Erosion Equation Research Articles

Численное моделирование самосогласованной динамики поверхностных вод, влекомых и взвешенных наносов: I. Влияние промышленной добычи песка на безопасность судоходства в русле р. Волга

A mathematical model of the joint dynamics of shallow waters, entrained and suspended sediments is constructed, which takes into account nonlinear fluid dynamics and bottom deformations. The dynamics of shallow waters is described by the Saint-Venant equations taking into account the spatially inhomogeneous distribution of the terrain. The transport of entrained sediments is described by the Exner equation generalized to the case of an inhomogeneous distribution of the parameters of the underlying surface. The dynamics of suspended sediments is described by the transport equation, which includes convective transport by water flow and the process of diffusion of the suspension in the liquid layer. For numerical integration of the Saint-Venant, Exner equations and suspended sediment dynamics, a stable and well-tested CSPH-TVD method of the second order of accuracy is used, the parallel CUDA algorithm of which is implemented in the form of a software package «EcoGIS-Simulation» for highperformance computing on supercomputers with graphics coprocessors (GPU). The conditions for the development of a quarry of non-metallic building materials (NSM) located at the mouth of the Partridge Volozhka of the Volga-Akhtuba floodplain on the 2549–2550 km section of the Volga River are considered. To study the safety of navigation from the lower reaches of the Volga hydroelectric dam to the entrance to the VDSK, numerical hydrodynamic modeling of the dynamics of channel processes in this section of the Volga River was carried out. Based on the results of mathematical modeling of the joint dynamics of surface waters, entrained and suspended sediments in the riverbed of the Volga River, it is concluded that the development of the NSM quarry considered in the work does not significantly affect the safety of navigation both along the main ship course «The lower reaches of the Volga hydroelectric dam — VDSK» and on additional — «Volgograd zaton» and «Volozhka Partridge».

Development of erosion equations for removal of organic coating on carbon fiber reinforced polymer surface by plastic abrasive

Development of erosion equations for removal of organic coating on carbon fiber reinforced polymer surface by plastic abrasive

Finite Element Numerical Simulation of Local Scour of a Three-Dimensional Cylinder under Steady Flow

Pile safety has received increasing attention in marine engineering, especially in the field of local scour. In this paper, a finite element numerical model is established for local scour around a cylinder in steady currents. The flow is described by unsteady Reynolds–averaged Navier–Stokes equations with a traditional turbulent closure model. The proposed scour model takes bed load into account. The Exner equation is solved to determine the bed variation and the moving mesh approach is used to capture the evolution of the bed. When the resulting slope exceeds the angle of repose, a novel sand-slide model based on Rodrigues' rotation formula is used to prevent simulation distortion. All the equations are discretized by the two-step Taylor–Galerkin algorithm, and the resulting approach is fast to implement with second-order accuracy in space. The numerical results are found to be in good agreement with the experimental data.

An assessment of rainfall kinetic energy functional relationships with GPM DPR

The kinetic energy (KE) of rainfall is an important parameter in estimating the rainfall erosivity factor, an essential parameter in the soil erosion equation. The global precipitation measurement dual-frequency precipitation radar (GPM DPR) can provide radar reflectivity at Ku- and Ka-band frequencies (Zku and Zka), rainfall rate (I, mm h−1), and drop size distribution parameters (mass-weighed mean diameter: Dm in mm and normalized intercept parameter: log10Nw, Nw in m−3 mm−1). The empirical relations between rainfallKEand GPM DPR parameters (KEtime–I, KEmm–Dm, KEtime–Zku, and KEtime–Zka relations) can allow us to estimate the KE at the locations where there are no ground-based measurements. In the present work, long-term measurements of impact type disdrometers located at three different locations (Zhongli, Feitsui, and Hsiayun) in north Taiwan are used to collect the raindrop size distribution (RSD) information of six seasons (spring, mei-yu, summer, autumn, winter, and typhoon). Measured RSDs in six seasons are used to estimate the rainfall intensity, mass-weighted mean diameter, rainfall KE flux (KEtime, J m–2 h−1), KE content (KEmm, J m−2 mm−1), radar reflectivity at Ku- and Ka-band frequencies. For the first time, present study establish and validate the rainfall KE functional relationships with GPM DPR data products (KEtime–I, KEmm–Dm, KEtime–Zku, and KEtime–Zka relations). The empirical relations between rainfall KE and GPM DPR parameters (I, Dm, Zku, and Zka) are established for six seasons of each disdrometer location. Derived KE relations did not show any spatial disparity for a given season, especially the KEmm–Dm, KEtime–Zku, and KEtime–Zka relations. On the other hand, a clear seasonal differences in the rainfall KE relations are noticed at each observational site. The established relations showed reasonable agreement in estimating the KE from the GPM DPR. However, in determining the KE, the KEmm–Dm relation showed outperformance over the remaining three relations (KEtime–I, KEtime–Zku, and KEtime–Zka relations).

