@article{BreuerBormannBronstertetal.2009, author = {Breuer, Lutz and Bormann, Helge and Bronstert, Axel and Croke, Barry F. W. and Frede, Hans-Georg and Gr{\"a}ff, Thomas and Hubrechts, Lode and Kite, Geoffrey and Lanini, Jordan and Leavesley, George and Lettenmaier, Dennis P. and Lindstroem, Goeran and Seibert, Jan and Sivapalan, Mayuran and Viney, Neil R. and Willems, Patrick}, title = {Assessing the impact of land use change on hydrology by ensemble modeling (LUCHEM) III : scenario analysis}, issn = {0309-1708}, doi = {10.1016/j.advwatres.2008.06.009}, year = {2009}, abstract = {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.}, language = {en} } @article{BreuerWillemsBormannetal.2009, author = {Breuer, Lutz and Willems, Patrick and Bormann, Helge and Bronstert, Axel and Croke, Barry and Frede, Hans Georg and Gr{\"a}ff, Thomas and Hubrechts, Lode and Kite, Geoffrey and Lanini, Jordan and Leavesley, George and Lettenmaier, Dennis P. and Lindstroem, Goeran and Seibert, Jan and Sivapalan, Mayuran and Viney, Neil R.}, title = {Assessing the impact of land use change on hydrology by ensemble modeling (LUCHEM) : I: model intercomparison with current land use}, issn = {0309-1708}, doi = {10.1016/j.advwatres.2008.10.003}, year = {2009}, abstract = {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.}, language = {en} } @article{BronstertCreutzfeldtGraeffetal.2012, author = {Bronstert, Axel and Creutzfeldt, Benjamin and Gr{\"a}ff, Thomas and Hajnsek, Irena and Heistermann, Maik and Itzerott, Sibylle and Jagdhuber, Thomas and Kneis, David and Lueck, Erika and Reusser, Dominik and Zehe, Erwin}, title = {Potentials and constraints of different types of soil moisture observations for flood simulations in headwater catchments}, series = {Natural hazards : journal of the International Society for the Prevention and Mitigation of Natural Hazards}, volume = {60}, journal = {Natural hazards : journal of the International Society for the Prevention and Mitigation of Natural Hazards}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0921-030X}, doi = {10.1007/s11069-011-9874-9}, pages = {879 -- 914}, year = {2012}, abstract = {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.}, language = {en} } @article{CreutzfeldtTrochGuentneretal.2014, author = {Creutzfeldt, Benjamin and Troch, Peter A. and Guentner, Andreas and Ferre, Ty P. A. and Gr{\"a}ff, Thomas and Merz, Bruno}, title = {Storage-discharge relationships at different catchment scales based on local high-precision gravimetry}, series = {Hydrological processes}, volume = {28}, journal = {Hydrological processes}, number = {3}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0885-6087}, doi = {10.1002/hyp.9689}, pages = {1465 -- 1475}, year = {2014}, abstract = {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.}, language = {en} } @article{EberhardSchaikSchibalskietal.2020, author = {Eberhard, Julius and Schaik, N. Loes M. B. and Schibalski, Anett and Gr{\"a}ff, Thomas}, title = {Simulating future salinity dynamics in a coastal marshland under different climate scenarios}, series = {Vadose zone journal}, volume = {19}, journal = {Vadose zone journal}, number = {1}, publisher = {Wiley}, address = {Hoboken}, issn = {1539-1663}, doi = {10.1002/vzj2.20008}, pages = {15}, year = {2020}, abstract = {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.}, language = {en} } @article{GraeffZeheReusseretal.2009, author = {Gr{\"a}ff, Thomas and Zehe, Erwin and Reusser, Dominik and Lueck, Erika and Schroeder, Boris and Wenk, Gerald and John, Hermann and Bronstert, Axel}, title = {Process identification through rejection of model structures in a mid-mountainous rural catchment : observations of rainfall-runoff response, geophysical conditions and model inter-comparison}, issn = {0885-6087}, doi = {10.1002/Hyp.7171}, year = {2009}, abstract = {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.