Soil and Water Conservation (SWC) structures, in particular stone bunds and conservation trenches, have been extensively installed in Tigray since the 1980's. As the effectiveness of stone bunds and ...trenches in reducing runoff and soil loss depends on their retention capacities, it
can be expected that this effectiveness declines over time due to infilling with sediment. However, little is known about the rate of this decline during subsequent years. We therefore assessed the effectiveness of SWC structures for two land use types, three slope classes and during three
consecutive rainy seasons. Rainfall, runoff and soil loss were measured using 21 large (600–1,000 m2) runoff plots at Mayleba catchment. Results show that all studied SWC structures are more effective in reducing soil loss than runoff. Conservation trenches are generally more
effective in reducing runoff and soil loss than stone bunds. However, due to their infilling with sediment, their effectiveness quickly declines over time. By the end of the third rainy season, their effectiveness was reduced to about one third of their initial effectiveness. The effectiveness
of stone bunds remained fairly constant during three consecutive rainy seasons. These findings have important implications, as they demonstrate that many of the installed SWC structures (especially in rangelands) are only very effective for short periods (one to two years). Regular sediment
removal from conservation trenches is therefore crucial to preserve their effectiveness over longer periods.
Cover management and support practices largely control the magnitude and variability of soil erosion. Although soil erosion models account for their importance (particularly by C- and P-factors in ...the Revised Universal Soil Loss Equation), obtaining spatially explicit quantitative field data on these factors remains challenging. Hence, also our insight into the effects of soil conservation measures at larger spatial scales remains limited. We analyzed the variation in C- and P-factors caused by human activities and climatic variables by reviewing 255 published articles reporting measured or calculated C- and P-factor values. We found a wide variation in both factor values across climatic zones, land use or cover types, and support practices. The average C-factor values decreased from arid (0.26) to humid (0.15) climates, whereas the average P-factor values increased (from 0.33 to 0.47, respectively). Thus, support practices reduce soil loss more effectively in drylands and drought-prone areas. The global average C-factor varies by one order of magnitude from cropland (0.34) to forest (0.03). Among the major crops, the average C-factor was highest for maize (0.42) followed by potato (0.40), among the major orchard crops, it was highest for olive (0.31), followed by vineyards (0.26). The P-factor ranged from 0.62 for contouring in cropland plots to 0.19 for trenches in uncultivated land. The C-factor results indicate that cultivated lands requiring intensive site preparation and weeding are most vulnerable to soil loss by sheet and rill erosion. The low P-factor for trenches, reduced tillage cultivation, and terraces suggests that significantly decreased soil loss is possible by implementing more efficient management practices. These results improve our understanding of the variation in C- and P-factors and support large-scale integrated catchment management interventions by applying soil erosion models where it is difficult to empirically determine the impact of particular land use or cover types and support practices: the datasets compiled in this study can support further modeling and land management attempts in different countries and geographic regions.
A collection of sepia photographs, taken during Great Britain's military expedition to Abyssinia in 1868, are the oldest landscape photographs from northern Ethiopia, and have been used to compare ...the status of vegetation and land management 140 years ago with that of contemporary times. Thirteen repeat landscape photographs, taken during the dry seasons of 1868 and 2008, were analyzed for various environmental indicators and show a significant improvement of vegetation cover. New eucalypt woodlands, introduced since the 1950s are visible and have provided a valuable alternative for house construction and fuel-wood, but more importantly there has also been locally important natural regeneration of indigenous trees and shrubs. The situation in respect to soil and water conservation measures in farmlands has also improved. According to both historical information and measured climatic data, rainfall conditions around 1868 and in the late 19th century were similar to those of the late 20th/early 21st century. Furthermore, despite a ten-fold increase in population density, land rehabilitation has been accomplished over extensive areas by large-scale implementation of reforestation and terracing activities, especially in the last two decades. In some cases repeat photography shows however that riparian vegetation has been washed away. This is related to river widening in recent degradation periods, particularly in the 1970s–1980s. More recently, riverbeds have become stabilized, and indicate a decreased runoff response. Environmental recovery programmes could not heal all scars, but this study shows that overall there has been a remarkable recovery of vegetation and also improved soil protection over the last 140 years, thereby invalidating hypotheses of the irreversibility of land degradation in semi-arid areas. In a highly degraded environment with high pressure on the land, rural communities were left with no alternative but to improve land husbandry: in northern Ethiopia such interventions have been demonstrably successful.
