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Slope Gradient (slope + gradient)

Distribution by Scientific Domains

Earth and Environmental Science	69%

Selected Abstracts

Assessment of shallow landslide susceptibility by means of multivariate statistical techniques

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2001
Cristina Baeza
Abstract Several multivariate statistical analyses have been performed to identify the most influential geological and geomorphological parameters on shallow landsliding and to quantify their relative contribution. A data set was first prepared including more than 30 attributes of 230 failed and unfailed slopes. The performance of principal component analysis, t-test and one-way test, allowed a preliminary selection of the most significant variables, which were used as input variables for the discriminant analysis. The function obtained has classified successfully 88·5 per cent of the overall slope population and 95·6 per cent of the failed slopes. Slope gradient, watershed area and land-use appeared as the most powerful discriminant factors. A landslide susceptibility map, based on the scores of the discriminant function, has been prepared for Ensija range in the Eastern Pyrenees. An index of relative landslide density shows that the results of the map are consistent. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Effectiveness of grass strips in trapping suspended sediments from runoff

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2010
Chengzhong Pan
Abstract Little information is available concerning the performance of grass strips for erosion control from steep cropland. An experiment was conducted on 5-m-long grass strips with slopes of 3°,15° that were subjected to silt laden runoff and simulated rainfall, to investigate the sediment trapping processes. The grass strips had three treatments including intact grass control (C), no litter (dead grass material covering the soil surface was removed) (NL), and no litter or leaves (only 2,3,cm grass stems and roots were reserved) (NLL). Generally the grass strips had a high effectiveness in trapping sediment from steep cropland runoff. Sediment trapping efficiency (STE) decreased with increasing slope gradient, and even for a 15° slope, STE was still more than 40%. Most sediment deposited in the backwater region before each grass strips. The removal of grass litter or/and leaves had no significant influence on STE. The sediment median size (D50) in inflow was greater than that in outflow, and the difference (,D50) decreased with increasing slope. A positive power relationship between STE and ,D50 can be obtained. Grass strips were more effective in trapping sediments coarser than 10 or 25,µm, but sediments finer than 1,µm were more readily removed from runoff than particles in the range of 2 to approximately 10,µm. Grass litter had less influence on flow velocity than leaves because the deposited sediment partially covered the litter layer. Mean flow velocity and its standard deviation were negatively correlated with STE, and they can help make good estimation of STE. Results from this study should be useful in planting and managing forage grass to effectively conserve soil loss by runoff from steep slopes on the Loess Plateau of China. Copyright © 2010 John Wiley & Sons, Ltd. [source]

The implications of data selection for regional erosion and sediment yield modelling

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 15 2009
Joris de Vente
Abstract Regional environmental models often require detailed data on topography, land cover, soil, and climate. Remote sensing derived data form an increasingly important source of information for these models. Yet, it is often not easy to decide what the most feasible source of information is and how different input data affect model outcomes. This paper compares the quality and performance of remote sensing derived data for regional soil erosion and sediment yield modelling with the WATEM-SEDEM model in south-east Spain. An ASTER-derived digital elevation model (DEM) was compared with the DEM obtained from the Shuttle Radar Topography Mission (SRTM), and land cover information from the CORINE database (CLC2000) was compared with classified ASTER satellite images. The SRTM DEM provided more accurate estimates of slope gradient and upslope drainage area than the ASTER DEM. The classified ASTER images provided a high accuracy (90%) land cover map, and due to its higher resolution, it showed a more fragmented landscape than the CORINE land cover data. Notwithstanding the differences in quality and level of detail, CORINE and ASTER land cover data in combination with the SRTM DEM or ASTER DEM allowed accurate predictions of sediment yield at the catchment scale. Although the absolute values of erosion and sediment deposition were different, the qualitative spatial pattern of the major sources and sinks of sediments was comparable, irrespective of the DEM and land cover data used. However, due to its lower accuracy, the quantitative spatial pattern of predictions with the ASTER DEM will be worse than with the SRTM DEM. Therefore, the SRTM DEM in combination with ASTER-derived land cover data presumably provide most accurate spatially distributed estimates of soil erosion and sediment yield. Nevertheless, model calibration is required for each data set and resolution and validation of the spatial pattern of predictions is urgently needed. Copyright © 2009 John Wiley & Sons, Ltd. [source]

The effects of slope and slope position on local and upstream fluid threshold friction velocities

