TY - THES A1 - Gräff, Thomas T1 - Soil moisture dynamics and soil moisture controlled runoff processes at different spatial scales : from observation to modelling T1 - Bodenfeuchtedynamik und deren Einfluss auf Abflussprozesse in unterschiedlichen Skalen : von der Beobachtung zur Modellierung N2 - Soil moisture is a key state variable that controls runoff formation, infiltration and partitioning of radiation into latent and sensible heat. However, the experimental characterisation of near surface soil moisture patterns and their controls on runoff formation remains a challenge. This subject was one aspect of the BMBF-funded OPAQUE project (operational discharge and flooding predictions in head catchments). As part of that project the focus of this dissertation is on: (1) testing the methodology and feasibility of the Spatial TDR technology in producing soil moisture profiles along TDR probes, including an inversion technique of the recorded signal in heterogeneous field soils, (2) the analysis of spatial variability and temporal dynamics of soil moisture at the field scale including field experiments and hydrological modelling, (3) the application of models of different complexity for understanding soil moisture dynamics and its importance for runoff generation as well as for improving the prediction of runoff volumes. To fulfil objective 1, several laboratory experiments were conducted to understand the influence of probe rod geometry and heterogeneities in the sampling volume under different wetness conditions. This includes a detailed analysis on how these error sources affect retrieval of soil moisture profiles in soils. Concerning objective 2 a sampling strategy of two TDR clusters installed in the head water of the Wilde Weißeritz catchment (Eastern Ore Mountains, Germany) was used to investigate how well “the catchment state” can be characterised by means of distributed soil moisture data observed at the field scale. A grassland site and a forested site both located on gentle slopes were instrumented with two Spatial TDR clusters that consist of up to 39 TDR probes. Process understanding was gained by modelling the interaction of evapotranspiration and soil moisture with the hydrological process model CATFLOW. A field scale irrigation experiment was carried out to investigate near subsurface processes at the hillslope scale. The interactions of soil moisture and runoff formation were analysed using discharge data from three nested catchments: the Becherbach with a size of 2 km², the Rehefeld catchment (17 km²) and the superordinate Ammelsdorf catchment (49 km²). Statistical analyses including observations of pre-event runoff, soil moisture and different rainfall characteristics were employed to predict stream flow volume. On the different scales a strong correlation between the average soil moisture and the runoff coefficients of rainfall-runoff events could be found, which almost explains equivalent variability as the pre-event runoff. Furthermore, there was a strong correlation between surface soil moisture and subsurface wetness with a hysteretic behaviour between runoff soil moisture. To fulfil objective 3 these findings were used in a generalised linear model (GLM) analysis which combines state variables describing the catchments antecedent wetness and variables describing the meteorological forcing in order to predict event runoff coefficients. GLM results were compared to simulations with the catchment model WaSiM ETH. Hereby were the model results of the GLMs always better than the simulations with WaSiM ETH. The GLM analysis indicated that the proposed sampling strategy of clustering TDR probes in typical functional units is a promising technique to explore soil moisture controls on runoff generation and can be an important link between the scales. Long term monitoring of such sites could yield valuable information for flood warning and forecasting by identifying critical soil moisture conditions for the former and providing a better representation of the initial moisture conditions for the latter. N2 - Abflussentwicklung, Infiltration und die Umverteilung von Strahlung in latenten und sensiblen Wärmestrom werden maßgeblich durch die Bodenfeuchte der vadosen Zone gesteuert. Trotz allem, gibt s wenig Arbeiten die sich mit der experimentellen Charakterisierung der Bodenfeuchteverteilung und ihre Auswirkung auf die Abflussbildung beschäftigen. Der Fokus dieser Dissertation wurde darauf ausgerichtet: (1) die Methode des Spatial TDR und deren Anwendbarkeit einschließlich der Inversion des TDR Signals in heterogenen Böden zu prüfen, (2) die Analyse der räumlichen und zeitlichen Dynamik der Bodenfeuchte auf der Feldskala einschließlich Feldexperimenten und hydrologischer Modellierung, (3) der Aufbau verschiedener Modellanwendungen unterschiedlicher Komplexität um die Bodenfeuchtedynamiken und die Abflussentwicklung zu verstehen und die Vorhersage des Abflussvolumens zu verbessern. Um die Zielsetzung 1 zu erreichen, wurden verschiedene Laborversuche durchgeführt. Hierbei wurde der Einfluss der Sondenstabgeometrie und verschiedener Heterogenitäten im Messvolumen bei verschiedenen Feuchtegehalten untersucht. Dies beinhaltete eine detaillierte Analyse wie diese Fehlerquellen die Inversion des Bodenfeuchteprofils beeinflussen. Betreffend der Zielsetzung 2, wurden 2 TDR-Cluster in den Quellgebieten der Wilden Weißeritz installiert (Osterzgebirge) und untersucht, wie gut der Gebietszustand mit räumlich hochaufgelösten Bodenfeuchtedaten der Feldskala charakterisiert werden kann. Um die Interaktion zwischen Evapotranspiration und Bodenfeuchte zu untersuchen wurde das hydrologische Prozessmodell CATFLOW angewendet. Ein Beregnungsversuch wurde durchgeführt um die Zwischenabflussprozesse auf der Hangskala zu verstehen. Die Interaktion zwischen Bodenfeuchte und Abflussentwicklung wurde anhand von drei einander zugeordneten Einzugsgebieten