首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:从到   被引次数:从到   他引次数:从到 提示：输入*表示无穷大
全文获取类型
  收费全文   10篇
  免费   1篇
专业分类
大气科学   2篇
地球物理   3篇
自然地理   6篇
出版年
  2022年   1篇
  2019年   2篇
  2018年   5篇
  2016年   2篇
  2010年   1篇
排序方式： 共有11条查询结果，搜索用时 218 毫秒
1.
Impact studies of catchment management in the developing world rarely include detailed hydrological components. Here, changes in the hydrological response of a 200‐ha catchment in north Ethiopia are investigated. The management included various soil and water conservation measures such as the construction of dry masonry stone bunds and check dams, the abandonment of post‐harvest grazing, and the establishment of woody vegetation. Measurements at the catchment outlet indicated a runoff depth of 5 mm or a runoff coefficient (RC) of 1·6% in the rainy season of 2006. Combined with runoff measurements at plot scale, this allowed calculating the runoff curve number (CN) for various land uses and land management techniques. The pre‐implementation runoff depth was then predicted using the CN values and a ponding adjustment factor, representing the abstraction of runoff induced by the 242 check dams in gullies. Using the 2006 rainfall depths, the runoff depth for the 2000 land management situation was predicted to be 26·5 mm (RC = 8%), in line with current RCs of nearby catchments. Monitoring of the ground water level indicated a rise after catchment management. The yearly rise in water table after the onset of the rains (ΔT) relative to the water surplus (WS) over the same period increased between 2002–2003 (ΔT/WS = 3·4) and 2006 (ΔT/WS >11·1). Emerging wells and irrigation are other indicators for improved water supply in the managed catchment. Cropped fields in the gullies indicate that farmers are less frightened for the destructive effects of flash floods. Due to increased soil water content, the crop growing period is prolonged. It can be concluded that this catchment management has resulted in a higher infiltration rate and a reduction of direct runoff volume by 81% which has had a positive influence on the catchment water balance. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
2.
Theoretical and Applied Climatology - Meteorological drought is among the key climate-related risks affecting Ethiopia. It indicates a shortage of precipitation over a long period, usually for a...  相似文献   
3.
Abstract

With the recent technological advances offered by SfM-photogrammetry, we now have the possibility to study gully erosion at very high spatial and temporal scales from multi-temporal DEMs, and thus to enhance our understanding of both gully erosion processes and controls. Here, we examine gully degradation and aggradation at a gully headcut and at four re-incisions along a gully reach in Northern Ethiopia. Environmental controls recorded are topography rainfall, runoff, land use and cover, land management, and soil characteristics. The overall vulnerability of the catchment to erosion is low as calculated from the RUSLE (average 11.83 t ha?1 y?1). This reflects the successful land management of the past years. The runoff coefficient was on average 7.3% (maximum 18.2%). Runoff events caused most geomorphic change in the gully, but slumping of the gully bank also occurred on dry days. Most geomorphic change was caused by one major rainfall event of 54.8 mm d?1, and smaller runoff events caused both degradation and aggradation, often asynchronous between studied sites. Although most research focuses on gully heads alone, re-incisions at lower locations can still cause important gully degradation, which ultimately will reach the gully head and cause instability.  相似文献   
4.
Transhumance between the Afar lowlands and Tigray escarpments has been a common practice in northern Ethiopia. However, the impact of transhumance on landscape changes in the marginal grabens has not been significantly researched. Hence, this study aims to understand the process of transhumance and the linkages between social and biophysical aspects of the graben landscapes of northern Ethiopia. Google Earth (2010?2016) and Landsat Imageries (1995?2015) were used to analyse the spatio‐temporal landscape changes. Normalized Difference Vegetation Index (NDVI) was applied to measure the change in vegetation cover. Interview and Focus Group Discussions were used to collect perceptions of communities on transhumance and landscape change. The findings reveal that transhumance caused conflicts between the lowlanders and highlanders, which in turn led to displacement of communities. Consequently, the NDVI value of the abandoned settlement increased over time. Conversely, the analysis of Google Earth Imageries and NDVI values show that vegetation cover of the new settlement has decreased. Moreover, the NDVI values of the transhumance areas showed little increase due to the establishments of exclosures in the escarpments. The findings of this study can, therefore, be used to develop targeted interventions aimed at solving transhumance‐induced conflicts, displacement of communities and conservation of natural resources.  相似文献   
5.
Despite many studies on land degradation in the Highlands of Northern Ethiopia, quantitative information regarding long-term changes in land use/cover (LUC) is rare. Hence, this study aims to investigate the LUC changes in the Geba catchment (5142 km2), Northern Ethiopia, over 80 years (1935–2014). Aerial photographs (APs) of the 1930s and Google Earth (GE) images (2014) were used. The point-count technique was utilized by overlaying a grid on APs and GE images. The occurrence of cropland, forest, grassland, shrubland, bare land, built-up areas and water body was counted to compute their fractions. A multivariate adaptive regression spline was applied to identify the explanatory factors of LUC and to create fractional maps of LUC. The results indicate significant changes of most types, except for forest and cropland. In the 1930s, shrubland (48%) was dominant, followed by cropland (39%). The fraction of cropland in 2014 (42%) remained approximately the same as in the 1930s, while shrubland significantly dropped to 37%. Forests shrank further from a meagre 6.3% in the 1930s to 2.3% in 2014. High overall accuracies (93% and 83%) and strong Kappa coefficients (89% and 72%) for point counts and fractional maps respectively indicate the validity of the techniques used for LUC mapping.  相似文献   
6.
