Soil erosion on terraced slopes is widespread in the Jinsha dry-hot valley region, resulting in substantial soil loss. Soil type plays a crucial role in shaping hydrodynamic properties, which in turn affect the patterns and intensity of soil erosion. To investigate the impact of soil type on runoff hydrodynamics on terraced slopes, a series of artificial rainfall experiments were conducted on selected terraced slopes with varying soil types. The results revealed that soil types primarily influenced the variation in runoff shear stress (z) during the initial 40 min of rainfall. Interestingly, the temporal evolution of runoff shear stress (z) exhibited notable similarities among different soil types during the final 80 min. Distinct logarithmic functions effectively depicted the relationship between runoff shear stress (z) and rainfall duration. The soil type of terraced slopes influenced not only the temporal variation but also the fluctuation characteristics of runoff hydrodynamic properties, including fluctuation range, rates of increase and decrease, and mean values. Specifically, the fluctuation of flow resistance (f) on terraced Dry red soil slope was 1.808-8.938 times greater than those observed on terraced Leptosol and Vertisol slopes. The critical dynamic conditions were also closely related to the soil types of terraced slopes and could be determined by both the shear stress (z) and the ratio of shear stress to resistance (Dsr). The identified critical dynamic conditions for sheet, rill, and gully erosion on terraced slopes in the Yuanmou dry-hot valley region were as follows: shear stresses (z) of 2.265-3.781 Pa, 3.546-6.316 Pa, and 5.251-6.253 Pa, respectively, and corresponding Dsr values of 0.037-0.471, 0.089-0.489, and 0.061-0.327, respectively. These findings provide valuable insights into the mechanisms of soil erosion on terraced slopes and offer a scientific basis for erosion prevention and ecological efforts in the Jinsha River Basin.

Vegetation plays a critical role in controlling gully erosion. However, few studies have clarified the effects of shrub and its components on gully bed erosion processes by altering the flow hydraulics and soil loss. In this study, a series of in situ scouring experiments were conducted to investigate the influence of shrub stem and litter on the concentrated flow pathway characteristics, hydraulic properties, and sediment yield during gully bed erosion. The experiments involved a typical shrub named Leucaena leucocephala, with five stem coverage (0 %, 0.15 %, 0.30 %, 0.60 %, and 1.20 %) and five litter amounts (0, 100, 200, 300, and 400 g m-2). Four different treatments were applied: stem and litter (SL), stem only (OS), litter only (OL), and a control bare gully bed (BG). The results showed that, compared to the bare gully bed, the various treatments significantly enhanced concentrated flow branching, increased Darcy-Weisbach friction factor (f), and reduced flow rate, velocity, shear stress, and soil loss rate. The combined effect produced by SL treatment on runoff and erosion was the strongest. Stems were most effective in reducing flow velocity and shear stress, contributing an average of 21.23 % and 7.54 %, respectively. Litter primarily increased the flow resistance f and reduced flow rate and soil loss rate, with average contributions of 123.59 %, 20.60 %, and 27.67 %, respectively. Increasing stem coverage and litter amount increased their contribution of controlling runoff and erosion. When the litter amount exceeded 200 g m-2, it gradually replaced stems as the dominant role in increasing flow resistance f and reducing concentrated flow and erosion in the both stems and litter covered gully beds. These findings enhance the understanding of how shrub and its components control gully development and highlight the importance of maintaining litter in the gully beds to mitigate gully erosion.

