Distributed Soil Erosion Model Research Articles

Linking soil erosion and sediment yield with landscape heterogeneity: Exploration using the lower Jinsha River Basin, China

Landscape heterogeneity, including compositional and spatial configuration, changes soil erosion and sediment yield (SESY) in watersheds by regulating hydrological processes. However, existing research has paid little attention to landscape composition. The Lower Jinsha River Basin (LJRB) has significant landscape heterogeneity and the highest sediment yields in the Yangtze River Basin, China. The spatially distributed soil erosion model WaTEM/SEDEM was used to evaluate the spatio-temporal changes in SESY in the LJRB from 1990 to 2020. Area information conservation method and semi-variogram were utilized to determine the optimal grain and extent size of landscape analysis. The landscape heterogeneity characteristics of the LJRB were analyzed for landscape composition and spatial configuration. Finally, statistical analysis was performed to determine the differences in SESY among different landscape composition types (LCTs) and to explore the relationship between landscape configuration and SESY. The optimal grain and extent size for analysis of the landscape pattern in the LJRB were 150 and 2100 m, respectively. Based on this, three types and ten subtypes of landscape composition were identified. Landscapes composed of forest, shrubs, grassland, and farmland were predominant in the study area, with a relatively even distribution of patches and minimum dominance of specific patch types. Additionally, the landscapes composed of forest, shrubs, grassland, farmland, and impervious surfaces were diverse, with the highest fragmentation. Landscapes comprising farmland and impervious surfaces occupied a minor proportion of the study area, but specific patches exhibited higher landscape connectivity. The magnitude of SESY in the LJRB gradually decreased during 1990–2020. Farmland and grassland were the land types with the highest magntidue of SESY in this region. Substantial sediment has been deposited in Xiangjiaba and Xiluodu reservoirs since they commenced operations. Increased proportions of farmland patches in some LCTs have significantly enhanced SESY. For LCTs dominated by farmland and impervious surfaces, reducing the dominance of the largest patch, decreasing patch aggregation, and increasing landscape-type diversity and evenness have helped mitigate SESY. The opposite is true for LCTs dominated by forests, shrubs, and grasslands. Collectively, the results of this study provide valuable progress in the capacity to support landscape restoration and comprehensive management of soil and water degradation in mountainous watersheds with similar characteristics to the LJRB.

Analysis and simulation of nitrogen loss during water erosion process on windward slope under wind-driven rain conditions

Wind-driven rain (WDR) is a common source of soil erosion in nature and usually occurs on windward slopes. This study investigated the effects of WDR events at different wind velocities of 0, 2, 3, 5, 7, 8 m s−1 and rainfall intensities of 30, 60, 90 mm h−1 on runoff, sediment yield, and total nitrogen (TN) loss processes on windward slopes. Additionally, the study constructed quantitative relationships between TN loss rate and simultaneous runoff and sediment using indoor simulated WDR experiments. The distributed soil erosion model KINEROS2 was then modified to embedded with these relationships, and used to simulate and verify the runoff, sediment yield, and TN loss processes during WDR events on windward slopes. The results showed an initial substantial increase followed by a gradual stabilization trend in runoff rates, sediment yield loss rates, and sediment-associated TN loss rates on windward slopes. As wind velocity increased from 0 to 8 m s−1 under a rainfall intensity of 90 mm h−1, the average runoff rate, sediment yield rate, and sediment-associated TN loss rate decreased linearly by 4.30%–16.13%, 9.82%–34.44%, and 14.54–46.42%, respectively. However, runoff-associated TN loss rate increased in a linear trend of 26.49%–137.59%. Similar trends were observed at rainfall intensities of 30 and 60 mm h−1. When simulated using the KINEROS2 and nitrogen migration model embedded with mathematical relationships between wind velocity and soil erosion and TN loss on windward slopes, the NSE and R2 of runoff, sediment, and TN loss processes were 0.49–0.83 and 0.59–0.89, 0.21–0.82 and 0.42–0.88, and 0.21–0.73 and 0.38–0.83, respectively. This study provides insights into the effects of WDR events on TN loss at plot scale and offers guidance for KINEROS2 application under WDR conditions at different slope directions and watershed scales.