analysiert. Statistische Analysen unter Berücksichtigung von Basisabfluss, Bodenvorfeuchte und verschiedenen Niederschlagscharakteristika wurden verwendet, um auf das Abflussvolumen zu schließen. Auf den verschiedenen Skalen konnte eine hohe Korrelation zwischen der mittleren Bodenfeuchte und dem Abflussbeiwert der Einzelereignisse festgestellt werden. Hierbei konnte die Bodenfeuchte genauso viel Variabilität erklären wie der Basisabfluss. Im Hinblick auf Zielsetzung 3 wurden “Generalised liner models” (GLM) genutzt. Dabei wurden Prädiktorvariablen die den Gebietszustand beschreiben und solche die die Meteorologische Randbedingungen beschreiben genutzt um den Abflussbeiwert zu schätzen. Die Ergebnisse der GLMs wurden mit Simulationsergebnissen des hydrologischen Gebietsmodells WaSiM ETH verglichen. Hierbei haben die GLMs eindeutig bessere Ergebnisse geliefert gegenüber den WaSiM Simulationen. Die GLM Analysen haben aufgezeigt, dass die verwendete Messstrategie mehrerer TDR-Cluster in typischen funktionalen Einheiten eine viel versprechende Methode ist, um den Einfluss der Bodenfeuchte auf die Abflussentwicklung zu verstehen und ein Bindeglied zwischen den Skalen darstellen zu können. Langzeitbeobachtungen solcher Standorte sind in der Lage wichtige Zusatzinformationen bei der Hochwasserwarnung und -vorhersage zu liefern durch die Identifizierung kritischer Gebietszustände für erstere und eine bessere Repräsentation der Vorfeuchte für letztere. KW - Bodenfeuchte KW - TDR KW - Heterogenität KW - Einzugsgebiet KW - Gebietszustand KW - Soil moisture KW - TDR KW - heterogeneity KW - catchment KW - runoff KW - catchment state Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-54470 ER - TY - JOUR A1 - Breuer, Lutz A1 - Bormann, Helge A1 - Bronstert, Axel A1 - Croke, Barry F. W. A1 - Frede, Hans-Georg A1 - Gräff, Thomas A1 - Hubrechts, Lode A1 - Kite, Geoffrey A1 - Lanini, Jordan A1 - Leavesley, George A1 - Lettenmaier, Dennis P. A1 - Lindstroem, Goeran A1 - Seibert, Jan A1 - Sivapalan, Mayuran A1 - Viney, Neil R. A1 - Willems, Patrick T1 - Assessing the impact of land use change on hydrology by ensemble modeling (LUCHEM) III : scenario analysis N2 - An ensemble of 10 hydrological models was applied to the same set of land use change scenarios. There was general agreement about the direction of changes in the mean annual discharge and 90% discharge percentile predicted by the ensemble members, although a considerable range in the magnitude of predictions for the scenarios and catchments under consideration was obvious. Differences in the magnitude of the increase were attributed to the different mean annual actual evapotranspiration rates for each land use type. The ensemble of model runs was further analyzed with deterministic and probabilistic ensemble methods. The deterministic ensemble method based on a trimmed mean resulted in a single somewhat more reliable scenario prediction. The probabilistic reliability ensemble averaging (REA) method allowed a quantification of the model structure uncertainty in the scenario predictions. It was concluded that the use of a model ensemble has greatly increased our confidence in the reliability of the model predictions. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/03091708 U6 - https://doi.org/10.1016/j.advwatres.2008.06.009 SN - 0309-1708 ER - TY - JOUR A1 - Zehe, Erwin A1 - Gräff, Thomas A1 - Morgner, Markus A1 - Bauer, Andreas A1 - Bronstert, Axel T1 - Plot and field scale soil moisture dynamics and subsurface wetness control on runoff generation in a headwater in the Ore Mountains N2 - This study presents an application of an innovative sampling strategy to assess soil moisture dynamics in a headwater of the Weisseritz in the German eastern Ore Mountains. A grassland site and a forested site were instrumented with two Spatial TDR clusters (STDR) that consist of 39 and 32 coated TDR probes of 60 cm length. Distributed time series of vertically averaged soil moisture data from both sites/ensembles were analyzed by statistical and geostatistical methods. Spatial variability and the spatial mean at the forested site were larger than at the grassland site. Furthermore, clustering of TDR probes in combination with long-term monitoring allowed identification of average spatial covariance structures at the small field scale for different wetness states. The correlation length of soil water content as well as the sill to nugget ratio at the grassland site increased with increasing average wetness and but, in contrast, were constant at the forested site. As soil properties at both the forested and grassland sites are extremely variable, this suggests that the correlation structure at the forested site is dominated by the pattern of throughfall and interception. We also found a very strong correlation between antecedent soil moisture at the forested site and runoff coefficients of rainfall-runoff events observed at gauge Rehefeld. Antecedent soil moisture at the forest site explains 92% of the variability in the runoff coefficients. By combining these results with a recession analysis we derived a first conceptual model of the dominant runoff mechanisms operating in this catchment. Finally, we employed a physically based hydrological model to shed light on the controls of soil- and plant morphological parameters on soil average soil moisture at the forested site and the grassland site, respectively. A homogeneous soil setup allowed, after fine tuning of plant morphological parameters, most of the time unbiased predictions of the observed average soil conditions observed at both field sites. We conclude that the proposed sampling strategy of clustering TDR probes is suitable to assess unbiased average soil moisture dynamics in critical functional units, in this case the forested site, which is a much better predictor for event scale runoff formation than pre-event discharge. Long term