SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "L773:0022 1694 "

Sökning: L773:0022 1694

  • Resultat 1-50 av 327
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Bendz, David, et al. (författare)
  • Evaporation from an active, uncovered landfill
  • 1996
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 182:1-4, s. 143-155
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect on evaporation of the presence of biodegradation heat in an uncovered biocell under operational conditions is elucidated. The contribution of the heat of biodegradation was investigated by measuring the temperature gradient in the top layer of a landfill. The evaporation was calculated by combining the energy budget with an expression for sensible heat flux, and taking the atmospheric stability into account by introducing the similarity theory of Monin and Obukhov. It was found that the biological heat enhanced the net energy flux and the actual evaporation by 20% and 10%, respectively.
  •  
2.
  • Bengtsson, Lars, et al. (författare)
  • Particle movement of melt water in a subdrained agricultural basin
  • 1992
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 135:1-4, s. 383-398
  • Tidskriftsartikel (refereegranskat)abstract
    • The pathways of melt water from a subdrained agricultural basin in southern Finland were investigated using oxygen-18 as tracer and measuring subdrainage water and total basin runoff. The flow paths for the melt water to reach the subdrains were through cracks in the ploughed layer and through regular spaced vertical sand-gravel drains. As long as the top soil was frozen a major part of the water that reached the agricultural basin outlet was snowmelt water. The basin runoff during the melt period 27 March- 1 3 April totalled 86 mm of which 20% was overland flow.
  •  
3.
  • Bengtsson, Lars, et al. (författare)
  • Water balance for landfills of different age
  • 1994
  • Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 158:3-4, s. 203-217
  • Tidskriftsartikel (refereegranskat)abstract
    • Water-related processes in landfills are discussed with emphasis on internal processes such as field capacity, moisture variation in time and space, and macropore flow. Runoff production and evaporation from landfills in Sweden of different age are investigated. It is clarified in what ways and for how long a closed municipal landfill differs from an ordinary land area from a hydrological point of view. 
  •  
4.
  • Berndtsson, Ronny (författare)
  • On the use of cross-correlation analysis in studies of patterns of rainfall variability
  • 1987
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 93:1-2, s. 113-134
  • Tidskriftsartikel (refereegranskat)abstract
    • Cross-correlation structures based on daily rainfall data recorded during a period of 5 years at 67 stations throughout Tunisia are used to examine spatial rainfall variability. Basic properties of the correlation-distance function such as cumulating period, exclusion versus inclusion of dry periods, and data volume are analysed. Analysis of the correlation patterns for each month shows that two periods (February-May, and September-November) are delimited by a period of great instability (December-January) and by the dry period (June-August). Three main rainfall regions can be distinguished, delimited and governed mainly by the topography and the coastal influence.
  •  
5.
  • Berndtsson, Ronny, et al. (författare)
  • Soil water and temperature patterns in an arid desert dune sand
  • 1996
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 185:1-4, s. 221-240
  • Tidskriftsartikel (refereegranskat)abstract
    • Under arid natural conditions, soil water content governs and limits the number and size of perennial plant species. Thus, plant-available soil water is the main constraint for sustainable control of desert encroachment. To evaluate possibilities for re-vegetation of bare sand surfaces, soil water and temperature patterns for typical sand dunes in a desert climate were investigated. Bare and vegetated soil transects were selected for observation of soil water content and temperature. The investigated soil transects covered crest-to-crest spacings (about 60 m horizontally and 15 m vertically) in a shifting sand dune area. Observations were made at Shapotou field research station bordering the Tengger Desert in Northwestern China. The paper presents two-dimensional properties of soil water content (0.1-3.0 m depth) and temperature (0-1.0 m depth) before and after rainfall. Rainfall (15-22 mm) affected soil water distribution down to 1.5-2.0 m and temperature distribution down to 1.0 m. Soil water appeared to be transported through the apparently highly pervious and homogeneous sand along the dune slopes. High water contents and, thus, infiltration occurred mainly at the non-sloping parts, i.e. the dune crests and bottoms. Rainfall changed the temperature patterns from a mainly horizontally layered appearance before the rainfall to increasingly vertically shaped patterns.
  •  
6.
  • Berndtsson, Ronny, et al. (författare)
  • Some Eulerian and Lagrangian statistical properties of rainfall at small space-time scales
  • 1994
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 153:1-4, s. 339-355
  • Tidskriftsartikel (refereegranskat)abstract
    • Management of urban hydrological systems requires a knowledge of short-term and small-scale rainfall properties. Small catchment areas, dense building structures, a high degree of impermeable areas, and resulting rapid runoff, mean that the properties of individual rain cells are important considerations. Accordingly, this paper characterizes mainly spatial rainfall properties on a scale suitable for urban hydrology. Because of the usually dominant advective velocity component of individual rain cells the Eulerian view (observations of the moving rain cell by a fixed rain gage network) gives a distorted picture in the direction of movement of the actual rain cell. The extent of distortion depends on the magnitude of the advective velocity. The Lagrangian approach (moving along with the same speed and direction as the cell) gives different information regarding cell characteristics (e.g. size) compared with the Eulerian approach. It is shown that the Lagrangian cell size as indicated by the spatial correlation structure on average is twice the size of the Eulerian cell size. Thus, it is argued that the Lagrangian approach provides a more realistic picture of the rainfall structures compared with the Eulerian approach. The cell properties exhibit a temporal persistence of the spatial characteristics in the direction of movement. This persistence is, however, not strong and thus a forecasting procedure using advection only does not seem appropriate.
  •  
7.
