Modeling surface runoff and soil erosion at various scales: data, process, and mathematical representation

Erosion can cause serious agricultural and environmental damages by impairing landscape, producing soil and land loss, reducing agricultural productivity, inducing water pollution, and threatening waterways and hydraulic structures. It also plays a significant role in the biogeochemical cycles of carbon, nitrogen, and phosphorus by redistributing significant amounts of nutrients over the Earth’s surface. The multi-scale and non-linear nature of the processes involved in runoff generation and in soil erosion and the high spatial and temporal resolution of the required input data create a challenging modeling environment. Improving our basic understanding and modeling capabilities on water erosion are required to assess its impact on the soil and water resources and to evaluate the efficiency and the cost of the measures for resolving the problems.

Aiming at advancing our ability of modeling soil erosion across spatial scales, this session focuses on recent studies supporting surface runoff and soil erosion modeling on natural or disturbed landscapes, as well as their environmental effects. We invite submissions concerning surface runoff and/or water erosion processes, at the plot, hillslope, watershed, regional, or global scales. Studies may include analyses of monitoring or experimental data applying recent technologies, or modeling investigations using physics based, conceptual, data driven, or other types of novel approaches, to improve the assessment of the multi-scale, multidisciplinary processes, and their coupling with biogeochemical cycles as well as soil functioning.

Conveners: Shmuel Assouline, Li Chen, Xianli Xu | Co-Conveners: Arnaud Temme, Tiejun Wang, Peter Finke
| Fri, 21 May, 15:00–16:30 (CEST)
| Fri, 21 May, 16:30–18:00 (CEST)

Oral: Fri, 21 May

Chairpersons: Li Chen, Shmuel Assouline, Xianli Xu
Erin Brooks, Mariana Dobre, Roger Lew, Chinmay Deval, Anurag Srivastava, and Pete Robichaud

Since the development and availability of GIS-based software and satellite imagery, there has been a vision that watershed managers would have near-real-time, three-dimensional hydrologic and soil erosion models that could easily assess impacts of watershed management decisions at high spatial resolutions across multiple scales.  Our research team has made significant advances to address this challenging problem especially in the forest environment. The technology and data retrieval and access has dramatically improved to the point where it is possible to provide useful, near-real-time, geospatial decision support for watershed managers.  This talk describes an online watershed model called WEPPcloud, widely used by the Forest Service and one of the FSWEPP suite of watershed tools, which is based fundamentally on a process-based hydrologic, soil erosion model (WEPP, Water Erosion Prediction Project).  WEPPcloud is driven by discoverable, data-rich geospatial mapping products (e.g. soils, topography, satellite-based vegetation characteristics) and management libraries. It accesses daily grid-based historical and future projected climatic data to provide a comprehensive spatially and temporally explicit assessment of the impacts of management decisions on hydrologic response and sediment transport.  Currently, WEPPcloud can be applied throughout the continental US, and beta versions are available for Australia and Europe. We will demonstrate this tools’ development and application to guide pre-fire fuel management and post-fire mitigation, flood risk for communities where drinking water supplies and water resources are vulnerable to wildfire. We will discuss the ongoing limitations, challenges and opportunities towards more fully incorporating geospatial hydrologic and soil erosion models into watershed management decisions.

How to cite: Brooks, E., Dobre, M., Lew, R., Deval, C., Srivastava, A., and Robichaud, P.: Timely Decision Support for Watershed Management with WEPPcloud, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-61,, 2021.

Andrea Urgilez-Clavijo, David Rivas-Tabares, Juan José Martín-Sotoca, and Ana M. Tarquis

The deforestation process is nowadays recognized as a global concern due to a variety of environmental issues associated with forest loss. Exacerbated deforestation rates in basins such as the Amazon river basin is contributing tremendously to environmental global degradation and climate change. Previous studies regarding the deforestation process suggest that soils and forest loss are correlated exhibiting non-linear and multi-scale behaviors. Based on this, we conduct a novel approach based on image analysis of the deforestation process to improve the understanding of local connections of this process in a Biosphere reserve in the Ecuadorian Amazon. Understanding the connections between deforested patches and how they are strengthening the deforestation process could provide new features for understanding forest loss associated with agricultural expansion. Thus, these map features can be used for modeling purposes of agricultural expansion and forest loss impact. This work is based on the assessment of cumulative images of deforestation in the Sumaco biosphere reserve in the Ecuadorian Amazon from 1985 to 2018. For this, we rigorously sampling every deforested pixel of the images through the moving window technique to calculate the fractal dimension of the connected pixels at different scales. Once fractal dimensions are calculated, we classify these values to mapping the existing relations. The mapping results show different complexity levels in local connections of the deforestation process. These spatial relations can improve the understanding of deforestation patterns and provide relevant information for decision-making to conservation programs.