Linkages between soil erosion and long-term changes of landscape pattern in a small watershed on the Chinese Loess Plateau

Understanding the response of soil erosion to the changes of land use and landscape pattern is valuable for the optimization of soil and water conservation measures in a watershed. This study selected a typical hilly-gully watershed of the Chinese Loess Plateau, the Zhifanggou watershed, to assess its long-term land use changes from 1938 to 2020 and their impacts on sediment yield by using the spatially distributed soil erosion model WaTEM/SEDEM with an average annual rainfall erosivity of 2000–2010. The results indicated that the main land use types in the Zhifanggou watershed were cropland, forest and grassland, and experienced two changing periods: rapid agricultural reclamation during 1938–1958 and vegetation restoration during 1958–2020. The average annual sediment yields varied consistently with land use changes, showing evident changes from 51.84 t ha−1 y−1 in 1938 to 254.1 t ha−1 y−1 in 1958 and then to 4.27 t ha−1 y−1 in 2020. Correlation analysis suggested that sediment yield was closely related to the landscape indices of interspersion and juxtaposition index and Perimeter-area fractal dimension. The results indicated that increased vegetation cover and high spatial heterogeneity of landscapes could alter sediment transport pathways, reduce sediment connectivity, and induce less sediment discharged into the river. Our findings could provide a good reference for optimizing soil and water conservation measures in the watershed.

Satellite observations reveal decreasing soil erosion in Northeast Inner Mongolia, China, over the past four decades

Knowledge regarding the soil erosion change patterns in Northeast Inner Mongolia (NIM) is essential for ecological security and sustainable development. Multisource satellite remote sensing with auxiliary data, including meteorology, land use, vegetation coverage, and digital elevation, was collected to establish a distributed soil erosion model to quantify the soil erosion intensity in Northeast Inner Mongolia. The results showed that soil erosion in Northeast Inner Mongolia, China, decreased by 100,654 km2 from 1978 to 2018. The area change rates of the mild, moderate, strong, intensive and severe soil erosion intensities were −48.91%, −41.41%, 32.63%, −91.15%, and −91.14%, respectively. The decrease in soil erosion was mainly located in the Hulunbuir and Tongliao regions. Our findings from satellite observations provide information about the soil erosion intensity and spatial distribution required for policy-making and the management of soil erosion prevention in Northeast Inner Mongolia.

A framework for testing large-scale distributed soil erosion and sediment delivery models: Dealing with uncertainty in models and the observational data

Evaluating distributed soil erosion models is challenging because of the uncertainty in models and measurements of system responses. Here, we present an approach to evaluate soil erosion and sediment delivery models, which incorporates sediment source fingerprinting and sediment-rating curve uncertainty into model testing. We applied the Generalized Likelihood Uncertainty Estimation (GLUE) methodology to the Sediment Delivery Distributed model (SEDD) for a large catchment in Southeast Brazil. The model was not rejected, as 23.4% of model realizations were considered behavioral. Fingerprinting results and SEDD simulations showed a partial agreement regarding the identification of the main sediment sources in the catchment. However, grid-based estimates of soil erosion and sediment delivery rates were highly uncertain, which restricted the model's usefulness for quantifying sediment dynamics. Although our results are case-specific, similar levels of error might be expected in erosion models elsewhere. The representation of such errors should be standard practice.

