TY - JOUR A1 - Yair, Aaron A1 - Bryan, Rorke B. A1 - Lavee, Hanoch A1 - Schwanghart, Wolfgang A1 - Kuhn, Nikolaus J. T1 - The resilience of a badland area to climate change in an arid environment JF - Catena : an interdisciplinary journal of soil science, hydrology, geomorphology focusing on geoecology and landscape evolution N2 - Badlands have long been considered as model landscapes due to their perceived close relationship between form and process. The often intense features of erosion have also attracted many geomorphologists because the associated high rates of erosion appeared to offer the opportunity for studying surface processes and the resulting forms. Recently, the perceived simplicity of badlands has been questioned because the expected relationships between driving forces for erosion and the resulting sediment yield could not be observed. Further, a high variability in erosion and sediment yield has been observed across scales. Finally, denudation based on currently observed erosion rates would have lead to the destruction of most badlands a long time ago. While the perceived simplicity of badlands has sparked a disproportional (compared to the land surface they cover) amount of research, our increasing amount of information has not necessarily increased our understanding of badlands in equal terms. Overall, badlands appear to be more complex than initially assumed. In this paper, we review 40 years of research in the Zin Valley Badlands in Israel to reconcile some of the conflicting results observed there and develop a perspective on the function of badlands as model landscapes. While the data collected in the Zin Valley clearly confirm that spatial and temporal patterns of geomorphic processes and their interaction with topography and surface properties have to be understood, we still conclude that the process of realizing complexity in the "simple" badlands has a model function both for our understanding as well as perspective on all landscape systems. KW - Badlands KW - Model landscape KW - Climate change KW - Resilience Y1 - 2013 U6 - https://doi.org/10.1016/j.catena.2012.04.006 SN - 0341-8162 VL - 106 IS - 4 SP - 12 EP - 21 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Schwanghart, Wolfgang A1 - Groom, Geoff A1 - Kuhn, Nikolaus J. A1 - Heckrath, Goswin T1 - Flow network derivation from a high resolution DEM in a low relief, agrarian landscape JF - Earth surface processes and landforms : the journal of the British Geomorphological Research Group N2 - Digital flow networks derived from digital elevation models (DEMs) sensitively react to errors due to measurement, data processing and data representation. Since high-resolution DEMs are increasingly used in geomorphological and hydrological research, automated and semi-automated procedures to reduce the impact of such errors on flow networks are required. One such technique is stream-carving, a hydrological conditioning technique to ensure drainage connectivity in DEMs towards the DEM edges. Here we test and modify a state-of-the-art carving algorithm for flow network derivation in a low-relief, agricultural landscape characterized by a large number of spurious, topographic depressions. Our results show that the investigated algorithm reconstructs a benchmark network insufficiently in terms of carving energy, distance and a topological network measure. The modification to the algorithm that performed best, combines the least-cost auxiliary topography (LCAT) carving with a constrained breaching algorithm that explicitly takes automatically identified channel locations into account. We applied our methods to a low relief landscape, but the results can be transferred to flow network derivation of DEMs in moderate to mountainous relief in situations where the valley bottom is broad and flat and precise derivations of the flow networks are needed. KW - digital terrain analysis KW - digital elevation model KW - hydrological conditioning KW - drainage networks Y1 - 2013 U6 - https://doi.org/10.1002/esp.3452 SN - 0197-9337 SN - 1096-9837 VL - 38 IS - 13 SP - 1576 EP - 1586 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Hikel, Harald A1 - Yair, Aaron A1 - Schwanghart, Wolfgang A1 - Hoffmann, Ulrike A1 - Strähl, Sarah A1 - Kuhn, Nikolaus J. T1 - Experimental investigation of soil ecohydrology on rocky desert slopes in the Negev Highlands, Israel JF - Zeitschrift für Geomorphologie N2 - Purpose: Dry land vegetation is expected to respond sensitively to climate change and the projected variability of rainfall events. Rainfall as a water source is an obvious factor for the water supply of vegetation. However, the interaction of water and surface on rocky desert slopes with a patchy soil cover is also vital for vegetation in drylands. In particular, runoff on rocky surfaces and infiltration capacity of soil patches determine plant available water. Process-based studies into rock-soil interaction benefit from rainfall simulation, but require an approach accounting for the micro-scale heterogeneity of the slope surfaces. This study therefore aims at developing a suitable procedure for examining rock-soil interaction and the relevance of soil volume for storing plant available water in the northern Negev, Israel. Materials and methods: To determine the amount of rainfall required to fill the available soil water storage capacity rainfall simulation experiments were conducted. The design of the rainfall-simulator and the selection of the plots aimed specifically at observing infiltration into small soil patches on a micro-scale relevant for the prevalent vegetation cover. Results and discussion: The preliminary results of the study in the Negev Desert indicate that the ratio between soil volume and frequency of rainfall events determine the effect of climate change on plant available water and thus ultimately vegetation cover. Conclusions: Based on the experiments examining runoff and soil moisture the qualitative understanding of hillslope ecohydrology in a rocky desert environment can be expanded into a quantitative assessment of the potential impact of varying rainfall conditions. The