Dynamic Modelling of Water and Wind Erosion in Australia over the Past Two Decades

Soil erosion caused by water and wind is a complicated natural process that has been accelerated by human activity. It results in increasing areas of land degradation, which further threaten the productive potential of landscapes. Consistent and continuous erosion monitoring will help identify the location, magnitude, and trends of soil erosion. This information can then be used to evaluate the impact of land management practices and inform programs that aim to improve soil conditions. In this study, we applied the Revised Universal Soil Loss Equation (RUSLE) and the Revised Wind Erosion Equation (RWEQ) to simulate water and wind erosion dynamics. With the emerging earth observation big data, we estimated the monthly and annual water erosion (with a resolution of 90 m) and wind erosion (at 1 km) from 2001 to 2020. We evaluated the performance of three gridded precipitation products (SILO, GPM, and TRMM) for monthly rainfall erosivity estimation using ground-based rainfall. For model validation, water erosion products were compared with existing products and wind erosion results were verified with observations. The datasets we developed are particularly useful for identifying finer-scale erosion dynamics, where more sustainable land management practices should be encouraged.

Effect of Land Use/Cover Change on Soil Wind Erosion in the Yellow River Basin since the 1990s

“Ecological conservation and high-quality development of the Yellow River Basin” is one of the fundamental national strategies related to national food security and ecological security in China. Evaluating the impact of land use/cover change (LUCC) on soil erosion is valuable to improving regional ecological environments and sustainable development. This study focused on the Yellow River Basin and used remote sensing data, the soil wind erosion modulus (SWEM) calculated with the revised wind erosion equation (RWEQ), to analyze the impact of regional scale LUCC from 1990 to 2018 on soil wind erosion. The main conclusions are as follows: (1) The total area of cultivated land, grass land, and unused land decreased, with a total reduction of 11,038.86 km²; total areas of forest land and built-up areas increased, increased by 2746.61 and 8356.77 km2, respectively, with differences within the region in these LUCC trends at different periods. From 1990 to 2000, the area of cultivated land increased by 1958.36 km2 and built-up land area increased by 1331.90 km2. The areas of forestland, grass land, water area, and unused land decreased. From 2000 to 2010, the area of cultivated land and grass land decreased by 4553.77 and 2351.39 km², respectively, whereas the areas of forestland and built-up land significantly increased. From 2010 to 2018, the area of cultivated land and grass land continued to decrease, and the area of built-up land continued to increase. (2) Since the 1990s, the SWEM has generally declined (Slope1990–2018 = −0.38 t/(ha·a)). Total amount of wind erosion in 2018 decreased by more than 50% compared with the amount in 1990. During this period, the intensity of wind erosion first increased and then decreased. In terms of the SWEM, 90.63% of the study area showed a decrease. (3) From 1990 to 2018, LUCC reduced the total amount of soil wind erosion by 15.57 million tons. From 1990 to 2000, the conversion of grass land/forest land to cultivated land and the expansion of desert resulted in a significant increase in soil wind erosion. From 2000 to 2018, the amount of soil wind erosion decreased at a rate of about 1.22 million tons/year, and the total amount of soil wind erosion decreased by 17.8921 million tons. During this period, the contribution rate of ecological programs (e.g., conversion of cultivated land to forest land and grass land, ecological engineering construction projects, etc.) to reduction of regional soil wind erosion was 59.13%, indicating that ecological programs have a positive role in reducing soil wind erosion intensity. The sustainable development of the ecological environment of the Yellow River Basin should be continued through strengthening ecological restoration and protection, to further consolidate gains made in this fragile ecosystem. This study provides scientific and technological support and relevant policy recommendations for the sustainable development of the Yellow River ecosystem under global change.