A Process-Based, Fully Distributed Soil Erosion and Sediment Transport Model for WRF-Hydro

A soil erosion and sediment transport model (WRF-Hydro-Sed) is introduced to WRF-Hydro. As a process-based, fully distributed soil erosion model, WRF-Hydro-Sed accounts for both overland and channel processes. Model performance is evaluated using observed rain gauge, streamflow, and sediment concentration data during rainfall events in the Goodwin Creek Experimental Watershed in Mississippi, USA. Both streamflow and sediment yield can be calibrated and validated successfully at a watershed scale during rainfall events. Further discussion reveals the model’s uncertainty and the applicability of calibrated hydro- and sediment parameters to different events. While an intensive calibration over multiple events can improve the model’s performance to a certain degree compared with single event-based calibration, it might not be an optimal strategy to carry out considering the tremendous computational resources needed.

A three-process-based distributed soil erosion model at catchment scale on the Loess Plateau of China

The Loess Plateau of China suffers from severe soil erosion. In the gullied rolling loess region, approximately half of the sediment derives from gully areas, which are the most prominent topographical features of this region. No existing soil erosion models are appropriate in accuracy or applicability for the Loess Plateau because existing models only consider slope and river erosion processes at the catchment scale. The absence of the gully erosion process in these models significantly limits their application to the Loess Plateau. Taking this issue into account, a three-process-based distributed soil erosion model, denoted by WEP-SED, is proposed to investigate soil erosion in this region based on the Water and Energy transfer Processes in Large river basins (WEP-L) model. In WEP-SED, a sequential “slope-gully-river” structure is built for the physically-based simulation of soil erosion and sediment yield. In this structure, soil erosion is integrated from six parts with successive transport relationships. The proposed model is applied to the upstream region of the Wenjiachuan hydrological station in the Kuye River basin. The simulated monthly average sediment transport rates from 1956 to 2010 at the Wenjiachuan hydrological station agree well with the observations, with a correlation coefficient of 0.76, an NSE of 0.58, and a relative error of −5.60%. Furthermore, the simulated average annual amount of gully erosion reaches 60.30% of the total soil erosion, reflecting the fact that the gully erosion is a serious problem and demonstrating that gully erosion must be considered separately in this area.

High precision tracing of soil and sediment movement using fluorescent tracers at hillslope scale

AbstractGenerating high resolution spatial information on the movement of sediment in response to soil erosion remains a major research challenge. In this paper we present a new tracing method that utilises LED (light emitting diode) light to induce fluorescence in a sand‐sized tracer, which is then detected, using a complementary metal oxide semiconductor (CMOS) sensor in a commercial digital camera, at mm‐resolution without the need for removal of soil material. First, we detail two complementary, but independent, methods for quantifying the concentration of tracer from images: particle counting and an intensity based method. We show that both methods can produce highly resolved estimates of particle concentrations under laboratory conditions. Secondly, we demonstrate the power of the method for collecting spatial information on soil redistribution by tillage, with mm precision, over an approximately 50 m hillslope and vertically down the soil profile. Our work demonstrates the potential to collect quantitative time‐resolved data about soil movement without disturbing the soil surface which is being studied, and with it the possibility to parameterise or evaluate dynamic distributed soil erosion models or to undertake fundamental research focused on particle movement that has been impossible to conduct previously. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Integrated, spatial distributed modelling of surface runoff and soil erosion during winter and spring

In cold climate regions a significant fraction of annual soil erosion in agricultural land occurs during snowmelt and rain on partially frozen soils. Physically based and spatially distributed soil erosion models have proved to be good tools for understanding the processes occurring at catchment scale during rainfall erosion. However, most existing erosion models do not account for snow in a suitable way. A combination of the UEBGrid snow pack model and the LISEM erosion model was therefore used in this study. The aim was to test and validate this model combination and to assess its utility in relation to quantification and process understanding. Applying this model combination to simulate surface runoff and soil erosion showed that, in principle, it is possible to satisfactorily simulate surface runoff and observed soil erosion patterns during winter. The values for the calibration parameters were similar for the two chosen winter periods when the rainfall and snowmelt episodes occurred. However, the calibration procedure showed that the utility of this combination had several limitations. It is hoped that this study can help to improve existing models and trigger new developments in including snow pack dynamics and soil freezing and thawing in soil erosion models.

