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    Torben Sonnenborg

    <p>By use of transient and distributed groundwater-surface water flow models, simulated time... more
    <p>By use of transient and distributed groundwater-surface water flow models, simulated time series of stream discharge and groundwater level for monitoring networks, groundwater bodies and river reaches have been analysed for a historical period and four different future scenarios toward 2100 in two large-scale catchments in Denmark. The purpose of the climate scenarios has been to qualify the existing knowledge on how future climate change most likely will impact hydrology, groundwater status and Ecological Quality Elements (EQR- Ecological flow in rivers). Another purpose has been to identify whether foreseen climate changes will be detected by the surface water and groundwater monitoring networks, and to which degree the River Basin Management Plan measures for supporting the goal of good quantitative status are robust to the projected changes in water balance and ecological flow. The developed hydrological models were run with climate inputs based on selected RCP4.5 and RCP8.5 climate model runs (RCP8.5 wet, median, dry and RCP4.5 median). Changes in groundwater quantitative status and ecological flow metrics were calculated based on 30-year model runs driven by RCP8.5 for 2071-2100 (RCP4.5 for 2041-70) and compared to 1981-2010.</p><p>Overall the four scenarios results in very significant water balance changes with increased precipitation: 3% to 27%, evapotranspiration: 6% to 17%, groundwater recharge: 0% to 49%, drainage flow: 0% to 71%, baseflow: 0% to 31% and overland flow: 16% to 281%. For one catchment an increase in abstraction of 23% to 171% due to an increase in irrigation demand by 36% to 113% is foreseen. The results have wide implications for groundwater flooding risks, quantitative status and ecological flow metrics. Most sensitive is changes in ecological flow conditions in rivers for fish, showing a relative high probability for decreased state for 10-20% of the reaches for the RCP8.5 wet and dry scenarios due to more extreme hydrological regimes toward 2071-2100. Maximum monthly runoff is increased for winter months by 100% for RCP8.5 wet and median scenarios and around 10% for RCP8.5 dry scenario. Annual maximum daily flows is simulated to increase by up to a factor of five, and late summer low flows decreased.</p><p>Impacts on groundwater levels and water balances of groundwater bodies will be significant, with increased seasonal fluctuations and also increased maximum and decreased minimum groundwater levels for 30 year periods for 2071-2100 compared to 1981-2010.</p><p>More rain, both when we look back on historical data and when we look forward with latest climate projections will result in more frequent flooding from groundwater and streams in the future. At the same time, the temperature and thus evapotranspiration rises. This means that in the long term we will have increased challenges with drought and increased irrigation demands on sandy soils while evapotranspiration will also increase on the clayey soils. This will result in greater fluctuation in the flow and groundwater levels between winters and summers, and between wet and dry years, challenging sustainable groundwater abstraction and maintaining good quantitative status of groundwater bodies.</p>
    ABSTRACT
    Research Interests:
    Projections of climate change impact are associated with a cascade of uncertainties including CO<sub>2</sub> emission scenario, climate model, downscaling and impact model. The relative importance of the individual uncertainty... more
    Projections of climate change impact are associated with a cascade of uncertainties including CO<sub>2</sub> emission scenario, climate model, downscaling and impact model. The relative importance of the individual uncertainty sources is expected to depend on several factors including the quantity that is projected. In the present study the impacts of climate model uncertainty and geological model uncertainty on hydraulic head, stream flow, travel time and capture zones are evaluated. Six versions of a physically based and distributed hydrological model, each containing a unique interpretation of the geological structure of the model area, are forced by 11 climate model projections. Each projection of future climate is a result of a GCM-RCM model combination (from the ENSEMBLES project) forced by the same CO<sub>2</sub> scenario (A1B). The changes from the reference period (1991–2010) to the future period (2081–2100) in projected hydrological variables are ev...