This study presents an innovative approach to calculating the failure probability of slopes by incorporating fuzzy limit-state functions, a method that significantly enhances the accuracy and efficiency of slope stability analysis. Unlike traditional probabilistic techniques, this approach utilizes a least squares support vector machine (LSSVM) optimized with a grey wolf optimizer (GWO) and K-fold cross-validation (CV) to approximate the limit-state function, thus reducing computational complexity. The novelty of this work lies in its application to one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) slope models, demonstrating its versatility and high precision. The proposed method consistently achieves error margins within 3% of Monte Carlo simulation (MCS) results, while substantially reducing computation time, particularly for 2D and 3D models. This makes the approach highly practical for real-world engineering applications. Furthermore, by applying fuzzy mathematics to handle uncertainties in geotechnical properties, the method offers a more realistic and comprehensive understanding of slope stability. As water is the main factor influencing the stability of slopes, this aspect is investigated by calculating the phreatic line after the change in water level. Relevant examples are used to show that the failure probability of a slope under water wading condition can increase by more than 20% (increase rates in 1D, 2D and 3D conditions being 25%, 27% and 31%, respectively) compared with the natural condition. The influence of diverse fuzzy membership functions-linear, normal, and Cauchy-on failure probability is also considered. This research not only provides a strategy for better calculation of the slope failure probability but also pioneers the integration of computational intelligence, fuzzy logic and fluid-dynamics in geotechnical engineering, presenting an innovative and efficient tool for slope stability analysis.

Changes in land use can alter the physicochemical properties of soil, thereby leading to variations in soil erosion resistance. In the past few decades, land use has changed very rapidly in the arid valley region in the Anning River Basin of Southwest China, but the impact of these changes on soil erosion resistance is still not yet clear. Thus, five typical land use types in this region, namely woodland, cropland, orchard land, abandoned land, and grassland, have been selected to explore the impact of land use types on soil erosion resistance, including factors such as the mean weight diameter (MWD), dispersion rate (DR), clay ratio (CR), soil organic carbon cementing agent index (SCAI), soil structure stability index (SSSI), K-factor, and comprehensive soil erosion resistance (CSER). The results showed that the land use type had a significant effect on soil erosion resistance, but the intensity of its influence varied across each soil erosion resistance index. Generally, woodland, abandoned land, and grassland demonstrated higher erosion resistance compared to cropland and orchard land. Additionally, surface soil exhibited stronger erosion resistance compared to subsoil, with the impact of land use types primarily concentrated in the surface soil layers. Moreover, soil organic matter content (SOM) emerged as the primary factor influencing soil erosion resistance. The research results can provide valuable guidance for regional land-use planning, aiming to reduce soil erosion and enhance the ecosystem’s service capacity, and can provide a theoretical basis for trade-offs between ecosystem services and food security.

High resolution Digital Elevation Models (DEMs) (e.g. <10 m) are critical for deriving topographic variables and thus erosion modelling. However, impacts of varying high DEM resolutions on erosion modelling results have been rarely assessed, particularly for topographically complex areas. In this study, DEMs with varying resolutions (0.1-20 m) were generated based on 3D point clouds acquired by Unmanned Aerial Vehicles Light Detection and Ranging (UAV-LiDAR) for a small catchment in the hilly and gully Loess Plateau. Water and Tillage Erosion Model and Sediment Delivery Model (WaTEM/SEDEM) was employed to simulate erosion processes at different resolutions, with results at 20 m resolution being validated based on differencing results of UAV-LiDAR-derived DEMs. Impacts of DEM resolutions on topographic factors extracted and modelling results for different geomorphic units were investigated, with results at 20 m resolution as a benchmark. Model validation demonstrated that WaTEM/SEDEM was able to fairly simulate soil erosion and deposition in the study catchment (0.51 <= NSE < 0.6, r = 0.75). Results showed that, as DEM resolutions coarsened, average slope gradient decreased, slope length, slope steepness and slope length (LS) factor and soil erosion volume increased, while sediment deposition volume firstly increased then decreased. Spatial patterns of erosion and deposition simulated at different resolutions showed a moderate consistency to those associated with benchmark resolution (0.46 < Kappa coefficient < 0.51), and the consistency increased as the resolution approached the benchmark. Impacts of DEM resolutions on the derived slope gradient, slope length, LS factor, and soil erosion volume over the study catchment were greater than those for hillslopes while less than those for gully slopes, while the impacts on deposition were also greater on gully slopes than over the catchment. The impacts on sediment yield were more complicated as a combined effects on erosion and deposition.