monitoring of such critical landscape elements could maybe yield valuable information for flood warning in headwaters. We thus think that STDR provides a good intersect of the advantages of permanent sampling and spatially highly resolved soil moisture sampling using mobile rods. Y1 - 2010 UR - http://www.copernicus.org/EGU/hess/hess.html U6 - https://doi.org/10.5194/hess-14-873-2010 SN - 1027-5606 ER - TY - JOUR A1 - Zehe, Erwin A1 - Gräff, Thomas A1 - Morgner, Markus A1 - Bauer, Andreas A1 - Bronstert, Axel T1 - Plot and field scale soil moisture dynamics and subsurface wetness control on runoff generation in a headwater in the Ore Mountains N2 - This study presents an application of an innovative sampling strategy to assess soil moisture dynamics in a headwater of the Weißeritz in the German eastern Ore Mountains. A grassland site and a forested site were instrumented with two Spatial TDR clusters (STDR) that consist of 39 and 32 coated TDR probes of 60 cm length. Distributed time series of vertically averaged soil moisture data from both sites/ensembles were analyzed by statistical and geostatistical methods. Spatial variability and the spatial mean at the forested site were larger than at the grassland site. Furthermore, clustering of TDR probes in combination with long-term monitoring allowed identification of average spatial covariance structures at the small field scale for different wetness states. The correlation length of soil water content as well as the sill to nugget ratio at the grassland site increased with increasing average wetness and but, in contrast, were constant at the forested site. As soil properties at both the forested and grassland sites are extremely variable, this suggests that the correlation structure at the forested site is dominated by the pattern of throughfall and interception. We also found a strong correlation between average soil moisture dynamics and runoff coefficients of rainfall-runoff events observed at gauge Rehefeld, which explains almost as much variability in the runoff coefficients as pre-event discharge. By combining these results with a recession analysis we derived a first conceptual model of the dominant runoff mechanisms operating in this catchment. Finally, long term simulations with a physically based hydrological model were in good/acceptable accordance with the time series of spatial average soil water content observed at the forested site and the grassland site, respectively. Both simulations used a homogeneous soil setup that closely reproduces observed average soil conditions observed at the field sites. This corroborates the proposed sampling strategy of clustering TDR probes in typical functional units is a promising technique to explore the soil moisture control on runoff generation. Long term monitoring of such sites could maybe yield valuable information for flood warning. The sampling strategy helps furthermore to unravel different types of soil moisture variability. Y1 - 2008 ER - TY - JOUR A1 - Bormann, Helge A1 - Breuer, Lutz A1 - Graff, Thomas A1 - Croke, Barry T1 - Assessing the impact of land use change on hydrology by ensemble modelling (LUCHEM) IV : model sensitivity to data aggregation and spatial (re-)distribution N2 - This paper analyses the effect of spatial resolution and distribution of model input data on the results of regional-scale land use scenarios using three different hydrological catchment models. A 25 m resolution data set of a mesoscale catchment and three land use scenarios are used. Data are systematically aggregated to resolutions up to 2 kill. Land use scenarios are spatially redistributed, both randomly and topography based. Using these data, water fluxes are calculated on a daily time step for a 16 year time period without further calibration. Simulation results are used to identify grid size, distribution and model dependent scenario effects. In the case of data aggregation, all applied models react sensitively to grid size. WASIM and TOPLATS simulate constant water balances for grid sizes from 50 m to 300-500 m, SWAT is more sensitive to input data aggregation, simulating constant water balances between 50 m and 200 m grid size. The calculation of scenario effects is less robust to data aggregation. The maximum acceptable grid size reduces to 200-300 m for TOPLATS and WASIM. In case of spatial distribution, SWAT and TOPLATS are slightly sensitive to a redistribution of land use (below 1.5% for water balance terms), whereas WASIM shows almost no reaction. Because the aggregation effects were stronger than the redistribution effects, it is concluded that spatial discretisation is more important than spatial distribution. As the aggregation effect was mainly associated with a change in land use fraction, it is concluded that accuracy of data sets is much more important than a high spatial resolution. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/03091708 U6 - https://doi.org/10.1016/j.advwatres.2008.01.002 SN - 0309-1708 ER - TY - JOUR A1 - Gräff, Thomas A1 - Zehe, Erwin A1 - Schläger, Stefan A1 - Morgner, Markus A1 - Bauer, Andreas A1 - Becker, Rolf A1 - Creutzfeldt, Benjamin A1 - Bronstert, Axel T1 - A quality assessment of spatial TDR soil moisture measurements in homogenous and heterogeneous media with laboratory experiments N2 - Investigation of transient soil moisture profiles yields valuable information of near- surface processes. A recently developed reconstruction algorithm based on the telegraph equation allows the inverse estimation of soil moisture profiles along coated, three rod TDR probes. Laboratory experiments were carried out to prove the results of the inversion and to understand the influence of probe rod deformation and solid objects close to the probe in heterogonous media. Differences in rod geometry can lead to serious misinterpretations in the soil moisture profile but have small influence on the average