Chinese progress in geomorphometry

Geomorphometry, the science of digital terrain analysis （DTA）, is an important focus of research in both geomorphology and geographical information science （GIS）. Given that 70% of China is mountainous, geomorphological research is popular among Chinese schol- ars, and the development of GIS over the last 30 years has led to significant advances in geomorphometric research. In this paper, we review Chinese progress in geomorphometry based on the published literature. There are three major areas of progress： digital terrain modelling methods, DTA methods, and applications of digital terrain models （DTMs）. First, traditional vector- and raster-based terrain modelling methods, including the assessment of uncertainty, have received widespread attention. New terrain modelling methods such as unified raster and vector, high-fidelity, and real-time dynamic geographical scene modelling have also attracted research attention and are now a major focus of digital terrain modelling research. Second, in addition to the popular DTA methods based on topographical derivatives geomorphological features, and hydrological factors extracted from DTMs, DTA methods have been extended to include analyses of the structure of underlying strata, ocean surface features and even socioeconomic spatial structures. Third, DTMs have been applied to fields including global climate change, analysis of various typical regions, lunar surface and other related fields. Clearly, Chinese scholars have made significant progress in geomorphometry. Chinese scholars have had the greatest international impact in areas including high-fidelity digital terrain modelling and DTM-based regional geomorphological analysis, particularly in the Loess Plateau and the Tibetan Plateau regions.

Applicability of SRTM data for landform characterisation and geomorphometry: a comparison with contour-derived parameters

Geomorphologic and hydrologic research heavily depends on digital elevation models(DEM)which are currently being prepared from digital contours.The present study examines the use and applicability of freely available global elevation data source(3 arc seconds finished Shuttle Radar Topography Mission(SRTM))in landform characterisation,geomorphometry,river basin studies and other allied scientific applications in comparison with contour elevation data derived from the surveyed topographical sheets.The relief data extracted from a conventionally digitised geo-information science dataset of topographic contours(1:50,000)are compared with the SRTM-DEM and the variations are analysed.The automated geomorphometric and landform parameters derived from the contour DEM and the computed statistical properties of those parameters have substantial agreement with the same parameters derived from the SRTM-DEM.At the same time,localised variations also exist in some spatial domains.Derivative landscape analysis outputs from the SRTM-DEM suggest the wide acceptability and applicability of the freely available SRTM data source,especially in the regional scale applications related to hydrological modelling,terrain characterisation,disaster management and land degradation studies.

Geomorphic signatures of active tectonics in Subansiri River Basin, eastern Himalayas

The Subansiri,a major tributary of the Brahmaputra with its catchment area(35763 km^2)spreading almost entirely in the Eastern Himalayas across almost all the major and local tectonic features in the area witnesses large numbers of seismic events.Active tectonic indices like relief and slope,drainage pattern,longitudinal profile,valley profile,hypsometry,valley asymmetry factors and transverse topographic symmetry index,stream length gradient,valley floor-height ratio extracted from SRTM 3 arcsecond data prove that the evolving basin morphology has substantial contribution from the Himalayan tectonics.Seismic data are incorporated in the study to establish the potentially active tectonic elements in the catchment area.The study shows that the western part of the Subansiri River Basin is profoundly tilted towards north in the upper catchment and towards east in the lower and middle part of the catchment.The predominant tectonic movements in the western part of the basin caused the tilting of the basin towards north in the upstream and towards east in the middle and lower parts.

Impact of geomorphometric parameters on the occurrence and distribution of landslides in Yamuna River Basin,North-Western Himalaya,India

The majority of landslides in the Indian Himalayas are triggered by rainfall and earthquake.The geology and geomorphology also play an important role and constitute the major predisposing factor controlling landslides.Additionally,active tectonics modify the landscape,impacting the occurrence and distribution of landslides.The objective of this study is to investigate the role of some of the major predisposing factors to assess landslide patterns in the Yamuna River Basin as it is prone to recurrent landslide hazards.The approach mainly deals with the application of geographical information system-based statistical analysis and quantifying frequency-area distribution of rainfalltriggered landslides for the years 2015 to 2017.The analysis shows that the frequency of landslides is highest in the slope range 40°-70°and the mean landslide size is higher in the slope range 0°-20°and 30°-40°,remaining constant on further increase in slope angle.The study shows that some critical slope range controls both the frequency and size of landslides.Landslides were mostly restricted to south facing slopes.About 91%of the landslide occur in the drainage density range of 1.2 to 2.1 km/km^(2) while landslides show very low occurrence in either lower(<1.2)or higher(>2.1)drainage density.Frequencysize distribution analysis of landslides depicts a distinct cutoff point but an indistinct rollover point.Under-sampling of small landslides can be a reasonable cause for this.Like other studies,the present data fits very well for medium and large landslides following an inverse power law with a scaling exponent of-2.16.Around 80% of landslides are smaller than the cutoff size and 20% larger than this value.The geology and tectonics of Lesser Himalayas and Sivaliks offer favorable conditions for frequent landslides.Areas such as Dehradun,Uttarkashi,Sirmaur,Shimla,and Solan are very prone to landslide activity owing to the presence of poorly consolidated sandstone,conglomerate,quartzites,phyllites,etc.Moreover,the majority of larger landslides are in the Dehradun district where precipitation,drainage density,and lithology are highly favorable to trigger large events.The present study has identified the critical range of predisposing factors responsible for landslides and presents the frequency-size distribution of landslides in the Yamuna River Basin.These are the key inputs in landslide susceptibility mapping and risk assessment.Therefore,the findings from the present analysis can be very helpful in landslide risk reduction and landslide hazard zonation and probably plan critical locations for installation of early warning signals.

