Effects of DEM resolution and source on soil erosion modelling: a case study using the WEPP model

Digital elevation models (DEMs) vary in resolution and accuracy by the production method. DEMs with different resolutions and accuracies can generate varied topographic and hydrological features, which can in turn affect predictions by soil erosion models, such as the WEPP (Water Erosion Prediction Project) model. This study investigates the effects of DEMs on deriving topographic and hydrological attributes, and on predicting watershed erosion using WEPP v2006.5. Six DEMs at three resolutions from three sources were prepared for two small forested watersheds located in northern Idaho, USA. These DEMs were used to calculate topographic and hydrological parameters that served as inputs to WEPP. The model results of sediment yields and runoffs were compared with field observations. For both watersheds, DEMs with different resolutions and sources generated varied watershed shapes and structures, which in turn led to different extracted hill slope and channel lengths and gradients, and produced substantially different erosion predictions by WEPP.     

Broad area mapping of monthly soil erosion risk using fuzzy decision tree approach: integration of multi-source data within GIS

Soil erosion poses a serious problem for sustainable agriculture and the environment. There is a need to develop a simple and practical approach for broad area mapping of soil erosion risk that uses the uncertain but available information as input data within the constraints of reasonable cost and time. In this work, a predictive approach for conducting analytical erosion risk assessment across broad areas is developed, which combines a fuzzy decision tree (FDT), remote sensing and Geographic Information System (GIS). This approach is applicable to situations with a limited amount of input data and can easily adjust assessment factors according to actual need. In this study, four dominating factors affecting soil erosion were considered: soil, topography, land cover and climate. GIS thematic layers of these factors were constructed followed by fuzzified analysis through trapezoidal shaped membership functions. Based on subdivided erosion response units (ERUs), an optimal FDT was determined to classify monthly soil erosion risk into five levels. High-risk and very high-risk soil erosion in the study area is mainly concentrated from June to August, with July and August showing the highest risk covering more than 80% of the study area. November to March is dominated by low risk over more than 90% of the study area, while medium risk is dominant in April, May, September and October. Compared with field survey data, the fuzzy decision erosion risk assessment approach was shown to be applicable and economical for rapidly identifying and locating soil erosion risk with limited input data by means of remote sensing and GIS.     

Impacts of DEM resolution,source, and resampling technique on SWAT-simulated streamflow

The sensitivity of streamflow simulated with the Soil and Water Assessment Tool (SWAT) model to Digital Elevation Model (DEM) resolution, DEM source and DEM resampling technique is still poorly understood. The objective of this study is to compare SWAT model streamflow estimates in the Johor River Basin (JRB), Malaysia for DEMs differing in resolution (from 20 to 1500 m), sources (Shuttle Radar Topography Mission: SRTM v4.1, Advanced Space-borne Thermal Emission and Reflection Radiometer: ASTER GDEM2, EarthEnv-DEM90 and Global Multi-resolution Terrain Elevation Data 2010: GMTED2010) and resampling technique (nearest neighbour, bilinear interpolation, cubic convolution and majority). The key findings were as follows: (1) SRTM v4.1 (Root Mean Square Error (RMSE) = 11.16 m) and EarthEnv-DEM90 (RMSE = 12.4 m) had better vertical accuracy over the JRB compared to the ASTER GDEM2 (RMSE = 16.95 m); (2) Accurate annual streamflow simulations were obtained by using nearly all of the DEM resolutions, as pointed out by a relative error (RE) lower than 7% from 20 to 50 m and from 100 to 800 m DEMs; (3) Prediction errors were the lowest for ASTER GDEM2 (RE = 3.9%), followed by SRTM v4.1 (RE = 5.4%), EarthEnv-DEM90 (RE = 6.3%), and GMTED2010 (RE = 7.3%); (4) the majority and nearest neighbour resampling techniques performed the best (RE of 6.0%), followed by bilinear interpolation (RE of 7.2%) and cubic convolution (7.5%). The study indicates that DEM resolution is the most sensitive SWAT model DEM parameter compared to DEM source and DEM resampling technique for streamflow simulation within SWAT.     

