Göran Lindström

Development and test of the distributed HBV-96 hydrological model

Abstract A comprehensive re-evaluation of the HBV hydrological model has been carried out. The objectives were to improve its potential for making use of spatially distributed data, to make it more physically sound and to improve the model performance. The new version, HBV-96, uses subbasin division with a typical resolution of 40 km z, although any resolution can be used. In addition, each subbasin is divided into elevation bands, vegetation and snow classes. Automatic weighting of precipitation and temperature stations was introduced and a new automatic calibration scheme was developed. The modifications led to significant improvements in model performance. In seven test basins the average value of the efficiency criterion R 2 increased from 86 to 89%, with improvements in both the calibration and verification periods.

Hydrological change - Climate change impact simulations for Sweden

Climate change resulting from the enhanced greenhouse effect is expected to give rise to changes in hydrological systems. This hydrological change, as with the change in climate variables, will vary regionally around the globe. Impact studies at local and regional scales are needed to assess how different regions will be affected. This study focuses on assessment of hydrological impacts of climate change over a wide range of Swedish basins. Different methods of transferring the signal of climate change from climate models to hydrological models were used. Several hydrological model simulations using regional climate model scenarios from Swedish Regional Climate Modelling Programme (SWECLIM) are presented. A principal conclusion is that subregional impacts to river flow vary considerably according to whether a basin is in northern or southern Sweden. Furthermore, projected hydrological change is just as dependent on the choice of the global climate model used for regional climate model boundary conditions as the choice of anthropogenic emissions scenario.

Runoff trends in Sweden 1807-2002

Abstract Abstract Time series of annual runoff volumes and annual and seasonal flood peaks in Sweden were analysed. The study included a total of 61 discharge series, with emphasis on the period 1901–2002. Three wet decades stand out in the 20th century: the 1920s, 1980s and 1990s, with a runoff anomaly of +8%. The 1970s were very dry. In a short perspective, both runoff volumes and flood magnitude increased substantially between 1970 and 2002, but similar conditions were experienced in the 1920s. The linear regression line for the average runoff from all of Sweden increased by 5% over the past century, but the trend was not statistically significant. The runoff in the 19th century was in fact even higher than in recent decades, although temperatures were lower. Flood levels increased slightly more than annual runoff volumes in northern Sweden. However, flood peaks in old data are probably underestimated. The largest increase was consequently found in less reliable data series. It is therefore difficult to conclude that flood levels are actually increasing.

Water and nutrient predictions in ungauged basins: set-up and evaluation of a model at the national scale

Abstract A dynamic water quality model, HYPE, was applied to a large, data-sparse region to study whether reliable information on water quantity and water quality could be obtained for both gauged and ungauged waterbodies. The model (called S-HYPE) was set up for all of Sweden (∼450 000 km2), divided into sub-basins with an average area of 28 km2. Readily available national databases were used for physiographic data, emissions and agricultural practices, fixed values for representative years were used. Daily precipitation and temperature were used as the dynamic forcing of the model. Model evaluation was based on data from several hundred monitoring sites, of which approximately 90% had not been used in calibration on a daily scale. Results were evaluated using the Nash-Sutcliffe efficiency (NSE), correlation and relative errors: 92% of the spatial variation was explained for specific water discharge, and 88% and 59% for total nitrogen and total phosphorus concentrations, respectively. Day-to-day variations were modelled with satisfactory results for water discharge and the seasonal variation of nitrogen concentrations was also generally well captured. In 20 large, unregulated rivers the median NSE for water discharge was 0.84, and the corresponding number for 76 partly-regulated river basins was 0.52. In small basins, the NSE was typically above 0.6. These major achievements relative to previous similar experiments were ascribed to the step-wise calibration process using representative gauged basins and the use of a modelling concept, whereby coefficients are linked to physiographic variables rather than to specific sites. Editor D. Koutsoyiannis Citation Strömqvist, J., Arheimer, B., Dahné, J., Donnelly, C. and Lindström, G., 2012. Water and nutrient predictions in ungauged basins: set-up and evaluation of a model at the national scale. Hydrological Sciences Journal, 57 (2), 229–247.

Hydrology under change: an evaluation protocol to investigate how hydrological models deal with changing catchments

Abstract Testing hydrological models under changing conditions is essential to evaluate their ability to cope with changing catchments and their suitability for impact studies. With this perspective in mind, a workshop dedicated to this issue was held at the 2013 General Assembly of the International Association of Hydrological Sciences (IAHS) in Göteborg, Sweden, in July 2013, during which the results of a common testing experiment were presented. Prior to the workshop, the participants had been invited to test their own models on a common set of basins showing varying conditions specifically set up for the workshop. All these basins experienced changes, either in physical characteristics (e.g. changes in land cover) or climate conditions (e.g. gradual temperature increase). This article presents the motivations and organization of this experiment—that is—the testing (calibration and evaluation) protocol and the common framework of statistical procedures and graphical tools used to assess the model performances. The basins datasets are also briefly introduced (a detailed description is provided in the associated Supplementary material).