}, language = {en} } @article{GraeffZeheSchlaegeretal.2010, author = {Gr{\"a}ff, Thomas and Zehe, Erwin and Schlaeger, Stefan and Morgner, Markus and Bauer, Andreas and Becker, Rolf and Creutzfeldt, Benjamin and Bronstert, Axel}, title = {A quality assessment of Spatial TDR soil moisture measurements in homogenous and heterogeneous media with laboratory experiments}, issn = {1027-5606}, doi = {10.5194/hess-14-1007-2010}, year = {2010}, abstract = {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.}, language = {en} } @article{GraeffZeheSchlaegeretal.2010, author = {Gr{\"a}ff, Thomas and Zehe, Erwin and Schl{\"a}ger, Stefan and Morgner, Markus and Bauer, Andreas and Becker, Rolf and Creutzfeldt, Benjamin and Bronstert, Axel}, title = {A quality assessment of spatial TDR soil moisture measurements in homogenous and heterogeneous media with laboratory experiments}, issn = {1812-2108}, doi = {10.5194/hessd-7-269-2010}, year = {2010}, abstract = {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.}, language = {en} } @article{MiegelGraeffFrancketal.2017, author = {Miegel, Konrad and Gr{\"a}ff, Thomas and Franck, Christian and Salzmann, Thomas and Bronstert, Axel and Walther, Marc and Oswald, Sascha}, title = {Auswirkungen des Sturmhochwassers der Ostsee am 4./5. Januar 2017 auf das renaturierte Nieder- moor „H{\"u}telmoor und Heiligensee" an der deut- schen Ostseek{\"u}ste}, series = {Hydrologie und Wasserbewirtschaftung}, volume = {61}, journal = {Hydrologie und Wasserbewirtschaftung}, number = {4}, publisher = {Bundesanst. f{\"u}r Gew{\"a}sserkunde}, address = {Koblenz}, issn = {1439-1783}, doi = {10.5675/HyWa_2017,4_2}, pages = {232 -- 243}, year = {2017}, abstract = {Entlang der K{\"u}stenniederung des Naturschutzgebietes „H{\"u}telmoor und Heiligensee", ca. 6 km nord{\"o}stlich von Rostock-Warnem{\"u}nde gelegen, wird seit dem Jahr 2000 die K{\"u}stend{\"u}ne nicht mehr instand gehalten. Im Rahmen der Renaturierung des Gebietes werden so grunds{\"a}tzlich wieder {\"U}berflutungen 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 Warnem{\"u}nde, der sich zwischen dem 10- und 20-j{\"a}hrlichen Hochwasserstand einordnet. Dennoch kam es bei diesem Ereignis nicht zum D{\"u}nendurchbruch und zur seeseitigen {\"U}berflutung, wohl aber zum binnenseitigen Einstrom von Salz- bzw. Brackwasser. Dieser erfolgte {\"u}ber den Graben, durch den das Gebiet normalerweise {\"u}ber die Warnow in die Ostsee entw{\"a}ssert. Durch das Einstr{\"o}men {\"u}ber die Sohlschwelle, sonst Auslass des Gebietes, stiegen die Wasserst{\"a}nde und Salzkonzentrationen in der s{\"u}dwestlichen H{\"a}lfte der Niederung an. Mit zunehmender Entfernung zur Sohlschwelle waren diese Auswirkungen jedoch geringer sp{\"u}rbar. Dies gilt wegen der Retentionswirkung der Niederung mehr f{\"u}r den Wasserstand als f{\"u}r die Salzkonzentration. W{\"a}hrend der Wasserstand durch den Einstau der Niederung und {\"U}berschwemmungen fl{\"a}chenhaft anstieg, breitete sich die Salzfront pr{\"a}ferentiell in den ehemaligen Entw{\"a}sserungsgr{\"a}ben, die trotz des Einstaus nach wie vor hydraulisch aktiv sind, eher linienhaft aus. Diese Interpretation beruht auf Messergebnissen von Wasserstand, elektrischer Leitf{\"a}higkeit und Wassertemperatur.}, language = {de} } @article{MuellervanSchaikBlumeetal.2014, author = {M{\"u}ller, Eva Nora and van Schaik, Loes and Blume, Theresa and Bronstert, Axel and Carus, Jana and Fleckenstein, Jan H. and Fohrer, Nicola and Geissler, Katja and Gerke, Horst H. and Gr{\"a}ff, Thomas and Hesse, Cornelia and Hildebrandt, Anke and H{\"o}lker, Franz and Hunke, Philip and K{\"o}rner, Katrin and Lewandowski, J{\"o}rg and Lohmann, Dirk and Meinikmann, Karin and Schibalski, Anett and Schmalz, Britta and Schr{\"o}der-Esselbach, Boris and Tietjen, Britta}, title = {Scales, key aspects, feedbacks and challenges of ecohydrological research in Germany}, series = {Hydrologie und Wasserbewirtschaftung}, volume = {58}, journal = {Hydrologie und Wasserbewirtschaftung}, number = {4}, publisher = {Bundesanst. f{\"u}r Gew{\"a}sserkunde}, address = {Koblenz}, issn = {1439-1783}, doi = {10.5675/HyWa_2014,4_2}, pages = {221 -- 240}, year = {2014}, abstract = {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.}, language = {de} }