soil moisture along the probe. Solids in the integration volume have almost no effect on average soil moisture but result in locally slightly decreased moisture values. Inverted profiles obtained in a loamy soil with a clay content of about 16% were in good agreement with independent measurements. Y1 - 2010 UR - http://www.hydrol-earth-syst-sci-discuss.net/volumes_and_issues.html U6 - https://doi.org/10.5194/hessd-7-269-2010 SN - 1812-2108 ER - TY - JOUR A1 - Gräff, Thomas A1 - Zehe, Erwin A1 - Schlaeger, Stefan A1 - Morgner, Markus A1 - Bauer, Andreas A1 - Becker, Rolf A1 - Creutzfeldt, Benjamin A1 - Bronstert, Axel T1 - A quality assessment of Spatial TDR soil moisture measurements in homogenous and heterogeneous media with laboratory experiments N2 - Investigation of transient soil moisture profiles yields valuable information of near- surface processes. A recently developed reconstruction algorithm based on the telegraph equation allows the inverse estimation of soil moisture profiles along coated, three rod TDR probes. Laboratory experiments were carried out to prove the results of the inversion and to understand the influence of probe rod deformation and solid objects close to the probe in heterogeneous media. Differences in rod geometry can lead to serious misinterpretations in the soil moisture profile, but have small influence on the average soil moisture along the probe. Solids in the integration volume have almost no effect on average soil moisture, but result in locally slightly decreased moisture values. Inverted profiles obtained in a loamy soil with a clay content of about 16% were in good agreement with independent measurements. Y1 - 2010 UR - http://www.copernicus.org/EGU/hess/hess.html U6 - https://doi.org/10.5194/hess-14-1007-2010 SN - 1027-5606 ER - TY - JOUR A1 - Bronstert, Axel A1 - Creutzfeldt, Benjamin A1 - Gräff, Thomas A1 - Hajnsek, Irena A1 - Heistermann, Maik A1 - Itzerott, Sibylle A1 - Jagdhuber, Thomas A1 - Kneis, David A1 - Lueck, Erika A1 - Reusser, Dominik A1 - Zehe, Erwin T1 - Potentials and constraints of different types of soil moisture observations for flood simulations in headwater catchments JF - Natural hazards : journal of the International Society for the Prevention and Mitigation of Natural Hazards N2 - Flood generation in mountainous headwater catchments is governed by rainfall intensities, by the spatial distribution of rainfall and by the state of the catchment prior to the rainfall, e. g. by the spatial pattern of the soil moisture, groundwater conditions and possibly snow. The work presented here explores the limits and potentials of measuring soil moisture with different methods and in different scales and their potential use for flood simulation. These measurements were obtained in 2007 and 2008 within a comprehensive multi-scale experiment in the Weisseritz headwater catchment in the Ore-Mountains, Germany. The following technologies have been applied jointly thermogravimetric method, frequency domain reflectometry (FDR) sensors, spatial time domain reflectometry (STDR) cluster, ground-penetrating radar (GPR), airborne polarimetric synthetic aperture radar (polarimetric SAR) and advanced synthetic aperture radar (ASAR) based on the satellite Envisat. We present exemplary soil measurement results, with spatial scales ranging from point scale, via hillslope and field scale, to the catchment scale. Only the spatial TDR cluster was able to record continuous data. The other methods are limited to the date of over-flights (airplane and satellite) or measurement campaigns on the ground. For possible use in flood simulation, the observation of soil moisture at multiple scales has to be combined with suitable hydrological modelling, using the hydrological model WaSiM-ETH. Therefore, several simulation experiments have been conducted in order to test both the usability of the recorded soil moisture data and the suitability of a distributed hydrological model to make use of this information. The measurement results show that airborne-based and satellite-based systems in particular provide information on the near-surface spatial distribution. However, there are still a variety of limitations, such as the need for parallel ground measurements (Envisat ASAR), uncertainties in polarimetric decomposition techniques (polarimetric SAR), very limited information from remote sensing methods about vegetated surfaces and the non-availability of continuous measurements. The model experiments showed the importance of soil moisture as an initial condition for physically based flood modelling. However, the observed moisture data reflect the surface or near-surface soil moisture only. Hence, only saturated overland flow might be related to these data. Other flood generation processes influenced by catchment wetness in the subsurface such as subsurface storm flow or quick groundwater drainage cannot be assessed by these data. One has to acknowledge that, in spite of innovative measuring techniques on all spatial scales, soil moisture data for entire vegetated catchments are still today not operationally available. Therefore, observations of soil moisture should primarily be used to improve the quality of continuous, distributed hydrological catchment models that simulate the spatial distribution of moisture internally. Thus, when and where soil moisture data are available, they should be compared with their simulated equivalents in order to improve the parameter estimates and possibly the structure of the hydrological model. KW - Soil moisture KW - Remote sensing KW - Hydrological modelling KW - Flood forecasting KW - Soil moisture measurement comparison Y1 - 2012 U6 - https://doi.org/10.1007/s11069-011-9874-9 SN - 0921-030X SN - 1573-0840 VL - 60 IS - 3 SP - 879 EP - 914 PB - Springer CY - New York ER - TY - JOUR A1 - Viney, Neil R. A1 - Bormann, Helge A1 - Breuer, Lutz A1 - Bronstert, Axel A1 - Croke, Barry