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• This paper provides a new idea for the genesis and evolution of loess tunnels in the Loess Plateau. • There are significant differences in the loess tunnel development density in the different topographic and micro-topographic units. • Spatial statistical modelling was employed to justify and predict the observed spatial distribution tendency of the loess tunnels. • The loess tunnel evolution process can be divided into five stages: the incubation stage, formation stage, development stage, failure stage, and withered stage. Loess tunnels are very common in the Loess Plateau, and they pose unique geological threats. Loess tunnels are often difficult to detect and control due to their concealment and sudden appearance. Thus far, research on the genesis and evolution of loess tunnels remains scarce. In this paper, the genesis and evolution mechanism of the loess tunnels in the Loess Plateau is studied in depth, and the location, shape, and size information are obtained via field investigations. The potential correlations between the loess sediment, the basic physical properties (depth, water content, particle size composition, collapsibility coefficient, and self-weight collapsibility coefficient), and the tunnel density are inferred based on the Pearson's correlation coefficients and tests on the physical and mechanical properties of the loess sediments. In addition, spatial statistical modelling is employed to justify and predict the observed spatial distribution of the loess tunnels assuming Gaussian Markov random fields. The formation of loess tunnels is due to a combination of factors, including the formation thickness, soil properties, joints and fissures, topography, hydrogeology, and climatic conditions. The thickness of the loess, loess sediment properties, and their spatial relationship jointly determine the material basis of the formation of the loess tunnels. The loess tunnels at different depths have different main controlling factors that are hierarchical by depth. The evolution process of loess tunnels can be divided into five stages: the incubation stage, formation stage, development stage, failure stage, and withered stage. The characteristics of each stage are discussed in detail. Our work provides novel insights into subsurface erosion from the aspect of soil tunnels. It improves our understanding of hill slope geomorphological evolution and also provides effective techniques for tunnel erosion control. [ABSTRACT FROM AUTHOR]

• Hillslope erosion dynamic model integrating vegetation effect was established. • Unified baseline parameters were obtained across different land uses. • Effect of vegetation on soil detachment and sediment transport was revealed. • Contribution rates of vegetation to sediment reduction along slopes were quantified. Developing a process-based soil erosion model that comprehensively considers the effects of vegetation is complex but crucial for evaluating sediment reduction during vegetation restoration. Current understanding of the effect of vegetation on sediment reduction along hillslopes across different land uses is limited. In this paper, we developed a dynamic model of hillslope erosion that integrates the effects of vegetation on soil detachability and hydrodynamics (VED) based on the feedback mechanism between soil detachment and sediment transport. The VED was calibrated and validated with runoff plot data for woodland, grassland, and farmland in the Wuding, Yan, Jing and Wei Rivers of the Loess Plateau in China. Unified baseline parameters and decay coefficients of vegetation were obtained. The model validation results indicated that the coefficient of determination, Nash–Sutcliffe simulation efficiency and relative error ranged from 0.59 to 0.99, 0.56 to 0.90, and −45.99 % to 46.36 %, respectively. The decay coefficients for soil detachment capacity (Φ), sediment transport capacity (T c), and the sediment reduction effect of vegetation exhibited the following order: woodland > grassland > farmland. Compared with VED, existing process-based soil erosion models failed to effectively characterize the influence of vegetation on Φ and T c on the Loess Plateau, with differences of several orders of magnitude. The individual contributions of runoff, soil detachability, and hydrodynamics with vegetation impact on sediment yield were quantified by VED. The contribution rates of vegetation to sediment reduction decreased gradually with increasing slope length because the soil detachment capacity of bare slopes exceeded that of vegetated slopes, resulting in a faster increase in sediment yield. The contribution rates of vegetation to sediment reduction for woodland, grassland, and farmland with 20 %–60 % vegetation covers were 66.75 %–99.95 %, 57.43 %–99.63 %, and 27.91 %–88.63 % in the boundary conditions of this study, respectively. The results reveal the potential for integrating VED into other distributed watershed hydrological and sediment models to assess the effects of vegetation restoration on sediment reduction at a watershed scale. [ABSTRACT FROM AUTHOR]

