scholarly journals Ephemeral stream dynamics, land cover changes and climate variability in the marginal grabens of the northern Ethiopian Rift Valley

Afrika Focus ◽  
2016 ◽  
Vol 29 (2) ◽  
Author(s):  
Biadgilgn Demissie
Keyword(s):  
Land Cover ◽  
Climate Variability ◽  
Rift Valley ◽  
Rainfall Variability ◽  
Bank Erosion ◽  
Ethiopian Rift ◽  
Land Cover Changes ◽  
Northern Ethiopia ◽  
Ephemeral Streams ◽  
Alluvial Deposits

This study focused on ephemeral streams morphodynamics and their relation with hydro-climatic and bio-physical characteristics in their headwater and graben floors in the marginal grabens along the northern Ethiopian Rift Valley. The Raya graben was taken as a case study area, which is the largest marginal graben in northern Ethiopia. The link between rainfall variability and land cover changes shows that there was a negative correlation between precipitation and deforestation which implies that an increase in precipitation decreases deforestation deterring the peasants from tree cutting. Regarding the relationship between upper catchment characteristics and river morphology, results show that upper catchment area is the most important controlling factor of the length of and the area occupied by the rivers in the graben bottom. A simple hydraulic analysis based on the change of specific discharge as the river ow approaches the bridges demonstrates that the abrupt change in channel width as the river approaches the bridge is the main cause of the thick deposition and, consequently, of the increased frequency of overbank oods upstream of the road bridges in the study area. The results related to channel bank erosion capacity of ash oods show that all the peak discharges were equally important in triggering channel bank erosion. Concomitantly, vegetated channels are much more resist- ant to channel bank erosion than non-vegetated banks. Land changes in graben bottoms dictate that the changes are not simply related to a distributary river system but that human interven- tion (e.g., the conversion of bushland and forests into cropland, settlement on alluvium, and avoidance of losing farmland to other land units) and natural vegetation regeneration (e.g., alluvial deposits into shrubland) are also important. Overall, the study suggests that to control the morphodynamics of the ephemeral rivers and their impact on farming activities in the gra- ben bottom, catchment rehabilitation activities need to focus both on the upper catchment and the river channels in the graben bottom. Key words: ephemeral streams, land change, graben, Rift Valley, land cover, climate variability 

scholarly journals Ephemeral stream dynamics, land cover changes and climate variability in the marginal grabens of the northern Ethiopian Rift Valley

Afrika Focus ◽  
2016 ◽  
Vol 29 (2) ◽  
pp. 93-100
Author(s):  
Biadgilgn Demissie
Keyword(s):  
Land Cover ◽  
Rift Valley ◽  
River Flow ◽  
Rainfall Variability ◽  
Bank Erosion ◽  
Ethiopian Rift ◽  
Land Cover Changes ◽  
Northern Ethiopia ◽  
River Channels ◽  
Alluvial Deposits

This study focused on ephemeral streams morphodynamics and their relation with hydro-climatic and bio-physical characteristics in their headwater and graben floors in the marginal grabens along the northern Ethiopian Rift Valley. The Raya graben was taken as a case study area, which is the largest marginal graben in northern Ethiopia. The link between rainfall variability and land cover changes shows that there was a negative correlation between precipitation and deforestation which implies that an increase in precipitation decreases deforestation deterring the peasants from tree cutting. Regarding the relationship between upper catchment characteristics and river morphology, results show that upper catchment area is the most important controlling factor of the length of and the area occupied by the rivers in the graben bottom. A simple hydraulic analysis based on the change of specific discharge as the river flow approaches the bridges demonstrates that the abrupt change in channel width as the river approaches the bridge is the main cause of the thick deposition and, consequently, of the increased frequency of overbank floods upstream of the road bridges in the study area. The results related to channel bank erosion capacity of flash floods show that all the peak discharges were equally important in triggering channel bank erosion. Concomitantly, vegetated channels are much more resistant to channel bank erosion than non-vegetated banks. Land changes in graben bottoms dictate that the changes are not simply related to a distributary river system but that human intervention (e.g., the conversion of bushland and forests into cropland, settlement on alluvium, and avoidance of losing farmland to other land units) and natural vegetation regeneration (e.g., alluvial deposits into shrubland) are also important. Overall, the study suggests that to control the morphodynamics of the ephemeral rivers and their impact on farming activities in the graben bottom, catchment rehabilitation activities need to focus both on the upper catchment and the river channels in the graben bottom.