Impact of Land Use Change and Dam Construction on Soil Erosion and Sediment Yield in the Black Soil Region, Northeastern China

AbstractSince the 1960s, the implemented soil conservation measures on steep slopes and the densely planted shelterbelts as well as the constructed reservoirs and ponds in Baiquan County, northeastern China have dramatically altered the landscape and would greatly influence soil erosion and sediment yield (SY). However, how these land use changes and the constructed dams affected soil erosion and SY still remained unclear. A physically distributed soil erosion model WaTEM/SEDEM that has been calibrated and validated using 25 reservoir SYs in the study area was applied using nine land use scenarios (land uses in 1954, 1975 and 2010, each with 8, 32 and without dams) to assess their impacts on sediment delivery at the Shuangyang catchment (915 km2). The results show that land use changes as well as the increased dam numbers progressively decreased catchment sediment delivery and the impact of dams on sediment delivery was more efficient under the intensified land use condition (1954 land use without reservoirs). With respect to 1954 land use without dams, current land use condition (2010 land use with 32 dams) was simulated to decrease SY by 61·8%. Soil conservation measures (terrace and contour tillage as well as shelterbelts) on the slopes greatly influenced SY and over 80% of the reduced SY were caused by land use changes. This study indicates that soil conservation measures are sustainable sediment control measures for the black soil region because the accumulation of sediment in dams causes shortening of the useful life in reservoirs and ponds and implies increasing financial costs. Copyright © 2016 John Wiley & Sons, Ltd.

Combining 137Cs measurements and a spatially distributed erosion model to assess soil redistribution in a hedgerow landscape in northwestern France (1960–2010)

Erosion is one of the main threats to soils and is associated with numerous environmental and economic impacts. At the landscape scale, soil redistribution patterns induced by water and tillage erosion are complex, and landscape structures play an important role in their spatial distribution. In this study, soil redistribution patterns, generated by both water and tillage erosion, were estimated in the vicinity of hedges in an agricultural landscape. Two complementary methods were employed to estimate soil redistribution from 1960 to 2010: 137Cs conversion models and a spatially distributed soil erosion model (LandSoil model). Both methods determined that hedges affected soil redistribution patterns, which led to soil deposition or limited soil erosion uphill from hedges, even though soil erosion rates were consistently higher than soil deposition rates. Depending on the method, mean soil redistribution rates ranged from −15.9 to −4.7tha−1yr−1 for all sampling points, from −4.8 to 2.2tha−1yr−1 in positions uphill from hedges and from −4.8 to −11.2tha−1yr−1 in positions located downhill from hedges. The impact of tillage on soil redistribution in the vicinity of hedges was found to be higher than that of water processes because 87% of net soil redistribution was linked to tillage. This confirmed the importance of including landscape structure and working at the landscape scale rather than at the plot scale to better estimate soil redistribution in agricultural areas.

Experimental validation of a 2D overland flow model using high resolution water depth and velocity data

• A 2D overland flow model is validated using high resolution depth and velocity data. • Manning and Keulegan formulations produce similar and satisfactory results. • More complex formulations do not improve model performance. • The friction coefficient can be related to the micro and macro-rugosity of the bed. • The model might be used as the hydraulic base of a distributed soil erosion model. This paper presents a validation of a two-dimensional overland flow model using empirical laboratory data. Unlike previous publications in which model performance is evaluated as the ability to predict an outlet hydrograph, we use high resolution 2D water depth and velocity data to analyze to what degree the model is able to reproduce the spatial distribution of these variables. Several overland flow conditions over two impervious surfaces of the order of one square meter with different micro and macro-roughness characteristics are studied. The first surface is a simplified representation of a sinusoidal terrain with three crests and furrows, while the second one is a mould of a real agricultural seedbed terrain. We analyze four different bed friction parameterizations and we show that the performance of formulations which consider the transition between laminar, smooth turbulent and rough turbulent flow do not improve the results obtained with Manning or Keulegan formulas for rough turbulent flow. The simulations performed show that using Keulegan formula with a physically-based definition of the bed roughness coefficient, a two-dimensional shallow water model is able to reproduce satisfactorily the flow hydrodynamics. It is shown that, even if the resolution of the topography data and numerical mesh are high enough to include all the small scale features of the bed surface, the roughness coefficient must account for the macro-roughness characteristics of the terrain in order to correctly reproduce the flow hydrodynamics.

