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1.
Abebech Abera Niko E.C. Verhoest Seifu A. Tilahun Tena Alamirew Enyew Adgo Michael M. Moges 《自然地理学》2019,40(3):227-251
This study was conducted to investigate technical and socio-political attributes that lead to the underperformance of two selected irrigation schemes (Shina and Bebeks) in the Lake Tana floodplains, Ethiopia. Irrigation application efficiency (AE) at nine experimental fields showed a wide range, from 20 to 80%, but was mostly between 40 and 60%. Irrigation water-use efficiency (IWUE) varied from 1.9 to 7.2 kg m?3 for onion and 0.9 to 1.2 kg m?3 for maize. The lined and earthen canal conveyance losses in Bebeks were 0.037 and 0.047 l s?1 m?1, whereas in Shina they were 0.033 and 0.044 l s?1 m?1, respectively. The overall consumed ratio (OCR) of water was 0.58 for Bebeks and varied from 0.73 to 1.2 in Shina. Both schemes are performing below the standard based on technical performance indicators. Irrigation water user associations (WUAs) were not implemented, but irrigation committees (ICs), composed of local political leaders, are managing both schemes. Canal and reservoir sedimentation from erosion of upstream catchment areas during the rainy season was the major problem. 相似文献
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Kassaye Aklilu Alemayehu Mohammed Abdella Kemal Angello Zelalem Abera 《Water Resources》2022,49(3):402-412
Water Resources - The hydraulic relationships of flow through the weir of different common shapes were investigated in this study. The hydraulic performances of weirs were carried out... 相似文献
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Melkamu Meseret Alemu 《资源与生态学报(英文版)》2019,10(1):77-85
Analysis of the nexus between vegetation dynamics and climatic parameters like surface temperature is essential in environmental and ecological studies and for monitoring of the natural resources. This study explored the spatio-temporal distribution of land surface temperature (LST) and Normalized Difference Vegetation Index (NDVI) and the relationship between them in the Andassa watershed from 1986 to 2016 periods using Landsat data. Monthly average air temperature data of three meteorological sites were used for validating the results. The findings of the study showed that the LST of the Andassa watershed has increased during the study periods. Overall, average LST has been rising with an increasing rate of 0.081°C per year. Other results of this study also showed that there has been a dynamic change in vegetation cover of the watershed in all seasons. There was also a negative correlation between LST and NDVI in all the studied years. From this study we can understand that there has been degradation of vegetation and intensification of LST from 1986 to 2016. 相似文献
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Ethiopia??s agriculture is predominantly rainfed and hence any irregularity in weather conditions has adverse welfare implications. Using panel data, this paper analyzes the effect of rainfall shocks on Ethiopian rural households?? food security and vulnerability over time while controlling for a range of other factors. To this end, we generate a time-variant household food security index which is developed by principal components analysis. Based on this index, households are classified into relative food security groups and their socioeconomic differences are assessed. The exploratory results show that compared to the less secured households, the more secured ones have male and literate household heads, tend to have a greater number of economically active household members, own more livestock, experience better rainfall outcome, and participate in local savings groups. Using the food security index as the dependent variable, we use a fixed effects instrumental variable regression model to identify determinants of households?? food security over time and find that rainfall variability is an important factor. Moreover, household size, participation in local savings groups, and livestock ownership positively affect food security. Results from multinomial logistic regression model complement the fixed effects instrumental variable regression results by showing that the level and variability of rainfall are important determinants of persistent food insecurity and vulnerability. The results highlight the need for efficient risk reduction and mitigation programs to improve risk exposure and coping ability of rural households. Careful promotion of investment in infrastructure to support irrigation and water resources development is one aspect worth considering. 相似文献
