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  • 1.
    Basirat, Farzad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Yang, Zhibing
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pore-scale modeling of wettability effects on CO2–brine displacement during geological storage2017In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 109, p. 181-195Article in journal (Refereed)
    Abstract [en]

    Wetting properties of reservoir rocks and caprocks can vary significantly, and they strongly influence geological storage of carbon dioxide in deep saline aquifers, during which CO2 is supposed to displace the resident brine and to become permanently trapped. Fundamental understanding of the effect of wettability on CO2-brine displacement is thus important for improving storage efficiency and security. In this study, we investigate the influence of wetting properties on two-phase flow of CO2 and brine at the pore scale. A numerical model based on the phase field method is implemented to simulate the two-phase flow of CO2-brine in a realistic pore geometry. Our focus is to study the pore-scale fluid-fluid displacement mechanisms under different wetting conditions and to quantify the effect of wettability on macroscopic parameters such as residual brine saturation, capillary pressure, relative permeability, and specific interfacial area. Our simulation results confirm that both the trapped wetting phase saturation and the normalized interfacial area increase with decreasing contact angle. However, the wetting condition does not appear to influence the CO2 breakthrough time and saturation. We also show that the macroscopic capillary pressures based on the pressure difference between inlet and outlet can differ significantly from the phase averaging capillary pressures for all contact angles when the capillary number is high ( log Ca > -5). This indicates that the inlet-outlet pressure difference may not be a good measure of the continuum-scale capillary pressure. In addition, the results show that the relative permeability of CO2 can be significantly lower in strongly water-wet conditions than in the intermediate-wet conditions.

  • 2.
    Brunner, Manuela Irene
    et al.
    Univ Zurich, Dept Geog, Zurich, Switzerland;Univ Grenoble Alpes, CNRS, IRD, IGE,Grenoble INP, Grenoble, France.
    Seibert, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Zurich, Dept Geog, Zurich, Switzerland.
    Favre, Anne-Catherine
    Univ Grenoble Alpes, CNRS, IRD, IGE,Grenoble INP, Grenoble, France.
    Representative sets of design hydrographs for ungauged catchments: A regional approach using probabilistic region memberships2018In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 112, p. 235-244Article in journal (Refereed)
    Abstract [en]

    Traditional design flood estimation approaches have focused on peak discharges and have often neglected other hydrograph characteristics such as hydrograph volume and shape. Synthetic design hydrograph estimation procedures overcome this deficiency by jointly considering peak discharge, hydrograph volume, and shape. Such procedures have recently been extended to allow for the consideration of process variability within a catchment by a flood-type specific construction of design hydrographs. However, they depend on observed runoff time series and are not directly applicable in ungauged catchments where such series are not available. To obtain reliable flood estimates, there is a need for an approach that allows for the consideration of process variability in the construction of synthetic design hydrographs in ungauged catchments. In this study, we therefore propose an approach that combines a bivariate index flood approach with event-type specific synthetic design hydrograph construction. First, regions of similar flood reactivity are delineated and a classification rule that enables the assignment of ungauged catchments to one of these reactivity regions is established. Second, event-type specific synthetic design hydrographs are constructed using the pooled data divided by event type from the corresponding reactivity region in a bivariate index flood procedure. The approach was tested and validated on a dataset of 163 Swiss catchments. The results indicated that 1) random forest is a suitable classification model for the assignment of an ungauged catchment to one of the reactivity regions, 2) the combination of a bivariate index flood approach and event-type specific synthetic design hydrograph construction enables the consideration of event types in ungauged catchments, and 3) the use of probabilistic class memberships in regional synthetic design hydrograph construction helps to alleviate the problem of misclassification. Event-type specific synthetic design hydrograph sets enable the inclusion of process variability into design flood estimation and can be used as a compromise between single best estimate synthetic design hydrographs and continuous simulation studies.