Vegetation plays a critical role in influencing runoff processes and soil loss during gully bed erosion. However, it is still unclear how the stem coverage affects gully bed erosion processes by altering the runoff hydraulics and soil sedimentation. A series of in situ scouring experiments were conducted to investigate the influence of shrub stem coverage on the concentrated flow pathway characteristics, hydrodynamic parameters, and sediment concentration during gully bed erosion processes. The Flow pathway characteristics expressed by the Number of flow pathways (FN), total Flow path Width (FW), Tortuosity Ratio (TR), and Fractal Dimension (FD) were quantified by analyzing photographs of the gully bed surface taken during experimental periods. Structural equation model was used to analyze the comprehensive effect of stem coverage on hydraulic erosion of gully beds. The results showed that FN, FW, and TR increased linearly, and FD increased exponentially as stem coverage increased. Compared with the bare gully bed, the flow velocity and shear stress of gully beds with shrub stem covers decreased by 17.47%-25.19% and 4.75%-11.42%, respectively, while the Darcy-Weisbach friction factor increased by 35.94%-68.71%. The sediment concentration of stem-covered gully beds decreased by 11.82%-26.93%. The increasing stem coverage promoted concentrated flow branching and significantly increased FW, which in turn altered hydraulic parameters, particularly reducing flow velocity, and ultimately reducing sediment concentrations indirectly. These results contribute to partially explaining the differences in flow hydraulics and soil loss of vegetated gully beds in previous studies that failed to account for changes in flow pathways. (c) 2025 International Research and Training Center on Erosion and Sedimentation, China Water and Power Press, and China Institute of Water Resources and Hydropower Research. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Gully erosion is the main source of sediment in watersheds, and the assessment of soil erosion and deposition in gully systems is very important for land utilization and watershed management. Soil erosion and sediment transport are multiscale, and the digital elevation model (DEM) is one of the most important means to study the scale effect of soil erosion and deposition. To clarify the effect of DEM cell size on soil erosion and deposition in gullies, a series of DEMs with cell sizes of 0.5, 0.7, 1, 1.5, 2, 2.5, 3, 4 and 5 m were generated based on detailed field measurements in dry-hot valley region. Meanwhile, the unit stream power erosion and deposition (USPED) model was chosen to simulate soil erosion and deposition in this study. The results showed that cell size can greatly influence the average slope and aspect of the DEMs, while the accuracy and average elevation of the DEMs were only affected intensively when the cell size exceeds 3 m. As for the spatial distribution pattern of soil erosion and deposition, the increase of the DEM cell size could cause a concentration of soil erosion and deposition in main channels while weakening the occurrence on hillslopes, and the spatial proximity of soil erosion and deposition would not change with the DEM cell size. The highly positive correlation in simulation results for soil erosion and deposition was primarily observed in DEM cell sizes range of 0.5 to 2 m and from 3 to 5 m. Meanwhile, a slight increase in DEM cell size would significantly affect the simulated results of soil erosion and deposition based on the USPED model when DEM cell size ranged from 0.5 to 0.7 m, whereas the change in DEM cell size would not affect the simulation results when DEM cell size was greater than 0.7 m. (1) This study was conducted based on detailed field investigation and measurement. (2) This study explored the effect of digital elevation model (DEM) cell size on basic topographic features, spatial distribution pattern of soil erosion and deposition, and relationship between simulated soil erosion and deposition based on the unit stream power erosion and deposition (USPED) model. image