Hybrid finite volume WENO and lattice Boltzmann method for shallow flows over erodible bed

A hybrid mesh-particle method is developed to simulate hydro- and morpho-dynamics in shallow flows. The well-balanced finite volume WENO and lattice Boltzmann methods were implemented to solve nonlinear shallow water and Exner equations, respectively and a splitting strategy coupled those two solvers. This strategy was known to suffer from numerical instability due to loss of hyperbolicity, but this problem was not observed in the present method. To achieve advanced interaction between two solvers, cross-computation and information exchange were performed at every step of the high-order Runge-Kutta method. Extensive numerical experiments verified whether the present hybrid method was implemented correctly, and the proposed method provided satisfactory results of the well-balanced property, the accuracy, and the stability in verification examples.

Analysis of Ecosystem Protection and Sustainable Development Strategies—Evidence Based on the RWEQ Model on the Loess Plateau, China

Environmental sustainability and high-quality development are global issues since soil deterioration and potential desertification are caused by human activities and global climate change, especially in arid and semi-arid areas. The Loess Plateau is one of the most severely eroded regions in the world. Since the “Grain for Green Program” was established on the Loess Plateau in the late 1990s as a result of the degradation of the soil, it has been an important state policy and demonstration project for ecological protection and sustainable development in China. Therefore, understanding the spatiotemporal changes of soil wind erosion, such as yearly and monthly fluctuations in various periods, under the scenarios of global climate change and human activities, is crucial for carrying out soil conservation initiatives in the Yellow River basin. The revised wind erosion equation (RWEQ) model was applied in this study to evaluate the dynamics of soil wind erosion on the Loess Plateau, China. The soil wind erosion was evaluated on the Loess Plateau from 1981 to 2019 to provide a creative idea for managing ecosystems at the regional scale. By examining the case of the Loess Plateau, we hope to be better able to comprehend the significance of putting environmental protection projects into action to enhance the ecological environment and the well-being of locals, as well as to offer recommendations for the future creation of effective and sustainable development strategies.

Evaluation of Inner Mongolia Wind Erosion Prevention Service Based on Land Use and the RWEQ Model

Inner Mongolia is the important ecological barrier zone in northern China, which plays an important role in the prevention and control of wind in the regional ecosystem. Based on the Revised Wind Erosion Equation (RWEQ) model and the cost-recovery method, this study simulated the wind erosion prevention service (WEPS) in Inner Mongolia in 2010 and 2015, investigated the spatial pattern of material and monetary value of WEPS, and analyzed the differences among various cities and various ecosystems. The results indicated that the total WEPS of Inner Mongolia was estimated to be 73.87×108 t in 2015, which was 4.61×108 t less than in 2010, while the monetary value of WEPS was calculated to be 738.66×108 yuan in 2015, which was 46.16×108 yuan less than in 2010. Among all the leagues and cities, Xilin Gol League supported the highest WEPS, reaching 18.65×108 t in 2015, while Wuhai provided the lowest. The WEPS of Hulunbeier increased the most, by 4.37×108 t from 2010 to 2015. The WEPS in the grassland ecosystem was the highest among the different ecosystems, accounting for more than 55% of the total WEPS in Inner Mongolia, but it was reduced by 1.05×108 t during the same period. The WEPS in the forest ecosystem increased the most, reaching 0.19×108 t. This study found that the implementation of projects such as returning farmland to forests and grasses and sand control effectively increased the WEPS by increasing the forest area. However, unsuitable land use increased the desertification of ecosystems which resulted in a reduction of WEPS in Inner Mongolia.

