Land degradation and recurrent drought are the major threats to rain-fed agriculture in the semi-arid Ethiopian highlands. Water harvesting has become a priority in the Tigray region since 1990. ...However, the success of water harvesting in reservoirs is limited due to reduced inflow. The aim of this study was to investigate the effects of typical land-use types, slope gradients, and different soil and water conservation (SWC) structures on runoff and soil loss at the runoff-plot scale. Six runoff measuring sites, corresponding to three slope gradients, were established for cropland (cultivated land for annual crop production) and rangeland (heavily grazed land on hillslopes with high rock-fragment cover) at Mayleba catchment in Tigray, Ethiopia. SWC structures tested were stone bunds, trenches, and stone bunds with trenches, in addition to control plots. In total, 21 large runoff plots (with lengths of 60 to 100 m) were monitored daily for runoff production and soil loss during the main rainy season (July-September) in 2010. The results show that the seasonal runoff coefficient (RCs) representing the fraction of rainfall measured as runoff was much higher for rangeland (0.38 < RCs < 0.50) compared to that for cropland (0.11 < RCS < 0.15). Seasonal soil loss (SLs) values were five to six times larger on rangeland (28.6 < SLs < 50.0 ton ha
−1
) compared to that for cropland (4.6 < SLs < 11.4 ton ha
−1
). Stone bunds with trenches were the most effective SWC structures in reducing runoff and soil loss. With the same SWC structures installed, RCs and SLs for both rangeland and cropland tend to decrease with increasing slope gradient mainly due to a corresponding increase in rock-fragment cover. The effects of SWC structures on runoff production and soil loss are considerable; hence, it is crucial to consider these effects for optimal design of water-harvesting schemes such as micro-dams that collect and store surface runoff for irrigation development in the Ethiopian highlands.
Severe land degradation and the consequent series of drought and famine episodes have caused major waves of human migration in Ethiopia over the past 5 decades. The main objective of this study was ...to assess the impacts of consecutive resettlement programs (spontaneous and planned) on the forests in southwest Ethiopia. The spatial distribution and extent of forest cover were mapped for the periods 1957, 1975, and 2007 based on visual interpretation of aerial photographs and satellite images. The rate of deforestation was analyzed using overlay and buffer analysis techniques available in ArcGIS software. Focus group discussions and household surveys were conducted to collect information on landscape (forest) change and the causes and consequences of deforestation. Results from the forest cover change analysis revealed that the study area lost large tracts (80%) of its forest cover between 1957 and 2007. Demographic, socioeconomic, and cultural changes introduced by migrants were the leading drivers of deforestation in the study area. In addition, the rate of deforestation in the region has been exacerbated by a low level of education and awareness of the local people about the benefits of forests, lack of regulations to protect the forests, habitat destruction to deter crop-damaging wild pests, forest clearing for fuelwood and charcoal making, and wood extraction for construction and household furniture purposes.
The European Commission's Thematic Strategy for Soil Protection (COM(2012)46) identified soil erosion as an important threat to European Union's (EU) soil resources. Gully erosion is an important but ...hitherto poorly understood component of this threat. Here we present the results of an unprecedented attempt to monitor the occurrence of gully erosion across the EU and UK. We integrate a soil erosion module into the 2018 LUCAS Topsoil Survey, which was conducted to monitor the soil health status across the EU and to support actions to prevent soil degradation. We discuss and explore opportunities to further improve this method. The 2018 LUCAS Topsoil Survey consisted of soil sampling (0–20 cm depth) and erosion observations conducted in ca. 10% (n = 24,759) of the 238,077 Land Use/Cover Area frame Survey (LUCAS) 2018 in-field survey sites. Gully erosion channels were detected for ca. 1% (211 sites) of the visited LUCAS Topsoil sites. Commission (false positives, 2.5%) and omission errors (false negatives, 5.6%) were found to be low and at a level that could not compromise the representativeness of the gully erosion survey. Overall, the findings indicate that the tested 2018 LUCAS Topsoil in-field gully erosion monitoring system is effective for detecting the incidence of gully erosion. The morphogenesis of the mapped gullies suggests that the approach is an effective tool to map permanent gullies, whereas it appears less effective to detect short-lived forms like ephemeral gullies. Spatial patterns emerging from the LUCAS Topsoil field observations provide new insights on typical gully formation sites across the EU and UK. This can help to design further targeted research activities. An extension of this approach to all LUCAS sites of 2022 would significantly enhance our understanding of the geographical distribution of gully erosion processes across the EU. Repeated every three years, LUCAS soil erosion surveys would contribute to assess the state of gully erosion in the EU over time. It will also enable monitoring and eventually predicting the dynamics of gully erosion. Data collected were part of the publicly available Gully Erosion LUCAS visual assessment (GE-LUCAS v1.0) inventory.
