations of the heavy metals in the water was Fe > Mn > Cr > Pb > Cu > Zn > Cu > Co > Ni. The HPI value indicates that all water sampling sites were highly contaminated. Oral and dermal HQs for both children and adults were in the order of Cr > Pb > Mn > Fe > Cu > Co > Ni > Zn. The HQ value greater than 1 was investigated for Cr, Pb, and Mn in both children and adults by ingestion and dermal routes from the river water. The CRs for both children and adults by ingestion of the river water followed the order Cr > Pb. According to the CRI value, the river water could be classified as a very high environmental risk. The EI results for the heavy metals detected in the sediments also followed the order: Fe > Cr > Cu > Pb > Mn > Co > Zn > Ni.

Modelling malaria vulnerability hotspot by using geospatial techniques: the case of Kindo Koysha Woreda, Wolaita Zone, Ethiopia

Malaria is a serious, acute disease spread by female Anopheles mosquito bites. Malaria is an epidemic in the Wolaita Zone, affecting 85% of the population despite the implementation of effective prevention and control measures in the area’s public health services. The main objective of this study is to apply geospatial techniques to environmental, socioeconomic, and epidemiological parameters that increase certain conditions for malaria incidence to identify malaria vulnerability hotspots using a multi-criteria evaluation method. The malaria vulnerability hotspot map is identified by using AHP and the malaria hotspot identification algorithm. The findings show that the research area is 51% very high and highly vulnerable (224.14 km2), 26% moderate (116.560 km2) and 23% low vulnerable (103.600 km2). The western part of the area, which is near the Omo River and has low elevation, is highly vulnerable to malaria incidence. Reliable malaria vulnerability hotspot maps are critical for estimating the scope of the problem and, consequently, the resources required to combat malaria.

Promotion of Improved Onion (Nafis Variety) Production Technology under Irrigated Conditions in Nyangatom District, Low Land Area of South Omo Zone

Onion is an important cash crop that could enhance the income of agro-pastoralists in Nyangatom woreda as the area has huge potential for water availability from the Omo River and fertile land. However, access to improved onion variety is limited in the area. Thus, this study aimed to demonstrate the improved onion variety with its agronomic management in the production season. Onion growers were purposely selected and have taken training on onion production by using recommended doses of fertilizers, pesticides, irrigation, and suitable agronomic practices. Each agro-pastoralist covered 0.064 hectares of land by improved onion. The recorded data from the field experiment and agro-pastoral perceptions were analyzed through simple descriptive and preference ranking tools. From the result of the demonstration trial, the mean bulb yield of the improved onion (Nafis variety) was 125 qt/ha. The average return obtained from the sale of onion bulbs per hectare was 334,925 Ethiopian birr. Moreover, the benefit-to-cost ratio of improved onion production was 8.34:1, which indicates the benefits outweigh the costs, suggesting a positive return on improved onion production in the area. The agro-pastoralist’s preference further showed that the Nafis variety was the best one or superior to the local variety in terms of its high-yielding ability, dark green leaf color, medium bulb size, and market preference. Therefore, the authors suggest the respective government and non-government bodies to further promote improved onion in the area.

Variation of the Omo Delta between 1990 and 2018: What remote sensing data reveal and models explain

AbstractDeltas, being areas where river sediments accumulate, are sensitive to changes in climate and anthropogenic processes that affect sediment generation. The Omo Delta, on the Ethiopia–Kenya border, is constantly changing due to fluctuating lake levels, a variable climate, and rapidly changing land use. Due to field data scarcity and the region's limited accessibility, we relied on remote sensing (RS) data to investigate delta extent between 1990 and 2018 and attempted to disentangle the effect of climatic from anthropogenic variables. We obtained a time series of delta extent from Landsat imagery using Random Forest (RF) classification. Using parametric and non‐parametric regression techniques, we regressed the delta extent on Lake Turkana levels, Omo River discharges, Omo‐Gibe Basin rainfall, tree cover loss, and irrigation extent. The RF algorithm distinguished water from land with high (>90%) accuracies and revealed Omo Delta extent fluctuations ranging from 949 km2 in 1993 to 651 km2 in 2000. Lake water level, which depends on the rainfall over the Omo‐Turkana Basin, emerged as the best predictor of delta extent. However, the annual rainfall over the Omo‐Gibe Basin showed no correlation with delta extent. The regression models further show a connection between delta extent, irrigation extent, and tree cover loss. We conclude that rainfall indirectly influences delta extent across the Omo‐Turkana Basin. Regression models indicate additional cumulative effects of human activity in the Omo‐Gibe Basin but fall short in explaining delta dynamics.