Gully erosion is widely recognized as a significant form of land degradation globally, posing threats to ecological security and human societal development because of its ability to generate substantial amount of sediment. Artificial slopes are commonly disturbed landforms that are susceptible to intensive gully erosion. Morphological characteristics play a crucial role in assessing the intensity of gully erosion and can be utilized to predict sediment yield. Notably, soil type has been identified as a key factor influencing the morphological characteristics of gullies. Consequently, a comprehensive analysis was conducted based on meticulous field investigations to examine the impact of soil type on the morphological characteristics of gullies on artificial slopes in the Dry-hot Valley Region of Southwest China. The results showed that the gully cross-sectional area (Ac), curvature (Cc), and shape index (Si) exhibited a decrease along the downslope direction of the artificial slopes for all three studied soil types, following power functions. Additionally, the soil type of the artificial slope significantly influenced the mean values of the gully cross-sectional morphological characteristics. Regarding the longitudinal morphological characteristics of the gullies, the largest longitudinal concavity (Ca), longitudinal curvature (Cl), and length-gradient index (Gl) values were observed for the Vertisol, Entisol, and Ferrasol, respectively. These findings suggested that gullies developed on different soil types exhibit significant variations, particularly in terms of longitudinal morphological characteristics. Furthermore, strong correlations were detected between the gully cross-sectional and longitudinal profile morphological characteristics, and the gully cross-sectional shape index (Si) was correlated with all the longitudinal profile morphological characteristics. This study offers valuable insights into the morphological characteristics of gullies on artificial slopes with different soil types. Such knowledge is of paramount importance for effectively preventing and controlling gully erosion in contemporary society. The morphological characteristics of gullies developed on artificial slopes with different soil types were investigated in Dry-hot Valley Region of Southwest China. The mean value of gully cross-sectional and longitudinal profile morphological characteristics significantly varied with the soil types of artificial slope. There is a strong correlation between the gully cross-sectional and longitudinal profile characteristics, and the gully cross-sectional shape index (Si) emerged as the most influential factor affecting all the longitudinal profile morphological characteristics. image

Runoff and sediment transport rates are important indicators for guiding regional economic development and ecological protection.It is important to clarify the dynamic evolution processes and inner connection of runoff and sediment transport rate for the rational development of soil and water resources in Longchuan River.In this study, the Mann-Kendall test, wavelet analysis and synchronization analysis have been used to analysis the change trend, mutation situation and variation cycles of runoff and sediment transport rate.The results showed that: runoff volume was generally stable, and sediment transport rate experienced a significant increasing trend at a rate of 4.29 kg/s/a in 1970-2008 in Longchuan River.The change cycles of runoff volume and sediment transport rate were different.The first principal cycles of seasonal and annual runoff volume were all 25a, while the second and third principal cycles were different.In contrast, the first and second principal cycles of sediment transport rate were respectively 29a and 6a.There was a significant linear relationship between sediment transport rate and runoff although the relationship between water and sediment was only synchronous in 1991-2008.

Geological conditions are important in the initiation and expansion of a gully. In order to explore the relationship between spatial distribution of gullies and the geological conditions, the methods of geospatial statistics and correlation analysis were used based on interpretations of high-resolution Google Earth images in the Dry-hot Valley (SW China). The results showed that the gullies had a clustering pattern in the study area (Moran's I = 0.89, P < 0.01). The correlation between geological conditions (lithology and faults) and clustering characteristics of gullies was strong in lithology (F-(6) = 139.75, p < 0.01, eta(2) = 0.184) and irrelevant in faults (F-(2) = 0.64, p > 0.05, eta(2) = 0.001). The resistance to erosion of a particular lithology had a negative correlation with the degree of gully clustering. The lithologies of sandstones, mudstones and siltstones, loose quaternary sediments, of phyllite and schist were conducive to gully development; however, the conglomerate, quartzite and marble, and granite may led to low gully clustering. The results will help to understand the law of spatial distribution of gullies at the regional scale and also provide a scientific reference for their controls.

