Faculty Publications
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Item Analysis of variability and trends in rainfall over northern Ethiopia(Springer Verlag service@springer.de, 2016) Kiros, G.; Shetty, A.; Nandagiri, L.Rainfall is a key component of the hydrological cycle, and its spatiotemporal variability is essential from the both scientific and practical perspectives. This study is focused on analysis of temporal variability and trends in historical rainfall records for stations in the Geba River basin. The Geba catchment is surrounded by the Danakil basin in the east, by the Tekeze River basin in the south, and the Werie River basin in the west which is located in the northern Ethiopia regional state of Tigray between 38° 38? E and 39° 48? E and 13° 18? N and 14° 15? N. The climate over the basin is semi-arid and has large elevation differences varying from 926 to 3301 m above mean sea level. Daily rainfall data of 43 years measured at seven stations in the basin for the period of 1971 to 2013 for annual and seasonal rainfall trends have been processed and used for the analysis. The non-parametric Mann–Kendall test and the Sen’s slope estimator have been used to identify the existence of trends and slope magnitude in rainfall. Results revealed that although there was a mix of positive and negative trends, they were no statistically significant except at one station which showed an increasing trend in annual rainfall. Considering rainfall in different seasons, an increase in rainfall was observed in two stations in the wet season which, however, was not statistically significant. For the remaining stations, a weak decline in wet season rainfall (not statistically significant at 95 % confidence level) for four stations and absence of trend for one station were noticed. Furthermore, no statistically significant trend (positive or negative) was evident for the dry season rainfall. Results of this study may prove useful in the preparation of climate change mitigation and adaptation strategies in rainfed agricultural and water supply systems in the region. © 2016, Saudi Society for Geosciences.Item Assessment of consumption and availability of water in the upper Omo-Gibe basin, Ethiopia(Springer, 2020) Nesru, M.; Nagaraj, M.K.; Shetty, A.Understanding water balance components is imperative for proper policy and decision making, specifically in the upper part of the Omo-Gibe basin (UOGB) Ethiopia. The objective of this study is to explore the possibility of assessing consumption and availability of water using freely available satellite data and secondary data. Using twenty-three rain gauge stations data, a spatial average of rainfall was computed using the Thiessen polygon approach. Actual evapotranspiration (ETa) was estimated through the Surface Energy Balance System (SEBS). Input data used are, 16 clouds free Moderate Resolution Imaging Spectroradiometer (MODIS) images covering the study area for estimation of the spatial distribution of actual evapotranspiration covering the whole cropping year from the months of November 2003 to October 2004. Additionally, Priestly and Taylor’s approach was used to estimate reference evapotranspiration (ET0). For the study period, the result of estimated precipitation and ETa showed that the UOGB received 41,080 mm3 of precipitation, while 24,135 mm3 become evapotranspired. The assessed outflow from the basin is 17.6% of the precipitation and demonstrated that water is a scares resource in the UOGB. © 2019, Saudi Society for Geosciences.Item Multi-variable calibration of hydrological model in the upper Omo-Gibe basin, Ethiopia(Springer, 2020) Nesru, M.; Shetty, A.; Nagaraj, M.K.The calibration of any hydrological model in any river basin is generally performed using a single hydrological variable. Spatially distributed hydrological modeling provides an opportunity to enhance the use of multi-variable calibration models. The objective of this study is to test the efficiency of satellite-based actual evapotranspiration in the HBV hydrological model to render the catchment water balance using multi-variable calibration in the upper Omo-Gibe basin in Ethiopia. Five years (2000–2004) meteorological data, streamflow, and actual evapotranspiration (ETa) based on remote sensing were used for calibration and validation purposes. The performance of the HBV model and the efficiency of SEBS–ETa were evaluated using certain calibration criteria (objective function). The model is first calibrated using only streamflow data to test HBV model performance and then calibrated using a multi-variable (streamflow and ETa) dataset to evaluate the efficiency of SEBS–ETa. Both model setups were validated in a multi-variable evaluation using streamflow and ETa data. In the first case, the model performed well enough for streamflow and poor for ETa, while in the latter case, the performance efficiency of SEBS–ETa and streamflow data shows satisfactory to good. This implies that the performance of hydrological models is enhanced by employing multi-variable calibration. © 2020, Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences.Item Flood susceptibility modeling based on morphometric parameters in Upper Awash River basin, Ethiopia using geospatial techniques(Springer Science and Business Media Deutschland GmbH, 2022) Tola, S.Y.; Shetty, A.The hydrological response, such as direct surface runoff, is linked to the characteristics of the watershed. Evaluation and knowledge of