Acknowledgements: The authors acknowledge the support of Project No. PGC2018-093854-B-
I00 of the Ministerio de Ciencia, Innovación y Universidades of Spain and the financial support from Boosting Agricultural Insurance based on Earth Observation data - BEACON project under agreement Nº 821964,funded under H2020EU, DT-SPACE-01-EO-2018-2020.

How to cite: Urgilez-Clavijo, A., Rivas-Tabares, D., Martín-Sotoca, J. J., and Tarquis, A. M.: Multiscale local connections of deforestation process in the Ecuadorian Amazon, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-55,, 2021.

Mingguo Zheng

Previous studies have suggested that runoff reduces with slope length, and the scaling trend diminishes with the degree of land degradation. This study further hypothesized that runoff is scale-independent and spatially uniform in extremely degraded landscapes. We tested the hypothesis on the Chinese Loess Plateau. Runoff data were collected from a densely rilled and gullied loess headwater with soil erosion intensity close to 20,000 t km-2 yr-1.  The data included observations from seven arable experimental plots of various lengths (20 to 164 m) and gradients (9 to 32°), as well as the headwater outlet. The results showed that the erosion-induced network of rills and gullies lowered runoff reinfiltration and resulted in exceptional high flow connectivity, thus obscuring the effects of other environmental conditions (mainly topography) and contributing to uniform runoff from the upper hillslope to the headwater outlet. The observations held at the event, annual, and mean annual time scales, implying that the investigated watershed is simply the sum of individual slopes. This study highlights the effect of erosion processes on the ensuing runoff yield. The effect should be fully addressed in studies of runoff yield in semi-arid areas, which are among the most erodible landscapes due to sparse land cover.

How to cite: Zheng, M.: Spatially uniform surface runoff as a result of erosion-induced high hydrolocial conncenctiviey over an extremelydegraded catchment , 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-65,, 2021.

Songbai wu and Li Chen

Whereas current erosion models are successful in quantitative estimates of soil erosion by water flow, modeling the coevolution of geomorphological features, particularly rill network properties and soil erosion on hillslopes, is still a major challenge. In this study, we propose a rill evolution modeling approach, and combine it with a rainfall-runoff and soil erosion model to simulate the feedback loop of hillslope geomorphic development and soil erosion processes. Rill evolution is mainly characterized by three rill network attributes, comprised of rill density, orientation angle, and rill width, all modeled with physical equations. The entire rainfall-runoff-erosion and rill evolution model is tested against a set of rill network evolution and soil erosion data from an experimental hillslope subjected to successive rainfall events. The simulated spatial and temporal variations of rill network characteristics and soil erosion agree well with the measured data. The results demonstrate that the three rill network characteristics continually alter the partitioning of interrill and rill flows and affect the interrill and rill flow erosivity and soil erosion, which in turn modify the rill geometry and rill network planform. Comparatively, existing approaches such as WEPP that ignore the rill evolution processes largely underestimate the hillslope soil erosion when using time independent model parameters. Moreover, a sensitivity analysis indicates that both the rill evolution and soil erosion processes are sensitive to the rill evolution parameters, rainfall intensity, and slope angle. These results can inform the development of general geomorphic evolution and soil erosion models on evolving rilled hillslopes.

How to cite: wu, S. and Chen, L.: Modeling soil erosion with evolving rills on hillslopes, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-30,, 2021.

