Sirak Tekleab - Academia.edu (original) (raw)

Papers by Sirak Tekleab

Climate change potentially induces ecological change in the Ethiopian Rift Valley Lakes Basin

Journal of Hydrology: Regional Studies

Hydrology and Earth System Sciences, Jun 26, 2014

Measurements of the stable isotopes oxygen-18 (18 O) and deuterium (2 H) were carried out in two ... more Measurements of the stable isotopes oxygen-18 (18 O) and deuterium (2 H) were carried out in two meso-scale catchments, Chemoga (358 km 2) and Jedeb (296 km 2) south of Lake Tana, Abay/Upper Blue Nile basin, Ethiopia. The region is of paramount importance for the water resources in the Nile basin, as more than 70 % of total Nile water flow originates from the Ethiopian highlands. Stable isotope compositions in precipitation, spring water and streamflow were analysed (i) to characterise the spatial and temporal variations of water fluxes; (ii) to estimate the mean residence time of water using a sine wave regression approach; and (iii) to identify runoff components using classical two-component hydrograph separations on a seasonal timescale. The results show that the isotopic composition of precipitation exhibits marked seasonal variations, which suggests different sources of moisture generation for the rainfall in the study area. The Atlantic-Indian Ocean, Congo basin, Upper White Nile and the Sudd swamps are the potential moisture source areas during the main rainy (summer) season, while the Indian-Arabian and Mediterranean Sea moisture source areas during little rain (spring) and dry (winter) seasons. The spatial variation in the isotopic composition is influenced by the amount effect as depicted by moderate coefficients of determination on a monthly timescale (R 2 varies from 0.38 to 0.68) and weak regression coefficients (R 2 varies from 0.18 to 0.58) for the altitude and temperature effects. A mean altitude effect accounting for −0.12 ‰/100 m for 18 O and −0.58 ‰/100 m for 2 H was discernible in precipitation isotope composition. Results from the hydrograph separation on a seasonal timescale indicate the dominance of event water, with an average of 71 and 64 % of the total runoff during the wet season in the Chemoga and Jedeb catchments, respectively. Moreover, the stable isotope compositions of streamflow samples were damped compared to the input function of precipitation for both catchments. This damping was used to estimate mean residence times of stream water of 4.1 and 6.0 months at the Chemoga and Jedeb catchment outlets, respectively. Short mean residence times and high fractions of event water components recommend catchment management measures aiming at reduction of overland flow/soil erosion and increasing of soil water retention and recharge to enable sustainable development in these agriculturally dominated catchments.

Hydrology, 2021

Analysis of the Groundwater flow can help to understand future water potential. This study has ex... more Analysis of the Groundwater flow can help to understand future water potential. This study has explored the predicted groundwater flow dynamics with climate change and anthropogenic stress in Hormat-Golina Sub-basin. Groundwater flow modeling in this Sub-basin has provided information about groundwater quantity as well as the quality aspect for decision-makers about groundwater accessibility. The initial head measured values before and after irrigation season has varied to a maximum of 0.8 m. The groundwater head level before and after irrigation season was varying from 9.3 m to 8.26 m in the Southern boundary. The groundwater head was obtained from 41.5 m to 38.83 m in the northwestern of the Subbasin. The maximum drawdown depth had found to 0.27 m and 2.6 m before and after irrigated season around the pumped wells. The increased pumping rate with decreased recharge rate was replying to the groundwater head at the end of 2021 decreased by 2.81 m in the northwestern boundary of the Sub-basin as compared as using constant pumping rate with recharge rate. While decreased pumping with increased recharge rate was replying to the groundwater head at the end of 2021 has increased by 2.23 m in the northwestern boundary of the Sub-basin as compared as using constant pumping rate. The impacts of climate change and human pressure on groundwater begot as the threats in those supply wells. Decreased pumping with increased recharge rate was accomplishing to restore and protect the groundwater resources, which is the best option for groundwater restoration and monitoring.