  • 3. Dang, Qian
    et al.
    Konar, Megan
    Reimer, Jeffrey
    Di Baldassarre, Giuliano
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Lin, Xiaomen
    Zeng, Ruije
    A theoretical model of water and trade2016In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 89, p. 32-41Article in journal (Refereed)
    Abstract [en]

    Water is an essential input for agricultural production. Agriculture, in turn, is globalized through the trade of agricultural commodities. In this paper, we develop a theoretical model that emphasizes four tradeoffs involving water-use decision-making that are important yet not always considered in a consistent framework. One tradeoff focuses on competition for water among different economic sectors. A second tradeoff examines the possibility that certain types of agricultural investments can offset water use. A third tradeoff explores the possibility that the rest of the world can be a source of supply or demand for a country's water-using commodities. The fourth tradeoff concerns how variability in water supplies influences farmer decision-making. We show conditions under which trade liberalization affect water use. Two policy scenarios to reduce water use are evaluated. First, we derive a target tax that reduces water use without offsetting the gains from trade liberalization, although important tradeoffs exist between economic performance and resource use. Second, we show how subsidization of water-saving technologies can allow producers to use less water without reducing agricultural production, making such subsidization an indirect means of influencing water use decision-making. Finally, we outline conditions under which riskiness of water availability affects water use. These theoretical model results generate hypotheses that can be tested empirically in future work.

  • 4.
    Fagerlund, Fritjof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Hellman, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Målqvist, Axel
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Multilevel Monte Carlo methods for computing failure probability of porous media flow systems2016In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 94, p. 498-509Article in journal (Refereed)
  • 5.
    Fagerlund, Fritjof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Odén, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Comparison of relative permeability-fluid saturation-capillary pressure relations in the modelling of non-aqueous phase liquid infiltration in variably saturated, layered media2006In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 29, no 11, p. 1705-1730Article in journal (Refereed)
    Abstract [en]

    The characteristic functions relating relative permeabilities and capillary pressures to fluid saturations (krSPc models) are of great importance for the modelling of sub-surface multi-phase flow and transport. In order to test their performance and to identify their important parameters, four well-known three-phase krSPc models have been tested against published experimental data on non-aqueous phase liquid (NAPL) migration in the unsaturated zone. Both homogenous systems and systems with embedded heterogeneities have been analysed.

    The results show that although there are differences between predictions based on the different models, all models exhibit some common problems and it is not obvious that any one model is more accurate than the other three. However, with the inclusion of a non-linear NAPL tortuosity factor, both the Brooks–Corey–Burdine and van Genuchten–Mualem models yield excellent fits to experimental data.

    For NAPLs with non-zero spreading coefficients no exact theory currently exists for scaling two-phase capillary pressure–saturation functions to three-phase systems. Different ways of applying the Parker et al. [Parker JC, Lenhard RJ, Kuppusamy T. A parametric model for constitutive properties governing multi-phase flow in porous media. Water Resour Res 1987;23:618–24] scaling method have therefore been tested. It was found that since the NAPL–gas capillary pressure function has the strongest influence on NAPL migration, the scaling procedure should focus on accuracy in this function.

  • 6. Gallart, F.
    et al.
    Latron, J.
    Llorens, P.
    Beven, Keith J
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Using internal catchment information to reduce the uncertainty of discharge and baseflow prediction2007In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 30, no 4, p. 808-823Article in journal (Refereed)
    Abstract [en]

    The semi-distributed hydrological model TOPMODEL was tested with data from the Can Vila research basin (Vallcebre) in order to verify its adequacy for simulating runoff and the relative contributions from saturated overland flow and groundwater flow. After a test of the overall performance of the model, only data from a wet period were selected for this work. The test was performed using the GLUE method. The model was conditioned on continuous discharge and water table records. Furthermore, point measurements of recession flow simultaneous with water table depth and the extent of saturated areas were used to condition the distributions of the more relevant parameters, using new or updated evaluation measures. A wide range of parameter sets provided acceptable results for flow simulation when the model was conditioned on flow data alone, and the uncertainty of prediction of the contribution from groundwater was extremely large. However, conditioning on water table records and the distribution of parameters obtained from point observations strongly reduced the uncertainty of predictions for both stream flow and groundwater contribution.