F. W. A1 - Frede, Hans-Georg A1 - Gräff, Thomas A1 - Hubrechts, Lode A1 - Huisman, Johan A. A1 - Jakeman, Anthony J. A1 - Kite, Geoffrey W. A1 - Lanini, Jordan A1 - Leavesley, George A1 - Lettenmaier, Dennis P. A1 - Lindstroem, Goeran A1 - Seibert, Jan A1 - Sivapalan, Murugesu A1 - Willems, Patrick T1 - Assessing the impact of land use change on hydrology by ensemble modelling (LUCHEM) II : ensemble combinations and predictions N2 - This paper reports on a project to compare predictions from a range of catchment models applied to a mesoscale river basin in central Germany and to assess various ensemble predictions of catchment streamflow. The models encompass a large range in inherent complexity and input requirements. In approximate order of decreasing complexity, they are DHSVM, MIKE-SHE, TOPLATS, WASIM-ETH, SWAT, PRMS, SLURP, HBV, LASCAM and IHACRES. The models are calibrated twice using different sets of input data. The two predictions from each model are then combined by simple averaging to produce a single-model ensemble. The 10 resulting single-model ensembles are combined in various ways to produce multi-model ensemble predictions. Both the single-model ensembles and the multi-model ensembles are shown to give predictions that are generally superior to those of their respective constituent models, both during a 7-year calibration period and a 9- year validation period. This occurs despite a considerable disparity in performance of the individual models. Even the weakest of models is shown to contribute useful information to the ensembles they are part of. The best model combination methods are a trimmed mean (constructed using the central four or six predictions each day) and a weighted mean ensemble (with weights calculated from calibration performance) that places relatively large weights on the better performing models. Conditional ensembles. in which separate model weights are used in different system states (e.g. summer and winter, high and low flows) generally yield little improvement over the weighted mean ensemble. However a conditional ensemble that discriminates between rising and receding flows shows moderate improvement. An analysis of ensemble predictions shows that the best ensembles are not necessarily those containing the best individual models. Conversely, it appears that some models that predict well individually do not necessarily combine well with other models in multi-model ensembles. The reasons behind these observations may relate to the effects of the weighting schemes, non- stationarity of the climate series and possible cross-correlations between models. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/03091708 U6 - https://doi.org/10.1016/j.advwatres.2008.05.006 SN - 0309-1708 ER - TY - JOUR A1 - Breuer, Lutz A1 - Willems, Patrick A1 - Bormann, Helge A1 - Bronstert, Axel A1 - Croke, Barry A1 - Frede, Hans Georg A1 - Gräff, Thomas A1 - Hubrechts, Lode A1 - Kite, Geoffrey A1 - Lanini, Jordan A1 - Leavesley, George A1 - Lettenmaier, Dennis P. A1 - Lindstroem, Goeran A1 - Seibert, Jan A1 - Sivapalan, Mayuran A1 - Viney, Neil R. T1 - Assessing the impact of land use change on hydrology by ensemble modeling (LUCHEM) : I: model intercomparison with current land use N2 - This paper introduces the project on 'Assessing the impact of land use change on hydrology by ensemble modeling (LUCHEM)' that aims at investigating the envelope of predictions on changes in hydrological fluxes due to land use change. As part of a series of four papers, this paper outlines the motivation and setup of LUCHEM, and presents a model intercomparison for the present-day simulation results. Such an intercomparison provides a valuable basis to investigate the effects of different model structures on model predictions and paves the ground for the analysis of the performance of multi-model ensembles and the reliability of the scenario predictions in companion papers. in this study, we applied a set of 10 lumped, semi-lumped and fully distributed hydrological models that have been previously used in land use change studies to the low mountainous Dill catchment. Germany. Substantial differences in model performance were observed with Nash-Sutcliffe efficiencies ranging from 0.53 to 0.92. Differences in model performance were attributed to (1) model input data, (2) model calibration and (3) the physical basis of the models. The models were applied with two sets of input data: an original and a homogenized data set. This homogenization of precipitation, temperature and leaf area index was performed to reduce the variation between the models. Homogenization improved the comparability of model simulations and resulted in a reduced average bias, although some variation in model data input remained. The effect of the physical differences between models on the long-term water balance was mainly attributed to differences in how models represent evapotranspiration. Semi-lumped and lumped conceptual models slightly outperformed the fully distributed and physically based models. This was attributed to the automatic model calibration typically used for this type of models. Overall, however, we conclude that there was no superior model if several measures of model performance are considered and that all models are suitable to participate in further multi-model ensemble set-ups and land use change scenario investigations. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/03091708 U6 - https://doi.org/10.1016/j.advwatres.2008.10.003 SN - 0309-1708 ER - TY - JOUR A1 - Gräff, Thomas A1 - Zehe, Erwin A1 - Reusser, Dominik A1 - Lueck, Erika A1 - Schroeder, Boris A1 - Wenk, Gerald A1 - John, Hermann A1 - Bronstert, Axel T1 - Process identification through rejection of model structures in a mid-mountainous rural catchment : observations of rainfall-runoff response, geophysical conditions and model inter-comparison N2 - The intention of the presented study is to gain a better understanding of the mechanisms that caused the bimodal rainfall-runoff responses which occurred up to the mid-1970s regularly in the Schafertal catchment and vanished after the onset of mining activities. Understanding, this process is a first step to understanding the ongoing hydrological change in this area. It is hypothesized that either subsurface stormflow, or fast displacement of groundwater, could cause the second delayed peak. A top-down analysis of rainfall-runoff data, field observations as well as process modelling are combined within a rejectionistic framework. A statistical analysis is used to test whether different predictors. which characterize the forcing. near surface water content and deeper subsurface store, allow the prediction of the type of rainfall-runoff response. Regression analysis is used with generalized linear models Lis they can deal with non-Gaussian error distributions Lis well its a non-stationary variance. The analysis reveals that the dominant predictors are the pre-event discharge (proxy of state of the groundwater store) and the precipitation amount, In the field campaign, the subsurface at a representative hillslope was investigated by means of electrical resistivity tomography in order to identify possible strata as flow paths for subsurface stormflow. A low resistivity in approximately 4 in depth-either due to a less permeable layer or the groundwater surface-was detected. The former Could serve as a flow path for subsurface stormflow. Finally, the physical-based hydrological model CATFLOW and the groundwater model FEFLOW are compared with respect to their ability to reproduce the bimodal runoff responses. The groundwater model is able to reproduce the observations, although it uses only an abstract representation of the hillslopes. Process model analysis as well Lis statistical analysis strongly suggest that fast displacement of groundwater is the dominant process underlying the bimodal runoff reactions. Y1 - 2009 UR - http://www3.interscience.wiley.com/journal/4125/home U6 - https://doi.org/10.1002/Hyp.7171 SN - 0885-6087 ER - TY - JOUR A1 - Eberhard, Julius A1 - Schaik, N. Loes M. B. A1 - Schibalski, Anett A1 - Gräff, Thomas T1 - Simulating future salinity dynamics in a coastal marshland under different climate scenarios JF - Vadose zone journal N2 - Salinization is a well-known problem in agricultural areas worldwide. In the last 20-30 yr, rising salinity in the upper, unconfined aquifer has been observed in the Freepsumer Meer, a grassland near the German North Sea coast. For investigating long-term development of salinity and water balance during 1961-2099, the one-dimensional Soil-Water-Atmosphere-Plant (SWAP) model was set up and calibrated for a soil column in the area. The model setup involves a deep aquifer as the source of salt through upward seepage. In the vertical salt transport equation, dispersion and advection are included. Six different regional outputs of statistical downscaling methods were used as climate scenarios. These comprise different rates of increasing surface temperature and different trends in seasonal rainfall. The simulation results exhibit opposing salinity trends for topsoil and deeper layers. Although projections of some scenarios entail decreasing salinities near the surface, most of them project a rise in subsoil salinity, with the strongest trends of up to +0.9 mg cm(-3) 100 yr(-1) at -65 cm. The results suggest that topsoil salinity trends in the study area are affected by the magnitude of winter rainfall trends, whereas high subsoil salinities correspond to low winter rainfall and high summer temperature. How these projected trends affect the vegetation and thereby future land use will depend on the future management of groundwater levels in the area. Y1 - 2020 U6 - https://doi.org/10.1002/vzj2.20008 SN - 1539-1663 VL - 19 IS - 1 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Philips, Andrea A1 - Walz, Ariane A1 - Bergner, Andreas G. N. A1 - Gräff, Thomas A1 - Heistermann, Maik A1 - Kienzler, Sarah A1 - Korup, Oliver A1 - Lipp, Torsten A1 - Schwanghart, Wolfgang A1 - Zeilinger, Gerold T1 - Immersive 3D geovisualization in higher education JF - Journal of geography in higher education N2 - In this study, we investigate how immersive 3D geovisualization can be used in higher education. Based on MacEachren and Kraak's geovisualization cube, we examine the usage of immersive 3D geovisualization and its usefulness in a research-based learning module on flood risk, called GEOSimulator. Results of a survey among participating students reveal benefits, such as better orientation in the study area, higher interactivity with the data, improved discourse among students and enhanced motivation through immersive 3D geovisualization. This suggests that immersive 3D visualization can effectively be used in higher education and that 3D CAVE settings enhance interactive learning between students. KW - immersive 3D geovisualization KW - 3D CAVE KW - higher education KW - learning success KW - student survey KW - flood risk Y1 - 2015 U6 - https://doi.org/10.1080/03098265.2015.1066314 SN - 0309-8265 SN - 1466-1845 VL - 39 IS - 3 SP - 437 EP - 449 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Wang, Wei-shi A1 - Oswald, Sascha Eric A1 - Gräff, Thomas A1 - Lensing, Hermann Josef A1 - Liu, Tie A1 - Strasser, Daniel A1 - Munz, Matthias T1 - Impact of river reconstruction on groundwater flow during bank filtration assessed by transient three-dimensional modelling of flow and heat transport JF - Hydrogeology journal : official journal of the International Association of Hydrogeologists N2 - Bank filtration (BF) is an established indirect water-treatment technology. The quality of water gained via BF depends on the subsurface capture zone, the mixing ratio (river water versus ambient groundwater), spatial and temporal distribution