Land use change (LUC) is a very important issue considering global dynamics and their responses t... more Land use change (LUC) is a very important issue considering global dynamics and their responses to environmental and socioeconomic drivers. Especially in fast changing developing countries, it is a scientific challenge to predict land use changes and their effects on water availability, flood risk and erosion rates. To address these issues, catchment models must be able to deal with land use dynamics. Unfortunately, many models handle land use in a static state way. The objective of this research is to investigate the effect of dynamic land use implementation into SWAT ("Soil and Water Assessment Tool") by developing the supportive tool "Land use Update and Soil Assessment" (LUPSA) and to improve the overall SW AT abilities to handle LUC. A catchment in the Choke Mountain Range (Ethiopia) was selected as test case where significant land use change occurred during the last decades. These dynamics were addressed by 5 land use maps based on interpretation of aerial photographs and satellite imageries, while several years of climate and discharge data were available. The available data for the test application were carefully analyzed and found to be limited in quantity and quality. LUPSA was applied to feed the SWAT model for the period of 1973 to 2003 with yearly land use updates. The annual LUC varied between-6% and +360% for different classes. The impact of land dynamics on the hydrological response was observed and shown at the daily discharge, the total annual runoff and the peakflow.. Also a higher proportion of low flow rates was found and caused more water stress. Considering the high uncertainties, SWAT was not able to produce reliable results due to the bad data quality. Nevertheless, the implementation of land cover dynamics in SWAT led to a significant change in the model outputs and demonstrated improved capabilities to handle their impacts on water resources. Further model testing is strongly recommended.

Hydrological Sciences Journal-journal Des Sciences Hydrologiques, Sep 25, 2015

The objective of this study is to understand the rainfall-runoff processes of the meso-scale Chem... more The objective of this study is to understand the rainfall-runoff processes of the meso-scale Chemoga and Jedeb catchments in the Abay/Upper Blue Nile basin, Ethiopia. Distributed conceptual modelling and different field data were used in the modelling process. Three different model representations with varying model complexity were employed to test the appropriate model structure. Parameters were conditioned within the Generalized Likelihood Uncertainty Estimation (GLUE) framework using both discharge and environmental isotope information indicating the ratio of new and old water during the wet season. It was demonstrated that the two catchments cannot be modelled equally well with the same model structure due to differences in the rainfallrunoff processes caused by different amounts of wetlands leading to different hydrological responses. Hence, a single model structure for the entire Abay/Upper Blue Nile cannot do justice to all the dominant hydrological processes in the various sub-catchments in the basin.

Assessment of Input Rainfall Uncertainty for Groundwater Recharge Estimation, Tikur-Wuha Watershed, Rift Valley Lakes Basin, Ethiopia

Journal of Water and Climate Change, May 31, 2023

A promising future development area to improve the accuracy of satellite rainfall estimates (SREs... more A promising future development area to improve the accuracy of satellite rainfall estimates (SREs) is accessing merits from different sources of data through combining algorithms. The main objective of this study is to assess the accuracy and importance of the fused multistage approach of bias correction. Accordingly, two versions of resampled and spatially bias-corrected Climate Hazards Group Infrared Precipitation (CHIRP) estimates were merged with ground measurements using a conditional merging procedure. Results of applied performance measures (i.e. seven) on corrected and merged CHIRP SREs show that the Percent of Detection (POD) and Percent Volume Error (PVE) have improved. Depending on the combination of coupled stations for validation, up to 70 and 50% PVE improvement was achieved at some stations for wet and dry periods, respectively. Moreover, the bias-corrected and conditionally merged CHIRP SREs have outperformed the estimates by resampling CHIRP with station dataset (CHIRPS) over the sparsely populated western part of the watershed. However, the devised method was limited in considering dry-day events during bias correction, which in turn has affected the performance of the bias correction of the CHIRPS product. Finally, future research should concentrate on such methods of fusing to understand the benefits of various approaches and produce more precise rainfall records.

Hydrology and Earth System Sciences, Jul 13, 2011

The water balances of twenty catchments in the Upper Blue Nile basin have been analyzed using a t... more The water balances of twenty catchments in the Upper Blue Nile basin have been analyzed using a top-down modeling approach based on Budyko's hypotheses. The objective of this study is to obtain better understanding of water balance dynamics of upper Blue Nile catchments on annual and monthly time scales and on a spatial scale of meso scale to large scale. The water balance analysis using a Budykotype curve at annual scale reveals that the aridity index does not exert a first order control in most of the catchments. This implies the need to increase model complexity to monthly time scale to include the effects of seasonal soil moisture dynamics. The dynamic water balance model used in this study predicts the direct runoff and other processes based on the limit concept; i.e. for dry environments since rainfall amount is small, the aridity index approaches to infinity or equivalently evaporation approaches rainfall and for wet environments where the rainfall amount is large, the aridity index approaches to zero and actual evaporation approaches the potential evaporation. The uncertainty of model parameters has been assessed using the GLUE (Generalized Likelihood Uncertainty Estimation) methodology. The results show that the majority of the parameters are reasonably well identifiable. However, the baseflow recession constant was poorly identifiable. Parameter uncertainty and model structural errors could be the reason for the poorly identifiable parameter. Moreover, a multi-objective model calibration strategy has been employed to emphasize the different aspects of the hydrographs on low and high flows.