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2008
Ning Huang
Abstract In deserts, dunes are common aeolian landforms, and parallel ridges are common in cultivated land. A computational fluid dynamics (CFD) model is used to simulate a stable wind blowing over slope beds of varying height and coupled with the slope-compensating fluid threshold friction velocity formula. The model accurately reproduced patterns of flow deceleration at the slope toe and stoss flow acceleration. Based on the CFD-based model, quantitative analyses of slope gradient and particle position on the initiation of particle movement are performed. Results indicate that the slope has a great influence on particle saltation in the windward slope, and the initiation of particle movement is particularly sensitive to particle position with respect to the slope. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central Japan

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2008
Fumitoshi Imaizumi
Abstract Landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention. We examined the effects of forest harvesting on the frequency of landslides and debris flows in the Sanko catchment (central Japan) using nine aerial photo periods covering 1964 to 2003. These photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912. Geology and slope gradient are rather uniformly distributed in the Sanko catchment, facilitating assessment of forest harvesting effects on mass wasting without complication of other factors. Trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery; the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting. Sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10-fold higher than in control sites. Total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5·8 × 103 m3 km,2 compared with 1·3 × 103 m3 km,2 in clearcuts >25 yr, indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability. Because landslide scars continue to produce sediment after initial failure, sediment supply from landslides continues for 45 yr in the Sanko catchment. To estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions, changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Effects of spatially structured vegetation patterns on hillslope erosion in a semiarid Mediterranean environment: a simulation study

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2005
Matthias Boer
Abstract A general trend of decreasing soil loss rates with increasing vegetation cover fraction is widely accepted. Field observations and experimental work, however, show that the form of the cover-erosion function can vary considerably, in particular for low cover conditions that prevail on arid and semiarid hillslopes. In this paper the structured spatial distribution of the vegetation cover and associated soil attributes is proposed as one of the possible causes of variation in cover,erosion relationships, in particular in dryland environments where patchy vegetation covers are common. A simulation approach was used to test the hypothesis that hillslope discharge and soil loss could be affected by variation in the spatial correlation structure of coupled vegetation cover and soil patterns alone. The Limburg Soil Erosion Model (LISEM) was parameterized and verified for a small catchment with discontinuous vegetation cover at Rambla Honda, SE Spain. Using the same parameter sets LISEM was subsequently used to simulate water and sediment fluxes on 1 ha hypothetical hillslopes with simulated spatial distributions of vegetation and soil parameters. Storms of constant rainfall intensity in the range of 30,70 mm h,1 and 10,30 min duration were applied. To quantify the effect of the spatial correlation structure of the vegetation and soil patterns, predicted discharge and soil loss rates from hillslopes with spatially structured distributions of vegetation and soil parameters were compared with those from hillslopes with spatially uniform distributions. The results showed that the spatial organization of bare and vegetated surfaces alone can have a substantial impact on predicted storm discharge and erosion. In general, water and sediment yields from hillslopes with spatially structured distributions of vegetation and soil parameters were greater than from identical hillslopes with spatially uniform distributions. Within a storm the effect of spatially structured vegetation and soil patterns was observed to be highly dynamic, and to depend on rainfall intensity and slope gradient. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Temporal and spatial variations in periglacial soil movements on alpine crest slopes

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2005
Norikazu Matsuoka
Abstract This paper describes up to ten years of continuous monitoring of frost heave, creep and associated parameters on high mountain crest slopes in the Japanese and Swiss Alps, aiming to evaluate spatial and interannual variations in the rates and controls of soil movement. Shallow frost creep re,ecting diurnal frost heave activity dominates the crest slopes that lack a vegetation mat and have a thin debris mantle with good drainage. Seasonal frost heave activity can induce slightly deeper movement where ,ne soil exists below the depth reached by diurnal freeze,thaw penetration, although the shallow bedrock impedes movements below 20 cm depth. As a result, downslope velocity pro,les display strong concavity with surface velocities of 2,50 cm a,1. The frost creep rates vary spatially, depending on the soil texture, slope gradient, frequency of temperature cycling across 0 °C and moisture availability during freeze,thaw periods. Soil movements recur in every freeze,thaw period, although with some interannual variations affected by the length of seasonal snow cover and the occurrence of precipitation during freeze,thaw periods. The Swiss Alps encounter more signi,cant interannual variations than the Japanese Alps, re,ecting the large variability of the annual snow regime. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Analysing soil variation in two dimensions with the discrete wavelet transform

