scholarly journals Characterisation of stable isotopes to identify residence times and runoff components in two meso-scale catchments in the Abay/Upper Blue Nile basin, Ethiopia

2014 ◽  
Vol 18 (6) ◽  
pp. 2415-2431 ◽  
Author(s):  
S. Tekleab ◽  
J. Wenninger ◽  
S. Uhlenbrook
Keyword(s):  
Stable Isotopes ◽  
Stable Isotope ◽  
Isotopic Composition ◽  
Residence Times ◽  
Nile Basin ◽  
Blue Nile ◽  
Source Areas ◽  
Blue Nile Basin ◽  
Mean Residence Times ◽  
Meso Scale

Abstract. Measurements of the stable isotopes oxygen-18 (18O) and deuterium (2H) were carried out in two meso-scale catchments, Chemoga (358 km2) and Jedeb (296 km2) 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 (R2 varies from 0.38 to 0.68) and weak regression coefficients (R2 varies from 0.18 to 0.58) for the altitude and temperature effects. A mean altitude effect accounting for −0.12‰/100 m for 18O and −0.58‰/100 m for 2H 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.

scholarly journals Identifying residence times and streamflow generation processes using δ<sup>18</sup>O and δ<sup>2</sup>H in meso-scale catchments in the Abay/Upper Blue Nile, Ethiopia

2013 ◽  
Vol 10 (8) ◽  
pp. 10333-10377 ◽  
Author(s):  
S. Tekleab ◽  
J. Wenninger ◽  
S. Uhlenbrook
Keyword(s):  
Stable Isotope ◽  
Isotopic Composition ◽  
Isotope Composition ◽  
Spring Water ◽  
Residence Times ◽  
Nile Basin ◽  
Source Areas ◽  
Mean Residence Times ◽  
Seasonal Time Scale ◽  
Meso Scale

Abstract. Measurements of the stable isotopes oxygen-18 (18O) and deuterium (2H) were carried out in two meso-scale catchments, Chemoga (358 km2) and Jedeb (296 km2) south of Lake Tana, Abay/Upper Blue Nile basin, Ethiopia. The region is of paramount importance for the water resources in the Nile basin. Stable isotope composition in precipitation, spring water and streamflow were analyzed (i) to characterize 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 at a seasonal time scale. The results show that the isotopic composition of precipitation exhibit marked seasonal variations, which suggests different sources of moisture generation for the rainfall in the study area. The Atlantic–Indian ocean, Congo basin, and the Sud swamps are the likely 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 of the isotopic composition is affected by the amount effect and to less extent by altitude and temperature effects. A mean altitude effect of −0.12‰ (100 m)−1 for 18O and −0.58‰ (100 m)−1 for 2H were discernable in precipitation isotope composition. The seasonal variations of the isotopic signature of the spring water exhibit a damped response as compared to the river waters, which shows that the spring water has longer residence times than the river water. Results from the hydrograph separation at a seasonal time scale 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 catchment, respectively. The stable isotope compositions of streamflow samples were damped compared to the input function of precipitation for both catchments and 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 outlet, respectively. Short mean residence times and high proportions of event water components suggest catchment management measure aiming at reduction of overland flow/soil erosion and increasing of soil water retention and recharge to enable sustainable development in these agricultural dominated catchments.

scholarly journals An efficient semi-distributed hillslope erosion model for the sub humid Ethiopian Highlands

2012 ◽  
Vol 9 (2) ◽  
pp. 2121-2155 ◽  
Author(s):  
S. A. Tilahun ◽  
C. D. Guzman ◽  
A. D. Zegeye ◽  
T. A. Engda ◽  
A. S. Collick ◽  
...  
Keyword(s):  
Surface Runoff ◽  
Overland Flow ◽  
Sediment Concentration ◽  
Base Flow ◽  
Nile Basin ◽  
Erosion Model ◽  
Blue Nile ◽  
Ethiopian Highlands ◽  
Source Areas ◽  
Blue Nile Basin