Feeding Ecology of Omo River Guerezas (Colobus guereza guereza) in Natural Versus Plantation Forests in the Central Highlands of Ethiopia

Feeding Ecology of Omo River Guerezas (Colobus guereza guereza) in Natural Versus Plantation Forests in the Central Highlands of Ethiopia

Hydrochemical Characterization and Water Quality Assessment for Drinking and Irrigation Purposes Using WQI and GIS Techniques in the Upper Omo River Basin, Southern Ethiopia

Groundwater is an important source of drinking water and irrigation in Ethiopia’s present study area of the upper Omo River catchment. The present study area has an increasing demand for high-quality groundwater. Extensive irrigation and urban expansion are ongoing in the study area, seriously compromising groundwater quality. A study was conducted in Ethiopia’s upper Omo River catchment to assess groundwater’s suitability for drinking water and agricultural purposes. In total, 58 water samples were collected for this study. Based on the WHO and Ethiopian standards for assessing water quality, the study’s results have been analyzed and compared. The groundwater’s primary ion and physicochemical properties were plotted using GIS technology. Based on the results of the hydrochemical analysis, three water quality index (WQI) zones were identified: excellent (58.82%), good (35.29%), and poor (5.88%). From the Piper diagram plots, five different types of water were identified as Ca-HCO3, Na-HCO3, mixed Ca-Na-HCO3, NaCl, and CaCl, out of the total of fifty-eight samples collected from the study area. The present study found that in the area, most water samples are suitable for drinking, except for a few parameters above the standards for drinking water set by the World Health Organization and Ethiopian drinking water quality standards. Except for the three samples, EC, SAR, and PI data indicate that most of the area’s water samples are suitable for irrigation. Water quality indices, irrigation water quality methods, and GIS techniques are crucial for assessing water quality based on the study.

Hydrologic Controls on Individual Ostracode Stable Isotopes in a Desert Lake: A Modern Baseline for Lake Turkana

AbstractStable carbon (δ13C) and oxygen (δ18O) isotope measurements in lacustrine ostracodes are widely used as paleolimnological indicators of past climate change. Previous work has used individual ostracode valves to resolve seasonal and subdecadal paleohydrological signals, yet replicated assessments of co‐occurring specimens from modern samples are rare. Here we focus on ostracodes from sediments collected in 1979 from Lake Turkana, an alkaline desert lake in tropical eastern Africa. Sourced from the Ethiopian highlands, the Omo River is the dominant inflow into this lake. We present individual ostracode valve analyses (IOVA) of δ13C and δ18O measurements (n = 329) of the extant benthic ostracode Sclerocypris clavularis from 17 sites spanning the entire lake (navg = ∼19 specimens/site). We demonstrate that the pooled statistics of individual valve measurements at each site are shaped by lake hydrology, superimposed over inter‐individual isotopic variations. Within‐site variance in IOVA‐δ13C is larger (∼60%) than that of IOVA‐δ18O. Yet, site‐based averages exhibit a systematic pattern, with higher δ values toward the southern part of the lake, away from Omo River inflow. We suggest that the latitudinal δ13C gradient may arise from low riverine δ13C and low organic matter δ13C as a productivity response to nutrient‐rich Omo River inflow toward the north. The δ18O pattern may be explained by the diminishing influence of Omo River inflows and more evaporation driving higher IOVA‐δ18O values toward the windier, southern basin. We conclude that pooled IOVA statistics in Omo‐Turkana sediments can aid interpretations of past regional paleohydrology and its variability in this basin.

Evaluation of General Circulation Models CMIP6 Performance and Future Climate Change over the Omo River Basin, Ethiopia

One of the world’s major issues is climate change, which has a significant impact on ecosystems, human beings, agricultural productivity, water resources, and environmental management. The General Circulation Models (GCMs), specially the recently released (coupled model intercomparison project six) CMIP6 are very indispensable to understand and support decision makers to identify adaptation strategies in response to future climate change in a basin. However, proper selection of skillful GCMs and future climate assessment is a prior task to climate impact studies. The objective of the study is an attempt to appraise the climate model’s performance and future climate scenarios of Shared Socioeconomic Pathways (SSPs) in the Omo River Basin. The performance evaluation of 20 GCMs of the CMIP6 was properly performed to reproduce the precipitation and the maximum temperature in the basin. Their performance has been carried out against the best selected mean monthly Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) precipitation and European Community Medium Water Range Weather Forecasts Version 5 (ECMWF-ERA5) maximum temperature. The GCMs of the CMIP6 were selected and ranked using the compromise programming method of multi-criteria decision making. The result shows that ensemble models and NorESM2-MM models have been designated to reproduce the precipitation and maximum temperature in the basin respectively. The Mann–Kendall trend test was executed to appraise the trend of selected CMIP6 models, and subsequently, downscaling and bias correction techniques were conducted. The projected seasonal precipitation of June, July, August, September (JJAS) and March, April, May (MAM) shows an increasing trend with 10.86, 17.66, 38.96 and 11.85, 22.1, and 40.7% under SSP2452031-2060, SSP5852031-2060, and SSP5852071-2100 scenarios respectively. Furthermore, increasing trends were detected in MAM by 12.8% and decreasing trends in JJAS were detected by 15.23% under SSP2452071-2100 scenario. The maximum temperature projection will be increased on average by 0.95, 1.78, 1.4, and 3.88 °C in JJAS and 1.53, 2.24, 1.56, and 3.89 °C in MAM under climate change scenarios of near-future SSP2452031-2060, SSP5852031-2060, far-future SSP2452071-2100, and SSP5852071-2100, respectively. Additionally, the basin has shown temporal-spatial climate fluctuation in terms of precipitation and maximum temperature.