Modeling the Impacts of Land Use Changes on Soil Erosion at the River Basin Scale

The potential for soil erosion is strongly affected by land use. A proper modeling approach should be selected to explicitly assess the impacts of land use changes on soil erosion at a river basin scale. The reliability of simulation results from erosion models is circumscribed by considerable spatial variation in many parameters. In this study, a grid–based distributed soil erosion and sediment transport model was used in conjunction with a laboratory rainfall simulation experiment to determine the impact of land use changes on soil erosion and sediment yield in a river basin during individual storms. Land use changes in the Lushi Basin, primarily in Henan, China, were analyzed by comparing the historical land use maps in 1990 and 1995. Through comparing the results for four selected storms that were compiled using these two land use maps, it was found that the average erosion rates increased from 1989 to 1996. The increase in average erosion rates followed the land use changes, especially the transformation of forest to farmland. The results indicated that even slight land use change, from forest to farmland or vice versa, had a significant effect on regional soil erosion rates and sediment supply to rivers.

A unit stream power based sediment transport function for overland flow

Soil erosion is a serious global problem requiring effective modeling for accurate assessment of sensitive areas and related erosion rates. The outcome of soil erosion models depends strongly on the estimation of sediment transport capacity. In most of the existing spatially distributed soil erosion models sediment transport capacity of overland flow is often estimated using stream flow transport capacity functions. The applicability of stream flow functions to overland flow conditions is questionable because hydraulic conditions like flow depth, slope steepness and surface roughness under overland flow are substantially different from stream flow conditions. Hence, the main objectives of this study were i) to check the suitability of five existing well known and widely used transport capacity functions (Yalin 1963; Low, 1989; Govers, 1990; modified Engelund and Hansen (Smith et al., 1995); and Abrahams et al., 2001) for use under overland flow conditions, and ii) to derive a new function based on unit stream power by dimensional analysis to quantify transport capacity for overland flow. To accomplish the objectives, experiments in a 3.0 m long and 0.5 m wide flume were carried out using four different sands (0.230, 0.536, 0.719, and 1.022 mm). The unit discharges used for experimentation ranged from 0.07 to 2.07 x 10(-3) m(2) s(-1) and slopes ranged from 5.2 to 17.6%. In this study, none of the predictions with the existing functions was in good agreement with measured results over the whole range of experimental conditions, especially at low flow intensities. The percentages of observations in which the discrepancy ratio ranged between 0.5 and 2.0 were: 65% (Yalin 1963), 74% (Low, 1989), 57% (Govers, 1990), 54% (modified Engelund and Hansen (Smith et al., 1995)), and 25% (Abrahams et al., 2001). The results showed that the selected functions reasonably estimate transport capacities only under those ranges of conditions for which they were formulated. Although the excess.shear stress concept based function (i.e. Low's function) produced excellent results, the degree of accuracy of the results varied substantially with grain size (P.O.(0.5-2.0): 53-100%). In contrast, the performance of the Govers' function, which is based on the unit stream power concept, was quite similar for all the selected sands (P.O.(0.5-2.0): 50-63%). Based on the unit stream power concept, a new function for low flow intensities was derived by dimensional analysis using the data gained from the flume experiments. (c) 2012 Elsevier B.V. All rights reserved.