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2004
R. M. Lark
Summary Complex spatial variation in soil can be analysed by wavelets into contributions at several scales or resolutions. The first applications were to data recorded at regular intervals in one dimension, i.e. on transects. The theory extends readily to two dimensions, but the application to small sets of gridded data such as one is likely to have from a soil survey requires special adaptation. This paper describes the extension of wavelet theory to two dimensions. The adaptation of the wavelet filters near the limits of a region that was successful in one dimension proved unsuitable in two dimensions. We therefore had to pad the data out symmetrically beyond the limits to minimize edge effects. With the above modifications and Daubechies's wavelet with two vanishing moments the analysis is applied to soil thickness, slope gradient, and direct solar beam radiation at the land surface recorded at 100-m intervals on a 60 × 101 square grid in south-west England. The analysis revealed contributions to the variance at several scales and for different directions and correlations between the variables that were not evident in maps of the original data. In particular, it showed how the thickness of the soil increasingly matches the geological structure with increasing dilation of the wavelet, this relationship being local to the strongly aligned outcrops. The analysis reveals a similar pattern in slope gradient, and a negative correlation with soil thickness, most clearly evident at the coarser scales. The solar beam radiation integrates slope gradient and azimuth, and the analysis emphasizes the relations with topography at the various spatial scales and reveals additional effects of aspect on soil thickness. [source]

Stone artifact scatters in western NSW, Australia: Geomorphic controls on artifact size and distribution

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2001
Patricia Fanning
Surface scatters of Aboriginal stone artifacts have been exposed in many parts of inland Australia by accelerated erosion that followed the introduction of pastoralism by European settlers in the 19th century. This paper reports on a set of techniques developed to investigate and quantify the effects of these post-discard disturbance processes in Sturt National Park in northwest NSW, Australia. Backwards, stepwise, linear regression showed the influence of geomorphic parameters such as slope gradient, elevation, landform, and contemporary surface processes on artifact distribution, with artifact maximum dimension as the dependent variable. The results indicate that, even at low gradients, artifact size and slope angle are significantly related, but that the variance in maximum dimension explained by gradient is very low. Similar results were found for the other geomorphic variables. We conclude that artifact movement by surface wash across these surfaces is unlikely to significantly affect artifact distribution. While vertically conflated surface scatters do not preserve "living floors" in a short-term, functional sense, their apparent horizontal integrity allows investigation of the long-term use of place by hunter-gatherer people in the past. Insofar as assemblage integrity is important for assessing site significance in the heritage management industry, our methods provide a means for assessing the degree to which a site has been damaged by water flow. © 2001 John Wiley & Sons, Inc. [source]

The effect of soil type, meteorological forcing and slope gradient on the simulation of internal erosion processes at the local scale

HYDROLOGICAL PROCESSES, Issue 13 2010
Guillaume Nord
Abstract Numerical simulation experiments of water erosion at the local scale (20 × 5 m) using a process-based model [Plot Soil Erosion Model_2D (PSEM_2D)] were carried out to test the effects of various environmental factors (soil type, meteorological forcing and slope gradient) on the runoff and erosion response and to determine the dominant processes that control the sediment yield at various slope lengths. The selected environmental factors corresponded to conditions for which the model had been fully tested beforehand. The use of a Green and Ampt model for infiltration explained the dominant role played by rainfall intensity in the runoff response. Sediment yield at the outlet of the simulated area was correlated positively with rainfall intensity and slope gradient, but was less sensitive to soil type. The relationship between sediment yield (soil loss per unit area) and slope length was greatly influenced by all environmental factors, but there was a general tendency towards higher sediment yield when the slope was longer. Contribution of rainfall erosion to gross erosion was dominant for all surfaces with slope lengths ranging from 4 to 20 m. The highest sediment yields corresponded to cases where flow erosion was activated. An increase in slope gradient resulted in flow detachment starting upstream. Sediment exported at the outlet of the simulated area came predominantly from the zone located near the outlet. The microrelief helped in the development of a rill network that controlled both the ratio between rainfall and flow erosion and the relationship between sediment yield and slope length. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Influences of grass and moss on runoff and sediment yield on sloped loess surfaces under simulated rainfall