Li Chengfang, Wang Zhongcheng, Li Zhenwei, and Xu Xianli

Soil erosion has a significant influence on nutrient redistribution and deposition. However, the effect of soil erosion on nutrient deposition remains unclear in karst areas such as southwest China, which represents an ecologically fragile zone experiencing severe soil erosion. The objective of this study was to investigate the characteristics of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) deposition in a karst watershed of southwest China over the past 60 years and evaluate the relationship between soil erosion and nutrient deposition. The peak-cluster depressions in southwest China are typical for the geomorphological type, which is an ideal place to determine the sediment chronology, and the estimation of sediment and nutrient deposition rates. Three soil profiles were excavated in a typical karst depression. The characteristics of 137Cs, 210Pbex, particle size distribution, and nutrients at different soil depths were investigated to evaluate the effect of soil erosion on nutrient deposition. Results showed that there was a significant negative correlation between nutrient concentrations and clay content (P<0.001). Generally, compared with 137Cs, 210Pbex had a higher correlation with SOC and TN. In an undisturbed sediment profile, Pb/Cs can reflect nutrient dynamics better than a single nuclide. The nutrient deposition rates increased before 1953, reached its maximum in 1954-1956, and then dropped rapidly from 1957 to 2015. The sediment deposition rates were negatively correlated with nutrient concentrations (P<0.01), but had a positive influence on nutrient deposition rates (P<0.01). This implies that the temporal variation in nutrient deposition rates over the past 60 years was dominated by soil erosion rather than nutrient concentrations. This study provides a new insight to explore the historical nutrient deposition rates in a peak-cluster karst depression, and may help effectively control soil erosion and sustainable development of agro-ecosystems.

How to cite: Chengfang, L., Zhongcheng, W., Zhenwei, L., and Xianli, X.: Soil erosion impacts on nutrient deposition in a typical karst watershed, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-74,, 2021.

Interactive: Fri, 21 May, 16:30–18:00<

Shuilong Yuan, Chen Li, Zhanbin Li, and Zeyu Zhang

As important soil and water conservation engineering measures, there are more than 100,000 check dams constructed on the Loess Plateau; these dams play a vital role in reducing floods and sediment in watersheds. However, the effects of check dams on hydrologic process are still unclear, particularly when they are deployed as a system for watershed soil and water management. This study examined the watershed hydrologic process modulated by the check dam system in a typical Loess Plateau catchment. By simulating scenarios with various numbers of check dams using a distributed physical-based hydrological model, the effects of the number of check dams on runoff generation and concentration were analyzed for the study catchment. The results showed that the presence of check dams reduced the peak discharge and the flood volume and extended the flood duration; the reduction effect on peak discharge was most significant among the three factors. The system of check dams substantially decreased the runoff coefficient, and the runoff coefficient reduction rate was greater for rainstorms with shorter return periods than for rainstorms with longer return periods. The check dams increased the capacity of the catchment regulating and storing floods and extended the average runoff concentration time in the catchment that flattened the instantaneous unit hydrograph. This study reveals the influencing mechanism of check dams on the hydrological process of a watershed under heavy rainstorm conditions and provides a theoretical basis for evaluating the effects of numerous check dams on regional hydrology and water resources on the Loess Plateau.

How to cite: Yuan, S., Li, C., Li, Z., and Zhang, Z.: Effects of a check dam system on the runoff generation and concentration processes of a catchment on the Loess Plateau, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-64,, 2021.

Li Wang, Fan Zhang, and Guanxing Wang

The impact of climate change on soil erosion is pronounced in high mountain area. In this study, the revised universal soil loss equation (RUSLE) model was improved for better calculation of soil erosion during snowmelt period by integrating a distributed hydrological model in upper Heihe river basin (UHRB). The results showed that the annual average soil erosion rate from 1982 to 2015 in the study area was 8.1 t ha-1 yr-1, belonging to the light grade. To evaluate the influence of climate change on soil erosion, detrended analysis of precipitation, temperature and NDVI was conducted. It was found that in detrended analysis of precipitation and temperature, the soil erosion of UHRB would decrease 26.5% and 3.0%, respectively. While in detrended analysis of NDVI, soil erosion would increase 9.9%. Compared with precipitation, the effect of temperature on total soil erosion was not significant, but the detrended analysis of temperature showed that the effect of temperature on soil erosion during snowmelt period can reach 70%. These finding were helpful for better understanding of the impact of climate change on soil erosion and provide a scientific basis for soil management in high mountain area under climate change in the future.

How to cite: Wang, L., Zhang, F., and Wang, G.: Influence of climate change on soil erosion in high mountain area: a case study of upper Heihe river basin, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-71,, 2021.