    In a major Danish funded research project (www.hyacints.dk) a coupling is being established between the HIRHAM regional climate model code from Danish Meteorological Institute and the MIKE SHE distributed hydrological model code from DHI.... more
    In a major Danish funded research project (www.hyacints.dk) a coupling is being established between the HIRHAM regional climate model code from Danish Meteorological Institute and the MIKE SHE distributed hydrological model code from DHI. The linkage between those two codes is a soil vegetation atmosphere transfer scheme, which is a module of MIKE SHE. The coupled model will be established
    Research Interests:
    ABSTRACT
    Research Interests:
    This paper investigates some of the uncertainties related to the use of regional climate model (RCM) data in hydrological simulations at the local scale, and the significance of regional hydrological change predictions considering climate... more
    This paper investigates some of the uncertainties related to the use of regional climate model (RCM) data in hydrological simulations at the local scale, and the significance of regional hydrological change predictions considering climate model uncertainties. In Denmark, future changes in climate are expected to result in more extreme hydrological conditions. Higher precipitation is predicted in winter resulting in flooding
    Research Interests:
    ABSTRACT A catchment scale model MACRO-MIKE SHE is applied for simulating changes in pesticide concentrations to the aquatic environment. The MACRO model is used to model the effect of changes in climate and pesticide management on... more
    ABSTRACT A catchment scale model MACRO-MIKE SHE is applied for simulating changes in pesticide concentrations to the aquatic environment. The MACRO model is used to model the effect of changes in climate and pesticide management on pesticide leaching from the unsaturated zone and simulated percolation as well as solute flow is propagated to the MIKE SHE model. The intensity based bias correction method for converting from Regional Climate Modelling data to hydrological input data is the most appropriate method as it best reflects changes in rainfall intensity, and thus also in intensity for MACRO simulated percolation and solute flow. Results show that increased percolation simulated by the MACRO model and propagated to the MIKE SHE model nearly all ends up in increased drainage to the river. Further, pesticide solute entering the saturated zone (SZ) is mainly leaving SZ via drainage (85-94%), base flow (3.8-11.3%) and overland flow (0-3.1 %). Mean concentrations in groundwater (SZ) increase by 30-99% for one type of herbicide under future climatic conditions, whereas mean concentrations decrease for two other types by app. 93 and 91 % respectively. Future climatic conditions lead to higher concentrations in surface water for the first type of herbicides, but to decreased concentrations for the another type of herbicide and insecticide. It is overall concluded that an integrated catchment scale modeling approach is essential for pesticide fate simulation taking account of all possible hydrologic pathways.
    Research Interests:
    With the European Union (EU) Water Framework Directive (WFD) the achievement of a good ecological status of surface waters and a good quantitative and qualitative status of groundwater has become obligatory. The ecological status of... more
    With the European Union (EU) Water Framework Directive (WFD) the achievement of a good ecological status of surface waters and a good quantitative and qualitative status of groundwater has become obligatory. The ecological status of surface water is here defined by biological, chemical, morphologica...
    ABSTRACT In this study six hydrological models that only differ with respect to their conceptual geological models are established for a 465 km2 area. The performances of the six models are evaluated in differential split-sample tests... more
    ABSTRACT In this study six hydrological models that only differ with respect to their conceptual geological models are established for a 465 km2 area. The performances of the six models are evaluated in differential split-sample tests against a unique data set with well documented groundwater head and discharge data for different periods with different groundwater abstractions. The calibration results of the six models are comparable, with no model being superior to the others. Though, the six models make very different predictions of changes in groundwater head and discharges as a response to changes in groundwater abstraction. This confirms the utmost importance of the conceptual geological model for making predictions of variables and conditions beyond the calibration situation. In most cases the observed changes in hydraulic head and discharge are within the range of the changes predicted by the six models implying that a multiple modeling approach can be useful in obtaining more robust assessments of likely prediction errors. We conclude that the use of multiple models appear to be a good alternative to traditional differential split-sample schemes. A model averaging analysis shows that model weights estimated from model performance in the calibration or validation situation in many cases are not optimal for making other predictions. Hence, the critical assumption that is always made in model averaging, namely that the model weights derived from the calibration situation are also optimal for model predictions, cannot be assumed to be generally valid.
    ABSTRACT Uncertainty analysis in hydrological modeling has become an essential step in the scientific interpretation of model results and a useful tool to support decision making. Among many uncertainty sources in the modeling practice,... more
    ABSTRACT Uncertainty analysis in hydrological modeling has become an essential step in the scientific interpretation of model results and a useful tool to support decision making. Among many uncertainty sources in the modeling practice, uncertainties in precipitation estimation play an important role since it is the main driving force for other hydrological processes. The present study demonstrates a statistical method for generating radar rainfall realizations that account for the uncertainties in radar-based quantitative precipitation estimation (QPE). The random sampling technique used to generate stochastic uncertainty fields is based on sequential Gaussian simulation. The hydrological impact of the uncertainties in radar QPE is analyzed by propagating the rainfall ensemble through a distributed and integrated water resources model. The study shows that the uncertainty of the simulated stream discharge depends on the intensity of the rainfall input signal. The coefficient of variation is calculated for simulated stream discharge and groundwater recharge at subcatchments with various sizes. The results reveal strong scale dependency showing higher variations of hydrological uncertainties at smaller catchments, especially for catchment areas smaller than 50 km2. The uncertainties from precipitation input are generally amplified in the hydrological model. This effect is less obvious for groundwater recharge but rather substantial for stream discharge, where the coefficient of variation increases by a factor of three.
    Page 1. Arbejdsrapport fra Miljøstyrelsen Nr. 17 2001 Retningslinier for opstilling af grundvandsmodeller Hans Jørgen Henriksen, Torben Sonnenborg, Heidi Barlebo Christiansen, Jens Christian Resfgaard, Bill Harrar og Per ...
    Page 1. DANMARKS OG GRØNLANDS GEOLOGISKE UNDERSØGELSE MILJØMINISTERIET DANMARKS OG GRØNLANDS GEOLOGISKE UNDERSØGELSE RAPPORT 2006/22 Klimaændringers betydning for vandkredsløbet i Danmark ...