  • 7.
    Gobeyn, Sacha
    et al.
    Univ Ghent, Lab Hydrol & Water Management, Coupure Links 653, B-9000 Ghent, Belgium..
    Van Wesemael, Alexandra
    Univ Ghent, Lab Hydrol & Water Management, Coupure Links 653, B-9000 Ghent, Belgium..
    Neal, Jeffrey
    Univ Bristol, Sch Geog Sci, Univ Rd, Bristol BS8 1SS, Avon, England..
    Lievens, Hans
    Univ Ghent, Lab Hydrol & Water Management, Coupure Links 653, B-9000 Ghent, Belgium.;NASA, Goddard Space Flight Ctr, Global Modeling & Assimilat Off, Greenbelt, MD 20771 USA..
    Van Eerdenbrugh, Katrien
    Univ Ghent, Lab Hydrol & Water Management, Coupure Links 653, B-9000 Ghent, Belgium..
    De Vleeschouwer, Niels
    Univ Ghent, Lab Hydrol & Water Management, Coupure Links 653, B-9000 Ghent, Belgium..
    Vernieuwe, Hilde
    Univ Ghent, Dept Math Modelling Stat & Bioinformat, KERMIT, Coupure Links 653, B-9000 Ghent, Belgium..
    Schumann, Guy J. -P.
    Univ Bristol, Sch Geog Sci, Univ Rd, Bristol BS8 1SS, Avon, England.;Remote Sensing Solut Inc, 248 E Foothill Blvd,Suite 200, Monrovia, CA 91016 USA..
    Di Baldassarre, Giuliano
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    De Baets, Bernard
    Univ Ghent, Dept Math Modelling Stat & Bioinformat, KERMIT, Coupure Links 653, B-9000 Ghent, Belgium..
    Bates, Paul D.
    Univ Bristol, Sch Geog Sci, Univ Rd, Bristol BS8 1SS, Avon, England..
    Verhoest, Niko E. C.
    Univ Ghent, Lab Hydrol & Water Management, Coupure Links 653, B-9000 Ghent, Belgium..
    Impact of the timing of a SAR image acquisition on the calibration of a flood inundation model2017In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 100, p. 126-138Article in journal (Refereed)
    Abstract [en]

    Synthetic Aperture Radar (SAR) data have proven to be a very useful source of information for the calibration of flood inundation models. Previous studies have focused on assigning uncertainties to SAR images in order to improve flood forecast systems (e.g. Giustarini et al. (2015) and Stephens et al. (2012)). This paper investigates whether the timing of a SAR acquisition of a flood has an important impact on the calibration of a flood inundation model. As no suitable time series of SAR data exists, we generate a sequence of consistent SAR images through the use of a synthetic framework. This framework uses two available ERS-2 SAR images of the study area, one taken during the flood event of interest, the second taken during a dry reference period. The obtained synthetic observations at different points in time during the flood event are used to calibrate the flood inundation model. The results of this study indicate that the uncertainty of the roughness parameters is lower when the model is calibrated with an image taken before rather than during or after the flood peak. The results also show that the error on the modelled extent is much lower when the model is calibrated with a pre-flood peak image than when calibrated with a near-flood peak or a post-flood peak image. It is concluded that the timing of the SAR image acquisition of the flood has a clear impact on the model calibration and consequently on the precision of the predicted flood extent.