HYDROLOGICAL PROCESSES, Issue 18 2006
Chengzhong Pan
Abstract It is important to evaluate the impacts of grasses on soil erosion process so as to use them effectively to control soil and water losses on the Loess Plateau. Laboratory-simulated rainfall experiments were conducted to investigate the runoff and sediment processes on sloped loess surfaces with and without the aboveground parts of grasses and moss (GAM: grass and moss; NGAM: no grass and moss) under slope gradients of 5°, 10°, 15°, 20°, 25° and 30°. The results show that runoff from GAM and NGAM plots increased up to a slope gradient of 10° and decreased thereafter, whereas the runoff coefficients increased with gradient. The average runoff rates and runoff coefficients of NGAM plots were less than those of GAM plots except for the 5° slope. This behaviour may be due to the reduction in water infiltration under moss. The difference between GAM and NGAM plots in average runoff rates varied from 1·4 to 8%. At the same gradients, NGAM plots yielded significantly (, = 0·05) more sediment than GAM plots. Average sediment deliveries for different slopes varied from 0·119 to 3·794 g m,2 min,1 from GAM plots, and from 0·765 to 16·128 g m,2 min,1 from NGAM plots. Sediment yields from GAM plots were reduced by 45 to 85%, compared with those from the NGAM plots. Plots at 30° yielded significantly higher sediments than at the other gradients. Total sediments S increased with slope gradients G in a linear form, i.e. S = 9·25G , 39·6 with R2 = 0·77*, for the GAM plots, and in an exponential model, i.e. S = 40·4 exp(0·1042G) with R2 = 0·93**, for the NGAM plots. In all cases, sediment deliveries decreased with time, and reached a relative steady state at a rainfall duration of 14 min. Compared with NGAM plots, the final percentage reductions in sediment delivery from GAM plots were higher than those at the initial time of rainfall at all slopes. Copyright © 2006 John Wiley & Sons, Ltd. [source]

A simulation model for unified interrill erosion and rill erosion on hillslopes

HYDROLOGICAL PROCESSES, Issue 3 2006
Q. Q. Liu
Abstract A mathematical model was developed for simulating runoff generation and soil erosion on hillslopes. The model is comprised of three modules: one for overland flow, one for soil infiltration, and one for soil erosion including rill erosion and interrill erosion. Rainfall and slope characteristics affecting soil erosion on hillslopes were analysed. The model results show that the slope length and gradient, time distribution rainfall, and distribution of rills have varying influence on soil erosion. Erosion rate increases nonlinearly with increase in the slope length; a long slope length leads to more serious erosion. The effect of the slope gradient on soil erosion can be both positive and negative. Thus, there exists a critical slope gradient for soil erosion, which is about 45° for the rate of erosion at the end of the slope and about 25° for the accumulated erosion. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A conditional GIS-interpolation-based model for mapping soil-water erosion processes in Lebanon

LAND DEGRADATION AND DEVELOPMENT, Issue 2 2008
R. Bou Kheir
Abstract Soil erosion by water is a major cause of landscape degradation in Mediterranean environments, including Lebanon. This paper proposes a conditional decision-rule interpolation-based model to predict the distribution of multiple erosion processes (i.e. sheet, mass and linear) in a representative area of Lebanon from the measured erosion signs in the field (root exposure, earth pillars, soil etching and drift and linear channels). First, erosion proxies were derived from the structural OASIS classification of Landsat thematic mapper (TM) imageries combined with the addition of several thematic erosion maps (slope gradient, aspect and curvature, drainage density, vegetal cover, soil infiltration and erodibility and rock infiltration/movement) under a geographic information systems (GIS) environment. Second, erosion signs were measured in the field, and interpolated by the statistical moments (means and variance) in the defined erosion proxies, thus producing quantitative erosion maps (t,ha,1) at a scale of 1:100,000. Seven decision rules were then generated and applied on these maps in order to produce the overall decisive erosion map reflecting all existing erosion processes, that is, equality (ER), dominance (DOR), bimodality (BR), masking (MR), aggravating (AR), dependence (DER) and independence (IR). The produced erosion maps are divided into seven classes ranging between 0 and more than 1·8,t,ha,1 for sheet erosion, and 0 and more than 10·5,t,ha,1 for mass and linear erosion. They are fairly matching with coincidences values equal to 43 per cent (sheet/linear), 48 per cent (sheet/mass) and 49 per cent (linear/mass). The overall accuracies of these maps were estimated to be 76 per cent (sheet erosion), 78 per cent (mass erosion) and 78·5 per cent (linear erosion). The overall decisive erosion map with 15 classes corresponds well to land management needs. The model used is relatively simple, and may also be applied to other areas. It is particularly useful when GIS database on factors influencing erosion is limited. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Spatial analysis of solifluction landforms and process rates in the Abisko Mountains, northern Sweden