study also illustrates the contribution of rainfall simulation experiments for studies on the impact of climate change. KW - Drylands KW - Ecohydrology KW - Rocky deserts KW - Rainfall simulation Y1 - 2013 U6 - https://doi.org/10.1127/0372-8854/2012/S-00116 SN - 0372-8854 VL - 57 IS - 2 SP - 39 EP - 58 PB - Cramer CY - Stuttgart ER - TY - JOUR A1 - Heckmann, Tobias A1 - Schwanghart, Wolfgang T1 - Geomorphic coupling and sediment connectivity in an alpine catchment - Exploring sediment cascades using graph theory JF - Geomorphology : an international journal on pure and applied geomorphology N2 - Through their relevance for sediment budgets and the sensitivity of geomorphic systems, geomorphic coupling and (sediment) connectivity represent important topics in geomorphology. Since the introduction of the systems perspective to physical geography by Chorley and Kennedy (1971), a catchment has been perceived as consisting of landscape elements (e.g. landforms, subcatchments) that are coupled by geomorphic processes through sediment transport. In this study, we present a novel application of mathematical graph theory to explore the network structure of coarse sediment pathways in a central alpine catchment. Numerical simulation models for rockfall, debris flows, and (hillslope and channel) fluvial processes are used to establish a spatially explicit graph model of sediment sources, pathways and sinks. The raster cells of a digital elevation model form the nodes of this graph, and simulated sediment trajectories represent the corresponding edges. Model results are validated by visual comparison with the field situation and aerial photos. The interaction of sediment pathways, i.e. where the deposits of a geomorphic process form the sources of another process, forms sediment cascades, represented by paths (a succession of edges) in the graph model. We show how this graph can be used to explore upslope (contributing area) and downslope (source to sink) functional connectivity by analysing its nodes, edges and paths. The analysis of the spatial distribution, composition and frequency of sediment cascades yields information on the relative importance of geomorphic processes and their interaction (however regardless of their transport capacity). In the study area, the analysis stresses the importance of mass movements and their interaction, e.g. the linkage of large rockfall source areas to debris flows that potentially enter the channel network. Moreover, it is shown that only a small percentage of the study area is coupled to the channel network which itself is longitudinally disconnected by natural and anthropogenic barriers. Besides the case study, we discuss the methodological framework and alternatives for node and edge representations of graph models in geomorphology. We conclude that graph theory provides an excellent methodological framework for the analysis of geomorphic systems, especially for the exploration of quantitative approaches towards sediment connectivity. KW - Geomorphic coupling KW - Sediment connectivity KW - Sediment cascades KW - Graph theory Y1 - 2013 U6 - https://doi.org/10.1016/j.geomorph.2012.10.033 SN - 0169-555X VL - 182 IS - 2 SP - 89 EP - 103 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Beck, Jan A1 - Holloway, Jeremy D. A1 - Schwanghart, Wolfgang T1 - Undersampling and the measurement of beta diversity JF - Methods in ecology and evolution : an official journal of the British Ecological Society N2 - Beta diversity is a conceptual link between diversity at local and regional scales. Various additional methodologies of quantifying this and related phenomena have been applied. Among them, measures of pairwise (dis)similarity of sites are particularly popular. Undersampling, i.e. not recording all taxa present at a site, is a common situation in ecological data. Bias in many metrics related to beta diversity must be expected, but only few studies have explicitly investigated the properties of various measures under undersampling conditions. On the basis of an empirical data set, representing near-complete local inventories of the Lepidoptera from an isolated Pacific island, as well as simulated communities with varying properties, we mimicked different levels of undersampling. We used 14 different approaches to quantify beta diversity, among them dataset-wide multiplicative partitioning (i.e. true beta diversity') and pairwise site x site dissimilarities. We compared their values from incomplete samples to true results from the full data. We used these comparisons to quantify undersampling bias and we calculated correlations of the dissimilarity measures of undersampled data with complete data of sites. Almost all tested metrics showed bias and low correlations under moderate to severe undersampling conditions (as well as deteriorating precision, i.e. large chance effects on results). Measures that used only species incidence were very sensitive to undersampling, while abundance-based metrics with high dependency on the distribution of the most common taxa were particularly robust. Simulated data showed sensitivity of results to the abundance distribution, confirming that data sets of high evenness and/or the application of metrics that are strongly affected by rare species are particularly sensitive to undersampling. The class of beta measure to be used should depend on the research question being asked as different metrics can lead to quite different conclusions even without undersampling effects. For each class of metric, there is a trade-off between robustness to undersampling and sensitivity to rare species. In consequence, using incidence-based metrics carries a particular risk of false conclusions when undersampled data are involved. Developing bias corrections for such metrics would be desirable. KW - Bray-Curtis KW - Chao KW - Effective number of species KW - Incomplete inventories KW - Jaccard KW - Macrolepidoptera KW - Morisita KW - Morisita-Horn KW - NESS KW - Norfolk Island Y1 - 2013 U6 - https://doi.org/10.1111/2041-210x.12023 SN - 2041-210X VL - 4 IS - 4 SP - 370 EP - 382 PB - Wiley-Blackwell CY - Hoboken ER -