of subsurface travel times, and subsurface temperature patterns. Surface-water infiltration into the adjacent aquifer is determined by the local hydraulic gradient and riverbed permeability, which could be altered by natural clogging, scouring and artificial decolmation processes. The seasonal behaviour of a BF system in Germany, and its development during and about 6 months after decolmation (canal reconstruction), was observed with a long-term monitoring programme. To quantify the spatial and temporal variation in the BF system, a transient flow and heat transport model was implemented and two model scenarios, 'with' and 'without' canal reconstruction, were generated. Overall, the simulated water heads and temperatures matched those observed. Increased hydraulic connection between the canal and aquifer caused by the canal reconstruction led to an increase of similar to 23% in the already high share of BF water abstracted by the nearby waterworks. Subsurface travel-time distribution substantially shifted towards shorter travel times. Flow paths with travel times <200 days increased by similar to 10% and those with <300 days by 15%. Generally, the periodic temperature signal, and the summer and winter temperature extrema, increased and penetrated deeper into the aquifer. The joint hydrological and thermal effects caused by the canal reconstruction might increase the potential of biodegradable compounds to further penetrate into the aquifer, also by potentially affecting the redox zonation in the aquifer. KW - bank filtration KW - groundwater KW - surface-water relations KW - groundwater modelling Y1 - 2019 U6 - https://doi.org/10.1007/s10040-019-02063-3 SN - 1431-2174 SN - 1435-0157 VL - 28 IS - 2 SP - 723 EP - 743 PB - Springer CY - Berlin ; Heidelberg [u.a.] ER - TY - JOUR A1 - Miegel, Konrad A1 - Gräff, Thomas A1 - Franck, Christian A1 - Salzmann, Thomas A1 - Bronstert, Axel A1 - Walther, Marc A1 - Oswald, Sascha Eric T1 - Auswirkungen des Sturmhochwassers der Ostsee am 4./5. Januar 2017 auf das renaturierte Nieder- moor „Hütelmoor und Heiligensee“ an der deut- schen Ostseeküste BT - Effects of the January 4/5 2017 storm surge on a restored fen at the German Baltic Sea coast JF - Hydrologie und Wasserbewirtschaftung N2 - Entlang der Küstenniederung des Naturschutzgebietes „Hütelmoor und Heiligensee“, ca. 6 km nordöstlich von Rostock-Warnemünde gelegen, wird seit dem Jahr 2000 die Küstendüne nicht mehr instand gehalten. Im Rahmen der Renaturierung des Gebietes werden so grundsätzlich wieder Überflutungen bei Ostseehochwassern zugelassen, was bisher jedoch noch nicht eingetreten ist. Am 4./5. Januar 2017 ereignete sich ein Sturmhochwasser der Ostsee, mit einem Scheitelwasserstand in Warnemünde, der sich zwischen dem 10- und 20-jährlichen Hochwasserstand einordnet. Dennoch kam es bei diesem Ereignis nicht zum Dünendurchbruch und zur seeseitigen Überflutung, wohl aber zum binnenseitigen Einstrom von Salz- bzw. Brackwasser. Dieser erfolgte über den Graben, durch den das Gebiet normalerweise über die Warnow in die Ostsee entwässert. Durch das Einströmen über die Sohlschwelle, sonst Auslass des Gebietes, stiegen die Wasserstände und Salzkonzentrationen in der südwestlichen Hälfte der Niederung an. Mit zunehmender Entfernung zur Sohlschwelle waren diese Auswirkungen jedoch geringer spürbar. Dies gilt wegen der Retentionswirkung der Niederung mehr für den Wasserstand als für die Salzkonzentration. Während der Wasserstand durch den Einstau der Niederung und Überschwemmungen flächenhaft anstieg, breitete sich die Salzfront präferentiell in den ehemaligen Entwässerungsgräben, die trotz des Einstaus nach wie vor hydraulisch aktiv sind, eher linienhaft aus. Diese Interpretation beruht auf Messergebnissen von Wasserstand, elektrischer Leitfähigkeit und Wassertemperatur. N2 - Maintenance and repair of the coastal dunes of the conservation area, Hutelmoor und Heiligensee" have been ceased for renaturation purposes since the year 2000 to aid flooding of the area during high water levels of the Baltic Sea. On January 4th and 5th 2017, the Baltic Sea experienced a storm surge resulting in a water level in Warnemunde with a 10-to 20-year reoccurrence rate. Nevertheless, the event caused neither a dune failure nor a sea-sided flooding, but did result in an upstream inflow of salt and brackwater through the trench which normally drains the area into the Baltic Sea via the Warnow. Water levels and salinity concentrations rose in the south-western part of the area due to the influx via a ground sill, which normally acts as the outlet of the lowland. The effects within the lowland were less pronounced with increasing distance to the ground sill, which proved to be even more significant for the water levels than for salinities due to the retention capabilities of the area. While water levels increased extensively as a result of the flooding, the salinity front is presumed to have spread primarily along the former draining channels. This interpretation is based on monitoring data of the water level as well as the environmental tracers electrical conductivity and water temperature. KW - Baltic Sea KW - storm surge KW - coastal lowland KW - flooding KW - salinization KW - environmental tracer KW - process analysis KW - Ostsee KW - Sturmhochwasser KW - Küstenniederung KW - Überflutung KW - Versalzung KW - Umwelttracer KW - Prozessgeschehen Y1 - 2017 U6 - https://doi.org/10.5675/HyWa_2017,4_2 SN - 1439-1783 VL - 61 IS - 4 SP - 232 EP - 243 PB - Bundesanst. für Gewässerkunde CY - Koblenz ER - TY - JOUR A1 - Creutzfeldt, Benjamin A1 - Troch, Peter A. A1 - Guentner, Andreas A1 - Ferre, Ty P. A. A1 - Gräff, Thomas A1 - Merz, Bruno T1 - Storage-discharge relationships at different catchment scales based on local high-precision gravimetry JF - Hydrological processes N2 - In hydrology, the storage-discharge relationship is a fundamental catchment property. Understanding