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2010
Hanna Ridefelt
Abstract The occurrence of turf-banked solifluction landforms in the Abisko region was analysed using a grid-based approach and statistical modelling through logistic regression. Significant parameters in the model were the vegetation index NDVI, annual incoming potential radiation, wetness index, slope gradient and elevation. The model had an acceptable discrimination capacity and rather low model-fit values, but clearly showed the importance of vegetation patterns for the occurrence of solifluction at a regional scale. Solifluction movement rates measured at eight sites were combined with model parameters and the annual duration of sun hours to regionalise solifluction movement rates through an unsupervised terrain classification. For comparison, the linear relationship between the probability of solifluction occurrence and variations in movement rates was also used to regionalise movement rates. Potential geomorphic work was calculated for six different areas within the region, with the greatest being for Kärkevagge, the area with the highest precipitation. The combination of a logistic regression model of mapped landforms and field measurements of solifluction rates represents a promising methodology to assess the occurrence and activity of the process at a regional scale. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Palaeo-ice streams, trough mouth fans and high-latitude continental slope sedimentation

BOREAS, Issue 1 2003
Colm Ó Cofaigh
The classical model of trough mouth fan (TMF) formation was developed in the Polar North Atlantic to explain large submarine fans situated in front of bathymetric troughs that extend across continental shelves to the shelf break. This model emphasizes the delivery of large volumes of subglacial sediment to the termini of ice streams flowing along troughs, and subsequent re-deposition of this glacigenic sediment down the continental slope via debris-flow processes. However, there is considerable variation in terms of the morphology and large-scale sediment architecture of continental slopes in front of palaeo-ice streams. This variability reflects differences in slope gradient, the relative contributions of meltwater sedimentation compared with debris-flow deposition, and sediment supply/geology of the adjacent continental shelf. TMF development is favoured under conditions of a low (<1°) slope gradient; a passive-margin tectonic setting; abundant, readily erodible sediments on the continental shelf - and thus associated high rates of sediment delivery to the shelf edge; and a wide continental shelf. The absence of large sediment fans on continental slopes in front of cross-shelf troughs should not, however, be taken to indicate the former absence of palaeo-ice streams in the geological record. [source]

Concentrated flow erosion rates reduced through biological geotextiles

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2009
T. Smets
Abstract Soil erosion by concentrated flow can cause serious environmental damage. Erosion-control geotextiles have considerable potential for reducing concentrated flow erosion. However, limited data are available on the erosion-reducing potential of geotextiles. In this study, the effectiveness of three biological geotextiles in reducing soil losses during concentrated flow is investigated. Hereto, runoff was simulated in a concentrated flow flume, filled with an erodible sandy loam on three slope gradients (13·5, 27·0 and 41·5%). Treatments included three biological geotextiles (borassus, buriti and bamboo) and one bare soil surface. Darcy,Weisbach friction coefficients ranged from 0·01 to 2·84. The highest values are observed for borassus covered soil surfaces, followed by buriti, bamboo and bare soil, respectively. The friction coefficients are linearly correlated with geotextile thickness. For the specific experimental conditions of this study, borassus geotextiles reduced soil detachment rate on average to 56%, buriti geotextiles to 59% and bamboo geotextiles to 66% of the soil detachment rate for bare soil surfaces. Total flow shear stress was the hydraulic parameter best predicting soil detachment rate for bare and geotextile covered surfaces (R2 = 0·75,0·84, p <0·001, n = 12,15). The highest resistance against soil detachment was observed for the borassus covered soil surfaces, followed by buriti, bamboo and bare soil surfaces, respectively. Overall, biological geotextiles are less effective in controlling concentrated flow erosion compared with interrill erosion. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Earth hummocks (thúfur): new insights to their thermal characteristics and development in eastern Lesotho, southern Africa