Regional Potential Wind Erosion Simulation Using Different Models in the Agro-Pastoral Ecotone of Northern China.

Wind erosion is crucial for assessing regional ecosystem services and sustainable development. The Agro-Pastoral Ecotone of northern China (APEC) is a typical region undergoing wind erosion and soil degradation. In this study, the National Wind Erosion Survey Model of China, the Integrated Wind Erosion Modeling System, and the regional versions of the Revised Wind Erosion Equation and Wind Erosion Prediction System were used to evaluate the regional potential wind erosion of the APEC during 2000 and 2012. The results showed that the potential wind erosion predicted by National Wind Erosion Survey Model of China (NWESMC), Revised Wind Erosion Equation (RWEQ), Wind Erosion Prediction System (WEPS), and Integrated Wind Erosion Modeling System (IWEMS) were significantly related to the observed wind erosion collected from published literature, but the observed data were generally smaller than the predicted values. The average potential wind erosions were 12.58, 25.87, 52.63, and 58.72 t hm−2 a−1 for NWESMC, RWEQ, WEPS, and IWEMS, respectively, while the spatial pattern and temporal trend of annual potential wind erosion were similar for different wind erosion models. Wind speed, soil moisture, and vegetation coverage were the dominant factors affecting regional wind erosion estimation. These results highlight that it is necessary to comprehensively calibrate and validate the selected wind erosion models. A long-term standard wind erosion monitoring network is urgently required. This study can serve as a useful reference for improving wind erosion models.

Vegetation Drastically Reduces Wind Erosion: An Implementation of the RWEQ in the Mongolian Gobi Steppe

Soil loss prevention is an important ecosystem service for protecting human and environmental health. Using spatiotemporal climate and environmental data of the Eastern Gobi Steppe, a region missing from previous studies of Mongolian wind-based soil erosion, we implemented the Revised Wind Erosion Equation (RWEQ) model to estimate soil loss. A replicable pipeline was developed to perform these computations, and made available openly. Soil loss was estimated on a monthly basis to analyze seasonal variations. The results show that the annual total soil loss was 61 × 1010 kg over an area of 69.3 × 103 km2, which is about 90 tonnes per hectare. Increasing fractional vegetation coverage to a uniform 50% coverage (doubling current vegetation coverage in every 1 km2) could reduce soil loss by 60%, highlighting the importance of protecting and increasing vegetation coverage in ecosystem service preservation.

A Predictor–corrector scheme for simulation of two-phase granular flows over a moved bed with a variable topography

In this paper, we propose a numerical simulation of two-phase shallow granular flows through a moved bed with a variable irregular topography via a predictor corrector scheme. This method consists of predictor and corrector stages. The predictor stage contains a parameter to control the numerical diffusion that is performed by utilizing limiters and Riemann invariant theory. The corrector stage recovers the balance conservation equation. In the first part, we solve numerically the one-dimensional equation for two-phase shallow granular flows over a fixed bed with irregular topography. In the second part, we consider the model equations for the bed-load sediment transport, the governing model equations consist of two components, specifically, a geophysical flows part and interstitial fluid. The sediment part is described by the Exner equation when the velocity can be considered to be the solid velocity, fluid velocity or a mean value of both of them.

Decoupled solution of the sediment transport and 2D shallow water equations using the finite volume method

In this paper was successfully implemented a numerical solution of the sediment transport and 2D shallow water equations using the decoupled approach. Different discharge formulas to approximate the solid discharge of the sediment were used. The flow field was calculated by solving the shallow water equations and was discretized using the finite volume method; the Godunov's method along with the Roe's Riemann solver was used to approximate the numerical fluxes. The sediment transport was modeled with the Exner equation which was discretized using the Roe's scheme and the finite volume method. In addition, it was proposed an algorithm to guarantee the mass balance in the whole domain for water and sediment at all time steps. The results were compared with experimental measurements reported by other authors to validate the implemented solution.