what controls this relationship is at the core of catchment science. To date, there are no direct methods to measure water storage at catchment scales (10(1)-10(3)km(2)). In this study, we use direct measurements of terrestrial water storage dynamics by means of superconducting gravimetry in a small headwater catchment of the Regen River, Germany, to derive empirical storage-discharge relationships in nested catchments of increasing scale. Our results show that the local storage measurements are strongly related to streamflow dynamics at larger scales (> 100km(2); correlation coefficient=0.78-0.81), but at small scale, no such relationship exists (similar to 1km(2); correlation coefficients=-0.11). The geologic setting in the region can explain both the disconnection between local water storage and headwater runoff, and the connectivity between headwater storage and streams draining larger catchment areas. More research is required to understand what controls the form of the observed storage-discharge relationships at the catchment scale. This study demonstrates that high-precision gravimetry can provide new insights into the complex relationship between state and response of hydrological systems. KW - water storage KW - high-precision gravimeter KW - storage-discharge relationship KW - nested catchments Y1 - 2014 U6 - https://doi.org/10.1002/hyp.9689 SN - 0885-6087 SN - 1099-1085 VL - 28 IS - 3 SP - 1465 EP - 1475 PB - Wiley-Blackwell CY - Hoboken ER - TY - GEN A1 - Kormann, Christoph A1 - Bronstert, Axel A1 - Francke, Till A1 - Recknagel, Thomas A1 - Gräff, Thomas T1 - Model-Based attribution of high-resolution streamflow trends in two alpine basins of Western Austria N2 - Several trend studies have shown that hydrological conditions are changing considerably in the Alpine region. However, the reasons for these changes are only partially understood and trend analyses alone are not able to shed much light. Hydrological modelling is one possible way to identify the trend drivers, i.e., to attribute the detected streamflow trends, given that the model captures all important processes causing the trends. We modelled the hydrological conditions for two alpine catchments in western Austria (a large, mostly lower-altitude catchment with wide valley plains and a nested high-altitude, glaciated headwater catchment) with the distributed, physically-oriented WaSiM-ETH model, which includes a dynamical glacier module. The model was calibrated in a transient mode, i.e., not only on several standard goodness measures and glacier extents, but also in such a way that the simulated streamflow trends fit with the observed ones during the investigation period 1980 to 2007. With this approach, it was possible to separate streamflow components, identify the trends of flow components, and study their relation to trends in atmospheric variables. In addition to trends in annual averages, highly resolved trends for each Julian day were derived, since they proved powerful in an earlier, data-based attribution study. We were able to show that annual and highly resolved trends can be modelled sufficiently well. The results provide a holistic, year-round picture of the drivers of alpine streamflow changes: Higher-altitude catchments are strongly affected by earlier firn melt and snowmelt in spring and increased ice melt throughout the ablation season. Changes in lower-altitude areas are mostly caused by earlier and lower snowmelt volumes. All highly resolved trends in streamflow and its components show an explicit similarity to the local temperature trends. Finally, results indicate that evapotranspiration has been increasing in the lower altitudes during the study period. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 364 KW - trend attribution KW - trend detection KW - climate change KW - trend drivers KW - hydrological modelling KW - alpine catchments KW - streamflow KW - hydroclimatology Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-400641 ER - TY - JOUR A1 - Müller, Eva Nora A1 - van Schaik, Loes A1 - Blume, Theresa A1 - Bronstert, Axel A1 - Carus, Jana A1 - Fleckenstein, Jan H. A1 - Fohrer, Nicola A1 - Geissler, Katja A1 - Gerke, Horst H. A1 - Gräff, Thomas A1 - Hesse, Cornelia A1 - Hildebrandt, Anke A1 - Hölker, Franz A1 - Hunke, Philip A1 - Körner, Katrin A1 - Lewandowski, Jörg A1 - Lohmann, Dirk A1 - Meinikmann, Karin A1 - Schibalski, Anett A1 - Schmalz, Britta A1 - Schröder-Esselbach, Boris A1 - Tietjen, Britta T1 - Scales, key aspects, feedbacks and challenges of ecohydrological research in Germany JF - Hydrologie und Wasserbewirtschaftung N2 - Ecohydrology analyses the interactions of biotic and abiotic aspects of our ecosystems and landscapes. It is a highly diverse discipline in terms of its thematic and methodical research foci. This article gives an overview of current German ecohydrological research approaches within plant-animal-soil-systems, meso-scale catchments and their river networks, lake systems, coastal areas and tidal rivers. It discusses their relevant spatial and temporal process scales and different types of interactions and feedback dynamics between hydrological and biotic processes and patterns. The following topics are considered key challenges: innovative analysis of the interdisciplinary scale continuum, development of dynamically coupled model systems, integrated monitoring of coupled processes at the interface and transition from basic to applied ecohydrological science to develop sustainable water and land resource management strategies under regional and global change. KW - Coastal regions KW - drylands KW - ecohydrological modelling KW - feedback KW - hyporheic zone KW - meso-scale ecosystems KW - plant-animal-soil-system KW - river networks Y1 - 2014 U6 - https://doi.org/10.5675/HyWa_2014,4_2 SN - 1439-1783 VL - 58 IS - 4 SP - 221 EP - 240 PB - Bundesanst. für Gewässerkunde CY - Koblenz ER -