  • 8.
    Hobe, Alex
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Swiss Fed Inst Technol, Geothermal Energy & Geofluids, Inst Geophys, Zurich, Switzerland.
    Vogler, Daniel
    Swiss Fed Inst Technol, Geothermal Energy & Geofluids, Inst Geophys, Zurich, Switzerland;Swiss Fed Inst Technol, Transport Proc & React Lab, Inst Proc Engn, Zurich, Switzerland.
    Seybold, Martin P.
    Univ Stuttgart, Inst Formal Methods Comp Sci, Stuttgart, Germany.
    Ebigbo, Anozie
    Swiss Fed Inst Technol, Geothermal Energy & Geofluids, Inst Geophys, Zurich, Switzerland.
    Settgast, Randolph R.
    Lawrence Livermore Natl Lab, Atmospher Earth & Energy Div, Livermore, CA USA.
    Saar, Martin O.
    Swiss Fed Inst Technol, Geothermal Energy & Geofluids, Inst Geophys, Zurich, Switzerland.
    Estimating fluid flow rates through fracture networks using combinatorial optimization2018In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 122, p. 85-97Article in journal (Refereed)
    Abstract [en]

    To enable fast uncertainty quantification of fluid flow in a discrete fracture network (DFN), we present two approaches to quickly compute fluid flow in DFNs using combinatorial optimization algorithms. Specifically, the presented Hanan Shortest Path Maxflow (HSPM) and Intersection Shortest Path Maxflow (ISPM) methods translate DFN geometries and properties to a graph on which a max flow algorithm computes a combinatorial flow, from which an overall fluid flow rate is estimated using a shortest path decomposition of this flow. The two approaches are assessed by comparing their predictions with results from explicit numerical simulations of simple test cases as well as stochastic DFN realizations covering a range of fracture densities. Both methods have a high accuracy and very low computational cost, which can facilitate much-needed in-depth analyses of the propagation of uncertainty in fracture and fracture-network properties to fluid flow rates.

  • 9. Montanari, Alberto
    et al.
    Di Baldassarre, Giuliano
    Data errors and hydrological modelling: The role of model structure to propagate observation uncertainty2013In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 51, p. 498-504Article in journal (Refereed)
  • 10. Montanari, Alberto
    et al.
    Di Baldassarre, Giuliano
    The role of model structure to propagate observation uncertainty2013In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 54, p. 242-244Article in journal (Refereed)
  • 11. Pappenberger, Florian
    et al.
    Beven, Keith J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Ratto, Marco
    Matgen, Patrick
    Multi-method global sensitivity analysis of flood inundation models2008In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 31, no 1, p. 1-14Article in journal (Refereed)
    Abstract [en]

    Global sensitivity analysis is a valuable tool in understanding flood inundation models and deriving decisions on strategies to reduce model uncertainty. In this paper, a sensitivity analysis of a one-dimensional flood inundation model (HEC-RAS) on the River Alzette, Luxembourg, is presented. It is impossible to define sensitivity in a unique way and different methods can lead to a difference in ranking of importance of model factors. In this paper five different methods (Sobol, Kullback-Leibler entropy, Morris, regionalised sensitivity analysis and regression) are applied and the outcomes on selected examples compared. It is demonstrated that the different methods lead to completely different ranking of importance of the parameter factors and that it is impossible to draw firm conclusions about the relative sensitivity of different factors. Moreover, the uncertainty inherent in the sensitivity methods is highlighted.

  • 12. Pappenberger, Florian
    et al.
    Matgen, Patrick
    Beven, Keith J.
    Henry, Jean-Baptiste
    Pfister, Laurent
    de, Paul Fraipont
    Influence of uncertain boundary conditions and model structure on flood inundation predictions2006In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 29, no 10, p. 1430-1449Article in journal (Refereed)
    Abstract [en]