Projecting potential evapotranspiration under climate change scenarios using the LARS-WG model in the Lake Ziway Watershed, Ethiopia

International Journal of Global Warming

Modeling Long-Term Water Allocation and Analysis of Alternative Strategic Scenarios in the Catchment Area of Bilate River, Rift Valley Lakes Basin, Ethiopia

Ethiopian Journal of Water Science and Technology

A water shortage stress might have resulted from the extensive water resources development plan i... more A water shortage stress might have resulted from the extensive water resources development plan in the Bilate catchment owing to the rapidly growing population, irrigation development expansion, climatic variability, and socioeconomic development. Furthermore, the lack of sufficient knowledge about available water resources and lack of coordination in water resources management skills in the basin often aggravates the competition of fixed waterresources among the users. Therefore, modeling long-term water allocation should be implemented to determine the optimal allocation of water resources, maximize the overall benefits without compromising ecological requirements, and propose mitigation measures that may alleviate the problem of water scarcity during peak demand periods. The Water Evaluation and Planning (WEAP) model is generally used in the formulation and evaluation of alternative plansfor responding to water-related problems and water resources developments. To assist in the a...

Hydrology Research

Droughts are defined by a prolonged absence of moisture. For making drought assessments, a drough... more Droughts are defined by a prolonged absence of moisture. For making drought assessments, a drought index is a crucial tool. This study aims to compare drought characteristics across the Central Main Ethiopian Rift using three drought indices – the Standardized Precipitation Index (SPI), the Reconnaissance Drought Index (RDI), and the Standardized Precipitation Evapotranspiration Index (SPEI) – from 1980 to 2017 at six climate sites in spring, summer, and a 6-month period (March - August). With 1% and 5% significance levels, Modified Mann-Kendall and Sen's Slope Estimators were used to determine trend and magnitude, respectively. The temporal fluctuations of the three drought indices revealed that droughts are frequent, unpredictable, and random. Furthermore, they behaved similarly and had significant links. At most places, the drought indices found no significant trends. However, in the spring season, Butajira (by the three indices) and Wulbareg (by the SPI) showed significantly...

Water, Dec 5, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Enhancing decision making tools for climate-smart water management in the Awash Basin, Ethiopia

Decision analysis techniques to meet water systems management challenges under climate change unc... more Decision analysis techniques to meet water systems management challenges under climate change uncertainty have improved with advances in computational technology in the last decades. Infusing improved design and decision analysis techniques in developing countries can be of paramount importance given their higher vulnerability to climate change, fewer professionals with sufficient capacity, and generally high incentive for rapid expansion of low-cost solutions. However, a large gap exists between scientific progress and practical and policy applications, especially in global south countries. In this paper we discuss the observed challenges in design, analysis and decision making process to achieve climate smart water management in the highly utilized Awash Basin of Ethiopia. The approach we followed is key-informant interviews with water professionals working across multiple disciplines (i.e., water supply, irrigation, hydropower infrastructure design) and working for different org...

Quantifying sensitivity of groundwater recharge to land use and land cover changes by improving model performance on the wetland dominated Tikur Wuha Watershed, Ethiopia

Water Cycle

Hydrology

Quantifying uncertainties in water resource prediction in data-scarce regions is essential for re... more Quantifying uncertainties in water resource prediction in data-scarce regions is essential for resource development. We use globally available datasets of precipitation and potential evapotranspiration for the regionalization of model parameters in the data-scarce regions of Ethiopia. A regional model was developed based on 14 gauged catchments. Three possible parameter sets were tested for regionalization: (1) the best calibration parameters, (2) the best validation parameter set derived from behavioral parameters during the validation period, and (3) the stable parameter sets. Weighted multiple linear regression was applied by assigning more weight to identifiable parameters, using a novel leave-one-out cross-validation technique for evaluation and uncertainty quantification. The regionalized parameter sets were applied to the remaining 35 ungauged catchments in the Ethiopian Rift Valley Lake Basin (RVLB) to provide regional water balance estimations. The monthly calibration of th...

Uncertainties of monthly discharge data and parameters in the ungauged catchments of the Ethiopian RVLB

In this study to quantify the uncertainty of the regionalization procedure, we apply all 14 regio... more In this study to quantify the uncertainty of the regionalization procedure, we apply all 14 regionalized models that were created for the leave-one-out evaluation to the ungauged catchments. With this regard, an ensemble of 14 predicted streamflow time series is produced for each ungauged catchment to reflect the regionalization uncertainty. We provide the summary of the data below: 1) We provided the Uncertainties of Monthly Discharge simulation for the ungauged catchments obtained from the regionalization. The data is provided by excel file as Uncertainties_of_Monthly_Discharge_Ungauged.xlsx. This file contains 35 sheets for the 35 ungauged catchment, and 14 prediction intervals (ensembles) on each sheet. The data ranges from 1995-2007 on a monthly scale and contains 156-row values for the 13-year simulation periods. 2) We also provided the Uncertainties of parameters for the ungauged catchments. The data is prepared in the file (Uncertainties_of_parameters_ungauged_catchments.xls...