• A novel macroscale terrain factor proposed, enlarges terrain break of gully erosion. • Computer sight simulates the factor, different from slope, openness, and hillshade. • Uncertainty caused by resolution, direction number, look distance and skip radius. • Human vision finds the critical value for gully shoulder line on the loess plateau. • P-N terrain is linked with repose angle under the complexity of loess landform. As a type of terrain break, the gully shoulder line is of great significance to locate the scope of surface failure and soil erosion. Based on the knowledge of the terrain structure of loess gullies, this paper modeled sight lines to calculate the three-dimensional maximum elevation angle (3D MEA). Then, a critical MEA value of 35° was determined via human vision to extract negative terrain and shoulder lines considering unmanned aerial vehicle (UAV)- and light detection and ranging (lidar)-based digital elevation models (DEMs). In addition to the DEM resolution, the uncertainties caused by the direction number, look distance and skip radius of computer sight were further examined. It was suggested that the process should involve observing at least 12 directions to detect complete information on terrain breaks. The simulation process required a relatively large look distance to analyze global terrain changes because a small distance could limit sight within the local window. The skip radius could result in the process ignoring nearby abrupt changes in terrain, thus causing negative terrain to be misclassified as positive terrain near shoulder lines. The concept of wall morphology was introduced to attribute the critical value to the repose angle of loess gullies. Eventually, the MEA was compared with many other parameters. It could be concluded that the slope is limited to the local scale, while the MEA could combine local and global scales using a large look distance. The hillshade is limited to one viewing direction, but the 3D MEA is a comprehensive layered index from multiple directions. This study is a novel exploration of interdisciplinary hydraulic engineering and information technology. This approach reduces terrain breaks from three-dimensional space into a one-dimensional index and simplifies shoulder lines as a critical 3D MEA value related to loess material properties. This research could be adopted for soil and water conservation. [ABSTRACT FROM AUTHOR]

• The elasticity index is adopted to tradeoff the benefits and ecological effects of land consolidation. • Soil erosion of slopes with vegetation is tolerable under climate change. • Slopes below 63° are stable in 6 slope scenarios. • The slope of 53° with Caragana microphylla is the optimal combination scheme. Soil erosion and slope instability restrict the cutting slopes, especially the high and steep slopes of a construction site. It is difficult for present research of observation experiments and investigation to deal with these problems under climate change. Focusing on gully land consolidation in the loess plateau of China, this paper put forward a technical procedure to explore the optimal combination scheme of slope-cutting and vegetation-planting in future climate change. The technical procedure includes scenarios design, model calculation, and scheme optimization. This paper selected a back catchment in Yangjuangou catchment of Yan'an City as a case study and designed 54 combined scenarios consisting of 6 slopes, 3 types of vegetation (including bare land), and 3 climate scenarios. The soil erosion and slope stability under different scenarios were quantified using FLAC/Slope software and Water Erosion Prediction Project (WEPP) model. This paper innovatively designed elasticity indicators to trade off the increase of the flat land area formed by land consolidation and the resulting reduction in slope stability and increase in soil erosion. It is found that the slope of 53° with Caragana microphylla could be the optimal combination scheme considering flat land creating and the safety of slopes. The technical procedure and the resulting parameters could support gully land consolidation in related areas and be referenced by other construction projects. [ABSTRACT FROM AUTHOR]