Scenic beauty is one of the most-commonly used indicators in the inventory and assessment of geosites for geoconservation, geoheritage management and geotourism development. It is an important driver ...of tourists to visit natural areas and it also provides support for the protection of natural heritage. Previous studies on scenic beauty mainly focused on landscape preference and physical characteristics of geosites that affect scenic beauty appreciation. The relationships between the scenic beauty of geosites, their scientific value and the geoscience knowledge of tourists has not been empirically investigated in detail. Hence, this study investigates this relationship using 34 geosites from southeastern Spain. For this purpose, 29 respondents with a geoscience background and who all visited the 34 geosites, 43 respondents with a geoscience background but who did not visit the geosites, and 104 respondents with no geoscience background and who did not visit the geosites, participated in a survey. The first group rated the scenic beauty and the scientific value of the geosites based on a direct field visit during which the scientific background of these geosites was given. On the other hand, the latter two groups rated scenic beauty using representative photos of the geosites. A five-point Likert scale was used to rate the scenic beauty and the scientific value of the geosites. We found a significant relationship between the scenic beauty of geosites and their scientific value, and this relationship becomes more significant if the geoscientific knowledge of the respondents increases. One-way ANOVA results indicated that a geoscience background contributed to higher perceived scenic beauty, especially for those geosites that in general were considered as more scenic by all the respondent groups. It was also found that geosites with viewpoints received in general higher scenic beauty and scientific value ratings.
► Land policies of the pre-1991 contributed largely to an increase in arable land while a decrease in vegetated land. ► The area under arable continued to increase but bare land which has declined in ...the post-1991. ► Agricultural policies played active roles in the change in area under water and indirectly contributed to the change of construction land. ► Crop yield and herd size per household have shown a reduction trend.
Policy has long been considered as one of the major driving forces for land use change and agricultural development. However, a designated and in-depth study on its interaction with land use change and agricultural development is still very limited. The authors, therefore, attempted to address this issue by using five villages representing three agro-ecologies (highland, midland and lowland) for the period between 1965 and 2007. The study indicated that land policies of the imperial and communist regimes contributed largely to the increase of arable land while a decrease in vegetated land. This is, however, reversed in the EPRDF regime. Land productivity/crop harvest (t/ha) and herd size per household have declined. Agricultural policies played active roles in the change of water area and indirectly contributed to the change of construction land.
The new assessment of soil loss by water erosion in Europe (Panagos et al., 2015a) was commented by Evans and Boardman (2016), who raised not only concerns related to the spatial differences outlined ...by our work compared to their visual semi-qualitative assessment conducted in Britain during the late eighties, but also generally to the suitability, validity and scientific robustness of the applied modelling approach. The objective of the pan-European assessment using the Revised Universal Soil Loss Equation (RUSLE) was not to outcompete any regional- or national-scale modelling, but to harmonize and improve our knowledge and our understanding of current soil erosion rates by water across the European Union. The focus of such a modelling project is on the differences and similarities between regions and countries beyond national borders and nationally adapted models. In order to do so, a state-of-the-art large-scale spatially distributed modelling exercise using harmonized datasets and a unified methodology to suit the pan-European scale was carried out. We reply that the semi-qualitative approach proposed by Evans and Boardman (2016) is not suitable for application at the European scale because of work force and time requirements, input data accessibility issues, accuracy of field-based estimates, subjectivity of soil loss estimates during the aerial and terrestrial photo interpretation, impossibility of upscaling or downscaling, inadequate representation of sheet erosion processes, lack of spatial and temporal representativeness, and lack of detailed description expressing the risk level. As such, their methodology has limited applicability, with today’s financial resources it is not feasible at European or at national scale and, most important, cannot respond to policy requests regarding scenarios of climate and land cover/use change. In contrast to Evans and Boardman (2016), we do know that RUSLE, like probably any other approach, is not able to reproduce “reality”. The latter is actually a misjudgment which has been extensively discussed 20years ago. Modelling in general and large-scale modelling specifically can per se not aim at an accurate prediction of point measurements, but tests our hypothesis on process understanding, relative spatial and temporal variations, scenario development and controlling factors (Oreskes et al., 1994). As such, our approach can be offered as a helpful tool to policy makers at pan-European scale. We are confident that the simple transparent structure of RUSLE as well as the discussion of the uncertainties of each modelling factor will help to supply objective guidance to policy makers.