Development of an automatic calibration scheme for the HBV hydrological model

An automatic calibration scheme for the HBV model (ACSH) was developed. The ACSH was based on the physical significance of the model parameters and structure. The inference of hydrologists in the manual calibration was adopted as the guideline. A slight modification of the model structure of the soil routine was suggested to avoid interdependence of the parameters. In total nine parameters, except the snow routine, Fc and MAXBAS, were calibrated automatically in two stages; first the soil moisture routine and then the others. There are six sets in two stages in total. Using the Powell method, the parameters in each step were calibrated simultaneously with carefully selected objective functions, and in particular a powerful objective function for the soil moisture routine. The steps were in a fixed order in the ACSH according to the model structure. The optimal values of the model parameters were stable, with the different initial values varying in considerable ranges. The automatic calibration gave the same model performance as the manual calibration when the ACSH was tested in two basins. The automatic calibration can thus be used as a reference or as an alternative solution of the model.

Transit times of water in soil lysimeters from modeling of oxygen-18

A proper description of water pathways and transit times is important in the simulation of groundwater acidification using hydrochemical models. A simple water balance model, describing water flow and transit times in different soil layers, was developed and tested by the use of the stable isotope 18O as a natural tracer in soil lysimeters. Drainage was collected from lysimeters of three depths: 15, 40, and 80 cm, from two sites in the Stubbetorp research basin in south-eastern Sweden. The content of 18O in the precipitation and in the drainage from the lysimeters was measured during 2 yr. 18O was regarded as an ideal tracer, and its concentration in the drainage was modeled using the concentration in the precipitation as input. The percolation from each soil layer was assumed to depend on the inflow and the soil moisture storage in the layer. The most important model parameter, the field capacity, was derived from field information. Sensitivity analysis showed that the model was rather insensitive to other parameter values. Although simple, the model gave good results, both for the flow of water and 18O. The best results were obtained, when ideal mixing in the upper horizons of the soil was combined with piston flow at greater depths. Preferential flow was not found to be of great importance, nor was immobile water. Particle flow velocities and transit times in the soil lysimeters were simulated. The average particle flow velocities were about 0.6 cm d−1. The use of a dynamic model made it possible to simulate the temporal variations in transit times for water in the soil lysimeters. The mean transit times for the 80 cm lysimeter ranged from about 3 to 6 mo with an average value of 4 mo.

Spillway design floods in Sweden: I. New guidelines

The new Swedish guidelines for the estimation of design floods for dams and spillways are presented, with emphasis on high-hazard dams. The method is based on a set of regional design precipitation sequences, rescaled for basin area, season and elevation above sea level, and a full hydrological model. A reservoir operation strategy is also a fundamental component of the guidelines. The most critical combination of flood generating factors is searched by systematically inserting the design precipitation sequence into a ten year climatological record, where the initial snowpack has been replaced by a statistical 30-year snowpack. The new guidelines are applicable to single reservoir systems as well as more complex hydroelectric schemes, and cover snowmelt floods, rain floods and combinations of the two. In order to study the probabilities of the computed floods and to avoid regional inconsistencies, extensive comparisons with observed floods and frequency analyses have been carried out.

Past and current climate change

This section describes long-term observed climatic changes in atmospheric parameters. The focus is on surface climate conditions, but changes in atmospheric circulation are discussed as they often are behind climatic variability seen on regional and local scales. For a summary introduction on mean atmospheric states and conditions in the Baltic Sea Basin see Annex 1.2 with sections on the general atmospheric circulation (A.1.2.1), surface air temperature (A.1.2.2), precipitation (A.1.2.3), clouds (A.1.2.4), and global radiation (A.1.2.5).

Recent Mild and Wet Years in Relation to Long Observation Records and Future Climate Change in Sweden

Recent mild and wet years in Sweden were compared with long observation series of temperature, precipitation and runoff. Spatial average series for northern and southern Sweden were constructed and analyzed for the period 1901-2002. Precipitation increased considerably during the period, whereas temperature and runoff increases were weaker. On average, for the whole country, the differences between the period 1991-2002 and 1901-1990 were +0.7 degrees C for temperature, +11% in precipitation and +7% in runoff. The differences in temperature and precipitation, but not runoff, were significant at the 5% level. However, the 1930s were equally mild, and the runoff was almost as high in the 1920s. The characteristic feature of the past decade is the combination of high temperature, precipitation and runoff. The deviation between the most recent decade and the preceding years is consistent with climate scenario projections for Sweden, but there are also differences in the seasonal pattern.