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GeoJournal - Qoltso is a seasonal crop that grows as weedy root crop where the land is cultivated for other cerials. The production and productivity of Qoltso is rapidly declining which resulted in... 相似文献
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This study is aimed at demonstrating the feasibility of the large scale LAI inversion algorithms using red and near infrared reflectance obtained from high resolution satellite imagery. Radiances in digital counts were obtained in 10 m resolution acquired on cloud free day of August 23, 2007, by the SPOT 5 high resolution geometric (HRG) instrument on mostly temperate hardwood forest located in the Great Lakes – St. Lawrence forest in Southern Quebec. Normalized difference vegetation index (NDVI), scaled difference vegetation index (SDVI) and modified soil-adjusted vegetation index (MSAVI) were applied to calculate gap fractions. LAI was inverted from the gap fraction using the common Beer–Lambert's law of light extinction under forest canopy. The robustness of the algorithm was evaluated using the ground-based LAI measurements and by applying the methods for the independently simulated reflectance data using PROSPECT + SAIL coupled radiative transfer models. Furthermore, the high resolution LAI was compared with MODIS LAI product. The effects of atmospheric corrections and scales were investigated for all of the LAI retrieval methods. NDVI was found to be not suitable index for large scale LAI inversion due to the sensitivity to scale and atmospheric effects. SDVI was virtually scale and atmospheric correction invariant. MSAVI was also scale invariant. Considering all sensitivity analysis, MSAVI performed best followed by SDVI for robust LAI inversion from high resolution imagery. 相似文献
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Melkamu Meseret Alemu 《资源与生态学报(英文版)》2019,(1)
本文分析了植被动态与地表温度等气候参数之间的关系,对环境和生态研究以及自然资源监测至关重要。本文首先利用Landsat数据探讨了1986年至2016年期间安达萨河流域地表温度(LST)和归一化植被指数(NDVI)的时空分布以及它们之间的关系,三个气象站点的月平均气温数据用于验证结果。该研究的结果表明,Andassa流域的LST在研究期间有所增加。总体而言,平均LST一直在上升,年增长率为0.081℃yr~(-1)。该研究结果还表明,所有季节的流域植被覆盖都发生了变化。在所有研究年份中,LST和NDVI之间存在负相关;从1986年到2016年,研究区植被具有退化趋势,地表温度有所升高。 相似文献
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V. Kazmin Alemu Shifferaw Tilahun Balcha 《International Journal of Earth Sciences》1978,67(2):531-546
In the Ethiopian Precambrian three complexes are recognized. The Lower Complex formed of high grade gneisses represents older (older than 2500 m. y.) cratonic basement. The Middle Complex (clastic metasediments) is presumably the Lower to Middle Proterozoic platform cover. The Upper Complex consists of low-grade rocks in following succession: ophiolitic rocks, andesitic metavolcanics and associated metasediments, clastic and to less extent carbonate sediments. Rifting of older basement at the beginning of Upper Proterozoic created northeasterly trending zones with oceanic crust branching from the Red Sea fold belt and grading southwards (in the Mozambique belt) into the zones of continental rifting. Closing of these rift zones terminated 1000 m. y. ago and was accompanied by subduction of oceanic crust which gave rise to island arc type volcanism. Continental collision resulted in crustal thickening and produced two stages of metamorphism: metamorphism of collision (around 1000 m. y. or earlier) and metamorphism of radioactive heating (younger than 1000 or 800 m. y.). The collision was oblique, so the significant transcurrent motion occurred in the Red Sea and the Mozambique belts.