Land degradation is not uniform, even in the same landscape, but nevertheless an overall consensus seems to grow on the fact that many areas are under way of rehabilitation. It is a debateable ...question whether the improving areas are improving because of interventions—or whether this has more to do with processes of innovation and adaptation. The international symposium ‘HighLand2006’ on land degradation and land rehabilitation, held in Mekelle (Ethiopia), from 21 to 25 September 2006, created a forum for those conducting research in East African Highlands as well as in similar regions around the globe to discuss findings. Tropical highlands (>1000
m a.s.l.) cover 4.5 million km
2 with an average population density of 33 inhabitants km
−2. Nearly all tropical highlands suffer from land degradation, especially medium to very high water erosion. Exchange of experiences during in-door sessions and excursions led to results which are condensed in this special issue. Studies presented tend to invalidate hypotheses on irreversibility of land degradation in tropical mountain areas. Circumstances are that in highly degraded environments, with high pressure on the land, no other alternatives are left open but to improve land husbandry; and that this is particularly successful in places where decision making processes at different levels in society give the highest priority to the implementation of soil and water conservation and other land rehabilitation, in situ and at catchment level.
Aims: Concentrated flow erosion resistance of herbaceous vegetation is linked to vegetation-level root length density (RLD). However, RLD measurements involve destructive and time-consuming sampling. ...Since plant species richness, functional diversity and functional composition are expected to affect RLD through either non-additive diversity effects or biomass ratio effects, we evaluated whether these measures can be used as a proxy for RLD in levee grassland communities. Location: Levee grassland communities, Scheldt estuary, northern Belgium. Methods: We assessed the strength of correlation between empirically quantified RLD and species richness, functional diversity and functional composition of levee grasslands. More specifically, we used nine below-ground and ten above-ground plant traits retrieved from public databases, and applied linear regressions and partial least square regressions. Results: Plant functional diversity was a better proxy for RLD than plant species richness, with better predictive performance for below-ground than for aboveground traits. More specifically, the highest predictive power was achieved through integration of functional diversity, functional composition and species richness. This suggests that variation in RLD is driven by a combination of both non-additive diversity effects and biomass ratio effects. Conclusions: This study provides a first positive indication of the value of plant functional traits retrieved from databases to predict RLD for river levee grasslands. Furthermore, although less reliable than below-ground traits, above-ground traits are still useful for RLD prediction when information on below-ground traits is lacking.
Data on sediment yield from 26 small cultivated catchments (10–10
000 ha) in central Belgium were collected, based on sedimentation rates in small flood retention ponds. Area specific sediment yield ...varies from 0.4 to 20.6 t ha
−1 year
−1 for catchments ranging from 7 to 4873 ha. Various catchment properties were analysed in order to understand this large variation in sediment yield. Catchment area alone explains 64% of the observed variance in area specific sediment yield. Although no other parameter could explain more, it is concluded that catchment area is not a valid parameter to link with sediment yield. Overall catchment geomorphology, e.g. presented by the hypsometric integral, is much more important in controlling sediment yield. The lack of data, however, made this not very clear. A multiple regression model including three morphological catchment properties is a valuable tool to predict total sediment yield (t year
−1) from catchments in central Belgium. This model has an efficiency of 0.81. Furthermore, it was concluded that the within-catchment spatial distribution of parameters, for instance slope steepness, is very important but difficult to obtain one single representative value. The use of spatially distributed erosion and sediment delivery models is therefore necessary. Accurate sediment yield data, like the one presented in this study, however, are needed to validate these models.