Turkana Low-Level Jet Influence on Southwest Ethiopia Climate

Abstract The Turkana Jet in northern Kenya is shown to modulate the climate of southwest Ethiopia’s Omo River Valley using in situ hydrometeorological data, satellite measurements, and atmospheric reanalyses from decadal to diurnal time scales. Temporal statistics from lowland (2.5°–5°N, 35°–38°E) and highland (6°–9°N, 35°–38°E) areas show that 850-hPa westward airflow over Lake Turkana is stronger in March and October but is weakened when western Indian Ocean sea temperatures become warmer than usual at intervals of 2–7 years. A case study on 24 March 2019 reveals how a stronger Turkana Jet induces warming and drying of the Omo Valley. A second case study on 27 September 2018 reveals Hadley cell subsidence over the southern flank of the Turkana Jet. We demonstrate how nocturnal airflow draining off the mountains joins the channelized jet. Satellite and atmospheric reanalyses exhibit realistic diurnal cycles in the east Omo mountains, but some products have incorrect phase and warm bias. Omo Valley soil moisture and runoff exhibit little trend in historical records and model projections; however, unpredictable multiyear wet and dry spells and a growing demand for water are ongoing concerns.

Applications of statistical and AHP models in groundwater potential mapping in the Mensa river catchment, Omo river valley, Ethiopia

Applications of statistical and AHP models in groundwater potential mapping in the Mensa river catchment, Omo river valley, Ethiopia

River delta eco-morphodynamics under changing scenarios: The case of Lake Turkana, Kenya

In this work we explore the impact that changes in local climate and river hydrology have on the morphodynamics of a river delta, particularly focusing on the evolution of the delta generating at the lake inlet. We investigated the case of the delta in the lower reach of the Omo River in Ethiopia, which flows into lake Turkana, Kenya. The lake is the fourth largest lake and the largest desert lake in the world. This case study is of particular interest because within the last decades three dams have been built within the Omo basin. Among these, the Gibe III dam had a huge impact on the river hydrology and the sediment supply. To quantify changes in land use and river morphology and relate these to climate change and river hydrology we collated a historical dataset by combining information from different satellite sources. We observed that the amount of bare sediments progressively diminished and the biomass became denser compared to the existence of sparse biomass in the past. We argue that this is due to the changes in river hydrology and sediment load imposed by the dam, which increased sediment erosion by deepening the channel. The presence of the dam also increased the low flow level and reduced the peak flow during flood season, reducing the natural oscillations of the water table. In consequence, the possibility to plant for the local population was removed during floods. Our findings also indicate that the hydrology and reduced sediment discharge have changed the downstream (e.g. lake level), and upstream (e.g. mouth bar deposition) boundary conditions controlling the evolution of the delta structure, respectively. As a result, the delta morphology became less dynamic and less complex.

The role of wind-wave related processes in redistributing river-derived terrigenous sediments in Lake Turkana: A modelling study

A complete annual cycle of the dynamics of fine-grained sediment supplied by the Omo and smaller rivers is simulated for Lake Turkana, one of the world’s large lakes, with the hydrodynamic, wave and sediment transport model Delft3D. The model is forced with river liquid and solid discharge and wind data in order to simulate cohesive sediment transport and resuspension. It simulates stratification due to salinity, wave generation and dissipation, and sediment advection and resuspension by waves and currents, with multiple cohesive sediment fractions. A comparison of the simulation results with remotely-sensed imagery and with available in-situ sediment deposition rates validates the model. By devising simulation scenarios in which certain processes were switched on or off, we investigated the contribution of waves, wind-induced surface and bottom currents, salinity-induced stratification and river jet, in resuspending and transporting fine sediments in the lake basin. With only the wind or river influence, most of the sediment deposition occurs in the first 10 km off the Omo River mouth and at a depth < 10 m. When waves are switched on, increased bed shear stresses resuspend most of the fine sediments, that are then deposited further and deeper in the first 30 km, in water depths > 30 m. This study sheds new light on sediment transport in Lake Turkana and in great lakes in general, favouring the view that wind-waves can be the main agent that transports sediment away from river mouths and to deeper areas, as opposed to river-plume or gravity-driven transport.