Abstract. During the last two decades, saturated excess runoff has become accepted as the main source for overland flow in humid regions. Erosion modeling has generally not kept up with this new reality and predictions are often not based on landscape topographic position, which is a main variable in saturation excess runoff. In addition, predicting sediment loss in Africa has been hampered by using models that have been developed in western countries and do not perform as well in the monsoon climate prevailing in most of the continent. The objective of this paper is to develop a simple erosion model that can be used in the Ethiopian highlands in Africa. We base our sediment prediction on a simple distributed saturated excess hydrology model that predicts surface runoff from severely degraded lands and from bottom lands that become saturated during the rainy season and estimates interflow and base flow from the remaining portions of the landscape. By developing an equation that relates surface runoff to sediment concentration generated from runoff source areas, assuming that base flow and interflow are sediment free, we were able to predict daily sediment concentrations from the Anjeni Watershed and Blue Nile Basin with a Nash Sutcliffe efficiency ranging from 0.64 to 0.77 using only two calibrated sediment parameters. Anjeni is a 113 ha watershed in the 17.4 million ha Blue Nile Basin in the Ethiopian Highlands. The daily flows were predicted with Nash Sutcliffe efficiency values ranging from 0.80 to 0.93 if degraded areas were assumed the major sediment source areas and covered 14% of the Anjeni watershed and 20% of the Blue Nile basin. The analysis suggests that identifying the runoff source areas and predicting the surface runoff correctly is an important step in predicting the sediment concentration.

scholarly journals Modelling rainfall–runoff processes of the Chemoga and Jedeb meso-scale catchments in the Abay/Upper Blue Nile basin, Ethiopia

2015 ◽  
pp. 1-18 ◽  
Author(s):  
Sirak Tekleab ◽  
Stefan Uhlenbrook ◽  
Hubert H.G. Savenije ◽  
Yasir Mohamed ◽  
Jochen Wenninger
Keyword(s):  
Rainfall Runoff ◽  
Nile Basin ◽  
Blue Nile ◽  
Blue Nile Basin ◽  
Meso Scale ◽  
Upper Blue Nile Basin

scholarly journals The Analysis of Short-Term Dataset of Water Stable Isotopes Provides Information on Hydrological Processes Occurring in Large Catchments from the Northern Italian Apennines

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1360 ◽  
Author(s):  
Cervi ◽  
Dadomo ◽  
Martinelli
Keyword(s):  
Stable Isotopes ◽  
Isotopic Composition ◽  
Sine Wave ◽  
Hydrological Processes ◽  
Water Molecules ◽  
Residence Times ◽  
Catchment Characteristics ◽  
Mean Residence Times ◽  
Italian Apennines ◽  
Short Time

This study discusses a dataset of water stable isotopes from precipitation (4 rain gauges) and surficial water (9 rivers) from the northern Italian Apennines, an area in which clay-rich bedrocks widely outcrop and the runoff response to precipitation events is very rapid. The dataset has been compiled starting from existing data that had previously been published in the literature and consists of monthly values of stable isotopes oxygen-18 (18O) and deuterium (2H) lasting over the period from January 2003 to December 2006 (precipitation) and from January 2006 to December 2007 (surficial water). For this period, mean residence times estimated by means of a sine-wave fitting technique make evident the significant differences over time spent by water molecules within the 9 catchments. Moreover, isotopic compositions of rivers deviated from those of precipitations revealing the influence of some catchment characteristics in differentiating the isotopic composition in rivers. Further correlations between mean residence times of river water and selected catchment characteristics reveal the role of orography and bedrocks in delaying the water molecules during their flow-paths. In addition, time series and cross–correlation analyses indicate a certain control by the main watershed divide on the isotopic composition of river waters, which is reflected in a progressive isotopic variation with longitude. The study shows that, despite using a short-time dataset (2-years for surficial water) of sparse stable isotopes can provide remarkable indications for depicting hydrological processes in large catchments made up of clay-rich bedrocks.

scholarly journals Multi-Dimensional Drought Assessment in Abbay/Upper Blue Nile Basin: The Importance of Shared Management and Regional Coordination Efforts for Mitigation

2021 ◽  
Vol 13 (9) ◽  
pp. 1835
Author(s):  
Yared Bayissa ◽  
Semu Moges ◽  
Assefa Melesse ◽  
Tsegaye Tadesse ◽  
Anteneh Z. Abiy ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Regional Scale ◽  
Earth Observation ◽  
Drought Indices ◽  
Severe Drought ◽  
Nile Basin ◽  
Blue Nile ◽  
Blue Nile Basin ◽  
Small Streams ◽  
Upper Blue Nile Basin