Longxi Cao, Xin Li, and Mingming Shi

Unpaved roads are common man-made features that distributed in agricultural or forest watersheds. Road construction will change the underlying topography and alter the surface hydrology, in turn would enhance runoff generation and result in high soil loss risk. Therefore road erosion should be considered as one of the main sediment sources and should be properly evaluated. Process-based erosion models provide efficient tools to precisely evaluate soil loss along unpaved roads. This study was performed using the hillslope version of the Water Erosion Prediction Project (WEPP) to estimate soil loss from 20 typical road segments in the red soil region of South China. The terrestrial laser scanning (TLS)-measured soil losses were used to validate the model simulations. The results showed that the WEPP model could reasonably predict the total soil loss in relatively short (less than 100m) and gentle (slope gradient lower than 10%) road segments. On the contrary, the WEPP simulated soil loss would result in underestimation for long or steep road segments. Detailed WEPP plot outputs along roads revealed that most of the peak soil loss rates cannot be adequately calculated as comparing with the TLS-measured values. The linear critical shear stress theory in WEPP model for soil detachment simulation might responsible for the underestimation of non-linear peaked soil losses in long or steep road segments. Meanwhile, the lack of upslope flow and the curved road tortuosity were also found to be connected to the relatively low efficiency of the model outputs. Nevertheless, the WEPP simulation could accurately fit the detailed trend of soil loss variation along road segment despite the underestimation. Furthermore, the simulated results could provide a reliable prediction of the maximum soil loss positions. Therefore, the WEPP model could be adopted to evaluate erosion risk of unpaved roads in red soil region of China.

How to cite: Cao, L., Li, X., and Shi, M.: Modelling soil erosion on unpaved road surface with process-based model and terrestrial laser scanning, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-85,, 2021.

Jie Wang and Li Chen

  Topography, one of the main factors in hillslope rainfall-runoff processes, is related to many environment problems initiated by rainfall, such as flash flood, soil erosion, and landslides, and crucial in hillslope hydrological models and large-scale hydrological-hydrodynamic models. This research investigated the effects of topography abstracted by the combination of longitudinal profile curvature and plan shape on the Hortonian rainfall-runoff processes. The results show that different profile curvature and plan shape leads to more than 10% difference in cumulative runoff and runoff rate and more than 20% difference in ponding time. Similar infiltration and runoff processes can occur on different hillslopes because of the similar slope gradient distributions, and partial area runoff can also occur in these hillslopes. The run-on effect causes more infiltration on convex hillslope topography. The soil property and rainfall temporal variability do not change the trends but can alter the magnitudes of the hillslope geometry effect. The study provides insights into the rainfall runoff processes on natural hillslopes that could benefit studies related to hillslope hydrology and geomorphology.

How to cite: Wang, J. and Chen, L.: The Effect of Hillslope Geometry on Hortonian Rainfall-Infiltration-Runoff Processes, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-39,, 2021.

Zihao Cao, Qihua Ke, Keli Zhang, and Zhuodong Zhang

Rocky desertification is a serious environmental issue in karst regions that restricts food production and hinders local economic development. Generally, soil loss is known as a dominant factor driving rocky desertification. However, it is difficult to couple rocky desertification with the soil loss rate based on a database from short-term field plot observations. Hence, it is imperative to reconstruct the history of soil loss over long-term periods and to correlate the rocky desertification process with the soil loss rate. In karst regions, the most common geomorphic landforms are closed peak-cluster depressions. Researchers have shown that estimating soil loss from hillslopes based on a sediment deposition rate in a peak-cluster depression is possible. In this study, two typical peak-cluster depressions with different degrees of rocky desertification were selected, and sediment cores with lengths of 2 m were sampled from the depressions to determine pollen taxa, soil properties and sediments dating at different depths.The results showed that the burial ages of the sediments in the depressions were different in the time series. During the past millennium, soil loss in the LJWD watershed showed an overall decreasing and then increasing trend. While the change in soil erosion was more complex in the DJT watershed, high and low rates appeared alternately in the 748±100 – 2018 period. The alluvial pollen analysis demonstrated that the soil erosion changes in both watersheds were closely related to human farming activities and vegetation landscape changes. The soil loss history over the past 1000 years was insufficient to reveal the evolution of rocky deserts in karst areas, indicating that the formation of rocky deserts should have occurred over a longer historical period. Overall, the optically stimulated luminescence (OSL) dating and palynological techniques were reliable in the investigation of local erosional history in karst regions.

How to cite: Cao, Z., Ke, Q., Zhang, K., and Zhang, Z.: A thousand-year erosional and sedimentation history in karst watersheds based on OSL dating and palynological techniques, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-34,, 2021.

Keerthika Nirmani Ranathunga, Peter Finke, Qiuzhen Yin, and Yanyan Yu

The Quaternary loess-paleosol deposits in the Chinese Loess Plateau (CLP) provide complete records of paleoclimates for better understanding differences in paleosol development. However, soil properties are overwritten due to climatic conditions in later periods; therefore the true paleosol development cannot easily be quantified. Only a calibrated soil model allows interglacial soil simulation in the CLP over long timescales. Therefore, our objective is to quantify the degree of paleosol development in three different paleosols in the CLP: S2, S4 and S5-1 using a calibrated process-based soil development model, SoilGen2.