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2005
Stefan W. Grab
Abstract The aspect-controlled variations in soil freezing within earth hummocks of eastern Lesotho (southern Africa) are analysed. Ground thermal data were measured for an earth hummock from late autumn to early spring in 1995 and 1996, using TinytalkÔ data loggers. During 1995, ground temperatures were recorded at 15 and 20 cm depth on the hummock north, east, south and west aspects, whilst in 1996 temperatures were recorded at 1 cm, 5 cm and 10 cm on the north and south aspects. The data from 1995 indicate that soil freezing commences on the hummock southern aspects and gradually progresses towards the western and northern aspects, whilst the eastern aspect remained unfrozen throughout winter. The data from 1996 indicate that a thick snow cover almost nullifies the temperature differences between the hummock northern and southern aspects. However, given the relative absence of snow during contemporary winters, freeze intensity and duration is longest on the hummock southern and western aspects, which helps explain earth hummock deformation (elongation and coalescence) in a southwesterly direction on slope gradients ,3°. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Modelling land use changes and their impact on soil erosion and sediment supply to rivers

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2002
Anton J. J. Van Rompaey
Abstract The potential for surface runoff and soil erosion is strongly affected by land use and cultivation. Therefore the modelling of land use changes is important with respect to the prediction of soil degradation and its on-site and off-site consequences. Land use changes during the past 250 years in the Dijle catchment (central Belgium) were analysed by comparing four historical topographic maps (1774, 1840, 1930 and 1990). A combination of land use transformation maps and biophysical land properties shows that certain decision rules are used for the conversion of forest into arable land or vice versa. During periods of increasing pressure on the land, forests were cleared mainly on areas with low slope gradients and favourable soil conditions, while in times of decreasing pressure land units with steep and unfavourable soil conditions were taken out of production. Possible future land use patterns were generated using stochastic simulations based on land use transformation probabilities. The outcome of these simulations was used to assess the soil erosion risk under different scenarios. The results indicate that even a relatively limited land use change, from forest to arable land or vice versa, has a significant effect on regional soil erosion rates and sediment supply to rivers. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Influences of grass and moss on runoff and sediment yield on sloped loess surfaces under simulated rainfall

Sensitivity analysis of snow patterns in Swiss ski resorts to shifts in temperature, precipitation and humidity under conditions of climate change

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2009
Bastienne Uhlmann
Abstract The value of snow as a resource has considerably increased in Swiss mountain regions, in particular in the context of winter tourism. In the perspective of a warming climate, it is thus important to quantify the potential changes in snow amount and duration that could have large repercussions on the economy of ski resorts. Because of the fine spatial variability of snow, the use of a Surface Energy Balance Model (SEBM) is adequate to simulate local snow cover evolution. A perturbation method has been developed to generate plausible future meteorological input data required for SEBM simulations in order to assess the changes in snow cover patterns. Current and future snow depths have also been simulated within the ski areas themselves. The results show a large decrease of the snow depths and duration, even at high elevation in a warmer climate and emphasize the sensitivity of snow to topographical characteristics of the resorts. The most vulnerable areas would be the Western regions of Switzerland or the Eastern Prealps whereas the Central Alps or Valais would be less affected. The study highlights the fact that not only the altitude of a domain but also its exposure, localization inland and slope gradients need to be taken into account when evaluating current and future snow depths. This method enables a precise assessment of the snow pattern over a small area. Copyright © 2008 Royal Meteorological Society [source]

Erosion modelling approach to simulate the effect of land management options on soil loss by considering catenary soil development and farmers perception

LAND DEGRADATION AND DEVELOPMENT, Issue 6 2008
A. C. Brunner
Abstract The prevention of soil erosion is one of the most essential requirements for sustainable agriculture in developing countries. In recent years it is widely recognized that more site-specific approaches are needed to assess variations in erosion susceptibility in order to select the most suitable land management methods for individual hillslope sections. This study quantifies the influence of different land management methods on soil erosion by modelling soil loss for individual soil-landscape units on a hillslope in Southern Uganda. The research combines a soil erosion modelling approach using the physically based Water Erosion Prediction Project (WEPP)-model with catenary soil development along hillslopes. Additionally, farmers' perceptions of soil erosion and sedimentation are considered in a hillslope mapping approach. The detailed soil survey confirmed a well-developed catenary soil sequence along the hillslope and the participatory hillslope mapping exercise proved that farmers can distinguish natural soil property changes using their local knowledge. WEPP-model simulations show that differences in soil properties, related to the topography along the hillslope, have a significant impact on total soil loss. Shoulder and backslope positions with steeper slope gradients were most sensitive to changes in land management. Furthermore, soil conservation techniques such as residue management and contouring could reduce soil erosion by up to 70 percent on erosion-sensitive slope sections compared to that under tillage practices presently used at the study site. The calibrated model may be used as a tool to provide quantitative information to farmers regarding more site-specific land management options. Copyright © 2008 John Wiley & Sons, Ltd. [source]