    In this study, the GLUE methodology is applied to establish the sensitivity of flood inundation predictions to uncertainty of the upstream boundary condition and bridges within the modelled region. An understanding of such uncertainties is essential to improve flood forecasting and floodplain mapping. The model has been evaluated on a large data set. This paper shows uncertainty of the upstream boundary can have significant impact on the model results, exceeding the importance of model parameter uncertainty in some areas. However, this depends on the hydraulic conditions in the reach e.g. internal boundary conditions and, for example, the amount of backwater within the modelled region. The type of bridge implementation can have local effects, which is strongly influenced by the bridge geometry (in this case the area of the culvert). However, the type of bridge will not merely influence the model performance within the region of the structure, but also other evaluation criteria such as the travel time. This also highlights the difficulties in establishing which parameters have to be more closely examined in order to achieve better fits. In this study no parameter set or model implementation that fulfils all evaluation criteria could be established. We propose four different approaches to this problem: closer investigation of anomalies; introduction of local parameters; increasing the size of acceptable error bounds; and resorting to local model evaluation. Moreover, we show that it can be advantageous to decouple the classification into behavioural and non-behavioural model data/parameter sets from the calculation of uncertainty bounds. (C) 2005 Elsevier Ltd. All rights reserved.

  • 13. Presho, Michael
    et al.
    Målqvist, Axel
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Ginting, Victor
    Density estimation of two-phase flow with multiscale and randomly perturbed data2010In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 33, p. 1130-1141Article in journal (Refereed)
  • 14.
    Quesada Montano, Beatriz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Ctr Nat Hazards & Disaster Sci CNDS, Uppsala, Sweden.; Centre for Geophysical Research, University of Costa Rica.
    Di Baldassarre, Giuliano
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Ctr Nat Hazards & Disaster Sci CNDS, Uppsala, Sweden.
    Rangecroft, Sally
    Birmingham University, School of Geography, Earth and Environmental Sciences, Birmingham, United Kingdom.
    Van Loon, Anne
    Birmingham University, School of Geography, Earth and Environmental Sciences, Birmingham, United Kingdom.
    Hydrological change: Towards a consistent approach to assess changes on both floods and droughts2018In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 111, p. 31-35Article in journal (Refereed)
    Abstract [en]

    Several studies have found that the frequency, magnitude and spatio-temporal distribution of droughts and floods have significantly increased in many regions of the world. Yet, most of the methods used in detecting trends in hydrological extremes 1) focus on either floods or droughts, and/or 2) base their assessment on characteristics that, even though useful for trend identification, cannot be directly used in decision making, e.g. integrated water resources management and disaster risk reduction. In this paper, we first discuss the need for a consistent approach to assess changes on both floods and droughts, and then propose a method based on the theory of runs and threshold levels. Flood and drought changes were assessed in terms of frequency, length and surplus/deficit volumes. This paper also presents an example application using streamflow data from two hydrometric stations along the Po River basin (Italy), Piacenza and Pontelagoscuro, and then discuss opportunities and challenges of the proposed method.

  • 15.
    Rasmusson, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Fagerlund, Fritjof
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Yvonne
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Calif Berkeley, Lawrence Berkeley Natl Lab, Div Earth Sci, Berkeley, CA 94720 USA..
    Rasmusson, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Prerequisites for density-driven instabilities and convective mixing under broad geological CO2 storage conditions2015In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 84, p. 136-151Article in journal (Refereed)
    Abstract [en]

    Direct atmospheric greenhouse gas emissions can be greatly reduced by CO2 sequestration in deep saline aquifers. One of the most secure and important mechanisms of CO2 trapping over large time scales is solubility trapping. In addition, the CO2 dissolution rate is greatly enhanced if density-driven convective mixing occurs. We present a systematic analysis of the prerequisites for density-driven instability and convective mixing over the broad temperature, pressure, salinity and permeability conditions that are found in geological CO2 storage. The onset of instability (Rayleigh-Darcy number, Ra), the onset time of instability and the steady convective flux are comprehensively calculated using a newly developed analysis tool that accounts for the thermodynamic and salinity dependence on solutally and thermally induced density change, viscosity, molecular and thermal diffusivity. Additionally, the relative influences of field characteristics are analysed through local and global sensitivity analyses. The results help to elucidate the trends of the Ra, onset time of instability and steady convective flux under field conditions. The impacts of storage depth and basin type (geothermal gradient) are also explored and the conditions that favour or hinder enhanced solubility trapping are identified. Contrary to previous studies, we conclude that the geothermal gradient has a non-negligible effect on density-driven instability and convective mixing when considering both direct and indirect thermal effects because cold basin conditions, for instance, render higher Ra compared to warm basin conditions. We also show that the largest Ra is obtained for conditions that correspond to relatively shallow depths, measuring approximately 800 m, indicating that CO2 storage at such depths favours the onset of density-driven instability and reduces onset times. However, shallow depths do not necessarily provide conditions that generate the largest steady convective fluxes; the salinity determines the storage depth at which the largest steady convective fluxes occur. Furthermore, we present a straight-forward and efficient procedure to estimate site-specific solutal Ra that accounts for thermodynamic and salinity dependence.