Land cover changes as impacted by spatio-temporal rainfall variability along the Ethiopian Rift Valley escarpment

2016 ◽  
Vol 17 (2) ◽  
pp. 451-463 ◽  
Author(s):  
Sofie Annys ◽  
Biadgilgn Demissie ◽  
Amanuel Zenebe Abraha ◽  
Miro Jacob ◽  
Jan Nyssen
Keyword(s):  
Land Cover ◽  
Rift Valley ◽  
Rainfall Variability ◽  
Ethiopian Rift ◽  
Land Cover Changes ◽  
Spatio Temporal

Detection and analysis of land-use and land-cover changes in the Midwest escarpment of the Ethiopian Rift Valley

2012 ◽  
Vol 7 (3) ◽  
pp. 239-260 ◽  
Author(s):  
Daniel Ayalew Mengistu ◽  
Daniel Kassahun Waktola ◽  
Muluneh Woldetsadik
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Rift Valley ◽  
Ethiopian Rift ◽  
Land Cover Changes

scholarly journals Drivers of Land Use-Land Cover Changes in the Central Rift Valley of Ethiopia

2019 ◽  
Vol 48 (7) ◽  
pp. 1333-1345
Author(s):  
Belew Bekele ◽  
Wei Wu ◽  
Eshetu Yirsaw
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Rift Valley ◽  
Land Cover Changes ◽  
Land Use Land Cover

scholarly journals Climate or land cover variations: what is driving observed changes in river peak flows? A data-based attribution study

2018 ◽  
Author(s):  
Jan De Niel ◽  
Patrick Willems
Keyword(s):  
Climate Change ◽  
Land Cover ◽  
Climate Variability ◽  
Hydrological Cycle ◽  
Hydrological Regime ◽  
Interaction Effects ◽  
Land Cover Changes ◽  
Peak Flows ◽  
Catchment Characteristics ◽  
Interaction Terms

Abstract. Climate change and land cover changes are influencing the hydrological regime of our rivers. The intensification of the hydrological cycle caused by climate change is projected to cause more flooding in winters and an increased urbanization could amplify these effects by a quicker runoff on paved surfaces. The relative importance of both drivers, however, is still uncertain and interaction effects between both drivers are not yet well understood. In order to better understand the hydrological impact of climate variability and land cover changes, including their interaction effects, we fitted a statistical model to historical data over 3 decades for 29 catchments in Flanders, covering various catchment characteristics. It was found that the catchment characteristics explain up to 18 % of changes in river peak flows, climate variability 6 % and land cover changes 8 %. Interaction terms explain up to 32 %. An increase in urban area of +1 % might cause increases in river peak flows up to +5 %.

The dynamics of urban expansion and land use/land cover changes using remote sensing and spatial metrics: the case of Mekelle City of northern Ethiopia

2017 ◽  
Vol 38 (14) ◽  
pp. 4107-4129 ◽  
Author(s):  
Ayele Almaw Fenta ◽  
Hiroshi Yasuda ◽  
Nigussie Haregeweyn ◽  
Ashebir Sewale Belay ◽  
Zelalem Hadush ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Land Use ◽  
Land Cover ◽  
Urban Expansion ◽  
Land Cover Changes ◽  
Northern Ethiopia ◽  
Land Use Land Cover ◽  
Spatial Metrics ◽  
Mekelle City

scholarly journals Land Use and Land Cover Change for Resilient Environment and Sustainable Development in the Ethiopian Rift Valley Region

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Getahun Hassen ◽  
Amare Bantider ◽  
Abiyot Legesse ◽  
Malesu Maimbo ◽  
Dereje Likissa
Keyword(s):  
Climate Change ◽  
Land Use ◽  
Sustainable Development ◽  
Land Cover ◽  
Land Cover Change ◽  
Rift Valley ◽  
Agroforestry System ◽  
Ethiopian Rift ◽  
Landsat 8 ◽  
Bare Land

Abstract Land use and land cover change (LULCC) are the result of different interacting socio-economic and environmental causes and consequences that have been known since the beginning of agriculture. The study intended to explore the implications and drivers of LULCC in the Ethiopian rift valley region of Gidabo river sub basin from 1986 to 2019. The researchers have triangulated the data from Landsat 5 (™), and Landsat 8 (OLI) with data obtained from key informants, focus groups and field observation, which is helpful to determine the interaction between the environment and the community. It is also important to mitigate environmental disaster (erosion, landslides, and climate change) and sustainable utilization of natural resources. The LULCC of the past 33 years implied that about 58.4 % of the area was changed to other Land use land cover (LULC) classes. This refers to the fact that about 14% of agroforestry, 2% of the settlement, 1.1% of the forest, and 1% of bare land were expanded at the expense of 10.3% of shrub/woodland, 6.3 % of grassland, and 1% of cropland classes. Therefore, as a result, the highest land cover (46.7%) was observed on the agroforestry system. Participants in group discussion and informant interviews attributed the expansion of agroforestry to the drivers, such as population density, cultural values (Songo, Babbo), traditional beliefs, land policy, and the insecurity resulting from climate change. Whereas, the drivers related to unproductive land, resettlement, urbanisation, and lack of agricultural inputs were considered as threats that will adversely affect the agroforestry system of the area. The study concluded that the high expansion of the agroforestry system has significant contribution to achieve a resilient environment and sustainable development, which integrates the socio-economic and environmental needs of the community. But greater attention should be given to the changes observed in shrub/woodland, grassland, and bare land to enhance environmental protection.