• A bibliometric analysis of Chinese Loess Plateau (CLP) studies was explored. • CLP research outputs increased exponentially during 1991–2018. • Keyword analysis indicated climate-related topics were the most popular study areas. • Research interests shifted from agriculture to ecology. • Government policies influence the choice of research hotspots. To understand the research trends and areas of focus on the Chinese Loess Plateau (CLP), a bibliometric study based on the Science Citation Index-Expanded (SCI-E) was performed. This study presented a comprehensive overview of the field based on the annual outputs, research areas, temporal trends in keywords, marked journals, institutions, and authors. In the SCI-E database, only 17 outputs occurred before 1991. Thus, we chose the study period between 1991 and 2018. The results revealed that the annual number of publications increased, with an especially rapid increase after 2006. Geology, environmental sciences and ecology, agriculture, water resources, and physical geography were the most popular Web of Science research areas. A keyword analysis indicated that "climate" was the most popular study area. After 2006, the research areas changed to "impact", "dynamics", and "land use change" topics in mechanisms and regulation. Since 2011, coupled effects among the environmental factors have been incorporated in research on the CLP. The areas of focus range from classical geology to agriculture research, ecological construction research, and research on the efficient use of resources. Catena and Palaeogeography Palaeoclimatology Palaeoecology were the most popular journals for researchers to publish their research results, and these two journals also had greater influence in the field with larger numbers of citations than other journals. The institution with the greatest research output and most citations was the Chinese Academy of Sciences. An Z. S., Fu B. J., Liu T. S., Ding Z. L., Shao M. A., and Lu H. Y. were the most competitive authors based on their large numbers of papers and citations. This paper presents an attempt to better understand the progress in research on the CLP. [ABSTRACT FROM AUTHOR]

• A novel approach reveal of the failure mechanism of slopes in tunnel environment. • The failure process is divided into five stages based on failure characteristics. • Tunnel is an important inducement of loess slope failure in tunnel environment. As a unique geological hazard, the occurrence of loess tunnels is closely related to slope failures. However, almost no research on the relationship between loess slope failures and tunnel erosions has been presented, which seriously restricts the deep understanding of the genesis mechanism and evolution process of loess slope failures. This paper focuses on revealing the failure mechanism of loess slopes in tunnel environments via methods including field investigation, exploration, field water injection tests, tracking tests and numerical simulations. The results show that the whole process of permeability coefficient of the soil layer in the test site is divided into three stages: the rapidly decreasing stage, the slowly decreasing stage and then the stable stage; the slope failure process is divided into five stages based on different failure characteristics: the soaking and softening stage, the erosion connecting stage, the slope local failure stage, the slump failure stage and the resting stage. Seepage has a great influence on loess slope failures in the tunnel environment, and it is as an important inducement of failure, while tunnels themselves play an aggravating catalytic role. The soil water interaction is shown to be an important internal cause of slope failure both by field tests and numerical simulations. The existence of tunnels is not conducive to the overall stability of the slope as tunnels expand the influence range of the soil-water interactions. This study re-evaluates the failure mechanism of loess slopes from a novel perspective based on the tunnel erosion environment. [ABSTRACT FROM AUTHOR]

Abstract: The Stochastic generation of storm patterns is often necessary for driving process-based hydrological and ecological models. CLIGEN is the only weather generator being able to generate internal storm patterns. Its goodness needs to be evaluated for its proper application. This paper aims to find the advantages and limitations of CLIGEN on semiarid areas and provide references for custom-built weather generators for the Loess Plateau. The daily rainfall time series (1957–2002) and breakpoint rainfall data (more than 20 years) on six stations on the Loess Plateau were used to estimate input parameters for CLIGEN and to compare with CLIGEN-generated 50 years of storm data. Precipitation occurrence (wet day and dry day sequence) is well-simulated without significant difference across months and sites. Errors of monthly average number of wet days range from −0.67 to 1.08 days, standard deviations range from −1.19 to 0.76 days, and the distributions of continuous number of wet and dry days on the semiarid Loess Plateau are adequately simulated. Daily rainfall amount is not simulated as well as precipitation occurrence. The relative errors of average daily rainfall range from −12.93% to 8.64% and those of standard deviations range from −21.35% to 27.46%. During the rain seasons (May–September), among 30 month–location combinations, all the Mann–Whitney tests for the means passed, 47% for squared ranks tests rejected the null hypothesis of equality of standard deviations, and 73% for K–S test suggested that the generated and measured distributions of daily rainfall were different at 0.01 level of significance Three variables to describe internal storm patterns in CLIGEN are storm duration, relative peak intensity, and time to peak. Storm duration was not well-reproduced because none of squared ranks tests and K–S test passed at the significance level of 0.01. The frequency of short duration storms (<300 min) was over-predicted while frequency of long duration storms (400–1200 min) was significantly under-predicted. The distribution of maximum 5 min rainfall intensity (ip5) was well-simulated for four sites out of the six because all tests passed. However, generated maximum ip5 for all six sites are around 190 mm/h, which are much larger than the measured (70 to 150 mm/h). Ip30 is simulated better than ip5, suggesting that CLIGEN can reliably generate rainfall erosivity. Time to peak was well-simulated because all the tests passed with P values significantly greater than the significance level of P =0.01. Improvement for CLIGEN has to be made in terms of the daily rainfall simulation in rainfall-concentrated seasons and storm pattern generation in order to generate reliable rainfall time series on the Loess plateau. [Copyright &y& Elsevier]