Spatial and temporal evolutions of vegetation coverage in the Tarim River Basin and their responses to phenology

Vegetation plays an important role in soil erosion, and its coverage as an important parameter appears in almost all soil erosion models, such as USLE (Universal Soil Loss Equation), RWEQ (Revised Wind Erosion Equation) and WEPS (Wind Erosion Prediction System) et al. In the past several decades, scientist have paid attention to photosynthetic vegetation coverage (PVC) based on Normalized Difference Vegetation Index (NDVI). However, in soil wind-eroded region, there is almost no PVC in the nongrowing season and is a large amount of nonphotosynthetic vegetation (NPVC) in the growing season. Because the effect of NPVC on soil erosion is the same as that of PVC, vegetation coverage (FVC) in soil erosion field would include PVC and NPVC. Based on field observation, NDVI and meteorological data et al., this paper studied temporal and spatial distribution of vegetation coverage in the Tarim River Basin, and its response to surface temperature (T) and rain (R). The main conclusions are as follows. (1) PVC based on NDVI, would result in an underestimation of FVC in the growing season with about 30%, which led to an overestimation of soil wind erosion with 12%, indicating great errors in the nongrowing season. (2) FVC had obvious region distributions. FVC with 10%∼40%, 40%∼70%, and>70% were distributed in the mountain of middle elevation and the edge of oasis, the cultivated of the oasis, and the alpine grass of the Kongque River Subbasin, respectively; FVC<10% was widely distributed. With increasing of FVC, its area proportion (y) decreased as an exponential function (y = 73.19e-0.038FVC). FVC in the Kongque River, Aksu River, and Weigan-Kuqa River subbasins was better than that in the Hotan River, Keriya River, Cheerchen River, and mainstream Tarim River subbasins. Since the restoration of the ecological environment in the Tarim River Basin in 2000, FVC of 0 ∼ 10% decreased, while that of 40%∼70% increased, and the other fluctuated. (3) There was a linear relationship (FVC = a1T + a2R + b, where a1, a2, and b were the fitting coefficients) among FVC, T, and R, although the coefficients would change in different subbasins or half-months.

Submarine channels formation driven by turbidity currents interacting with an erodible bed.

In this article, we explore the submarine channel formation driven by the interaction of turbidity currents with an erodible bed. The theoretical analysis considers the three-dimensional continuity and momentum equations of the fluid phase, and the advection–diffusion and Exner equations of the solid phase. The governing equations are linearized by imposing periodic perturbations on the base flow. We study the response of both the base flow (profiles of velocity and suspended sediment concentration) and perturbations (growth rate and perturbation fields) to changes in key parameters related to the flow and sediment transport. The growth rate and the critical wavenumber are examined for a given quintet formed by the gravitational parameter, longitudinal bed slope, sediment concentration at the edge of the driving layer, Rouse number and erosion coefficient. The critical wavenumber reduces with an increase in gravitational parameter, longitudinal bed slope, sediment concentration at the edge of the driving layer and erosion coefficient, while it increases with the Rouse number. For the submarine channel formation, we identify the upper threshold values for the gravitational parameter, longitudinal bed slope, sediment concentration at the edge of the driving layer and erosion coefficient and the lower threshold value for the Rouse number.