Gully erosion is a common form of soil erosion in dry-hot valleys, and it often brings serious land degradation. A multi-criteria method integrating the characteristics of the longitudinal profile (LP), the cross profile (CP) and the knickpoints of gullies was applied to identify the development stage of gullies in Yuanmou County, Yunnan Province, in southwestern China. Firstly, based on the high-resolution data sources produced by an unmanned aerial vehicle (UAV), 50 gullies were selected as the typical ones in Tutujiliangzi and Shadi village. The LPs were extracted, and their morphological indices, information entropy and fitting functions were calculated. The morphological characteristics of the CPs and the presence or absence of knickpoints were recorded. The results show that the period of the gullies in Tutujiliangzi and Shadi is dominated by the deep incision period and the equilibrium adjustment period, which means that most gullies are in the period of the severe erosion stage. Among the gullies, 13 LPs’ morphological index is between 0.636 and 0.933, and the morphology of the LP presents an upward convex shape; the cross profiles are mainly V-shaped and U-shaped. Thirty-two LPs’ morphological index is between 1.005~2.384, which presents a slightly concave shape; the cross profiles are mainly repeated U-shapes. The remaining five LPs have a morphological index of 0.592, 0.462, 1.061, 1.344 and 0.888, respectively; the LPs of upstream and downstream are different. The LPs of the Tutujiliangzi gullies are nearly straight lines and slightly concave, while those of the Shadi village gullies are convex and nearly straight lines. The knickpoints and step-pools in Shadi village are more developed, while the gullies in Tutujiliangzi develop more rapidly. This study shows that in counties with similar conditions, these conditions such as temperature and precipitation, local topographic changes, soil properties and vegetation conditions have obvious effects on the development of gullies.

Gully erosion is one of the major contributors to severe land degradation in the Yuanmou Dry-hot Valley Region, Southwest China. Grass has been proved to have great advantages in gully erosion control. This study aimed to detect the influence of grass basal diameter on change processes of runoff velocity, sediment transport rate, and runoff energy consumption. A series of scouring tests were conducted based on a field experimental platform under the same flow discharge, and the impacts of different grass basal diameter (d) (0, 17, 43, 70, and 98 mm) on variations of runoff velocity (v), sediment transport capacity (St), and runoff energy consumption (Ec) were explored in this study. The results showed that values of runoff velocity and sediment transport capacity decreased notably with the increase of grass basal diameter, and two declining power functions can be found (v = 0.689*d^(− 0.106), p < 0.01; St = 0.741–2.228E-11*d^4.701, p < 0.01). As for the spatiotemporal variation, the influence of grass basal diameter on runoff velocity had obvious stage features, and the influence on sediment transport capacity mainly concentrated on spatial variation in the downstream of gully bed (16th–20th m away from gully head). Furthermore, the increasing of grass basal diameter could effectively enhance runoff energy consumption, and a logistic growth function had been found. Finally, the grass basal diameter of 70 mm proved to be the critical grass basal diameter for effectively reducing runoff erosion force and increasing runoff energy consumption in gully beds in this study. These results indicate that the grass growth can effectively reduce runoff erosion force and increase runoff energy consumption, and in general, this function will be enhanced with the improvement of grass basal diameter in gully beds.

The construction of cascade reservoirs on the Lancang River (the upper Mekong) has an important influence on the distribution and accumulation of heavy metals. Heavy metal contents in porewater provide vital information about their bioavailability, studies on this aspect are rare until now. In this study, sediment cores were collected from four adjacent cascade reservoirs in the upper Mekong River to study the distribution, potential sources, diffusive fluxes and toxicity of heavy metals in porewater. The findings indicated that the average contents of Mn, Fe, As, Ni, Cu, Zn, Cd, and Pb in the sediment porewater were 6442, 644, 11.50, 2.62, 1.23, 3.95, 0.031, and 0.24 µg/L, respectively; these contents varied as the sediment depth increased. Correlation analysis and principal component analysis showed that Cu, Zn, Cd and Pb were mainly associated with anthropogenic sources, As, Mn and Fe were primarily affected by natural inputs, and Ni was affected by a combination of natural and anthropogenic effects. The diffusive fluxes of Mn, Fe, As, Ni, Cu, Zn, Cd, and Pb in the cascade reservoirs of the Lancang River were 919 – 35,022, 2.12 – 2881, 0.17 – 750, 0.71 – 7.70, 2.30 – 31.18, (-3.35) – 6.40, 0.06 – 0.54, and (-0.52) – 4.08 µg/(m2 day), respectively. The results of toxic units suggested that the contamination and toxicity of heavy metals in porewater were not serious. Overall, in the cascade reservoirs, the content and toxicity of heavy metals in porewater of the upstream reservoirs were higher than that of the downstream reservoirs. The operation of the cascade reservoirs enabled greater accumulation of contaminants in sediments of the upstream reservoirs. This research gives strong support for the prevention of heavy metal contamination and the sustainability of water resources under the running condition of cascade reservoirs on such a large international river (the Lancang-Mekong River).