Integration of farmers'' knowledge and perception with researchers'' knowledge is important for planning resource-conserving technologies. In many places in the world, farmer participation has been shown to be essential in the planning of sustainable land management. The findings of a participatory approach (PA) for integrated conservation planning in the Danangou catchment—a small catchment situated in the heart of Loess Plateau—are presented in this paper. The work was carried out by an interdisciplinary team during the period 1997–2000. The PA is an interactive learning process between local farmers and researchers. The process was facilitated by several visualisation and diagramming methods. This formed part of an integrated conservation planning approach, where three tools including PA, land evaluation and soil erosion modelling were combined within the entire conservation planning process.The Danangou catchment is characterised by its distribution of cropping systems on all degrees of slope to meet the food needs of the villagers. Farmers'' criteria on land suitability, including slope aspect and soil workability, were evaluated. Farmers approved several biological and physical conservative measures, which provided one of the important bases for formulating different land use scenarios (LU scenarios). The factors influencing farmers in choosing different LU scenarios were analysed, including (1) current household economy in relation to production from the land; and (2) prediction of changes in the household economy due to different LU scenarios.The farmers'' vision on implementation of the LU scenarios, i.e. gradually converting cropping land, conforms well with the plans of the local government. However, due to the poor living standard and lack of off-farm employment, any effort to improve land use towards more sustainable practices seemed to be difficult to implement without support from the government in terms of food, seedlings and also sources of employment for the villagers. The strategy for conversion work in connection with the central government policy on re-greening the Loess Plateau must focus first on areas where off-farm activities are available or potentially available. A diversity of conservation alternatives was found to meet the needs of different farmers'' groups. It is recommended that alternatives be developed by an active collaboration between farmers, extensionists and researchers. [Copyright &y& Elsevier]

The participatory approach is recognised world-wide as a desirable approach for the success of research and development projects in the field of land management and conservation. A participatory approach (PA) for soil and water conservation is presented in this paper. The approach was one important part of Integrated Participatory Conservation Planning (IPCP) and aimed at involving farmers as our research partners in the whole conservation planning process in order to define relevant alternatives for sustainable land use. The work was carried out in the small catchment of Danangou, situated in the heart of the Loess plateau of China, by a multidisciplinary and multinational team, during the period 1998–2000 as part of the EROChina project.Several participatory methods, including group and team dynamics methods, sampling methods, interviewing and dialogue methods and visualisation and diagramming methods, were used for different purposes through a three-step process of the PA. The PA process can be described as researchers learning about local conditions (Step 1), followed by analyses of land use carried out by local farmers (Step 2), and finishing with farmer–researcher two-way feedback on the different land use scenarios (LUS) and their potential effects on erosion and household economy (Step 3). A Participatory Household Economy Analysis (PHEA) was developed and shown to be a suitable method for analysing the current and the potential changes in the household economy due to different land use scenarios (Step 3). The three steps of PA integrated closely with the modelling and land evaluation tools of the IPCP.The PA developed involved interactive learning between professionals and farmers, seek multiple perspectives and make use of systematic and structured learning processes and give a highly effective participation. The approach is promising in improving farmers'' awareness of environmental problems and solutions, as well as in linking local and scientific knowledge. The conditions for the successful use of the participatory methods in local conditions as well as of the teamwork are also discussed. [Copyright &y& Elsevier]