Grasses and trees are often used to stabilize gully banks. However, the effectiveness of such biological conservation measures has not been investigated for the Ethiopian highlands. This study ...investigates the reinforcement that plant roots may provide to strengthen gully banks in Ethiopia. The root systems of 26 indigenous and exotic plant species of 3 plant life forms (grasses, shrubs, and trees) were sampled, and root tensile strength and distribution were determined. The RipRoot model was used to quantify the additional cohesion derived from the plant roots. Among all tested roots, Eleusine floccifolia (grass), Tephrosia vogelii (tree), and Rosa abyssinica (shrub) had the strongest roots for each life form. The root volumetric ratio (root volume divided by soil volume) in the top 0.6 m of soil ranged from 0.03% to 0.46%. Roots of Digitaria abyssinica provided the maximum added cohesion (10.6 kPa) over this depth. For a given plant species, root volumetric ratio had a greater effect on additional cohesion than root tensile strength. Plant species with a fibrous root system provided greater additional cohesion values in the top 0.6 m (on average 3.4 vs. 1.7 kPa for tap root systems) and could potentially enhance gully bank stability for shallow gullies more than plants having a tap root system. To effectively rehabilitate larger gullies, plants should be integrated with other gully rehabilitation measures, such as regrading of gully banks and structural measures such as check dams to trap sediments, thereby reducing the effective gully bank height relative to rooting depth.
► We simulated implementation of conservation agriculture (CA) in the 187-ha May Zeg-zeg (MZZ) catchment in Ethiopia. ► EdGCM simulation predicts an increase in precipitation of more than 100mmyr−1 ...by 2040. ► Annual runoff coefficients in MZZ would decrease from the current 30% to 19% after catchment-wide implementation of CA. ► Sheet and rill erosion rate in cropland would become 581tyr−1 instead of 1109tyr−1, if CA were practiced in MZZ. ► Under a future, wetter North-East-African climate, CA would increase infiltration and keep runoff coefficients under control.
This study evaluates the practice of conservation agriculture (CA) in the May Zeg-zeg catchment (MZZ; 187ha) in the North Ethiopian Highlands as a soil management technique for reducing soil loss and runoff, and assesses the consequences of future large-scale implementation on soil and hydrology at catchment-level. The study of such practice is important especially under conditions of climate change, since EdGCM (Educational Global Climate Model) simulation predicts by 2040 an increase in precipitation by more than 100mmyr−1 in the study area. Firstly, field-saturated infiltration rates, together with soil texture and soil organic carbon contents, were measured. The relation with local topography allows to generate a pedotransfer function for field-saturated infiltration rate, and spatial interpolation with Linear Regression Mapping was used to map field-saturated infiltration rates optimally within the catchment. Secondly, on several farmlands, CA was checked against plain tillage (PT) for values of field-saturated infiltration rates, soil organic carbon, runoff and soil loss. Results show no significant differences for infiltration rates but significant differences for runoff and soil loss (as measured in the period 2005–2011). Runoff coefficients were 30.4% for PT and 18.8% for CA; soil losses were 35.4tha−1yr−1 for PT and 14.4tha−1yr−1 for CA. Thirdly, all collected information was used to predict future catchment hydrological response for full-implementation of CA under the predicted wetter climate (simulation with EdGCM). Curve Numbers for farmlands with CA were calculated. An area-weighted Curve Number allows the simulation of the 2011 rainy season runoff, predicting a total runoff depth of 23.5mm under CA and 27.9mm under PT. Furthermore, the Revised Universal Soil Loss Equation management factor P was calibrated for CA. Results also show the important influence of increased surface roughness on water ponding, modeled with a hydrologic conservation balance. By coupling this model with the infiltration rate map, a ‘ponding map’ of the catchment was established. Finally, a sediment budget for a full future implementation scenario of CA has been estimated, predicting a large impact of CA on sheet and rill erosion rates, since total soil loss due to sheet and rill erosion in cropland would become 581tyr−1 instead of 1109tyr−1, if CA would be practiced in MZZ. Simulation of several policy scenarios shows that especially under a future wetter North-East-African climate, CA would be a beneficial alternative for the current plain tillage, as it will increase infiltration and keep runoff coefficients under control.
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