Background and aims - Although soils and topography are reported to be key factors determining vegetation patterns, there are very few studies on this topic in tropical Africa. Given the young nature ...of the soils of Nech Sar National park, we hypothesised that the woody
vegetation would be related to both topsoil and subsoil characteristics. As topography also determines soil characteristics, we investigated whether soil and topography could be considered independently.Methods - Abundance of woody plant species was measured in 19 stratified
randomly selected plots of 20 m × 20 m. At the centre of each plot a soil profile pit was dug and samples were taken from each horizon. Topographic characteristics were derived from a 30 m × 30 m digital elevation model. TWINSPAN and Detrended Correspondence Analysis (DCA) were
used to identify major patterns in species composition. Factor Analysis was used to assess the variability of, and correlation between, the soil characteristics. Differences between the vegetation groups in-terms of stand and environmental characteristics was tested with the Mann-Whitney U
test. DCA axes describing the major variation in vegetation patterns were correlated with soil and topographic characteristics.Results - Forest vegetation was found on Fluvisols and Gleyic Cambisols while bushland was found on Andosols and Vertic Cambisols. The vegetation
gradient from forest to bushland (DCA-1) was correlated with both topsoil and subsoil characteristics reflecting parent material and alkalinity; these could however not be dissociated from topography. In contrast, variation both within the forest and the bushland (DCA-2) was not correlated
with environmental characteristics. We attribute this variation to disturbances such as collection of firewood or logging, and to the absence of large browser or scarcity of wildfires.Conclusions - This study calls for giving equal attention to topsoil and subsoil for elucidating
woody vegetation patterns. Though vegetation patterns vary with topography, a comprehensive understanding requires insights into soils.
This paper proposes a statistical decision-tree model to analyze landslide susceptibility in a wide area of the Akaishi Mountains, Japan. The objectives of this study were to validate the ...decision-tree model by comparing landslide susceptibility and actual landslide occurrence, and to reveal the relationships among landslide occurrence, topography, and geology. Landslide susceptibility was examined through ensemble learning with a decision tree. Decision trees are advantageous in that estimation processes and order of important explanatory variables are explicitly represented by the tree structures. Topographic characteristics (elevation, slope angle, profile curvature, plan curvature, and dissection and undissection height) and geological data were used as the explanatory variables. These topographic characteristics were calculated from digital elevation models (DEMs). The objective variables were landslide occurrence and reactivation data between 1992 and 2002 that were depicted by satellite image analysis. Landslide susceptibility was validated by comparing actual data on landslides that occurred and reactivated after the model was constructed (between 2002 and 2004).
This study revealed that, from 2002 to 2004, landslides tended to occur and reactivate in catchments with high landslide susceptibility. The landslide susceptibility map thus depicts the actual landslide occurrence and reactivation in the Akaishi Mountains. This result indicates that the decision-tree model has appropriate accuracy for estimating the probabilities of future landslides. The tree structure indicates that landslides occurred and reactivated frequently in the catchments that had an average slope angle exceeding ca. 29° and a mode of slope angle exceeding 33°, which agree well with previous studies. A decision tree also quantitatively expresses important explanatory variables at the higher order of the tree structure.
Ice aprons are poorly studied and not well-defined thin ice bodies adhering to high altitude steep rock faces, but are present in most Alpine-type high mountain environments worldwide. This study ...aims to precisely define ice aprons based on a detailed analysis of their topographical characteristics in the Mont Blanc massif (western European Alps). For this, we accurately identified and precisely mapped 423 ice aprons using a combination of high-resolution optical satellite images from 2019. To better understand their relationship with other types of glaciers, especially the steep slope glaciers and other surface ice bodies, we built a detailed inventory at the scale of the massif that incorporates nine different types of perennial surface ice bodies. In addition, an analysis using different topographic factors helped us to better understand the preferred locations of the ice aprons. We show that they predominantly occur on west-oriented steep and topographically rugged rock slopes above the local Equilibrium Line Altitude (~3200 m a.s.l.), with concave profile curvatures around them that facilitate snow accumulation. They are also found in areas underlain by permafrost. The extensive inventory also helped us to identify different types of ice aprons based on their relationships with glaciers/ice bodies. The analysis shows that ice aprons existing at the headwall of large glaciers above a bergschrund are the most dominant ice apron type in the study area, with ~82% of the total.