scholarly journals Natural Groundwater Recharge Response to Climate Variability and Land Cover Change Perturbations in Basins with Contrasting Climate and Geology in Tanzania

Earth ◽  
2021 ◽  
Vol 2 (3) ◽  
pp. 556-585
Author(s):  
Kassim Ramadhani Mussa ◽  
Ibrahimu Chikira Mjemah ◽  
Revocatus Lazaro Machunda
Keyword(s):  
Land Use ◽  
Soil Moisture ◽  
Land Cover ◽  
Climate Variability ◽  
Groundwater Recharge ◽  
Land Cover Changes ◽  
Moisture Balance ◽  
Two Temperature ◽  
Semi Arid ◽  
Soil Moisture Balance

The response of aquifers with contrasting climate and geology to climate and land cover change perturbations through natural groundwater recharge remains inadequately understood. In Tanzania and elsewhere in the world, studies have been conducted to assess the impact of climate change and variability, and land use/cover changes on stream flow using different models, but similar studies on groundwater dynamics are inadequate. This study, therefore, examined the influence of land use/cover and climate dynamics on natural groundwater recharge in basins with contrasting climate and geology in Tanzania, applying the modified soil moisture balance method, coupled with the curve number (CN). The method hinges on the balance between the incoming water from precipitation and the outflow of water by evapotranspiration. The different parameters in the soil moisture balance method were computed using the Thornthwaite Water Balance software. The potential evapotranspiration (PET) was calculated using the daily maximum and minimum temperatures, utilizing two-temperature-based PET methods, Penman–Monteith (PM) and Hargreaves–Samani (HS). The rainfall data were obtained from the gauging stations under the Tanzania Meteorological Agency and some additional data were acquired from climate observatories management by water basins. The results show that there has been a quasi-stable CN in the Singida semi-arid, fractured crystalline basement aquifer (74.2 in 1997, 73.64 in 2005, and 73.87 in 2018). In the Kimbiji, humid, Neogene sedimentary aquifer, the CN has been steadily increasing (66.69 in 1997, 69.08 in 2008, and 71.42 in 2016), indicating the rapid land cover changes in the Kimbiji aquifer as compared to the Singida aquifer. For the Kimbiji humid aquifer, the PET calculated using the Penman–Monteith (PM) method for the 1996/1997, 2007/2008, and 2015/2016 hydrological years were 1156.5, 1079.5, and 1143.9 mm/year, respectively, while for the Hargreaves–Samani (HS) method, the PET was found to be 1046.1, 1138.3, and 1204.4 mm/year for the 1996/1997, 2007/2008, and 2015/2016 hydrological years, respectively. For the Singida semi-arid aquifer, the PM PET method resulted in 2083.3, 2053.6, and 1875.4 mm/year for the 1996/1997, 2004/2005, and 2017/2018 hydrological years, respectively. The HS method produced relatively lower PET values for the semi-arid area (1839.4, 1814.7, and 1710.2 mm/year) for the 1996/1997, 2004/2005, and 2017/2018 hydrological years, respectively. It was equally revealed that the recharge and aridity indices correspond with the PET calculated using two temperature-dependent methods. The decline of certain land covers (forests) and increase in others (built-up areas) have contributed to the increase in surface runoff in each study area, possibly resulting in the decreasing trend of groundwater recharge. An overestimation of the PET using the HS method in the Kimbiji humid aquifer was observed, which was relatively smaller than the overestimation of the PET using the PM method in the Singida semi-arid aquifer. Despite the difference in climate and geology, the response of the two aquifers to rainfall is similar. The combined influence of climate and land cover changes on natural groundwater recharge was observed to be prominent in the Kimbiji aquifer, while only climate variability appreciably influences natural groundwater recharge in the Singida semi-arid aquifer. El Nino and the Southern Oscillation as part of the climate variability phenomenon dwarfed the time lags between rainfall and recharge in the two basins, regardless of their difference in climate and geology.

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