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  • 1.
    Ahlkrona, Malva
    SMHI.
    Phospherous in a Biogeochemical Lake Model2002Report (Other academic)
    Abstract [en]

    BIOLA isa biogeochemical lake model within the V ASTRA research programme. The model's

    main purpose is to predict the ecological responses to changed nutrient loads. The phosphorus simulations were not satisfactory and the sediment was thought to be the critical part. The aim of this work was to improve the phosphorus simulations. Therefore a new sediment approach has been developed. Three main changes of the sediment processes were carried through:

    • Resuspension of sediments from erosion and transportation bottoms was added

    • The sediments were divided into an upper, aerobic, and a lower, anaerobic, layer

    • The relation between sorbed and dissolved phosphorus in the sediments was described by

    Langmuir isotherms, with a sorption 2.5 times higher at aerobic compared to anaerobic

    conditions

    The modelling of total phosphorus and blue-green algae was improved. Especially the timing of high concentration peaks was much better. One problem still lingering is the modelled oxygen levels, which were much higher than the observed levels. Therefore the model has not been tested for anaerobic conditions. A verage release rates from the sediments were 2.5 mg Pa-1 <luring the summer, which is reasonable. A 20-year simulation of step-response was run with increased and decreased nutrient loads. Roughly four years after the change, the model had reached a new equilibrium.

  • 2.
    Arheimer, Berit
    et al.
    SMHI, Research Department, Hydrology.
    Brandt, Maja
    SMHI, Core Services.
    Grahn, Gun
    SMHI.
    Roos, Elisabet
    SMHI.
    Sjöö, Allan
    SMHI.
    Modellerad kvävetransport, retention och källfördelning för södra Sverige1997Report (Other academic)
  • 3.
    Bergström, Sten
    SMHI, Research Department, Hydrology.
    The HBV model – its structure and applications1992Report (Other academic)
  • 4.
    Bergström, Sten
    et al.
    SMHI, Research Department, Hydrology.
    Carlsson, Bengt
    SMHI, Research Department, Hydrology.
    Hydrology of the Baltic Basin: Inflow of fresh water from rivers and land for the period 1950–19901993Report (Other academic)
    Abstract [en]

    A data base of monthly inflow of fresh water from rivers and land to the Baltic Sea and its subbasins is created. The data base covers the period 1950 - 1990 and is based on observations from the national hydrological services of the surrounding countries.

    The main features of the data base are presented including river flow of selected rivers and total inflow to the Baltic Sea and its subbasins. Long term, seasonal and short term variabilities are analysed and the effects of hydropower development are identified. An earlier data base by Mikulski (1982) is used for comparison and extension of the record to cover the period 1921 - 1990.

    It is concluded that the variability of inflow is great and that the decade 1981 - 1990 is the wettest in 70 years. The increase in runoff is mainly due to increasing river flow during the cold seasons. The effects of hydropower development are noticeable in the records for the Bothnian Bay and the Bothnian Sea.

  • 5.
    Bergström, Sten
    et al.
    SMHI, Research Department, Hydrology.
    Sandén, Per
    SMHI.
    Gardelin, Marie
    SMHI, Professional Services.
    Analysis of climate-induced hydrochemical variations in till aquifers1990Report (Other academic)
    Abstract [en]

    An investigation of the relations between climatological factors and short term variabilityin groundwater storage and hydrochemistry in till aquifers is performed. The analysis isbased on a simple empirical hydrological model, the PULSE model, and groundwaterrecords from four sites in Sweden.The model proved to be capable of describing the dynamics of groundwater levels ordischarge, and at one of the sites it was possible to describe hydrochemical variations aswell. The application to the remaining three sites illustrated that groundwater chemistryshows a much more complex pattem of variations than does corresponding streamflowin this type of basin. The importance of areal variabilities within the recharge area isdiscussed and illustrated by a distribution of the model into two submodels when applyingit to one of the basins.

  • 6.
    Brandt, Maja
    SMHI, Core Services.
    Human impacts and weather-dependent effects on water balance and water quality in some Swedish river basins1990Report (Other academic)
    Abstract [en]

    The weather has a great effect on the water balance and, indirectly, affects water quality of river systems. At the same tirne, man-made changes in the Iandscape and other human activities have a great impact. To be able to distinguish the human irnpacts from the effects of natura! weather fluctuations we need observations and measurements but also analysis tools.