Propagation of vertical and horizontal source data errors into a TIN with linear interpolation

Digital elevation models (DEMs) have been widely used for a range of applications and form the basis of many GIS-related tasks. An essential aspect of a DEM is its accuracy, which depends on a variety of factors, such as source data quality, interpolation methods, data sampling density and the surface topographical characteristics. In recent years, point measurements acquired directly from land surveying such as differential global positioning system and light detection and ranging have become increasingly popular. These topographical data points can be used as the source data for the creation of DEMs at a local or regional scale. The errors in point measurements can be estimated in some cases. The focus of this article is on how the errors in the source data propagate into DEMs. The interpolation method considered is a triangulated irregular network (TIN) with linear interpolation. Both horizontal and vertical errors in source data points are considered in this study. An analytical method is derived for the error propagation into any particular point of interest within a TIN model. The solution is validated using Monte Carlo simulations and survey data obtained from a terrestrial laser scanner.     

The impact of resolution on the accuracy of hydrologic data derived from DEMs

1 Introduction Automated extraction of drainage features from DEMs is an effective alternative to the tedious manual mapping from topographic maps. The derived hydrologic characteristics include stream-channel networks, delineation of catchment boundaries, catchment area, catchment length, stream-channel long profiles and stream order etc. Other important characteristics of river catchments, such as the stream-channel density, stream-channel bifurcation ratios, stream-channel order, number…     

The impact of resolution on the accuracy of hydrologic data derived from DEMs

Hydrologic data derived from digital elevation models (DEM) has been regarded as an effective method in the spatial analysis of geographical information systems (GIS). However, both DEM resolution and terrain complexity has impacts on the accuracy of hydrologic derivatives. In this study, a multi-resolution and multi-relief comparative approach was used as a major methodology to investigate the accuracy of hydrologic data derived from DEMs. The experiment reveals that DEM terrain representation error affects the accuracy of DEM hydrological derivatives (drainage networks and watershed etc.). Coarser DEM resolutions can usually cause worse results. However, uncertain result commonly exists in this calculation. The derivative errors can be found closely related with DEM vertical resolution and terrain roughness. DEM vertical resolution can be found closely related with the accuracy of DEM hydrological derivatives, especially in the smooth plain area. If the mean slope is less than 4 degrees, the derived hydrologic data are usually unreliable. This result may be helpful in estimating the accuracy of the hydrologic derivatives and determining the DEM resolution that is appropriate to the accuracy requirement of a particular user. By applying a threshold value to subset the cells of a higher accumulation flow, a stream network of a specific network density can be extracted. Some very important geomorphologic characteristics, e.g., shallow and deep gullies, can be separately extracted by means of adjusting the threshold value. However, such a flow accumulationbased processing method can not correctly derive those streams that pass through the working area because it is hard to accumulate enough flow direction values to express the stream channels at the stream's entrance area. Consequently, errors will definitely occur at the stream’s entrance area. In addition, erroneous derivatives can also be found in deriving some particular rivers, e.g., perched (hanging up) rivers, anastomosing rivers and braided rivers. Therefore, more work should be done to develop and perfect the algorithms.     

清至民国洛川塬土地利用演变及其对土壤侵蚀的影响

依据史料和已有研究,恢复了洛川塬土地利用的演变过程及其对土壤侵蚀的影响。研究表明,清至民国时期是一个由土地垦殖的初步恢复到土地垦殖力度的增强、垦殖范围的扩大,再至战乱、自然灾害后期的重建以及民国时期土地垦殖发展的过程。地貌的复杂性、降水的不稳定性,对土地开垦造成客观限制;政策制度的推行对土地开垦起到主导作用;而人口因素是土地开垦的根本动力。土地开垦面积随不同时期的人口变化而呈现显著差异,即土地开垦面积和人口数量之间成正相关关系。洛川塬环境伴随着人口增长、土地利用强度增强而逐步恶化。这种恶化是地理环境系统自我调节能力减弱,继而引发土壤侵蚀加剧,并呈现为人为加速侵蚀和自然侵蚀交相混合的共同作用。     

The classification and assessment of freeze-thaw erosion in Tibet

Freeze-thaw erosion is the third largest soil erosion type after water erosion and wind erosion. Restricted by many factors, few researches on freeze-thaw erosion have so far been done at home and abroad, especially those on the assessment method of freeze-thaw erosion. Based on the comprehensive analysis of impact factors of free-thaw erosion, this paper chooses six indexes, including the annual temperature range, annual precipitation, slope, aspect, vegetation and soil, to build the model for relative classification of freeze-thaw erosion using weighted and additive methods, and realizes the relative classification of the freeze-thaw erosion in Tibet with the support of GIS software. Then a synthetic assessment of freeze-thaw erosion in Tibet has been carried out according to the relative classification result. The result shows that the distribution of freeze-thaw eroded area is very extensive in Tibet, accounting for 55.3% of the total local land area; the spatial differentiation of freeze-thaw erosion with different intensities is obvious; and the difference in distribution among different regions is also obvious.     

