Model of position-dynamic structure of river basins

In this work, we have presented semi automated means of modeling of position-dynamic structure (PDS) of river basins’ landscapes with application of geo-informational systems (GIS). Results of modeling were tested on the basin of one of headwaters. The structure of the model includes landscape lines, layers, sub-regions and regions. The model takes into account conditions of formation of landscape’s PDS in mountain and plain parts of river basinsyesБелгородский государственный университе

Projected climate change and its impacts on glaciers and water resources in the headwaters of the Tarim River, NW China/Kyrgyzstan

This study was conducted within the project SuMaRiO (Sustainable Management of River Oases along the Tarim River; http://www.sumario.de/), funded by the German Federal Ministry of Education and Research (BMBF grants 01LL0918J, 01LL0918I and 01LL0918B). T. Bolch acknowledges funding by Deutsche Forschungsgemeinschaft (DFG, BO3199/2–1). Open Access funding enabled and organized by Projekt DEAL.Glacierised river catchments are highly sensitive to climate change, while large populations may depend on their water resources. The irrigation agriculture and the communities along the Tarim River, NW China, strongly depend on the discharge from the glacierised catchments surrounding the Taklamakan Desert. While recent increasing discharge has been beneficial for the agricultural sector, future runoff under climate change is uncertain. We assess three climate change scenarios by forcing two glacio-hydrological models with output of eight general circulation models. The models have different glaciological modelling approaches but were both calibrated to discharge and glacier mass balance observations. Projected changes in climate, glacier cover and river discharge are examined over the twenty-first century and generally point to warmer and wetter conditions. The model ensemble projects median temperature and precipitation increases of + 1.9–5.3 °C and + 9–24%, respectively, until the end of the century compared to the 1971–2000 reference period. Glacier area is projected to shrink by 15–73% (model medians, range over scenarios), depending on the catchment. River discharge is projected to first increase by about 20% in the Aksu River catchments with subsequent decreases of up to 20%. In contrast, discharge in the drier Hotan and Yarkant catchments is projected to increase by 15–60% towards the end of the century. The large uncertainties mainly relate to the climate model ensemble and the limited observations to constrain the glacio-hydrological models. Sustainable water resource management will be key to avert the risks associated with the projected changes and their uncertainties.Publisher PDFPeer reviewe

On the dynamic nature of hydrological similarity

The increasing diversity and resolution of spatially distributed data on terrestrial systems greatly enhance the potential of hydrological modeling. Optimal and parsimonious use of these data sources requires, however, that we better understand (a) which system characteristics exert primary controls on hydrological dynamics and (b) to what level of detail do those characteristics need to be represented in a model. In this study we develop and test an approach to explore these questions that draws upon information theoretic and thermodynamic reasoning, using spatially distributed topographic information as a straightforward example. Specifically, we subdivide a mesoscale catchment into 105 hillslopes and represent each by a two-dimensional numerical hillslope model. These hillslope models differ exclusively with respect to topography-related parameters derived from a digital elevation model (DEM); the remaining setup and meteorological forcing for each are identical. We analyze the degree of similarity of simulated discharge and storage among the hillslopes as a function of time by examining the Shannon information entropy. We furthermore derive a “compressed” catchment model by clustering the hillslope models into functional groups of similar runoff generation using normalized mutual information (NMI) as a distance measure. Our results reveal that, within our given model environment, only a portion of the entire amount of topographic information stored within a digital elevation model is relevant for the simulation of distributed runoff and storage dynamics. This manifests through a possible compression of the model ensemble from the entire set of 105 hillslopes to only 6 hillslopes, each representing a different functional group, which leads to no substantial loss in model performance. Importantly, we find that the concept of hydrological similarity is not necessarily time invariant. On the contrary, the Shannon entropy as measure for diversity in the simulation ensemble shows a distinct annual pattern, with periods of highly redundant simulations, reflecting coherent and organized dynamics, and periods where hillslopes operate in distinctly different ways. We conclude that the proposed approach provides a powerful framework for understanding and diagnosing how and when process organization and functional similarity of hydrological systems emerge in time. Our approach is neither restricted to the model nor to model targets or the data source we selected in this study. Overall, we propose that the concepts of hydrological systems acting similarly (and thus giving rise to redundancy) or displaying unique functionality (and thus being irreplaceable) are not mutually exclusive. They are in fact of complementary nature, and systems operate by gradually changing to different levels of organization in time