The geographical distribution characteristics of villages characterised by ethnic minorities are determined by the selection of the site when the village was initially established. The location of ...inherited and well-preserved minority villages must be exceptionally compatible with the natural terrain, with a logical relationship. Nonetheless, the issue of village location, which is directly related to the development of the features of the geographical distribution, has received little attention from scholars. The average nearest proximity index, Voronoi, kernel density analysis, proximity analysis, and the Geographical Detector (GeoDetector) were used to analyse the geographic distribution characteristics of villages and their correlation with terrain, as well as the difference between the influence of each terrain factor. The findings indicated the following. (1) The geographical distribution of minority villages in Fujian Province is of the agglomeration type, with a significant “mononuclear” feature, and the topography has a facilitating effect on the clustering distribution of villages. (2) The geographical distribution of minority villages in each city of Fujian Province coexisted with the agglomeration type and the dispersion type, and the role of topography in promoting the agglomeration-type distribution of villages was not affected by the distribution density of villages. (3) The site selection of Fujian-minority villages is characterised by medium altitude, moderate slope, sun exposure, and no obvious hydrophilicity. Minority villages are mainly located in areas with an elevation of 202–647 m; a slope of 6–15°; a flat land aspect with a south slope, southeast slope, or southwest slope; and distance of 500–1500 m from 5–20 m wide rivers of level 2. (4) The site selection of Fujian minority villages is influenced by various topographic factors, such as elevation, slope, aspect, river buffer, river width, and river level, among which river width has the most substantial effect. (5) All topographic factors have a two-factor enhancing relationship with each other, aspect and slope have the most substantial effect and play a dominant role in site selection. The research findings illuminate the internal logic of the geographical distribution differentiation of villages characterised by ethnic minorities, which is critical for promoting the protection of modern ethnic-minority villages.
Geomorphologic characteristics of a basin affect mass movement, water and sediment transport. The purpose of this study is to examine coupling relationship between topography and soil erosion in ...Loess Plateau during past 50 years (1960–2011). We firstly describe the distribution patterns of topographic characteristics and sediment discharge in specific river basins. By using mathematical methods (PCA method, linear regression and ANOVA analysis) and topographic variables, we build a comprehensive index – Erosion Topography Index (ETI). According to the research, the following findings are obtained. Firstly, average sediment discharge varies from 0.13 × 108 t to 7.56 × 108 t along the Yellow River from the upper-stream to down-stream. The sediment discharge of this region decreased 60%–90% since the year of 1980, and decrease tendency is more obvious after the year 2000 compared to the period of 1980–2011. Secondly, topographic characteristics and the Erosion Topography Index has similar distribution pattern. Thirdly, there is no significant linear correlation between ETI and all four sediment discharge variables (average sediment, total sediment, sediment of 1980–2011, and sediment of 2000–2011), but there are significant positive linear correlations (p < 0.05) between ETI and each sediment discharge variable. Furthermore, the correlation between ETI and sediment of 2000–2011 is stronger (p = 0.035) than other variables, and the gradient coefficient of them is higher (k = 0.667) than other variables too. Except the topographic characteristics, the vegetation coverage and human activities should be other factors that can influence the variations of sediment discharge in Loss Plateau.