Drought is one of the least understood and complex natural hazards often characterized by a significant decrease in water availability for a prolonged period. It can be manifested in one or more forms as meteorological, agricultural, hydrological, and/or socio-economic drought. The overarching objective of this study is to demonstrate and characterize the different forms of droughts and to assess the multidimensional nature of drought in the Abbay/ Upper Blue Nile River (UBN) basin and its national and regional scale implications. In this study, multiple drought indices derived from in situ and earth observation-based hydro-climatic variables were used. The meteorological drought was characterized using the Standardized Precipitation Index (SPI) computed from the earth observation-based gridded CHIRPS (Climate Hazards Group InfraRed Precipitation with Station) rainfall data. Agricultural and hydrological droughts were characterized by using the Soil Moisture Deficit Index (SMDI) and Standardized Runoff-discharge Index (SRI), respectively. The monthly time series of SMDI was derived from model-based gridded soil moisture and SRI from observed streamflow data from 1982 to 2019. The preliminary result illustrates the good performance of the drought indices in capturing the historic severe drought events (e.g., 1984 and 2002) and the spatial extents across the basin. The results further indicated that all forms of droughts (i.e., meteorological, agricultural, and hydrological) occurred concurrently in Abbay/Upper Blue Nile basin with a Pearson correlation coefficient ranges from 0.5 to 0.85 both Kiremt and annual aggregate periods. The concurrent nature of drought is leading to a multi-dimensional socio-economic crisis as indicated by rainfall, and soil moisture deficits, and drying of small streams. Multi-dimensional drought mitigation necessitates regional cooperation and watershed management to protect both the common water sources of the Abbay/Upper Blue Nile basin and the socio-economic activities of the society in the basin. This study also underlines the need for multi-scale drought monitoring and management practices in the basin.

scholarly journals Changes in ecosystem service values strongly influenced by human activities in contrasting agro-ecological environments

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Mulatu Liyew Berihun ◽  
Atsushi Tsunekawa ◽  
Nigussie Haregeweyn ◽  
Mitsuru Tsubo ◽  
Ayele Almaw Fenta
Keyword(s):  
Population Growth ◽  
Ecosystem Service ◽  
Cultivated Land ◽  
Nile Basin ◽  
Grazing Land ◽  
Blue Nile ◽  
Lulc Changes ◽  
Blue Nile Basin ◽  
The Impact ◽  
Upper Blue Nile Basin

Abstract Background Evaluating the impacts of land-use/land-cover (LULC) changes on ecosystem service values (ESVs) is essential for sustainable use and management of ecosystems. In this study, we evaluated the impact of human activity driven LULC changes on ESVs over the period 1982–2016/17 in contrasting agro-ecological environments: Guder (highland), Aba Gerima (midland), and Debatie (lowland) watersheds of the Upper Blue Nile basin, Ethiopia. Results During the study period, the continuous expansion of cultivated land at the expense of natural vegetation (bushland, forest, and grazing land) severely reduced the total ESV by about US$ 58 thousand (35%) in Aba Gerima and US$ 31 thousand (29%) in Debatie watersheds. In contrast, the unprecedented expansion of plantations, mainly through the planting of Acacia decurrens, led, from 2006, to a ESV rebound by about US$ 71 thousand (54%) in Guder watershed, after it had decreased by about US$ 61 thousand (32%) between 1982 and 2006. The reduction in natural forest area was the major contributor to the loss of total ESV in the study watersheds, ranging from US$ 31 thousand (63%) in Debatie to US$ 96.9 thousand (70%) in Guder between 1982 and 2016/17. On an area-specific basis, LULC changes reduced the average ESV from US$ 560 ha−1 year−1 (1982) in Guder to US$ 306 ha−1 year−1 (2017) in Debatie watersheds. Specific ESVs such as provisioning (mainly as food production) and regulating services (mainly as erosion control and climate regulation) accounted for most of the total ESVs estimated for the study watersheds. Conclusions In most cases, the total and specific ESVs of the watersheds were negatively associated with the population growth, which in turn was positively associated with the expansion of cultivated land over the study period. In Guder, however, ESVs were positively associated with population growth, especially after 2012. This is mainly due to the expansion of Acacia decurrens plantations. Our results suggest, therefore, that future policy measures and directions should focus on improving vegetation cover through planting multipurpose trees such as Acacia decurrens to prevent future loss of ESV in the midland and lowland regions of the Upper Blue Nile basin and beyond. However, caution must be taken during plantation of invasive species as they may have undesirable consequences.

scholarly journals SWAT and HBV Models' response to streamflow estimation in the Upper Blue Nile Basin, Ethiopia

2021 ◽  
Author(s):  
Belay B. Bizuneh ◽  
Mamaru A. Moges ◽  
Berhanu G. Sinshaw ◽  
Mulu S. Kerebih
Keyword(s):  
Nile Basin ◽  
Blue Nile ◽  
Blue Nile Basin ◽  
Streamflow Estimation ◽  
Upper Blue Nile Basin
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