    In this thesis the PULSE and HBV hydrological models have been used as the analysis tools. Examples are given from forest management, in particular clearcuning, drainage and biomass increase, and from mining and agricultural activities. The models include conceptual descriptions of the most significant hydrological processes and are capable of coping with. weather-dependent fluctuations. Observed air temperature, precipitation and an estimate of the potential evapotranspiration are input data to the models.

    Simple hydrochemical and nitrogen leaching subroutines have been Iinked to the PULSE water balance model.These subroutines have been used to quantify weather-dependent and human effects on pH downstream from a mine tailings deposit and on nitrogen Ieaching from different non-point sources, especially from arable land.

    The applications illustrate the advantage of this type of model for analysis of man-made irnpacts and short-term climatological fluctuations. As the models are restricted to stationary conditions they cannot be used for forecasting of long-term changes due to changes in atmospheric deposition, land use or climate, unless the local effects of these changes are known. Other methods of analysing effects of man-made changes have also been tested, such as conventional comparative investigations, regression analysis and trend analysis. The use of these methods is exemplified by an analysis of human effects on erosion and sediment transport. It was found to be much more difficult to quantify effects with these sirnpler methods

  • 7.
    Carlsson, Bengt
    et al.
    SMHI, Research Department, Hydrology.
    Bergström, Sten
    SMHI, Research Department, Hydrology.
    The TELFLOOD project: Rainfall – Runoff Modelling and forecasting1998Report (Other academic)
    Abstract [en]

    The aim of the TELFLOOD project is to improve methods for hydrological forecasting in steep

    catchments. The hydrological modelling task of SMHI has been to improve the HBV model and to

    develop and test routines for model updating and forecasting.

    A new response routine, based on the variable contributing area concept, has been developed and

    proved to be successful in several experimental basins in Sweden, Italy and Ireland

    . The technique

    uses the contributing area in a way that is consistent with the procedure for soil moisture accounting

    and does not require further free parameters. Model improvements are significant to the standard

    HBV-96 version, in particular as concems minor floods after dry periods.

    A new updating routine, based on state corrections of the storages of the HBV model, was

    developed and tested. For some events it proved to be more efficient than the standard method

    based on input corrections.

  • 8.
    Carlsson, Bengt
    et al.
    SMHI, Research Department, Hydrology.
    Bergström, Sten
    SMHI, Core Services.
    Andréasson, Johan
    SMHI, Professional Services.
    Hellström, Sara-Sofia
    SMHI, Core Services.
    Framtidens översvämningsrisker2006Report (Other academic)
    Abstract [en]

    A study of the impacts of global warming on future risks for floods and inundations in Sweden has been carried out on contract from Länsförsäkringsbolagens Forskningsfond. The work focussed on River Dalälven and the big lakes Vänern, Mälaren and Hjälmaren but some nationwide analyses were carried out as well. The methodology was based on two global climate models, two assumptions about the future emissions of greenhouse gases and a regional climate model for dynamical downscaling to Swedish conditions. The regional climate scenarios are further processed by the HBV hydrological model and the resulting river runoff or water levels are treated statistically by frequency analysis. The results show that future risk exposure is changing in a different way depending on location in the country. The situation seems to be aggravated in particular in the Vänern area in southwest Sweden and along its outlet, River Göta älv. There will also be increased risks in the western parts of the Scandinavian mountains. The risks for heavy rainfalls, which may cause severe local flooding are likely to increase even though it is difficult to discern a consistent regional pattern between the models, in this respect. The study has also addressed the uncertainty in the assessments of flood risks. It is obvious that uncertainties in the global climate scenarios are responsible for a lot of the uncertainty in the end results, but there are also uncertainties inflicted by the strategy used when transferring the climate change signal from climate models to the hydrological model.