GIS tools for preliminary debris-flow assessment at regional scale

The assessment of the areas endangered by debris flows is a major issue in the context of mountain watershed management. Depending on the scale of analysis, different methods are required for the assessment of the areas exposed to debris flows.While 2-D numerical models are advised for detailed mapping of inundation areas on individual alluvial fans, preliminary recognition of hazard areas at the regional scale can be adequately performed by less data-demanding methods, which enable priority ranking of channels and alluvial fans at risk by debris flows. This contribution focuses on a simple and fast procedure that has been implemented for regionalscale identification of debris-flow prone channels and prioritization of the related alluvial fans. The methodology is based on the analysis of morphometric parameters derived from Digital Elevation Models(DEMs). Potential initiation sites of debris flows are identified as the DEM cells that exceed a threshold of slope-dependent contributing area. Channel reaches corresponding to debris flows propagation, deceleration and stopping conditions are derived from thresholds of local slope. An analysis of longitudinal profiles is used for the computation of the runout distance of debris flows. Information on erosion-resistant bedrock channels and sediment availability surveyed in the field are taken into account in the applications. A set of software tools was developed and made available(https://github.com/Hydrogeomorphology Tools) to facilitate the application of the procedure. This approach, which has been extensively validated by means of field checks, has been extensively applied in the eastern Italian Alps. This contribution discusses potential and limitations of the method in the frame of the management of small mountain watersheds.

Assessment of the Relationships among Catchments’ Morphometric Parameters and Hydrologic Indices

In Greece the hydrological analysis of ephemeral streams has been especially difficult due to the lack of precipitation and discharge gauges. This study focuses on the investigation of possible relationship between morphometric characteristics of small to medium drainage basins and hydrological indices in order to discover morphometric parameters “predictors” of flash flood potential of ungauged catchments. Twenty-two morphometric parameters of twenty-seven drainage basins (ranging in area between 3.6 km2 and 330.5 km2) located in the northern part of the Peloponnese in southern Greece were calculated utilizing GIS software ArcGIS10. Hydrological modeling was performed using a simplified Matlab implementation of TOPMODEL, a conceptual model based on the principle of variable contributing area to runoff production through saturated overland flow, and LISEM, a physically based hydrologic and soil erosion model. Rainfall-runoff simulations were performed for an extreme precipitation event. The simulations outcomes, which include the peak discharge, time to peak and the percentage runoff, were correlated with the morphometric parameters of the catchments. Results were not consistent between the two models, probably due to their different structure, with the LISEM results being closer to what is anticipated. The results demonstrate that area, length of the basin, perimeter and compactness factor appear better correlated with the peak discharge (Qpeak) of the catchment. The same parameters as well as Melton’s number correlate with percentage runoff (C), while “celerity” of the flood wave (length of the basin/time to peak) is better correlated with relief, indicating that as the relief becomes greater, the response of the basin becomes fastest.

Landslide inventory validation and susceptibility mapping in the Gerecse Hills, Hungary

Landslides pose a threat to property both in the populated and cultivated areas of the Gerecse Hills (Hungary). The currently available landslide inventory database holds the records from many sites in the area, but the database is out-of-date. Here we address the problem of revising the National Landslides Cadastre landslide inventory database by creating a landslide suscept-ibility map with a multivariate model based on likelihood ratio functions. The model is applied to the TanDEM-X DEM (0.4″ res.), the current landslide inventory of the area, and data acquired from geological maps. By comparing the distributions of four variables in the landslide and non-landslide area with grid computation methods, the model yields landslide susceptibility estimates for the study area. The estimations show to what extent a certain area is similar to the sample areas, therefore, its likelihood to be affected by landslides in the future. The accuracy of the model predictions was checked in the field and compared to the results of our previous study using the SRTM-1 DEM for a similar analysis. The model gave accurate estimates when certain correction measures were applied to the input datasets. The limitations of the model, the input datasets, and the suggested correction measures are also discussed.

Geomorphometric relief classification with the κ-median method in the Silesian Upland,southern Poland

The aim of this study is geomorphometric relief classification of a temperate latitude upland area in Central Europe.The Silesian Upland represents diversified structural relief which contains a fan-shaped configuration of long thresholds and wide erosion depressions.A 20 m × 20 m digital elevation model(DEM)provided input data for the analysis.The κ-median method was applied to examine morphometric variables of the relief.The aim of these activities was to identify clusters with objects of similar mathematical characteristics.These clusters were the basis of landform classification.Smaller numbers of clusters 4 transparently show hypsometric relationships.Key elements of the morphology of the area were clearly visible.The division into 6 clusters gives the best results-a detailed but clear image of the morphological diversity by distinguishing characteristic landform elements.The results for 8 clusters show significant background noise and are ambiguous,which makes them diflBcult to identify.Our research has confirmed that the κ-median method is a useful tool for landform classifications.We determined optimal parameters of this method(filtering window size,DEM resolution,number of clusters,aspect influence).