西藏冻融侵蚀的分级和评价

Freeze-thaw erosion is the third largest soil erosion type after water erosion and wind erosion. Restricted by many factors, few researches on freeze-thaw erosion have so far been done at home and abroad, especially those on the assessment method of freeze-thaw erosion. Based on the comprehensive analysis of impact factors of free-thaw erosion, this paper chooses six indexes, including the annual temperature range, annual precipitation, slope, aspect, vegetation and soil, to build the model for relative classification of freeze-thaw erosion using weighted and additive methods, and realizes the relative classification of the freeze-thaw erosion in Tibet with the support of GIS software. Then a synthetic assessment of freeze-thaw erosion in Tibet has been carried out according to the relative classification result. The result shows that the distribution of freeze-thaw eroded area is very extensive in Tibet, accounting for 55.3% of the total local land area; the spatial differentiation of freeze-thaw erosion with different intensities is obvious; and the difference in distribution among different regions is also obvious.     

基于FloodArea模型的暴雨洪涝灾害风险预评估技术及效果检验北大核心CSCD

利用陕西气象站点逐小时降水实况、精细化格点预报、数字高程、土地利用、灾情等资料,应用水动力模型FloodArea对暴雨洪涝进行淹没模拟,在淹没水深和范围的基础上叠置承灾体属性,引入承灾体的灾损曲线,建立暴雨洪涝灾害风险预评估模型,并从数量占比和灾情占比两个角度,以县为单元进行验证,利用格点降水量预报对陕西6次大范围暴雨过程灾害风险进行预评估以及效果检验。结果表明:暴雨洪涝气象风险预估结果与实际受灾地区分布基本吻合,正确预报率73.2%,模拟结果可信度高,对于降水区域集中暴雨的风险预评估性能较分散性暴雨较高,漏报率相对低,但是空报率较高;建立的暴雨洪涝灾害风险预评估及效果检验流程,提高了气象服务的针对性,可以用于洪涝风险预评估的实际业务中,对暴雨洪涝风险管理提供技术支撑。     

Dynamic identification of soil erosion risk in the middle reaches of the Yellow River Basin in China from 1978 to 2010

Soil erosion has become a significant environmental problem that threatens ecosystems globally. The risks posed by soil erosion, the trends in the spatial distribution in soil erosion, and the status, intensity, and conservation priority level in the middle reaches of the Yellow River Basin were identified from 1978 to 2010. This study employed a multi-criteria evaluation method integrated with GIS and multi-source remote sensing data including land use, slope gradient and vegetation fractional coverage (VFC). The erosion status in the study region improved from 1978 to 2010; areas of extremely severe, more severe, and severe soil erosion decreased from 0.05%, 0.94%, and 11.25% in 1978 to 0.04%, 0.81%, and 10.28% in 1998, respectively, and to 0.03%, 0.59%, and 6.87% in 2010, respectively. Compared to the period from 1978 to 1998, the area classed as improvement grade erosion increased by about 47,210.18 km² from 1998 to 2010, while the area classed as deterioration grade erosion decreased by about 17,738.29 km². Almost all severe erosion regions fall in the 1st and 2nd conservation priority levels, which areas accounted for 3.86% and 1.11% of the study area in the two periods, respectively. This study identified regions where soil erosion control is required and the results provide a reference for policymakers to implement soil conservation measures in the future.     