Despite many studies on land degradation in the Highlands of Northern Ethiopia, quantitative information regarding long-term changes in land use/cover(LUC) is rare. Hence, this study aims to investigate the LUC changes in the Geba catchment(5142 km2), Northern Ethiopia, over 80 years(1935–2014). Aerial photographs(APs) of the 1930 s and Google Earth(GE) images(2014) were used. The point-count technique was utilized by overlaying a grid on APs and GE images. The occurrence of cropland, forest, grassland, shrubland, bare land, built-up areas and water body was counted to compute their fractions. A multivariate adaptive regression spline was applied to identify the explanatory factors of LUC and to create fractional maps of LUC. The results indicate significant changes of most types, except for forest and cropland. In the 1930 s, shrubland(48%) was dominant, followed by cropland(39%). The fraction of cropland in 2014(42%) remained approximately the same as in the 1930 s, while shrubland significantly dropped to 37%. Forests shrank further from a meagre 6.3% in the 1930 s to 2.3% in 2014. High overall accuracies(93% and 83%) and strong Kappa coefficients(89% and 72%) for point counts and fractional maps respectively indicate the validity of the techniques used for LUC mapping.  相似文献   
7.
Climate indices are the diagnostic tools used to define the state of climate system. The main objective of this study was to investigate the climate index change in future time periods in the upper Baro basin of Ethiopia. The daily precipitation and maximum and minimum temperature data were downscaled using Statistical Downscaling Model (SDSM). The precipitation and temperature data were estimated according to UK Hadley Centre Coupled Model version 3 (HadCM3) global circulation model with medium-high (A2) and medium-low emission (B2) scenarios in three future time interval periods. The De Martonne Aridity Index and Pinna Combinative Index change of the future time periods centered at 2020s, 2050s, and 2080s was computed. The analysis was based on percentage change between the baseline and three future time periods. The monthly De Martonne Aridity Index result showed that there are months in the dry season classified as semi-dry with value of less than 20 and the land needs irrigation in these months. The Pinna Combinative Index value also showed the same trend like that of the De Martonne Aridity Index and a high correlation coefficient was noticed, verifying similar trend of the two indices for the three future time period changes. Overall, humidity is expected to decrease in most of the months in the three future time periods for both A2 and B2 emission scenarios because of the increment of temperature in the future.  相似文献   
8.
Soil degradation causes low land productivity. To tackle soil degradation, soil management practices have been implemented in the study area. However, less attention has been given to the management of physical soil quality. Hence, the objective of this study is to evaluate soil physical properties of long-used cultivated lands. Twelve Land Mapping Units (LMUs) were identified by overlaying slope and soil maps. Twelve composite and 12 undisturbed soil samples were collected from the 12 LMUs, and soil physical properties analyzed. Soil bulk density varied from 1.22 g cm?3 in LMU3 to 1.68 g cm?3 in LMU4. Available water capacity ranged from 0.09 in LMU4 to 0.17 in LMU3. Stability index (SI) values ranged from a low of 3.58 at LUM10 to 62.5 at LMU3; stability quotient (SQ) values ranged from 79.4 at LMU9 to 2782.8 at LUM3. Highest and lowest soil crust index values were found to be 1.53 in LMU5 and 0.29 in LMU9. This study indicated that poor soil management practice in the study area has caused soil physical degradation. Therefore, this study provides insight into improved land management of long-used cultivated land in the semi-arid region of the study area and other similar environments.  相似文献   
9.
This study was conducted to quantify agricultural land degradation in the Ruba Gered watershed, Ethiopia. The watershed was divided into 12 land mapping units (LMU) after superimposing maps of soil, slope, land use/cover, and elevation. Subsequently, cultivated land was delineated to assess degradation types and severity based on standard approaches. Sheet erosion was estimated using the revised universal soil loss equation. Composite soil samples were collected from each LMU to quantify key soil nutrients (OM, total nitrogen, available phosphorus, and available potassium) lost by sheet erosion. The annual average soil loss due to sheet erosion was estimated to be 17.4 t ha?1 yr?1, with average annual nutrient losses estimated as 246.5 kg ha?1 organic matter, 12.4 kg ha?1 total nitrogen, 0.1 kg ha?1 available phosphorus, and 1.6 kg ha?1 available potassium. The study revealed that substantial quantities of soil and nutrients are lost every year in the study area due to severe sheet erosion. This amount of nutrient loss severely degrades soil and reduces soil fertility.  相似文献   
10.
Marginal grabens are major development corridors in Ethiopia, and need to be understood for proper assessment of the hydrological budget. This study investigates the water balance of the Aba’ala graben (553 km2) in the period 2015–2016 under the challenge of data scarcity. We measured the rainfall and river discharge in order to analyse the runoff components of the graben. The rainfall volume in the Aba’ala graben showed erratic behaviour, which led to rapid flood runoff of the major river into the graben bottom. The average annual inflow and outflow of the graben bottom for the period 2015–2016 amounted to 364 and 254 hm3, respectively. However, flood runoff and evapotranspiration had a marked effect on water availability. Water storage took 36% of the water inflow into the graben bottom. Sustainable water management could reduce the temporal variation of the water storage in Aba’ala graben.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号