  • 16.
    Ridolfi, E.
    et al.
    Univ Perugia, DICA, I-06100 Perugia, Italy..
    Rianna, M.
    Sapienza Univ Roma, DICEA, Rome, Italy..
    Trani, G.
    Sapienza Univ Roma, DICEA, Rome, Italy..
    Alfonso, L.
    UNESCO IHE, Hydroinformat Chair Grp, Delft, Netherlands..
    Di Baldassarre, Giuliano
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Napolitano, F.
    Sapienza Univ Roma, DICEA, Rome, Italy..
    Russo, F.
    Sapienza Univ Roma, DICEA, Rome, Italy..
    A new methodology to define homogeneous regions through an entropy based clustering method2016In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 96, p. 237-250Article in journal (Refereed)
    Abstract [en]

    One of the most crucial steps in flow frequency studies is the definition of Homogenous Regions (HRs), i.e. areas with similar hydrological behavior. This is essential in ungauged catchments, as HR allows information to be transferred from a neighboring river basin. This study proposes a new, entropy-based approach to define HRs, in which regions are defined as homogeneous if their hydrometric stations capture redundant information. The problem is handled through the definition of the Information Transferred Index (ITI) as the ratio between redundant information and the total information provided by pairs of stations. The methodology is compared with a traditional, distance-based clustering method through a Monte Carlo experiment and a jack-knife procedure. Results indicate that the ITI-based method performs Well, adding value to current methodologies to define HRs.

  • 17. Romanowicz, Renata J.
    et al.
    Young, Peter C.
    Beven, Keith J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pappenberger, Florian
    A data based mechanistic approach to nonlinear flood routing and adaptive flood level forecasting2008In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 31, no 8, p. 1048-1056Article in journal (Refereed)
    Abstract [en]

    Operational flood forecasting requires accurate forecasts with a suitable lead time, in order to be able to issue appropriate warnings and take appropriate emergency actions. Recent improvements in both flood plain characterization and computational capabilities have made the use of distributed flood inundation models more common. However, problems remain with the application of such models. There are still uncertainties associated with the identifiability of parameters, with the computational burden of calculating distributed estimates of predictive uncertainty, and with the adaptive use of such models for operational, real-time flood inundation forecasting. Moreover, the application of distributed models is complex, costly and requires high degrees of skill. This paper presents an alternative to distributed inundation models for real-time flood forecasting that provides fast and accurate, medium to short-term forecasts. The Data Based Mechanistic (DBM) methodology exploits a State Dependent Parameter (SDP) modelling approach to derive a nonlinear dependence between the water levels measured at gauging stations along the river. The transformation of water levels depends on the relative geometry of the channel cross-sections, without the need to apply rating curve transformations to the discharge. The relationship obtained is used to transform water levels as an input to a linear, on-line, real-time and adaptive stochastic DBM model. The approach provides an estimate of the prediction uncertainties, including allowing for heterescadasticity of the multi-step-ahead forecasting errors. The approach is illustrated using an 80 km reach of the River Severn, in the UK.