山区土地利用/覆被变化对土壤侵蚀的影响

本文以福建省山区为例,在对福建省水土保持实验站、建瓯市牛坑龙水土保持试验站长期观测、实验资料深入分析对比的基础之上,探讨了土地利用/土地覆被变化对土壤侵蚀的影响规律。分析结果表明,土地利用/土地覆被变化对径流的产生和土壤侵蚀有重要影响,植被的覆盖度的变化直接影响着径流系数和土壤侵蚀模数;植被的覆盖度和径流系数呈负线性关系,随着覆盖度的增加径流系数逐渐减小;植被覆盖度和土壤侵蚀模数为负指数关系,随着植被覆盖度的增大,土壤侵蚀模数急剧下降。     

开封市黄河滩区土地资源规避洪水风险的安全利用

基于ArcGIS与ERDAS遥感影像制图软件,利用2007年SPOT2.5m分辨率遥感影像,结合实地调查,详细编绘了开封市段黄河河道边界、开封段黄河滩区土地资源的利用现状。采用1992~2007年最大洪峰时期的TM影像与沿河水文站点的观测资料,提取1992~2007年7个典型日期的河道行洪边缘线,与本底数据叠加,编制了开封段不同常遇洪水流量下滩区淹没范围。按照黄河下游二维水沙数学模型,采用2004年汛后河道大断面资料,计算生成不同流量级大洪水在滩区的可能淹没范围图(淹没区边界)。在此基础上,结合土地资源管理与河道行洪安全性的要求,总结当前黄河下游滩区利用开发的现状与存在问题,制订土地安全利用规避洪险的原则,规划土地安全利用分区,分为临河风险缓冲带、近河宜耕地带、相对稳定利用带(中风险带)和稳定利用带。提出了黄河滩区土地资源合理安全利用的对策。     

基于土壤侵蚀控制度的黄土高原水土流失治理潜力研究

以整个黄土高原为研究对象,首先将水土保持措施容量定义为某一区域能容纳的最大适宜水土保持措施量。根据梯田、林地和草地的适宜布设区域,在地理信息系统（GIS）软件的支持下,确定了黄土高原的水土保持措施容量。使用修正通用土壤流失方程（RUSLE）,计算了最小可能土壤侵蚀模数和2010年现状土壤侵蚀模数,并将水土保持措施容量下的最小可能土壤侵蚀模数与现状土壤侵蚀模数之比定义为土壤侵蚀控制度。随后使用土壤侵蚀控制度,对黄土高原水土流失治理潜力进行了研究。结果显示：黄土高原2010年现状土壤侵蚀模数为3355 t·km^-2·a^-1,最小可能土壤侵蚀模数为1921 t·km^-2·a^-1,土壤侵蚀控制度为0.57,属于中等水平。相比于现状条件,在水土保持措施容量条件下,微度侵蚀区比例从50.48%提高至57.71%,林草覆盖率从56.74%增加至69.15%,梯田所占比例由4.36%增加到19.03%,人均粮食产量可从418 kg·a^-1提高至459 kg·a^-1。研究成果对于黄土高原生态文明建设具有一定的指导意义。     

基于GIS的淤泥质潮滩侵蚀堆积空间分析

通过野外滩地长期水准详测资料，利用地理信息系统的GRID和TIN模块产生潮滩高程、坡度、二维剖面、侵蚀与堆积分布图，并获取测点所在位置的高程、坡度和侵蚀量，对获取的数据及空间分布图进行分析，结果表明：侵蚀主要发生在-7m以上的岸坡和潮滩，堆积主要出现于广阔的深水岸坡和7部分高滩，侵蚀速率以滩前深槽岸坡最快，年侵蚀率达17.9cm/a，并呈加速趋势，海岸线向陆后退速率为31m/a，侵蚀、堆积的闭合深度约为-9.5m，空间分布表现为自北而南的3个明显分带，即潮滩轻微侵蚀区，滩前深槽岸坡强烈侵蚀区和深水岸坡缓积区，东西向比较，东部，中部侵蚀大于西部。     

藏东地区斜坡土壤冻融侵蚀力学机制及敏感性分析

冻融侵蚀是青藏高原草甸覆盖区的主要侵蚀方式,以气候条件一致的藏东地区斜坡表层土壤侵蚀为对象,基于区域地质条件和土体赋存特征,分析了土壤剥蚀输移的力学过程,探索了缓变的隐性因子和灾变的显性因子对冻融侵蚀的作用机制.结果表明:①地表冻融侵蚀是自基岩风化和土壤演化起始,经历冻融拉裂破坏与沙土输移,到重新裸露基岩的一个循环演化...     