Erosion prediction of bypass crossover sub in eccentric operating positions in horizontal wells

Erosion wear is a serious problem in the fracturing process. The erosion of the bypass crossover sub, particularly in eccentric position, during fracturing in high flow rate and high proppant concentration can make a big difference in erosion results. CFD technology with Euler–Lagrangian approach is employed to solve the continuous phase and the discrete phase. In the fluid phase, realizable k−ϵ model was used to calculate the turbulent flows, and the Lagrangian method was applied to track the particle motion in the solid phase. In order to validate the accuracy of numerical simulation, scale model testing is used to obtain velocity of flow field in bypass crossover sub. The velocity profile is measured by a laser Doppler Anemonmetry (LDA). CFD simulation results are in a good agreement with experiment data. In this study, the particle trajectories and volume fraction in central and eccentric positions were obtained by simulation. This work aimed to conduct a detailed study on the flow phenomena of bypass crossover sub and analyze the difference in the bypass crossover sub between central and eccentric positions in terms of the magnitude of erosion rates and severe erosion locations and find out which erosion model is the most applicable to predict erosion. The numerical results show that the erosion contours predicted by the three erosion models have huge differences. Oka et al. erosion model is in a good agreement with practical observations by analyzing erosion patterns of the three erosion equations at specified locations and comparing them with actual image. The simulation of different flow rates and sand volume fraction were carried out. This research can help predict the erosion of bypass crossover sub more accurately and provide references for erosion prediction, as well as experiences for designing and improving the bypass crossover sub of horizontal wells in engineering.

Transportational Cyclic Steps Created by Submarine Long-Runout Turbidity Currents

In recent years, it has become a common understanding among researchers that one of the significant agents for forming a variety of submarine geomorphologies is turbidity currents that travel long distances, so-called long-runout turbidity currents. In this study, we present a mathematical model of the formation of cyclic steps due to long-runout turbidity currents based on the assumption that the highly concentrated layer near the bottom of the turbidity currents achieves an equilibrium state. The model uses the four governing equations: the momentum equation, the continuity equation, the diffusion/dispersion equation of suspended sediment, and the continuity equation of sediment on the bed (the Exner equation). We simplify the governing equations by ignoring the entrainment from ambient water since there is a distinct density interface above the highly concentrated lower layer of long-runout turbidity currents. We determine the dimensions of cyclic steps based on the solution. Agreement between the predictions and field observations turns out to be reasonable.

Identification of driving forces for windbreak and sand fixation services in semiarid and arid areas: A case of Inner Mongolia, China

Soil wind erosion is a global problem that leads to increasingly serious regional land degradation, where the need for windbreak and sand fixation services (WSFS) is substantial. Inner Mongolia plays an important role in global semiarid and arid areas and the severe land degradation resulting from soil wind erosion warrants an urgent solution. However, the mechanism of influence of various driving factors on windbreak and sand fixation services is still not fully studied. In this paper, the revised wind erosion equation (RWEQ) model was used to synthesize the monthly spatiotemporal dynamics of soil wind erosion modulus (SWEM) and WSFS in Inner Mongolia from January 2000 to February 2020 from a semi-monthly scale. The influencing factors of WSFS were examined from both natural and anthropogenic aspects. Results show that over the past 20 years, the average SWEM in Inner Mongolia was 118.06 t ha−1 yr−1, the areas with severe wind erosion were mainly concentrated in the desert areas in the southwest of Inner Mongolia, and the forests in the northeast suffered less soil wind erosion. Meanwhile, the average WSFS was 181.11 × 108 t yr−1, with the high-value areas mainly located in major deserts, sandy land, and the area bordering Mongolia in the north and the low-value areas mainly located in the densely forested northeast and the Gobi Desert in the northwest. Both SWEM and WSFS showed a clear downward trend and a certain periodicity over the past 20 years. WSFS showed two peaks a year (April and October). Among the natural factors, precipitation and NDVI showed a significant correlation with WSFS and were identified as the main driving factors of WSFS, whereas temperature had no significant correlation. Among the anthropogenic factors, farming and animal husbandry intensity and GDP showed a positive correlation with WSFS, whereas population showed a negative correlation. These four types of factors were identified as socio-economic factors that drive WSFS. Meanwhile, WSFS did not show any significant correlation with the administrative area. Land use change contributed to a large proportion of WSFS change, thereby suggesting that the intensity of human activities is another central driver of WSFS.