Multi-pronged assessment of land degradation in West Africa to assess the importance of atmospheric fertilization in masking the processes involved

Separating human-induced land degradation from that caused by natural processes in the world of global climate and atmospheric change is a challenging task, but important for developing mitigation strategies. Current remote-sensing data and spatio-temporal analyses allow the distinction of climate and human-induced land degradation on a sub-continental scale, but the underlying processes cannot be discerned at this scale. This study is conducted at a river-basin scale to (1) identify land degradation hotspots in a basin or sub-basin, and (2) assess the correspondence and divergence of land degradation assessed by NDVI shifts with and without accounting for atmospheric fertilization with that based on soil erosion assessment at a sub-basin scale. Long-term remote sensing (NDVI) and rainfall data were used to identify human-induced land degradation hotspot areas in the Volta basin. The results were compared with the critical zone of soil loss in the White Volta sub-basin derived from a spatially distributed soil erosion model, validated by field-measured data. A spatial comparison of the above studies revealed that the biomass productivity (NDVI)-based land degradation assessment grossly underestimated the extent to which soil is being lost, unless a correction was included to account for atmospheric fertilization. Based on inter-annual NDVI signals land degradation was evident in about 8% of the Volta basin's landmass, but when accounting for atmospheric fertilization, as much as 65% of the land is losing some of its vital attributes such as soil quality or vegetation productivity. The study demonstrates the need for using a multi-pronged assessment strategy in land degradation assessment that offers an insight of the processes involved in land degradation.

MODELLING THE EFFECT OF VEGETATION COVER AND DIFFERENT TILLAGE PRACTICES ON SOIL EROSION IN VINEYARDS: A CASE STUDY IN VRÁBLE (SLOVAKIA) USING WATEM/SEDEM

ABSTRACTVineyards represent one of the most erosion‐prone types of cultivated land. Because of this, cultivation practices are very important in reducing the soil erosion risk in vineyard regions. The aim of this paper was to assess the impact of various management practices on soil loss in vineyards. Effects of tillage, hoeing, rotavating and grass cover were evaluated in small vineyards located in southwestern Slovakia in the Vráble viticultural district. Erosion and deposition rates were estimated using the levelling method. This method is based on an evaluation of variability of the soil surface against vineyard poles measured between the year of pole insertion and the year of measurement. On the basis of the measured data, a WATEM/SEDEM distributed soil erosion model was calibrated, and the total soil loss from the vineyards under different management conditions was estimated. The model shows rather good performance in modelling soil erosion, but at the same time, it shows lower reliability in modelling soil deposition. Downslope tilled vineyards were the most eroded; the erosion in rotavated vineyards is somewhat reduced. The most protective tillage system is hoeing. Considerably lower soil loss was estimated with the use of vegetation cover between vine rows, which is in accordance with agro‐environmental schemes supporting use of grass cover as an erosion prevention measure in vineyards. Copyright © 2012 John Wiley & Sons, Ltd.

Modeling the impacts of agroforestry systems on the spatial patterns of soil erosion risk in three catchments of Claveria, the Philippines

Agroforestry is one of the preferred land-use options for smallholder farms in tropical landscapes due to its ability to increase land productivity and protect soil from erosion. We investigated the impacts of agroforestry and traditional monocropping systems on the spatial patterns of soil erosion risk in three catchment areas of Claveria, the Philippines, using WaTEM/SEDEM, a spatially distributed soil erosion model. The model predicts soil loss in catchments based on the Revised Universal Soil Loss Equation (RUSLE) by taking into account the influences of rainfall, soil erodibility, vegetation cover and 2-dimensional variations in landscape structure. The predicted soil erosion rates were transformed into risk values in order to identify areas with higher risk for erosion. Model results indicate a large spatial variability in soil erosion risk patterns, with higher risks occurring on slopes greater than 8% on land under non-agroforestry use. The soil erosion risk maps were used to formulate site-specific agroforestry recommendations for future landscape amelioration plans.