Picturing and modeling catchments by representative hillslopes

This study explores the suitability of a single hillslope as a parsimonious representation of a catchment in a physically based model. We test this hypothesis by picturing two distinctly different catchments in perceptual models and translating these pictures into parametric setups of 2-D physically based hillslope models. The model parametrizations are based on a comprehensive field data set, expert knowledge and process-based reasoning. Evaluation against streamflow data highlights that both models predicted the annual pattern of streamflow generation as well as the hydrographs acceptably. However, a look beyond performance measures revealed deficiencies in streamflow simulations during the summer season and during individual rainfall–runoff events as well as a mismatch between observed and simulated soil water dynamics. Some of these shortcomings can be related to our perception of the systems and to the chosen hydrological model, while others point to limitations of the representative hillslope concept itself. Nevertheless, our results confirm that representative hillslope models are a suitable tool to assess the importance of different data sources as well as to challenge our perception of the dominant hydrological processes we want to represent therein. Consequently, these models are a promising step forward in the search for the optimal representation of catchments in physically based models

Picturing and modeling catchments by representative hillslopes

This study explores the suitability of a single hillslope as a parsimonious representation of a catchment in a physically based model. We test this hypothesis by picturing two distinctly different catchments in perceptual models and translating these pictures into parametric setups of 2-D physically based hillslope models. The model parametrizations are based on a comprehensive field data set, expert knowledge and process-based reasoning. Evaluation against streamflow data highlights that both models predicted the annual pattern of streamflow generation as well as the hydrographs acceptably. However, a look beyond performance measures revealed deficiencies in streamflow simulations during the summer season and during individual rainfall–runoff events as well as a mismatch between observed and simulated soil water dynamics. Some of these shortcomings can be related to our perception of the systems and to the chosen hydrological model, while others point to limitations of the representative hillslope concept itself. Nevertheless, our results confirm that representative hillslope models are a suitable tool to assess the importance of different data sources as well as to challenge our perception of the dominant hydrological processes we want to represent therein. Consequently, these models are a promising step forward in the search for the optimal representation of catchments in physically based models