Geological conditions are important in the initiation and expansion of gullies. This study explored the spatial distribution of gullies and the influence of geological conditions in the Yuanmou dry–hot valley based on interpretations of high-resolution Google Earth images using geospatial statistics and correlation methods. The gullies showed a clustering pattern in the Yuanmou dry–hot valley (Moran’s I = 0.93, P < 0.01). The geological conditions (lithology and faults) were correlated with the clustering characteristics of gullies (Tau-y 0.13 and 0.003, respectively), but the degree of correlation between faults and the clustering characteristics of gullies was weak. The resistance to erosion of a particular lithology had a negative correlation with the development of gullies; lithologies with higher resistance to erosion led to a lower clustering of gullies, although this non-negative correlation may be related to other factors. Regions with strong faulting may favor the development of gullies. These results help our understanding of gully formation at the region scale and also provide a scientific reference for the regional control of gullies.

The variations in extreme precipitation and their relation to large-scale climate circulation were investigated over a typical transitional climate zone named the Qinling-Dabashan Mountains from 1961 to 2018.In this study, the spatial and temporal variations in eleven extreme precipitation indices are determined using the Sen's method, Mann test and heuristic segmentation method.The relations between extreme precipitation and the Asia summer monsoon are analyzed by cross wavelet transform methods.The major findings of this research are as follows: (1) the spatial distribution of extreme precipitation changes over time in the Qinling-Dabashan Mountains: higher precipitation intensity occur in the middle and southeastern regions, while other regions exhibit adverse variation patterns.(2) Temporally, the regional trends of only the annual total wet day precipitation are dominant in the Qinling-Dabashan Mountains and its subregions.However, the regional trends of extreme precipitation are not statistically significant.In addition, the extreme precipitation in the Qinling-Dabashan Mountains and its subregions was sensitive to environmental changes from 1961 to 2018, including intensive human activity, the Asian summer monsoon and steep terrain.Sensitivity to environmental change implies flash floods and other natural disasters from 1961 to 2018.(3) The East Asian Summer Monsoon has a stronger influence than the South Asian Summer Monsoon on extreme precipitation.The results of this research will aid decision-makers in their response to recent climate change scenarios in the Qinling-Dabashan Mountains.

Gully erosion is well-developed in the Jinsha dry-hot valley region, which has caused serious soil losses. Gully volume is regarded as an effective indicator that can reflect the development intensity of gully erosion, and the evolutionary processes of gullies can be predicted based on the dynamic variation in gully volume. Establishing an effective prediction model of gully volume is essential to determine gully volume accurately and conveniently. Therefore, in this work, an empirical prediction model of gully volume was constructed and verified based on detailed morphological features acquired by elaborate field investigations and measurements in 134 gullies. The results showed the mean value of gully length, width, depth, cross-section area, volume, and vertical gradient decreased with the weakness of the activity degree of the gully, although the decrease in processes of these parameters had some differences. Moreover, a series of empirical prediction models of gully volume was constructed, and gully length was demonstrated to be a better predictor than other morphological features. Lastly, the effectiveness test showed the model of V = aL<^>b was the most effective in predicting gully volume among the different models established in this study. Our results provide a useful approach to predict gully volume in dry-hot valley regions.