  • 9.
    Carlsson, Bengt
    et al.
    SMHI, Research Department, Hydrology.
    Sanner, Håkan
    SMHI, Core Services.
    Influence of river regulation on runoff to the Gulf of Bothnia: Gulf of Bothnia Year 19911994Report (Other academic)
  • 10.
    Harlin, Joakim
    SMHI.
    Hydrological modelling of extreme floods in Sweden1992Report (Other academic)
    Abstract [en]

    The Swedish guidelines for design flood determination are examined with emphasis on sensitivity analyses of modelling aspects. The research is mainly based on conceptual hydrological modelling with the HBV model. An automatic calibration methodology is presented and discussed. The influence of model calibration, model structure and climatic variability on the design flood simulation as well as the preset meteorological and hydrological conditions suggested in the guidelines are studied. The thesis also includes a discussion of the annual exceedance probability of the Swedish design floods by comparisons with observed extreme floods and frequency analyses.

    The design precipitation and snowpack magnitude are the most important rescriptions in the Swedish guidelines for design flood determination. Consequently, the regional design precipitation sequence and all suggested correction factors to the design rainfall sequence (area, altitude and season) are crucial. In application, the most important factors are: choice of  hydrological model, model calibration and selected climate period. These factors can lead to an uncertainty in the order of plus/minus 20 % on the design flood peak in catchments with good quality data and good model performance. In catchments with poor data quality, the uncertainty in design flood simulation will be larger. The corresponding uncertainty on reservoir water stage development will depend on local conditions.

  • 11.
    Johansson, Barbro
    SMHI, Professional Services.
    Modelling the effects of wetland drainage on high flows1993Report (Other academic)
    Abstract [en]

    The effects of drainage on high flows hav~ been studied by means of a conceptual runoff

    model (HBV/PULSE). To find parameters, typical for drained wetlands, the model was

    calibrated for two small catchments, one in central Sweden and one in south eastem Finland,

    where runoff data were available for drained and undrained conditions. The catchments had

    different characteristics, and the calibration procedure yielded two different parameter sets.

    The drainage effects in these small basins were studied by simulating the runoff, for a specific

    period, using model parameters for drained and undrained conditions.

    In the Swedish catchment,

    the effects on the runoff were almost negligible.

    In the Finnish catchment, the peak and

    low flows, as well as the total runoff volume increased considerably during the first

    10 years

    after drainage.

    The drainage parameters found for the small experimental basins, were also used to simulate

    the drainage of a 1000 km

    2 catchment in central Sweden, with a 20 % coverage of swamps.

    Hard.ly any effects could be seen when the parameters from the small Swedish basin were

    used. With the Finnish parameters there was a slight increase in peak and low flows, and the

    total runoff volume increased by 3.5 %. When extreme flows were simulated, by entering a

    design area rainf all sequence into the model, the diff erences between peak flows for drained

    and undrained conditions were fully negligible.

  • 12.
    Johansson, Barbro
    SMHI, Professional Services.
    Precipitation and Temperature in the HBV Model: A Comparison of Interpolation Methods2000Report (Other academic)
    Abstract [en]

    This report presents an evaluation of three different methods for estimation of areal precipitation and temperature

    , with

    special emphasis on their applicability for runoff modelling in the Scandinavian mountains. All three methods estimate

    the areal values as a weighted mean of the observations at nearby meteorological stations. The weights are determined

    by:

    a)

    a manual subjective selection of the most representative stations

    b)

    inverse square distance weighting

    c)

    optimal interpolation

    The methods were tested for a mountainous region in the north-western part of Sweden, which is an area with few

    meteorological stations and complex precipitation gradients. The elevation range is some 1500m

    , but meteorological

    stations are normally located at low altitudes in the valleys. For the subjective and inverse distance weighting methods,

    precipitation was extrapolated to higher elevations by assuming a linear increase with elevation

    . For the optimal

    interpolation method the climatological spatial variation in precipitation was described by means of the standard

    deviation, related to topographical features. Temperature was extrapolated using the wet adiabatic lapse rate. The

    evaluation included comparison of areal estimates, verification against point observations and the water balance

    equation and sensitivity analyses with respect to method parameters and network changes.

    For operational runoff modelling in Sweden, areal precipitation and temperature have tradit

    ionally been estimated by the

    subjective weighting method. This evaluation showed that for routine applications this time-consuming method can be

    replaced by optimal interpolation

    . Inverse-distance weighting can not be recommended in areas with few stations and

    complex gradients

    .