Rock slope instability in alpine geomorphic systems, Switzerland

Faced with the hazard potential and geomorphic importance of rock slopes adjusting to glacier retreat and current climate warming, the motivation of this dissertation is to increase our systemic and process understanding of rock slope instability in alpine geomorphic systems. It is hypothesised that a deeper understanding of rock slope instability can be achieved by thinking and working across scales and accounting for the emergence of non-linear, complex rock slope systems. For this reason, a novel hierarchical methodological approach has been developed. The methodology integrates multivariate modelling and geomorphic field mapping at the valley-scale, rockwall-scale geotechnical, geomorphological and sedimentological field surveys in the Turtmann Valley and Swiss National Park as well as numerical frost cracking modelling and laboratory weathering simulations at the intact rock scale. By means of this multi-method and, most importantly, multiscale systems approach, some progress was made towards current research debates about (i) the key controls of rock slope instability in areas affected by glacier retreat, (ii) associated paraglacial and short-term rockfall activity and (iii) their geomorphic consequences for alpine sediment cascade systems.Felsinstabilitäten in alpinen geomorphologischen Systemen, Schweiz Die Instabilität von Felswänden ist ein komplexes Phänomen das in Zeit und Magnitude variiert. Vor allem in Hochgebirgsregionen sind Felsinstabilitäten von großer Relevanz für die langzeitliche Relieferosion und Landschaftsentwicklung, sowie für die Sedimentproduktion und Effizienz von alpinen Sedimentflüssen. Die damit verbundene Disposition von Sturzereignissen stellt zudem ein ernstzunehmendes Naturgefahrenpotenzial für Mensch und Infrastruktur dar. Untersuchungen zeigen weltweit, und speziell für die Schweizer Alpen, eine Zunahme von Felsinstabilitäten unterschiedlicher Magnituden in den letzten Jahrzehnten. Das komplexe Zusammenspiel von topoklimatischen, kryosphärischen und felsmechanischen Kontrollfaktoren, insbesondere in von Gletscherrückzug betroffenen alpinen Tälern, ist jedoch noch unzureichend verstanden. Folglich stehen nur begrenzt Informationen über die kurz- und langzeitlichen Konsequenzen von Felsinstabilitäten bezüglich Magnituden, Intensitäten und Frequenzen von Sturzprozessen in alpinen Kaskadensystem zur Verfügung. Angesichts dieser Wissenslücken hat diese Doktorarbeit zum Ziel unser System- und Prozessverständnis von alpinen Felsinstabilitäten auf unterschiedlichen Zeit- und Raumskalen zu vertiefen. Ein neuer multiskaliger methodologischer Ansatz wird entwickelt, welcher erlaubt die Skalenabhängigkeit und Emergenz von Felssystemen zu adressieren. Die Arbeit umfasst fünf empirische Studien auf unterschiedlichen räumlichen und zeitlichen Skalen mit Untersuchungsgebieten im Turtmanntal (Schweizer Waliser Alpen) und Schweizer National Park. Auf der größten und längsten Skale untersucht diese Arbeit Hauptkontrollfaktoren für die raumzeitliche Aktivität von Felsinstabilitäten in alpinen Tälern seit dem letzten Glazialen Maximum. Zum ersten Mal in der Sturzprozessforschung wird ein Random Forest Klassifikationsalgorithmus angewandt und durch die Kombination mit einem Hauptkomponenten-basierten, logistischen Regressionsmodell weiter entwickelt. Die Modellkombination zeigt auf, dass Permafrostdegradation im Laufe des Gletscherrückzugs einer der wichtigsten Kontrollfaktoren für die Instabilität entgletscherter Felswände darstellt. Mit Hilfe eines ergodischen Ansatzes werden drei Szenarien paraglazialer Felsanpassung entwickelt, welches nichtlineare tektonische und strukturelle Konditionierungen von Permafrostwänden berücksichtigt. Die Arbeit liefert zudem quantitative und qualitative Beweise für die geomorphologische Signifikanz von Felsinstabilitäten für Sedimentkaskaden in alpinen Einzugsgebieten. Die Kombination aus einem GIS-basierten Konnektivitätsmodell und einer detaillierten geomorphologischen Feldkartierung ermöglicht es Sedimentflüsse von instabilen Felswänden zum fluvialen System zu identifiziert und im Hinblick auf ihre Effizienz zu bewerten. Die feld- und modellierungsbasierten Beobachtungen zeigen eine Dominanz von Sturzprozesse kleiner bis mittlerer Magnitude. Allerdings wird deutlich, dass aktuell ein Drittel des gespeicherten Sturzmaterials aufgrund der glazialen Talmorphometrie vom Hauptkaskadensystem entkoppelt ist. Auf der Skale individueller Felswände analysiert diese Arbeit die Ursache-Wirkung Beziehung zwischen Felsverwitterung, Felsinstabilität sowie Materialspeicherung auf Schutthalden in drei vergletscherten Hängetälern. Ein neuer holistischer Ansatz wird vorgestellt, welcher abduktive Schutthaldenuntersuchungen mit deduktiven geotechnischen Kartierungen an Felswänden, einem zweijährigen Felstemperaturmonitoring und numerischer Frostverwitterungsmodellierung integriert. Dieser integrative Ansatz zeigt auf, dass die Komplexität aus Kluftabstand, der vorgegebenen Kinematik aus Haupttrennflächen sowie der tiefenvariierenden Intensität saisonaler Eissegregation wesentlich das jährlich-dekadische Frequenz-Magnituden Spektrum von Sturzprozessen steuert sowie, in Kombination mit Permafrostdegradation, die langzeitliche Variabilität von Sedimentproduktion und Formeigenschaften von Schutthalden kontrolliert. Auf der Skale des intakten Fels widmet sich diese Arbeit der Frage nach der individuellen und synergetischen Verwitterungseffizienz hochfrequenter thermaler Zyklen und täglicher Eiskristallisation in Glimmerschiefer geringer Porosität. Ein neuartiges zweiphasiges Laborexperiment liefert Evidenzen für mikroskalige, strukturabhängige Felsermüdung in Folge wiederholter Frostzyklen, insbesondere in Felsproben, welche zuvor einer Phase thermalen Stresses ausgesetzt waren. Die Langzeitmessungen zeigen sowohl positive als auch negative Feedbackeffekte im Laufe verändernder mechanischer Felseigenschaften. Diese Beobachtungen haben Implikationen für aktuelle Forschungsdebatte über die Rolle subkrtitischer Verwitterungsmechanismen für oberflächennahe Felsinstabilitäten. Diese Arbeit hebt hervor, dass geomorphologische Forschung dringend mehr Aufmerksamkeit auf die Quellgebiete in alpinen Systemen, also Felswände und ihre inhärenten Systemeigenschaften, richten muss. Zudem zeigen die Befunde dieser Arbeit auf, dass die Instabilität von Felswänden eine Skalenfrage ist. Jede räumliche und zeitliche Skale ist mit unterschiedlichen Kausalzusammenhängen und Erklärungen verbunden hinsichtlich Hauptkontrollfaktoren, raumzeitlicher Sturzprozessaktivität und geomorphologischen Effekten für Sedimentkaskaden. Um diese Skalenabhängigkeit und Nichtlinearität von Felssystemen zu adressieren, liefert diese Arbeit verschiedene praktische und philosophische Lösungsansätze für zukünftige Forschung