Gully erosion is a major cause of regional environmental deterioration. In order to examine the relationships among morphological parameters of gullies under diverse conditions, 112 gullies were measured with GPS-RTK and Total Station in Yuanmou Dry-Hot Valley; then, a digital evaluation model (DEM) was created by ArcGIS, and five parameters (L-S - straight length of gully, L-T - length of gully thalweg, W - width, A - erosional area, V - gully volume) were extracted and calculated. The results showed a positive skewing of leptokurtic distribution for all morphological parameters, most of which were concentrated in the low-value zones and were small in size. Comparisons between multiple fitting functions revealed that the power function is the best fitting model, with all le values greater than 0.7; the R-2 value corresponding to the fitting function of V-L-s and V-L-t is the same as 0,76; the coefficient b of V-W is the largest among the 4 fitting functions; the maximum R-2 (0.94) is found between V-A. Compared to the V-shaped gully, the U-shaped gully has a better fitting effect because of the larger R-2 value; the coefficient a of the V-shaped gully is generally larger than that of the U-shaped gully. The fitting effect of a stable gully which has a larger le value is better than that of an active gully, and the coefficients a, b fitted by each morphological parameter are considerably close. The le value in dry red soil is larger than that in vertisol, which shows a better fitting effect, and the le values of V-L-s and V-L-t are equal, respectively, which shows that the fitting effect of V-L-s and V- L-t is consistent when estimating the volume of gullies under the two soil types. The results will help to promote the estimation accuracy of gully volume based on the interpretation of remote sensing images.

As a common type of microtopography in rill channels, the formation and dynamics of step-pools are prerequisites for the occurrence of rills. However, the evolution of step-pools in a rill (SPRs) is still unclear. Scouring experiments in field plots were conducted to explore the dynamic evolution of SPRs and the effect of steps on pools under conditions of strong runoff and soil-like materials aggregated with gravels in Yuanmou Dry-Hot Valley (SW China). Using three-dimensional laser scanning, spatial analysis of a GIS (geographic information system), and statistical analysis, 11 parameters were used to characterize step-pool morphology. The results showed that SPRs formed after several scourings at particular locations, and some of them disappeared in the late stage. A diverse range of SPRs formed, with geometrical parameters initially increasing, then stabilizing, and finally decreasing. During scouring, pool shape transformed from a deep V-shape to a shallow V-shape and then to a U-shape. The evolution of a typical pool included initial, active, stable and fading stages. There were 59 oval-shaped pools (88.06% of the total number of pools) in plane form and 37 deep pools (55.22%) in cross-section, and significant differences in the plane form and profile morphology of a pool presented themselves during its evolution. SPRs developed more easily in dry red soil-like materials compared with vertisol-like materials. The geometrical parameters of pools correlated with step size; and pools became deeper with increasing step height, and longer with increasing step height and decreasing step slope. The spatial heterogeneity of soil-like materials, as well as hydraulic conditions, led to complex and nonlinear SPR evolution. It is helpful to further understand the mechanism of rill incision and evolution.

Gully erosion is the main cause of global land degradation. The factors controlling gully erosion at watershed scale have been extensively studied, but the spatial pattern of gullies and their primary environmental factors are unclear. In order to explore the primary factors at the regional scale of over thousands of square kilometers, 34 sample areas were selected in northeastern China and 10 environmental factors were proposed. Based on gully interpretations from high-resolution Google Earth images and spatial analysis, kernel density estimation (with polyline features), and correlation analysis, the results show that the maximum kernel density (KD) of the 34 sample areas ranged from 0.11 to 87.16, and there were significant positive correlations between the average KD and the maximum value and standard deviation. At the regional scale, topography (relief amplitude, slope, surface roughness, surface incision, and elevation with correlation coefficients (ρ) of 0.60, 0.59, 0.57, 0.48, and 0.41 respectively) was the primary environmental factor, with a significant positive correlation with KD. The correlation coefficients of the normalized difference vegetation index (NDVI) (ρ = 0.32), annual precipitation (ρ = 0.19), and soil (silt, sand, and clay content with ρ of 0.139, −0.117, and 0.085, respectively) decreased successively with the KD. At sample area scale, there were six areas with weak correlations between environmental factors and KD, 20 areas with topographic factors, six areas with annual precipitation, and two areas with NDVI as the primary factor. The correlation between soil texture and KD was low. There were different positive or negative correlations between the environmental factors and KD. The spatial distribution of gullies in northeastern China is heterogeneous, and the primary environmental factors were diverse. This study will help to understand the spatial pattern and formation mechanism of gullies at large scale.