Surface Energy Balance Algorithm for Land (SEBAL) based Evapotranspiration Estimation in Lower Gilgel Abay Catchment Lake Tana Sub-Basin, Ethiopia

Agricultural and Veterinary Sciences, 2019

Irrigation and Drainage Systems Engineering, 2021

Deficit irrigation is one of agricultural water management practice in arid area in which the irr... more Deficit irrigation is one of agricultural water management practice in arid area in which the irrigation water management has to be improved so that water supply to the crop can be reduced while still achieving high yield. The main objective of this study was to improve agricultural water use efficiency (WUE) of onion under different deficit irrigation levels. Randomized complete block design (RCBD) with eleven treatments and three replications was used. The treatments were: full irrigation (0% deficit as a control), and 25% and 50% of crop water requirement (CWR) deficit throughout growing season, and one period deficit treatments (25% and 50% of CWR deficit at initial, development, bulb formation and maturity stages). Treatment 10 (50% of CWR deficit at bulb formation stage) showed the minimum harvest index (0.68) and 25% of CWR deficit at initial and maturity stages respectively showed the maximum harvest index. Yield response factor (ky) indicated that onion was sensitive (yield reduced) for water deficit at development and bulb formation stages. The maximum water use efficiency (4.98 kg/m 3) was observed at 50% of CWR deficit throughout growing season and the minimum (3.22 kg/m 3) was observed at 50% of CWR deficit at bulb formation stage. Water deficit at initial and maturity growth periods had insignificant impact on WUE of onion. Generally, this result indicated that water deficit at bulb formation growth period of onion reduce more water use efficiency than water deficit on other growth periods.

Journal of Water and Climate Change, 2022

The purpose of this study is to predict future changes in precipitation in the Central Ethiopian ... more The purpose of this study is to predict future changes in precipitation in the Central Ethiopian Main Rift, which is vulnerable to climate change. The Long Ashton Research Station Weather Generator (LARS-WG) model was applied to project precipitation based on five global climate models (GCMs) (EC-EARTH, MIROC-ESM, HadGEM2-ES, INM-CM4, and CCSM4) from Coupled Model Intercomparison Project phase 5 (CMIP5) under two representative concentration pathways (RCP4.5 and RCP8.5) in the periods of 2041–2060 compared to the baseline period of 1976–2005. The model's calibration and validation results showed that it could predict future precipitation. According to the analysis, the mean rainfall is expected to increase in January (up to 14.2%) and December (up to 27.8%) under the RCP 4.5 and RCP 8.5 scenarios, respectively. However, a drop is anticipated in June (up to 8.2%) and May (up to 7%) under the RCP 4.5 and RCP 8.5 scenarios, respectively. In both scenarios, summer precipitation (usu...

Regionalization and association with global climate drivers of rainfall in the Rift Valley Lakes Basin of Ethiopia

Theoretical and Applied Climatology, 2022

Regionalization and evaluation of associations of hydro-climatic variables with indices of global... more Regionalization and evaluation of associations of hydro-climatic variables with indices of global climate drivers are helpful for local-scale seasonal forecasting of weather patterns and planning water resources management. The main objective was to regionalize the Ethiopian Rift Valley Lakes Basin into homogenous sub-regions based on monthly and seasonal rainfalls and investigate the influence of some global climate drivers at the scale of the sub-regions to devise predictive tools. The dataset used monthly rainfall and global and regional climate indices anomalies from 1983 to 2014. Principal component analysis (PCA), Pearson correlation, and multivariate linear regression methods were applied using SPSS and R software. Based on PCA analysis, three principal components were identified which have a significant association with global climate indices. Over the study period, there were nine moderates to strong El Niño and six La Niña events; the warming phases received more rainfall and less in the cooling phase. Lagged sea surface temperature (SST) and atmospheric variables were selected as predictors based on significant associations with regional rainfall. The multiple linear regression analysis revealed the possibilities of deriving seasonal forecasts at the local level. The study showed that the model derived an excellent and scientifically robust seasonal rainfall prediction skill in a short lead time of the different seasons at a range of 30 to 80% in the sub-regional level. The capabilities of rainfall prediction skills help reduce climate-induced hazards in planning and decision-making processes by providing timely and specific climate information.