Relationships between Landslide Types and Topographic Attributes in a Loess Catchment,China

Topographic attributes have been identified as the most important factor in controlling the initiation and distribution of shallow landslides triggered by rainfall.As a result,these landslides influence the evolution of local surface topography.In this research,an area of 2.6 km 2 loess catchment in the Huachi County was selected as the study area locating in the Chinese Loess Plateau.The landslides inventory and landslide types were mapped using global position system(GPS) and field mapping.The landslide inventory shows that these shallow landslides involve different movement types including slide,creep and fall.Meanwhile,main topographic attributes were generated based on a high resolution digital terrain model(5 m × 5 m),including aspect,slope shape,elevation,slope angle and contributing area.These maps were overlaid with the spatial distributions of total landslides and each type of landslides in a geographic information system(GIS),respectively,to assess their spatial frequency distributions and relative failure potentials related to these selected topographic attributes.The spatial analysis results revealed that there is a close relation between the topographic attributes of the postlandsliding local surface and the types of landslide movement.Meanwhile,the types of landslide movement have some obvious differences in local topographic attributes,which can influence the relative failure potential of different types of landslides.These results have practical significance to mitigate natural hazard and understandgeomorphologic process in thick loess area.

Small Islands DEMs and Topographic Attributes Analysis： A Comparative Study among SRTM-V4,1, ASTER-V2,1, High Topographic Contours Map and DGPS

Rising sea levels due to global warming and climate change impact may prove a disaster for small islands. Accurate DEM （digital elevation model） can help to understand SLR （sea level rise） impact, coastal zones flooding risks assessment and hydrological attributes modeling and extraction. Currently, DEMs are available from several different sources using active and passive remote sensing systems. This research compares absolute surface heights accuracies retrieved from three independent DEMs datasets. The Shuttle Radar Topographic Mission （SRTM-V4.1） and the Advanced Space borne Thermal Emission and Reflection Radiometer （ASTER-V2.1） with 30-m pixel size, and a DEM-5 of 5-m spatial resolution generated from high topographic contour lines map at scale of 1：5,000 using simple Kriging interpolation method. Moreover, topographic attributes （slope and aspect） have been retrieved and compared. For the elevations validation purposes, a dataset of 400 GCPs uniformly distributed over the study site were used. These were measured using a DGPS assuring ± 1 and ± 2 cm accuracies, respectively, for planimerry and altimetry. The obtained results show that globally the landscape scale plays an important role in the selection of the DEM pixel size, which must reflect the real topographic attributes. Indeed, the derived DEM-5 from high topographic contours map （1：5,000） using simple Kriging exhibit the best accuracy of ±0.65 m which is less than the tolerance or the total error （±0.78 m） calculated based on errors sources propagation. Then, the results show an accuracy of ± 3.00 m for SRTM-V4.1 which is less than the absolute vertical height accuracy （±5.6 m） advocated by NASA for African continent and Middle-East regions. As well, the achieved ASTER accuracy was ± 8.40 m compared to the estimated error （±17.01 m） by USGS and JAXA. Obviously, high spatial resolution and accurate DEM-5 is a crucial requirement to simulate and evaluate costal zones inundation under different SLR and storm flow scenarios for small islands. Decidedly, the elevation of small islands with topographic features not higher than 134 m can be estimated using SRTM-V4.1 with relatively acceptable accuracy. Whereas, this DEM is not significantly consistent for accurate SLR scenarios simulations. Without doubt, ASTER-V2.1 DEM was an excellent alternative compared to SRTM with 90-m pixel size, but actually with SRTM-V4.1 full resolution （30-m） ASTER-V2.1 will likely see its limited uses in geosciences applications. Indeed, ASTER is not providing accurate information to simulate the impact of SLR scenarios on small islands.

Comparison of SRTM-V4.1 and ASTER-V2.1 for Accurate Topographic Attributes and Hydrologic Indices Extraction in Flooded Areas