    The evaluation also showed that none of the methods correctly described the spatial variation in precipitation and

    temperature in the investigated region. They are thus not directly applicable for non-routine modelling applications

    where the estimation of runoff is not the sole objective. All methods also proved to be sensitive to at least some of the

    necessary parameters like, e

    .g., elevation dependency. This pointed to possible improvements of the estimates, as the

    parameters for the evaluation were selected without special consideration to local conditions

    . The optimal interpolation

    method seemed to be the least sensitive to changes in the meteorological network.

  • 13.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Floods in Sweden – Trends and occurrence1993Report (Other academic)
    Abstract [en]

    Sweden experienced a number of large floods in the 1980-ies. This raised the question of whether floods were becoming more frequent. A systematic study on floods was carried out, to provide a perspective to past and future floods. Frequency analysis was made using 16 methods. A split-sample test was used for evaluation of the predictive power of the methods. Numerical criteria were used for measuring the goodness of fit. The return periods of observed floods were estirnated by use of plotting positions.

    No convincing evidence of trends was found. The 1980-ies had larger floods than usual, where as the 1970-ies had few high floods, especially, in the auturnn. This may have led to the, irnpression of a trend. No evidence of autocorrelation or periodicity was found. For most of Sweden, the spring was found to be the season with highest extremes. The flood-moderating effect of regulation was illustrated, although floods were also found to occur in regulated systems. The results from the frequency analysis depended on the choice of criteria. In general, however, distributions with two parameters performed best. Neither a two component model treating spring and autumn separately, three parameter distributions, nor regional analyses gave any irnprovements. The spatial correlation within the data was considerable.

  • 14.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Vattentillgång och höga flöden i Sverige under 1900-talet2002Report (Other academic)
    Abstract [en]

    Water resources and floods in Sweden were studied with respect to trends and occurrence, with emphasis on the period 1901-2000. Two periods stand out when it comes to annual runoff: the 1920s, and the two last decades in the study period, with a runoff anomaly compared to the whole century of about +8%. The 1970s was the driest decade, with a runoff about 9 % below the century average. The most deviating 30-year period was 1951-80 with an anomaly of -5 % compared to 1901-2000. The few records that are available from the 19th century indicate an even higher runoff, but at lower temperatures. A linear regression to the runoff <luring the whole 20 th century gives an increase of 4 %, but the change was not statistically significant. The analysis of flood peaks suffers from uncertainties in the data. Flood peaks in old data were probably underestimated, since readings were made less frequently than today. A linear regression to annual flood peaks <luring the period 1911-2000 indicates an increase with about 10 %. This increase is almost significant at the 95 % level. The clearest increase was, however, found in basins with the less reliable observations. A smaller increase was obtained for an alternative selection of stations, which were considered to be more reliable. No significant trend was found in the selection of more reliable data. Seen in a shorter perspective, the autumn floods increased considerably <luring the period 1970-2000. Similar autumn floods, were, however; experienced in the 1920s. No increased frequency of very high floods, with a retum period of at least 10 years, could be determined.

  • 15.
    Lindström, Göran
    et al.
    SMHI, Research Department, Hydrology.
    Gardelin, Marie
    SMHI, Professional Services.
    Johansson, Barbro
    SMHI, Professional Services.
    Persson, Magnus
    SMHI.
    Bergström, Sten
    SMHI, Research Department, Hydrology.
    HBV-96 – En areellt fördelad modell för vattenkrafthydrologin1996Report (Other academic)
  • 16.
    Lindström, Göran
    et al.
    SMHI, Research Department, Hydrology.
    Gardelin, Marie
    SMHI, Professional Services.
    Persson, Magnus
    SMHI.
    Conceptual modelling of evapotranspiration for simulations of climate change effects1994Report (Other academic)
    Abstract [en]

    The evapotranspiration routines in existing conceptual hydrological models have been identified as one of the weaknesses which appear when these rnodels are used for the simulation of hydrological effects of a changing clirnate. The hydrological models in operational use today usually have a very superficial description of evapotranspiration. They have, nevertheless, been able to yield reasonable results. The objective of this paper is to analyse and suggest modifications of existing evapotranspiration routines in conceptual hydrological models to make them more appropriate for use in simulation of the effects of a changing climate on water resources.