Debris flow susceptibility mapping (DFSM) has been reported in many studies, however, the irrational use of the same conditioning factor system for DFSM in regional-scale has not been thoroughly ...resolved. In this paper, a region-partitioning method that is based on the topographic characteristics of watershed units was developed with the objective of establishing multiple conditioning factor systems for regional-scale DFSM. First, watershed units were selected as the mapping units and created throughout the entire research area. Four topographical factors, namely, elevation, slope, aspect and relative height difference, were selected as the basis for clustering watershed units. The
k
-means clustering analysis was used to cluster the watershed units according to their topographic characteristics to partition the study area into several parts. Then, the information gain ratio method was used to filter out superfluous factors to establish conditioning factor systems in each region for the subsequent debris flow susceptibility modeling. Last, a debris flow susceptibility map of the whole study area was acquired by merging the maps from all parts. DFSM of Yongji County in Jilin Province, China was selected as a case study, and the analytical hierarchy process method was used to conduct a comparative analysis to evaluate the performance of the region-partitioning method. The area under curve (AUC) values showed that the partitioning of the study area into two parts improved the prediction rate from 0.812 to 0.916. The results demonstrate that the region-partitioning method on the basis of topographic characteristics of watershed units can realize more reasonable regional-scale DFSM. Hence, the developed region-partitioning method can be used as a guide for regional-scale DFSM to mitigate the imminent debris flow risk.
To investigate the topographic characteristics of optic disc hemorrhage (DH) and the factors associated with DH area in POAG.
We enrolled 128 POAG eyes (with DH) of 128 patients consecutively. ...Digital red-free retinal nerve fiber layer (RNFL) photographs and digital color stereo disc photographs of the enrolled eyes were reviewed, and the DH locations were measured. The DH area was calculated based on RNFL deviation map/RNFL photographs overlay image.
Disc hemorrhages were most common in the inferotemporal inferior sector (58.0%) and the disc rim (40.6%) in terms of octant and proximal location, respectively. In a multivariate analysis, a larger DH area was associated with older age (P < 0.01), use of acetylsalicylic acid (P = 0.03), lower cup-to-disc ratio (P < 0.01), and lower baseline IOP (P = 0.01). In normal-baseline IOP-POAG eyes (n = 88), the overall DH area and length of maximum radial extent of DH were larger than in high-baseline IOP-POAG eyes (n = 40) (P = 0.04 and 0.03, respectively).
In POAG eyes, DH was larger in area and longer in length in cases of normal-baseline IOP than in cases of high-baseline IOP. This suggests the possibility that previous studies' findings of higher DH prevalence and incidence in normal-baseline IOP-POAG eyes were partially affected by these topographic characteristics, which make DH more easily detectable.
Using land use types in multiple spatial scales (entire basin, buffer zones, and slopes) as well as statistical and spatial analysis, relationships between land use types and concentrations of ...dissolved trace metals were determined in the Le’an River Basin, China. The result showed that farmland and urban land were determined as the source of the pollutants, while forestland and grassland were identified as the sink of the pollutants. The temporal differences of relationships between land use types and concentrations of dissolved trace metals mainly due to the discrepancy of rainfall characteristics. Land use type close to river was a better indicator for the effectiveness of concentrations of trace metals, especially at scale of 0–200 m. Forestland and grassland on lower slopes greatly affected the water quality, and the former had no significant or weak influences on higher slopes. Urban land had the greater positive correlations with concentrations of dissolved trace metals on higher slopes, which are mainly due to frequent mining activity. Further analysis suggested that the buffer zones with low slope needed to be seriously taken into consideration for effective land use management in similar basin.
Abstract
The evaluation of hydrological models for a specific catchment is normally based on the model performance according to the selected performance criteria. However, the catchment ...rainfall-runoff characteristics could be used for the selection of a suitable hydrological model in study area, which, also, for the problem solve of the model application in ungauged basins. In this study, six conceptual models were applied in three semi-humid or semi-arid catchments to investigate the correlation between catchment characteristics and model structure selection. In addition, the impacts of precipitation and topography in model simulation were analyzed. The results show that runoff generation are highly impacted by catchment topographic index and land cover change, and the influence of slope for river channel is greater than mean slope for the whole catchment due to the runoff generation for partial area. For the catchments under similar climate condition, the impact of topographic features for runoff generation process is greater than the difference of precipitation. It indicates that for a specific catchment, the selection of appropriate model should base on better understanding of the rainfall-runoff relationship. The method of incorporating additional runoff generation module in the traditional model can significantly improve the accuracy of flood simulation.
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