基于DEM 的数字降水径流模型在黄河小花间的应用

DEM是目前用于流域地形分析的主要数据，在流域地形分析及水质构建等方面形成了比较成熟的算法，基于DEM的水文模拟技术的应用给传统的水文模拟方法带来了根本性的变化，基于栅格型DEM，应用最新引进的WMS专业水文处理软件，结合Arc/info、Areview地理信息系统工具，以黄河小花间（小浪底-花园口区间）卢氏以上流域作为研究区，进行了数字降水径流模型的应用研究。     

基于多维视角的“城市病”诊断分析及其风险预估研究进展与发展趋势

特大城市群地区“城市病”问题是目前国内外相关研究的热点问题。全面认识城镇化与生态环境之间复杂的互动关系,才能对特大城市群地区“城市病”进行机理性剖析,并建立“城市病”病情诊断与风险预估的方法和技术体系。本文围绕“‘城市病’病因分析—‘城市病’病情诊断—‘城市病’风险预估”的研究主线,基于多维视角评述了“城市病”诊断分析及风险预估的研究进展,并提出了目前国内外研究中存在的主要问题,包括“城市病”的形成机理尚不清晰、对“城市病”的诊断多停留在表面、“城市病”风险预估研究不平衡、研究尺度单一。最后对研究趋势进行了展望：研究方向上,城镇化与生态环境的交互作用研究将持续深入,微观过程与城市整体机能及表象内在联系的综合研究将得到强化,生态系统服务研究将在“城市病”诊断分析及风险预估发挥更大作用;研究方法上,数据获取与模型构建技术的发展将有助于推动城市问题的综合研究。     

The relief of the Swiss Alps and adjacent areas and its relation to lithology and structure: topographic analysis from a 250-m DEM

In this paper we discuss the large-scale geomorphological characteristics of the Swiss Alps based on numerical analysis of a digital elevation model and compare these to an erodibility map constructed from a geotechnical map of Switzerland and regional geomorphological studies. Comparing the erodibility map with the large-scale morphometry shows an intimate relationship between mountain-scale erodibility and topography. On average, higher mean elevations and steeper mean slopes correlate with regions where rocks of low erodibility prevail. Areas with high peaks as well as the main water divides are controlled by the presence of bedrock with low to very low detachability. The drainage network of the Swiss Alps shows a close relationship to the lithological differences as well. Major longitudinal valleys follow easily erodible units. In the eastern and western part of the Swiss Alps, the highest values of local relief are located to the south of the main water divide, whereas in the central part, local relief is higher to the north of the main water divide. The large-scale geomorphic characteristics regarded in the framework of the geological history of uplift and denudation suggest that low and very low erodibilities lead to the development of areas of high elevations which are likely to persist over periods of 10–15 Ma. As the analysis of the Lepontine area shows, 20 Ma after cessation of exhumation, such high elevations are likely to be worn down and to manifest themselves as high relief only.     

Modeling spatial and temporal change of soil erosion based on multi-temporal remotely sensed data

In order to monitor the pattern, distribution, and trend of land use/cover change (LUCC) and its impacts on soil erosion, it is highly appropriate to adopt Remote Sensing (RS) data and Geographic Information System (GIS) to analyze, assess, simulate, and predict the spatial and temporal evolution dynamics. In this paper, multi-temporal Landsat TM/ETM+ remotely sensed data are used to generate land cover maps by image classification, and the Cellular Automata Markov (CA_Markov) model is employed to simulate the evolution and trend of landscape pattern change. Furthermore, the Revised Universal Soil Loss Equation (RUSLE) is used to evaluate the situation of soil erosion in the case study mining area. The trend of soil erosion is analyzed according to total/average amount of soil erosion, and the rainfall (R), cover management (C), and support practice (P) factors in RUSLE relevant to soil erosion are determined. The change trends of soil erosion and the relationship between land cover types and soil erosion amount are analyzed. The results demonstrate that the CA_Markov model is suitable to simulate and predict LUCC trends with good efficiency and accuracy, and RUSLE can calculate the total soil erosion effectively. In the study area, there was minimal erosion grade and this is expected to continue to decline in the next few years, according to our prediction results.