    The following rnodifications of the evapotranspiration routine were formulated and tested in the HBV model: Ternperature anomaly correction of evapotranspiration, potential evapotranspiration by a simplified Thornthwaite type formula, interception submodel, spatially distributed evapotranspiration routine and alternative forrnulations of lake evapotranspiration. Sensitivity analyses were thereafter rnade to illustrate the effects of uncertainty in the hydrological model structure versus those of the uncertainty in the climate change predictions.

  • 17.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Johnell, Anna
    SMHI, Professional Services.
    Jacobsson, Karin
    SMHI, Professional Services.
    Hydrologiska ensembleprognoser2006Report (Other academic)
    Abstract [en]

    Since July 2004, a system for hydrological ensemble forecasting has been operational at SMHI. The system uses meteorological ensemble forecasts of precipitation and temperature from ECMWF as input to the hydrological HBV model, which generates an ensemble of discharge forecasts. In this report, the hydrological ensemble prediction system (EPS) is firstly described, along with some general features of the forecasts. Some preparatory analyses of the ECMWF meteorological forecasts and spring flood EPS forecasts are made. The main part of the report is an evaluation of 18 months of 9-day hydrological ensemble forecasts in 45 Swedish catchments. In the deterministic evaluation, the EPS median forecast is compared with the categorical PMP forecast. The results indicate an overall similar performance of the two forecast types. It is also shown that the spread of the EPS forecasts is related to the forecast error. In the probabilistic evaluation, the accuracy of probabilities calculated from the EPS spread is investigated. A percentile-based evaluation shows that the spread is underestimated. A threshold-based evaluation shows that the probability of exceeding some high discharge threshold level is overestimated. Finally, a simple method to correct the EPS spread is developed and tested, and different ways to present EPS forecasts are discussed.

  • 18.
    Pers, Charlotta
    SMHI, Research Department, Hydrology.
    Model description of BIOLA - a biogeochemical lake model2002Report (Other academic)
    Abstract [en]

    The biogeochemical lake model BIOLA was developed to be used for eutrophication studies in

    Sweden

    . Eutrophication is a threat for lakes in populated areas, and this model was developed to be

    a tool for managing lakes suffering from eutrophication. There are several measures that can be

    taken to reduce eutrophication. When considering different measures simulations of their effects,

    with models such as BIOLA, can contribute with information.

    The model is a biogeochemical lake module coupled to a one-dimensional hydrodynamic model.

    The model simulates the continuous change of lake stratification and water quality due to weather,

    inflow

    , outflow and biogeochemical processes in the lake and in the sediments. It simulates changes

    over time in nutrient and biological state at different depths. The most important variables simulated

    by the model are inorganic nutrients and phytoplankton in the water. Other variables include

    nutrients and organic matter in the sediments.

    The model has shown to be able to simulate changing nutrient and plankton dynamics. The result

    from three studied lakes are reviewed.

  • 19.
    Sandén, Per
    et al.
    SMHI.
    Wärfvinge, Per
    SMHI.
    Modelling groundwater response to acidification1992Report (Other academic)
    Abstract [en]

    The observed acidification of lakes and forest soils in Sweden has raised concem over the future of groundwater resources. Many of the processes which effect groundwater quality occur above the water table in the insaturated soil. Models of the hydrology and chemistry in this zone were developed and the results of that work are presented in this report. The overall objective of this project was to obtain a better understanding of the chemical and hydrological processes involved in the acidification of soil and groundwater in order to estimate future changes due to changes in acid deposition in relation to other acidifying processes.

    This work concluded of this report is that the groundwater in Sweden is vulnerable to acid deposition and that drastic reductions in emissions are necessary to protect this water. The model development provides a set of tools which are generally applicable to the hydrochemistry of acidification. They demand limited calibration and the requirements for input data and parameter values can usually be met. This makes it possible to use the models for assessment of groundwater acidification. The spatial and climatic variabilities of parameters and driving variables, however, are large. The uncertainties introduced by this variability must be considered when the results are used for decision making.

1 - 19 of 19
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