Predicting spatial patterns of sediment delivery and impacts of land‐use scenarios on sediment transport in Czech catchments

AbstractFor the Czech Republic one of the most dangerous effects of soil erosion and sediment transport processes is water quality degradation, due to secondary pollutants. The WaTEM/SEDEM model, developed at Katholic University (KU) Leuven in Belgium, was tested as a prediction tool within several different Czech catchments. WaTEM/SEDEM is a spatially distributed soil erosion model running on raster GIS basis.The Watershed of Hostivar reservoir (ca 100 km2) is examined in this study. Soil loss and sediment transport have been estimated for the present state of the land use. Terrain surveys allowed us to identify actual erosion and deposition spots within the watershed and compare these with the model prediction. From the surveys, covering as yet only one season, the spatial accuracy of the model (correspondence of erosion/sedimentation occurrence with prediction) was estimated as 56 per cent. In 32 per cent the surveyed effects were predicted wrongly and in 12 per cent the correspondence was not clear.Different scenarios of possible land use changes were applied and their effect on sediment transport and the reservoir's siltation have been determined. The scenarios describe several land‐use management alternatives. C‐factor changes (crop rotation changes) were applied to selected fields—either the fields with highest soil losses or the fields with highest sediment yields (transition fields). Affected areas were increased in five steps up to ten per cent of the catchment's area. From the scenarios it is clear that focussing on ‘transition’ fields with high sediment outflow and converting them to sediment ‘traps’ gives rise to more efficiency concerning the prevention of siltation than assessing the fields only by considering the USLE erosivity prediction. Copyright © 2009 John Wiley & Sons, Ltd.

Spatially distributed data for erosion model calibration and validation: The Ganspoel and Kinderveld datasets

Recent experience in distributed modelling has revealed that the performance of process-based erosion and hydrological models are extremely sensitive to parameter estimations and that predictions are often poor. It is also observed that quite different parameter sets may lead to very similar results and that no ‘best’ parameter set can be identified. In this study, we describe a dataset that offers possibilities for improved evaluation and parameterisation of spatially distributed soil erosion models. The dataset combines rainfall, runoff and sediment discharge data collected at the outlet and field surveys within the catchments that describe soil surface characteristics and soil erosion features. This offers clear advantages over traditional model evaluation as not only the simulated overall system response, integrated over time and space, but also the simulated internal system dynamics can be compared with measured data. The paper discusses and illustrates the use of the dataset to narrow uncertainties associated with model predictions.

The influence of both process descriptions and runoff patterns on predictions from a spatially distributed soil erosion model

AbstractSpatially distributed, process‐based erosion models have been built to predict both erosion and deposition rates and patterns. However, predictions by these models often do not meet our expectations. There are several possible reasons for this, which can be subdivided into three groups: (i) process descriptions within the models may be incomplete or incorrect, leading to structural errors (model error); (ii) parameterization is difficult leading to a high degree of uncertainty regarding model inputs (input error); and (iii) the spatial implementation of the model (the spatial discretization and the routing methods used) may be inadequate. Hitherto, most studies of erosion model performance have focused on input parameter uncertainty: the effects of process description and spatial implementation of the model have often been neglected. In this study an attempt is made to compare some aspects of the effects of process description, parameter uncertainty and model implementation on model performance. A series of model runs was carried out to evaluate to what extent the predictions of the spatially distributed erosion model LISEM are affected by the description of the hydraulic resistance, the parameter values used to characterize hydraulic resistance as well as the routing algorithm used to generate the runoff pattern.The process description used for overland flow resistance and velocity has a clear effect on the erosion and deposition rates predicted by the model. However, relatively minor variations in a single parameter value (hydraulic roughness) appear to affect model output more strongly than variations in the process description itself. The use of different routing algorithms leads to notably different erosion and deposition patterns, but total erosion and deposition rates are much less affected. Copyright © 2005 John Wiley & Sons, Ltd.