This research compares the potential of SRTM-V4.1 and ASTER-V2.1 with 30-m pixel size to derive topographic attributes （elevation, slopes, aspects, and flow accumulation） and hydrologic indices such as STI （sediment transport index）, CTI （compound topographic index） and SPI （stream power index） to detect areas associated with flash floods cansed by rainfall storms and sediment accumulation. The study area is Guelmim city in Morocco, which has been flooded several times over the past 50 years, and which was declared a ＂disaster area＂ in December 2014 after violent rainfall storms killed 46 people and caused significant damage to the infrastructure. The obtained results indicate that the SRTM DEM performs better than ASTER in terms of micro-topography, hydrologic-network and structural information characterization. In addition, with reference to a topographic contours map （1：50000）, the derived global height surfaces accuracies are ＋3.15 m and 4-9.17 m for SRTM and ASTER, respectively. These accuracies are significantly influenced by topography; errors are larger （SRTM = 11.34 m, ASTER = 19.20 m） for high altitude terrain with strong slopes, while they are smaller （SRTM = 1.92 m, ASTER = 3.76 m） in the low to medium-relief areas with indulgent slopes. Moreover, all the considered hydrological indices are significantly characterized with SRTM compared to ASTER. They demonstrated that the rainfall and the topographic morphology are the major contributing factors in flash flooding and catastrophic inundation in this area. The runoff waterpower delivers vulnerable topsoil and contributes strongly to the erosion and transport of soil material and sediment to the plain areas through waterpower and gravity. Likewise, the role of the lithology associated with the terrain morphology is decisive in the erosion risk and land degradation in this region.

Spatial distribution pattern of Picea schrenkiana population in the Middle Tianshan Mountains and the relationship with topographic attributes

The spatial distribution of plant populations is an important feature of population structure and it de- termines the population＇s ecological preferences, biological characteristics and relationships with environmental factors. The point pattern analysis method was adopted to study the distribution pattern of Picea schrenkiana indi- viduals of different size classes and the correlations between two size classes as well as the impact of topog- raphical attributes on the population distribution. With increasing diameter at breast height, the plant density of the P. schrenkiana population showed a declining trend. Old trees showed a random distribution at a small spatial scale （0-12 m）, whereas saplings, small trees and big trees all had an aggregated distribution at all scales. With the increase of tree age, the scales at which maximal aggregation occurred gradually increased and the aggregation strength decreased. At a small scale （0-16 m）, all size classes showed a negative correlation and the larger the difference between tree size, the more significant the negative correlation. The number of medium, big and old trees had a significantly positive correlation with elevations, whereas the number of saplings and small trees was not significantly correlated with elevations. The numbers of saplings, small and medium trees showed a significant positive correlation with slope gradient, whereas the number of big trees was not significantly correlated, and the number of old trees was negatively correlated with gradient. With the exception of old trees, saplings, small, me- dium and big trees showed negative correlations with convexity index. The study provides a theoretical basis for the conservation, rehabilitation and sustainable management of forest ecosystems in the Tianshan Mountains.

Relationships between Soil Depth and Terrain Attributes in a Semi Arid Hilly Region in Western Iran

Soil depth generally varies in mountainous regions in rather complex ways.Conventional soil survey methods for evaluating the soil depth in mountainous and hilly regions require a lot of time,effort and consequently relatively large budget to perform.This study was conducted to explore the relationships between soil depth and topographic attributes in a hilly region in western Iran.For this,one hundred sampling points were selected using randomly stratified methodology,and considering all geomorphic surfaces including summit,shoulder,backslope,footslope and toeslope;and soil depth was actually measured.Eleven primary and secondary topographic attributes were derived from the digital elevation model(DEM) at the study area.The result of multiple linear regression indicated that slope,wetness index,catchment area and sediment transport index,which were included in the model,could explain about 76 % of total variability in soil depth at the selected site.This proposed approach may be applicable to other hilly regions in the semi-arid areas at a larger scale.

Spatial variability of soil development indices and their compatibility with soil taxonomic classes in a hilly landscape: a case study at Bandar village, Northern Iran

Soil complexity and its multivariable nature restrict the precision of soil maps that are essential tools for soil sustainable management. Most methods developed for reducing impurities of soil map units focus on soil external properties. Taking into account the soil internal properties like geochemical weathering indices could increase the map unit's purity. However, the compatibility of these indices with Soil Taxonomic Classes has not been studied yet. This study has been performed in a hilly region with different soil types, vegetation and diverse topographic attributes to illustrate the spatial variability of soil weathering indices and their compatibility with Soil Taxonomic Classes. The grid sampling is at 100 m interval. Physico-chemical and total elemental analyses were performed on 184 and 56 soil samples respectively. Eight topographic attributes and 14 common soil development indices were determined. Principal components analysis(PCA) was done to identify the most important components. The results indicated that Morphological Index(MI) was the best index to show the degree ofsoil development in the studied region. Spatial distribution of Soil Taxonomic Classes showed relatively good compatibility with the first principal component(PC1), Vogt(V) and morphological indices. This study showed that using soil development indices with the conventional methods could be helpful tools in soil survey investigations.