The variations of paleosol development were compared by clay% and calcium carbonate content% and anorthite content (kg/m2) in the simulated paleosol.

Our results show that paleosol development is stronger in S5-1, S4, S2 in the studied paleosols in decreasing order of intensity. Each paleosol showed distinct variations in clay migration and decalcification processes under varying climate and dust deposition at the time of development. The model correctly simulated the two-sub paleosol units in paleosol S2. In conclusion, the results indicate that the (calibrated) SoilGen2 model combined with modeled climate can quantify and describe the paleosol development in the CLP fairly.

How to cite: Ranathunga, K. N., Finke, P., Yin, Q., and Yu, Y.: Quantifying paleosol development during three interglacial periods in the Chinese Loess Plateau by soil-climate modeling. , 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-66,, 2021.

Cheng Si, Yu Xingxiu, Li Zhenwei, Xu Xianli, and Ding Mingming

Quantifying the relative contributions of climate and human activities to changes in sediment discharge is closely related to regional water resources, soil management and even the healthy operation of ecosystems. However, few studies used different methods to decompose influences of climatic variability and human activities on sediment discharge change, especially in karst regions of southwest China where experiencing severe soil erosion. This study systematically reviewed four different methods including simple linear regression method, double mass curve method, sediment identify factor analysis, and elastic coefficient method to separate the contribution of climate change and human activities to sediment discharge variation in four karst watersheds of southwest during 1955 to 2015. The trend and abrupt change year of sediment discharge in four watersheds were obtained by nonparametric Mann-Kendall test. Result showed that the sediment discharge in four watersheds all decreased significantly (P<0.05), and the abrupt change years were 2003, 2003, 2004 and 2004 for Wujiang, Yujiang, Hongshui, and Xijiang watersheds, respectively. The simple linear regression method, double mass curve method and elastic coefficient method all indicated that the sediment discharge was mainly influenced by human activities, with the contribution rate ranging from 73% to 101%. For the sediment identify factor analysis method, the sediment concentration is the principal factor influencing sediment discharge variation, and the contribution rate of sediment discharge varied from 100% to 154%. The results can provide good reference value for evaluating the influence of the climate and human activities on sediment discharge, and is significance for proper formulation of regional soil conservation policy in karst watersheds.

How to cite: Si, C., Xingxiu, Y., Zhenwei, L., Xianli, X., and Mingming, D.: Using four different approaches to separate the effects of climate change and human activities on sediment discharge in karst watersheds, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-89,, 2021.

Jianghu He, Keli Zhang, Zihao Cao, and Qihua Ke

Soil erosion is a severe issue in Southwest China due to complex karst geomorphology and excessive farming activities. It is also difficult to observe and evaluate using traditional research methods. Fortunately, as a supplement to traditional methods, the 137Cs tracing technique has strong potential to monitor and evaluate soil loss in karst regions. However, 137Cs might move downward with tiny particles under adequate rainfall conditions. This is critical because it directly affects accuracy of using the 137Cs conversion model to evaluate soil erosion. Thus, in our study, in order to explore whether tracers actually moved vertically and to evaluate the movement distance and the factors influencing the movement, magnetic powder (Fe3O4) and rare earth oxides (CeO2 and La2O3) were used as the substitute tracers under different conditions (rainfall and leaching area) of a simulated leaching experiment, which possess similar properties as 137Cs and have no toxicity problems in humans and the environment. The results showed that tracers moved downward 6 cm when water was added to simulate 1-10-year rainfall conditions and 8 cm when water was added to simulate 15-20-year rainfall conditions. The movement distance of tracers increased slowly with increasing water input, and the concentration of the tracers that moved related indirectly to the leaching area. Tracer movement at the edge of the simulated profile was affected by tracer type and concentration since there was no transition layer between soil and plastic column. Our field observations in two karst watersheds showed that ignoring the vertical movement of tracer can cause the overestimation of soil loss amount by 6.90% and 22.22% respectively. This study proved that in the karst area of Southwest China with abundant rainfall, 137Cs would move vertically, and the soil loss will be overestimated if the vertical movement distance of the tracer is ignored.

How to cite: He, J., Zhang, K., Cao, Z., and Ke, Q.: Tracer vertical movement and its affecting factors in karst soil profiles using the simulated leaching method, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-33,, 2021.