Knowledge of the geographical distribution of soils is indispensable for policy and decision makers to achieve the goal of increasing agricultural production and reduce poverty, particularly in the ...Global South. A study was conducted to better understand the soilscapes of the Giba catchment (900-3300 m a.s.l.; 5133 km2) in northern Ethiopia, so as to sustain soil use and management. To characterise the chemical and physical properties of the different benchmark soils and to classify them in line with the World Reference Base of Soil Resources, 141 soil profile pits and 1381 soil augerings at representative sites were analysed. The dominant soil units identified are Leptosol and bare rock (19% coverage), Vertic Cambisol (14%), Regosol and Cambisol (10%), Skeletic/Leptic Cambisol and Regosol (9%), Rendzic Leptosol (7%), Calcaric/Calcic Vertisol (6%), Chromic Luvisol (6%) and Chromic/Pellic Vertisol (5%). Together these eight soil units cover almost 75% of the catchment. Topography and parent material are the major influencing factors that explain the soil distribution. Besides these two factors, land cover that is strongly impacted by human activities, may not be overlooked. Our soil suitability study shows that currently, after thousands of years of agricultural land use, a new dynamic equilibrium has come into existence in the soilscape, in which ca. 40% of the catchment is very suitable, and 25% is moderately suitable for agricultural production. In view of such large suitable areas, the Giba catchment has a good agricultural potential if soil erosion rates can be controlled, soil fertility (particularly nitrogen) increased, available water optimally used, and henceforth crop yields increased.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•In Uganda, decentralised platforms are used as spatial tactics to centralise power for the ruling party.•Decentralised platforms may co-produce unequal risk through blame dissolution and scale ...jumping.•A problematic implementation of decentralised platforms prevents competent disaster governance.
The international agenda for disaster risk reduction, through the Hyogo Framework for Action and the Sendai Framework for disaster risk reduction, promotes decentralised platforms as an indispensable strategy to achieve effective and efficient disaster risk management. Based on empirical data from the Rwenzori Mountains region, we question the implications of this type of network governance for disaster risk management. We embed our observations in an analytical framework that combines literature on network governance with insights from politics of disaster, notably scale and blame theories. In this study, we investigate the implications for disaster risk reduction through the analysis of three processes of scale structuration observed in contemporary West Uganda: (i) incomplete decentralisation, (ii) blame dissolution, and (iii) scale jumping. We argue that decentralised platforms in Uganda co-produce unequal risk, as they are used as spatial tactics to centralise power for the ruling party and enable blame dissolution and scale jumping. From our analysis we draw broader conclusions on drivers and implications of the implementation of disaster network governance in countries that are primarily governed hierarchically and that endorse the international frameworks of disaster risk reduction.
Purpose
The Ethiopian highlands are a fragile environment characterized by steep slopes, intense rainfall, a sparse vegetation cover, and the occurrence of flash floods. Although important efforts ...have been made to mitigate the ongoing soil erosion and land degradation problems, the sediment dynamics at medium-sized catchment scale (100–10,000 km
2
) are not fully understood. Therefore, this study aims to provide a better understanding of sediment export processes and the importance of flash flood events in semi-arid tropical catchments.
Materials and methods
Measuring campaigns were conducted in ten sub-catchments of the Geba, a tributary of the Tekeze, representative of the northern Ethiopian highlands. During two to four rainy seasons, the rivers were sampled for their suspended sediment concentration (SSC) and runoff discharge.
Results and discussion
Variations in SSC and sediment grain size distribution indicate changes in sediment supply during the rainy season due to the depletion of readily available sediments and the development of a vegetation cover. Also, during flood events, changes in sediment supply are observed. Sediment yields (i.e., 497–6,543 t km
−2
year
−1
) are higher than suggested by previous studies and correlate with rainfall depth. The majority of sediment export occurs during a few short but intense flash floods. No clear effect of implemented soil and water conservation measures could be detected in the sediment yields of the catchments.
Conclusions
Sediment export rates in the Ethiopian highlands are high, are characterized by important changes in sediment supply, and are mainly controlled by the occurrence and magnitude of flash flood events. Mitigation measures to reduce sediment yield at the catchment scale should therefore not only focus on the reduction of hillslope erosion rates but also on the magnitude of these floods.
PDF