Effect of the Belt and Road Initiatives on Trade and Its Related LUCC and Ecosystem Services of Central Asian Nations

Economic development and trade activities are some of the main driving forces leading to land use and land cover changes (LUCC) with impacts on ecosystem services (ESs) functions. As the origin of the Belt and Road Initiative (BRI) initiated by China, Central Asia nations (CANs) provide a prism to examine the impact of LUCC and ESs changes brought by the BRI. The impacts of LUCC and ecological influences were evaluated. The land use transfer matrix and dynamic index, the Vector Autoregressive (VAR) model, the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST), the Carnegie Ames–Stanford Approach (CASA) model, and the Revised Wind Erosion Equation (RWEQ) model were used to evaluate the impact of export trade from the CANs to China (ETCC) on LUCC and ESs in the CANs before and after the BRI. Results showed that before and after BRI (2001–2020), agricultural land and construction land increased by 59,120 km2 and 7617 km2, respectively, while ecological land decreased by 66,737 km2. The annual growth rate of agricultural land and the annual reduction rate of ecological land after the BRI were higher than that before the BRI, while the annual growth rate of construction slowed down. Among the ecological land, the forestland increased by 5828 km2 continuously, while the grassland increased by 12,719 km2 and then decreased of 13,132 km2. The trends for LUCC spatial variation were similar. The development of ETCC positively affected the changes in agricultural and construction land in the CANs and negatively affected the changes in ecological land. The average contribution rates of the ETCC to changes in agriculture, construction, and ecological lands after the BRI were higher than those before the BRI. They increased by 5.01%, 3.33% and 5.01%, respectively. The ESs after the BRI improved compared with those before the BRI, indicating that, during short-term implementation of the BRI, ETCC growth also ensures the ecological protection of CANs. This study provides a reference for dealing with trade, land management and environmental protection relations between member countries of international economic alliances worldwide.

Measuring Compound Soil Erosion by Wind and Water in the Eastern Agro–Pastoral Ecotone of Northern China

Land degradation induced by soil erosion is widespread in semiarid regions globally and is common in the agro–pastoral ecotone of northern China. Most researchers identify soil erosion by wind and water as independent processes, and there is a lack of research regarding the relative contributions of wind and water erosion and the interactions between them in what is referred to here as compound soil erosion (CSE). CSE may occur in situations where wind more effectively erodes a surface already subject to water erosion, where rainfall impacts a surface previously exposed by wind erosion, or where material already deposited by wind is subject to water erosion. In this paper, we use the Chinese Soil Loss Equation (CSLE) and the Revised Wind Erosion Equation (RWEQ) to calculate the rate of soil erosion and map the distribution of three types of soil erosion classified as (i) wind (wind-erod), (ii) water (water-erod), and (iii) CSE (CSE-erod) for the study area that spans more than 400,000 km2 of sand- and loess-covered northern China. According to minimum threshold values for mild erosion, we identify water-erod, wind-erod, and CSE-erod land as occurring across 41.41%, 13.39%, and 27.69% of the total area, while mean soil erosion rates for water-erod, wind-erod, and CSE-erod land were calculated as 6877.65 t km−2 yr−1, 1481.47 t km−2 yr−1, and 5989.49 t km−2 yr−1, respectively. Land subject to CSE-erod is predominantly distributed around the margins of those areas that experience wind erosion and water erosion independently. The CSLE and RWEQ do not facilitate a direct assessment of the interactions between wind and water erosion, so we use these equations here only to derive estimates of the relative contributions of wind erosion and water erosion to total soil erosion and the actual mechanisms controlling the interactions between wind and water erosion require further field investigation. It is concluded that CSE is an important but underappreciated process in semiarid regions and needs to be accounted for in land degradation assessments as it has substantial impacts on agricultural productivity and sustainable development in regions with sandy and/or loess-covered surfaces.