  • 18. Smith, Paul
    et al.
    Beven, Keith J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tawn, Jonathan A.
    Informal likelihood measures in model assessment: Theoretic development and investigation2008In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 31, no 8, p. 1087-1100Article in journal (Refereed)
    Abstract [en]

    Within hydrology performance criteria such as the Nash-Sutcliffe efficiency have been used to condition the parameter space of a model. Their use is motivated by the fact that the stochastic error series between a model output and corresponding observations is the result of the composite effect of multiple error sources which cannot be described, even in form, a priori. This paper formalises the use of such performance criteria within a Bayesian framework, such as Generalised Likelihood Uncertainty Estimation (GLUE), by introducing the concept of informal Likelihoods. Informal Likelihoods are used to characterise desirable features in the relationship between the model output and corresponding observed data. A number of common performance criteria are considered as Informal Likelihoods. Analytical results and a simulation indicate all of the performance criteria considered as Informal Likelihoods in this paper have one or more properties which may be considered undesirable, but may perform no less well in conditioning model parameters than formal likelihoods for which the assumptions are only mildly incorrect.

  • 19.
    Yang, Zhibing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. MIT, Dept Civil & Environm Engn, 77 Massachusetts Ave, Cambridge, MA 02139 USA.
    Neuweiler, Insa
    Leibniz Univ Hannover, Inst Fluid Mech & Environm Phys Civil Engn, Hannover, Germany.
    Meheust, Yves
    Univ Rennes 1, Geosci Geosci Rennes UMR CNRS 6118, Rennes, France.
    Fagerlund, Fritjof
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Fluid trapping during capillary displacement in fractures2016In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 95, p. 264-275Article in journal (Refereed)
    Abstract [en]

    The spatial distribution of fluid phases and the geometry of fluid–fluid interfaces resulting from immiscible displacement in fractures cast decisive influence on a range of macroscopic flow parameters. Most importantly, these are the relative permeabilities of the fluids as well as the macroscopic irreducible saturations. They also influence parameters for component (solute) transport, as it usually occurs through one of the fluid phase only. Here, we present a numerical investigation on the critical role of aperture variation and spatial correlation on fluid trapping and the morphology of fluid phase distributions in a geological fracture. We consider drainage in the capillary dominated regime. The correlation scale, that is, the scale over which the two facing fracture walls are matched, varies among the investigated geometries between L/256 and L (self-affine fields), L being the domain/fracture length. The aperture variability is quantified by the coefficient of variation (δ), ranging among the various geometries from 0.05 to 0.25. We use an invasion percolation based model which has been shown to properly reproduce displacement patterns observed in previous experiments. We present a quantitative analysis of the size distribution of trapped fluid clusters. We show that when the in-plane curvature is considered, the amount of trapped fluid mass first increases with increasing correlation scale Lc and then decreases as Lc further increases from some intermediate scale towards the domain length scale L. The in-plane curvature contributes to smoothening the invasion front and to dampening the entrapment of fluid clusters of a certain size range that depends on the combination of random aperture standard deviation and spatial correlation.

  • 20. Zhang, Danrong
    et al.
    Beven, Keith
    Environmental Science/Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK.
    Mermoud, Andr
    A comparison of non-linear least square and GLUE for model calibration and uncertainty estimation for pesticide transport in soils2006In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 29, no 12, p. 1924-1933Article in journal (Refereed)
    Abstract [en]

    The problems of calibrating soil hydraulic and transport parameters are well documented, particularly when data are limited. Programs such as CXTFIT, UUCODE and PEST, based on well established principles of statistical inference, will often provide good fits to limited observations giving the impression that a useful model of a particular soil system has been obtained. This may be the case, but such an approach may grossly underestimate the uncertainties associated with future predictions of the system and resulting dependent variables. In this paper, this is illustrated by an application of CXTFIT within the generalised likelihood uncertainty estimation (GLUE) approach to model calibration which is based on a quite different philosophy. CXTFIT gives very good fits to the observed breakthrough curves for several different model formulations, resulting in very small parameter uncertainty estimates. The application of GLUE, however, shows that much wider ranges of parameter values can provide acceptable fits to the data. The wider range of potential outcomes should be more robust in model prediction, especially when used to constrain field scale models.

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