    A new, closed-form hysteretic model of the capillary pressure-saturation and relative permeability-saturation relationship has been implemented into ITOUGH2. The hysteretic capillary pressure function is based on the van Genuchten model,... more
    A new, closed-form hysteretic model of the capillary pressure-saturation and relative permeability-saturation relationship has been implemented into ITOUGH2. The hysteretic capillary pressure function is based on the van Genuchten model, with a modified version of the dependent domain model of Mualem to describe the scanning curves. Hysteresis in the relative permeability relations is considered to be mainly a result of nonwetting fluid entrap- ment. The hysteresis model was used in combination with inverse modeling techniques to examine the potential of a simple drainage- imbibition experiment to determine hysteretic hydraulic properties.
    ABSTRACT Future changes in climate are expected to result in more extreme hydrological conditions globally. For Denmark, most climate models predict increases in annual precipitation, with higher intensity rainfall events occurring in... more
    ABSTRACT Future changes in climate are expected to result in more extreme hydrological conditions globally. For Denmark, most climate models predict increases in annual precipitation, with higher intensity rainfall events occurring in winter and reduced precipitation and higher evapotranspiration in summer. Changes in the quantity, timing, and delivery of precipitation is expected to result in higher rates of groundwater recharge in the winter months, as well as flooding and water logging in low lying areas, and decreased water tables, dry root zones, and reduced low flows in the summer months. There is, however, variability between climate models on the direction and strength of the climate change signal. Additionally, regional climate models (RCMs) are subject to systematic errors making their outputs, especially precipitation, require further downscaling and bias correction prior to use in hydrological simulations. Consequently, hydrological outputs simulated under climate change compound the uncertainties within individual climate model predictions, between various climate models, and in the choice of downscaling and bias correction method. This study compares 11 transient climate change scenarios from the EU project ENSMEBLES, which makes available a matrix of GCM-RCM pairings for all of Europe at a 25 km2 grid scale to the year 2100. Temperature, precipitation, and potential evapotranspiration (calculated from climate model outputs) are downscaled using two methods: a monthly delta change approach that transfers absolute (state variables) or relative (flux variables) climate change from the RCM scenarios to the observed data, and a seasonal histogram equalization method that fits gamma distributions based on the instensity of daily observed and scenario data (flux variables) and scales scenario data based on the difference in gamma functions. Downscaling is spatially distributed within Denmark according to the seven sub-model regions in the National Water Resources Model (DK-model), delineated based on natural hydrological boundaries. The MIKE-SHE based DK-model is composed of a relatively simple root zone component for estimating net precipitation, a comprehensive three-dimensional groundwater component for estimating recharge and hydraulic head in different geological layers, and a river component for stream flow routing and calculating stream-aquifer interaction. The downscaled climate change scenarios are used to force DK-model simulations of hydrogeological outputs for all of Denmark. Precipitation changes and differences in rainfall intensity under the two downscaling methods are analyzed for all 11 scenarios. The impact of climate change on groundwater recharge and the relationship with rainfall intensity and potential evapotranspiration is analyzed across the seven sub-regions in Denmark and between all climate scenarios using both downscaling methods.
    ABSTRACT
    A new, closed-form hysteretic model of the capillary pressure-saturation and relative permeability-saturation relationship has been implemented into ITOUGH2. The hysteretic capillary pressure function is based on the van Genuchten model,... more
    A new, closed-form hysteretic model of the capillary pressure-saturation and relative permeability-saturation relationship has been implemented into ITOUGH2. The hysteretic capillary pressure function is based on the van Genuchten model, with a modified version of the dependent domain model of Mualem to describe the scanning curves. Hysteresis in the relative permeability relations is considered to be mainly a result of nonwetting fluid entrap- ment. The hysteresis model was used in combination with inverse modeling techniques to examine the potential of a simple drainage- imbibition experiment to determine hysteretic hydraulic properties.
    Page 1. Arbejdsrapport fra Miljøstyrelsen Nr. 17 2001 Retningslinier for opstilling af grundvandsmodeller Hans Jørgen Henriksen, Torben Sonnenborg, Heidi Barlebo Christiansen, Jens Christian Resfgaard, Bill Harrar og Per ...
    ... with computational cells running dry during the simulation, the bottom of the uppermost layer (layer 1) is calculated as three meters below the groundwater table (based ... Towards east and west, the boundaries are located in the sea... more
    ... with computational cells running dry during the simulation, the bottom of the uppermost layer (layer 1) is calculated as three meters below the groundwater table (based ... Towards east and west, the boundaries are located in the sea and a constant potential head of zero ...
    Page 1. Deep saltwater in Chalk of North-West Europe: origin, interface characteristics and development over geological time Ellen P. Bonnesen & Flemming Larsen & Torben O. Sonnenborg & Kurt Klitten... more
    Page 1. Deep saltwater in Chalk of North-West Europe: origin, interface characteristics and development over geological time Ellen P. Bonnesen & Flemming Larsen & Torben O. Sonnenborg & Kurt Klitten & Lars Stemmerik ...