geomorphometric parameters in relation to floods and the identification of specific flood-prone sites in the basin are critical for mitigation measures. Despite advancements in geospatial tools, the utilization of geospatial data in many river basins prone to flooding and erosion is minimal. Morphometric aspects: linear, areal, and relief analysis of the Upper Awash River basin were performed in four subbasins to better understand the hydrological signatures behaviour. The topographic wetness index (TWI) and topographic position index (TPI) were also used to determine the extent of inundation. The aggregated parameters revealed that SB-1 is highly susceptible to flooding, SB-3 and SB-4 are moderately susceptible, and SB-2 is low. However, based on the geomorphologic instantaneous unit hydrograph, SB-2 and SB-4 demonstrated rapid response and a high flood generating potential. The degree of susceptibility was determined by incorporating the TWI and TPI through overlay analysis. Overall, the Upper Awash River basin accounts for 23%, 42%, and 36% of the total bay has been classified as high, medium, and low flood-prone, respectively. According to the study, topographic indices (TWI and TPI) are critical attributes that show specific flood potential areas and inundation extents in addition to morphometric parameter-based flood susceptibility analysis. The analysis provided input for holistic water and soil erosion management by providing the hydrological behaviour of the stream, geomorphological characteristics, basin responsiveness, and stream power to flood potential and denudation characteristics in the subbasins. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Land cover change and its implications to hydrological variables and soil erodibility in Lower Baro watershed, Ethiopia: a systematic review(Springer Science and Business Media Deutschland GmbH, 2023) Deneke, F.; Shetty, A.; Fufa, F.Water-induced soil erodibility is the most severe kind of land degradation, with substantial environmental and social consequences. Few studies have been conducted on land cover change and soil erodibility in Ethiopia. During the data search, 83 articles were looked at, with studies published from 2007 to 2022. Only 2% of the abstracts that were considered for assessment were eventually accepted. The review was conducted using the preferred reporting items for systematic reviews and a meta-analysis approach. According to this study, when compared to the values predicted in the river basin’s master plan, Baro Akobo’s estimated surface water potential has been reduced by about 3.6 Bm3. As a result, changes in land cover affected a variety of fundamental processes in watersheds, at several spatial and temporal scales. As a result, of the reviewed, in lower Baro, built-up/settlement, agricultural land, water body, bare/outcrop, and commercial farm all rose by roughly + 195, + 48, + 35, + 35, and + 1%, respectively. Shrubland, rangeland, forest land, and wetland, on the other hand, all decreased by − 1, − 0.5, − 5, and − 10%, respectively. The K-factors are 0.31, 0.23, 0.14, and 0.07 for chromatic vertisols, humic cambisols, eutric cambisols, and eutric nitosols, respectively. From the results of the review studies, the RUSLE looks to be a good alternative for assessing soil erodibility in lower Baro, and soil water conservation measures are crucial for minimizing soil erodibility. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Quantification of change in land cover and rainfall variability impact on flood hydrology using a hydrological model in the Ethiopian river basin(Springer Science and Business Media Deutschland GmbH, 2023) Tola, S.Y.; Shetty, A.Changes in land cover and climate are the dominant factors that significantly impact the hydrological process. However, the impact on flood response behaviour varies spatiotemporally. This study quantitatively assessed the effects of individual and coupled changes in land cover and climate on peak and high flows in the upstream and downstream parts of the Upper Awash River basin. Two time periods were chosen for comparison: baseline (1988–2001) and evaluation (2002–2015). The Soil Water and Assessment Tool (SWAT) was used to estimate the impact of these changes. The model satisfactorily simulated daily and extreme flows. The evaluation of annual maximal discharge variability between 1985 and 2015 at upstream and downstream stations showed significant positive and insignificant negative trends, respectively. However, the sub-basin’s annual wet day rainfall (PRCPTOT) showed a downward trend. The annual maximal discharge–PRCPTOT relationship was significant during the baseline but later had no significance. The SWAT model showed that the main factor that affected the changes in upstream flow was the land cover change, increasing peak and high flow by 38.69% and 11.95%, respectively, compared to the baseline period. However, combined changes resulted in downstream peak and high flow reductions of 19.55% and 50.33%, respectively. As a result, changes in flood characteristics are strong functions of land cover, especially in the upstream sub-basin and land cover and climate in the downstream sub-basin. Overall, the impact of changes in the cropland-dominated basin was noticeably different. The study assists water resource managers in understanding the causes of hydrological dynamics and developing mitigation strategies. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Extreme hydroclimatic variability and impact of local and global climate system anomalies on extreme flow in the Upper Awash River basin(Springer, 2023) Tola, S.Y.; Shetty, A.Extreme hydroclimatic variability in a changing climate and the possible causes of extreme hydrological variability are essential for effectively mitigating floods. The study aims to investigate the variability of extreme hydroclimatic conditions and the relationship between anomalies in extreme local precipitation, ENSO indicators (Southern Oscillation index (SOI), Niño 3.4, and multivariate ENSO index (MEI)), and extreme flow indices in the Upper Awash River basin, Ethiopia. The analysis used standardized anomaly index and coefficient of variation statistics to examine variability, the modified Mann-Kendall and Pettitt tests for trend and change point analysis, and Spearman’s correlation test to explore relationships. The study revealed that the basin-wise extreme precipitation indices had less variability but higher variability spatially, while the extreme flow indices showed high variability. Furthermore, the basin experienced extreme wet to normal wet conditions in the 1990s compared to the 2000s. The maximum temperature increased significantly, while the minimum temperature decreased significantly (except at a few northwest stations), with a considerable shift in the 1990s and 2000s. Anomalies, extreme to normal wet conditions, and a decrease in extreme precipitation were consistent with the extreme flow at the basin outlet, Hombole station. However, the extreme flow indices at Melka Kunture increased significantly and shifted upward (2003/2005), and the anomalies in extremely wet and very wet precipitation in the northwest were possibly responsible for this change. The study also revealed that the annual wet and very wet days of precipitation strongly affected the extreme flow in the basin. The effect of annual wet day precipitation, annual maximum precipitation, and ENSO anomalies on extreme flow at the Hombole was significant. These findings enhance the understanding of extreme hydroclimatic variability and prospective flood predictability and aid flood risk management. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.Item Integrated spatial and temporal variability of the system water use efficiency in a lower Baro River watershed, Ethiopia(IWA Publishing, 2023) Befikadu, F.; Shetty, A.; Fufa, F.The Baro Akobo River is representative of lower Baro watersheds with lost soils. Under eight landscapes, the geospatial and temporal variability of system water use efficiency (sWUE) were examined in a total area of 20,325 km2. This study used GIS, RS, Cropwat8.0, and EasyFit software. The anticipated irrigation requirement for the selected crop’s driest five months of May, February, March, January, and April was 1, 0.9, 0.78, 0.78, and 0.34 l/s/h, respectively. The sub-catchment had maximum critical test values of σ = 12.6, μ = 11.9, and γ = 0, while Sor Metu showed the smallest value of 0.80, 1.75, and 0.03. Across the watershed, the sWUE varies with runoff, with a coefficient of variation of 71%. The overall accuracy of the land cover change was 81%, the Landsat 8 images of the soil-adjusted vegetation index showed a maximum value of 0.87 and a minimum of 1.5. The normalized vegetation index ranged from a maximum of 0.58 to a minimum of 1. By 2050, the sWUE will be 10% lower temporally, but its spatial variability will be 25% higher. Therefore, soil infiltration and water storage improve, which decreases runoff and the water lost by ET and raises sWUE. © 2023 The Authors.Item Flood hazard map of the Becho floodplain, Ethiopia, using nonstationary frequency model(Springer Science and Business Media Deutschland GmbH, 2024) Tola, S.Y.; Shetty, A.Flood estimates based on stationary flood frequency models are commonly used as inputs to flood hazard mapping. However, changing flood characteristics caused by climate change necessitate more accurate assessments of the probabilities of rare flood events. This study aims to develop a flood hazard map based on the nonstationary flood frequency using a generalized extreme value distribution model for the Becho floodplain in the upper Awash River basin. The distributional location parameter was modeled as a function of rainfall amount of different durations, annual total precipitation from wet days, yearly mean maximum temperature and time as covariates. The one-dimensional Hydrological Engineering Center River Analysis System (HEC-RAS) hydraulic model with steady flow analysis was used to generate flood hazard map input, depth and velocity, and inundation extent for different return periods. The result indicated that the model as a function of rainfall, such as monthly rainfall (August) and annual wet day precipitation, provided the best fit to the observed hydrological data. Rainfall as a covariate can explain the variation in the peak flood series. The developed hazard map based on depth alone and the combination of depth and velocity thresholds resulted in more than 70% of the floodplain area being classified as a high hazard zone under 2, 25, 50, and 100-years return periods. The current study assists water resource managers in considering changing environmental factors and an alternative flood frequency model for developing flood hazard management and mitigation strategies. © The Author(s) under exclusive licence to Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences 2023.