Zusammenfassung Im Präkambrium Äthiopiens lassen sich drei Einheiten unterscheiden. Die unterste Einheit, bestehend aus hochgradig metamorphen Gneisen, ist ein älterer (älter als 2,5 Mrd. Jahre) kratonischer Sockel. Der mittlere Komplex (klastische Metasedimente) stellt wahrscheinlich die altbis mittelproterozoische Plattform-Sedimentbedeckung dar. Die obere Einheit besteht aus niedrigmetamorphen Gesteinen: Ophiolithe, andesitische Metavulkanite und damit verbundene Metasedimente, sowie klastische und untergeordnet karbonatische Ablagerungen. Das Auseinanderreißen des älteren Sockels zu Beginn des Jungproterozoikums bewirkte in nordöstliche Richtung verlaufende Zonen mit ozeanischer Kruste, die vom Faltengürtel des Roten Meeres abbiegen und sich südwärts (zum Mozambique-Gürtel hin) in das kontinentale Riftsystem eingliedern. Dei Abschluß dieser Riftsysteme endete vor 1 Mrd. Jahren, begleitet von einer Subduktion ozeanischer Kruste, die mit Vulkanismus vom Typ der Inselbögen verbunden war. Die Kollision kontinentaler Platten verursachte Krustenverdickungen und erzeugte zwei Stadien der Metamorphose: Kollisions-Metamorphose (vor ca. 1 Mrd. Jahren oder früher) und Metamorphose durch radioaktive Aufheizung (jünger als 1 oder 0,8 Mrd. Jahre). Die Kollision verlief schräg, so daß die signifikanten Querbewegungen im Roten-Meerund Mozambique-Gürtel erfolgten.
Résumé On peut reconnaître trois complexes dans le Précambrien de l'Ethiopie. Le complexe inférieur, formé de gneiss de degré de métamorphisme élevé, représente le socle cratonique le plus ancien (plus vieux que 2500 M.). Le complexe moyen (des métasédiments détritiques) est présumé être une couverture de plateforme du Protérozoïque inférieur à moyen. Le complexe supérieur consiste en roches peu métamorphiques se succédant comme suit: roches ophiolithiques, métavolcanites andésitiques avec sédiments associés, sédiments clastiques et en moindre proportion des sédiments carbonatés. La fracturation du vieux socle au debut du Protérozoïque supérieur créa des zones d'effondrement de direction nord-est, avec croûte océanique, branchées sur la ceinture plissé de la Mer Rouge, et passant vers le sud (dans la ceinture du Mozambique) à une zone de fracturation continentale. La fermeture de cette zone d'affaissement se termina il y a quelque 1000 M., et fut accompagnée par une subduction de la croûte océanique qui donna naissance à un volcanisme du type guirlande insulaire. La collision continentale entraîna un épaississement crustal et produisit deux phases de métamorphisme: métamorphisme de collision (environ 1000 M. ou plus tôt) et métamorphisme par réchauffement radioactif (plus récent que 1000 M. ou 800 M.). La collision se fit obliquement, produisant ainsi un mouvement transcurrent important dans les ceintures de la Mer Rouge et du Mozambique.
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Abera Tessema 《Natural Resources Research》2017,26(4):465-488
Radial basis function link neural network (RBFLN) and fuzzy-weights of evidence (fuzzy-WofE) methods were used to assess regional-scale prospectivity for chromite deposits in the Western Limb and the Nietverdiend layered mafic intrusion of the Bushveld Complex in South Africa. Five predictor maps derived from geological, geochemical and geophysical data were processed in a GIS environment and used as spatial proxy for critical processes that were most probably responsible for the formation of the chromite deposits in the study area. The RBFLN was trained using input feature vectors that correspond to known deposits, prospects and non-deposits. The training was initiated by varying the number of radial basis functions (RBFs) and iterations. The results of training the RBFLN provided optimum number of RBFs and iterations that were used for classification of the input feature vectors. The results show that the network classified 73% of the validation deposits into highly prospective areas for chromite deposit, covering 6.5% of the study area. The RBFLN entirely classified all the non-deposit validation points into low prospectivity areas, occupying 86.6% of the study area. In general, the efficiency of the RBFLN in classifying the validation deposits and non-deposits indicates the degree of spatial relationship between the input feature vectors and the training points, which represent chrome mines and prospects. The RBFLN and fuzzy-WofE analyses used in this study are important in guiding identification of regional-scale prospect areas where further chromite exploration can be carried out. 相似文献