  • Berndtsson, Ronny, et al. (författare)
  • Spatial and temporal characteristics of high-intensive rainfall in northern Tunisia
  • 1986
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 87:3-4, s. 285-298
  • Tidskriftsartikel (refereegranskat)abstract
    • When dealing with urban design, it is essential to have knowledge of the magnitude of the spatial variability of short high-intensive rainstorms. Most of the studies of high-intensive rainfall, conducted during recent years, concern regions with a humid climate. Still, the largest temporal and spatial variations in rainfall are to be found in arid and semi-arid regions. This paper sums up findings regarding rainfall variability, observed in a small catchment in northern Tunisia during a period of 2 yr. Point and areal intensities are presented for the ten most high-intensive storms observed. Storm-centered areal reduction factors are calculated for different durations and areas.
  •  
8.
  • Berndtsson, Ronny, et al. (författare)
  • Spatial and temporal scales in rainfall analysis : Some aspects and future perspectives
  • 1988
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 100:1-3, s. 293-313
  • Tidskriftsartikel (refereegranskat)abstract
    • Aspects of spatial and temporal rainfall variability and rainfall analysis in relation to some water management problems are surveyed and discussed. It is concluded that relevant modelling of hydrological processes in which the rainfall is a driving force is vital with respect to possibilities of finding solutions to increasing environmental problems following urbanization and industrialization. However, modern computer methods and our knowledge of the spatial and dynamic properties of rainfall fields are seldom used in practical engineering applications. This causes errors and uncertainties in the calculated output. Bridging the gaps between researchers and engineers may overcome some of these problems. It is also argued that experimental studies in a variety of climates and physiographical conditions using an interdisciplinary approach are needed in order to further investigate the scale and dynamics of spatial rainfall variability.
  •  
9.
  • Berndtsson, Ronny, et al. (författare)
  • Spatial variability of infiltration in a semi-arid environment
  • 1987
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 90:1-2, s. 117-133
  • Tidskriftsartikel (refereegranskat)abstract
    • Fifty-two double-ring infiltrometer tests, performed in a small, partly urbanized catchment in northern Tunisia are analyzed. Spatial variability is characterized by use of cross-correlation functions. Spatial patterns of infiltration properties are shown to be governed by geomorphology and occurring vegetation. Different geomorphological zones and zones with equal density of vegetation tend to be oriented in a parallel pattern in relation to the wadi. Statistical properties of infiltration capacities depending on geomorphological zone are presented.
  •  
10.
  • Kawamura, Akira, et al. (författare)
  • Real-time tracking of convective rainfall properties using a two-dimensional advection-diffusion model
  • 1997
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 203:1-4, s. 109-118
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a need to improve rainfall forecasting capabilities for small ungaged urban catchments to reduce flooding hazards and pollution release. For this purpose, information is required on small-scale and short-term convective cell behavior. We use a two-dimensional stochastic advection-diffusion model to parameterize the space-time rainfall intensity from convective rainfall. The rainfall intensity resulting from different separable components of the rain cell, such as apparent turbulent diffusion and development/decay of rainfall intensity, is quantified for 10 observed and, for southern Sweden, representative high-intensity rainfall events. This is done following a Lagrangian approach. It is shown the used model was able to respond to rapid changes in observed rainfall intensity in both space and time, thus giving a small average root-mean-square error for all 10 events (0.06 mm min-1). When dividing the total rainfall intensity into apparent turbulent diffusion and development/decay terms, respectively, it was shown that D(y,center) and γ(center) contribute approximately equally to the observed rainfall intensity. The D(x,center) is usually only half the value of D(y,center), thus indicating less intensity contribution from this term and that the general elliptical shape of rain cells are elongated in the direction of movement. The observations indicate that the cumulus stage represents half and the dissipating stage half of the total cell development, respectively. The results can be used as first choice of parameter values when modeling rain cell movement over ungaged areas and the presented methodology can be used to study the effects of different cell components on total rainfall intensity.
  •  
11.
  • Klove, B., et al. (författare)
  • Runoff generation in a plough-drained cutover fen in Central Finland
  • 1999
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 218:3-4, s. 157-168
  • Tidskriftsartikel (refereegranskat)abstract
    • The hydrology of a cutover fen was studied from May to October in 1995 and 1996. Rainfall equivalent depths were measured every 15 min and stream runoff was continuously monitored. Water table depths were measured bi-weekly during 1995 and continuously during 1996. Storm runoff was separated into different components; rain falling directly into channels and rapid groundwater response based on a contributing area method and on different electrical conductivities of rain-, ground- and streamwater. The results show three sources of storm runoff from cutover fens. Frequent small runoff peaks were caused by rain falling directly into channels. The amount of quick runoff increased when rain fell on wet soil, resulting in intermediate sized runoff peaks generated by rapid groundwater response. The largest runoff values were observed after prolonged rainfall when water from the upper part of the catchment flooded the fen. (C) 1999 Elsevier Science B.V. All rights reserved.
  •  
12.
  • Olsson, Jonas, et al. (författare)
  • An analysis of the rainfall time structure by box counting-some practical implications
  • 1992
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 137:1-4, s. 261-277
  • Tidskriftsartikel (refereegranskat)abstract
    • The scale-invariant behavior of the rainfall time structure was investigated by applying the box counting method to rainfall time series. Two years of minute observations, 90 years of daily observations and 170 years of monthly observations were analyzed and the results were interpreted and related to physical properties of the rainfall process. This paper discusses the question of whether an hypothesis of temporal scale invariance is valid for rainfall and the possibilities of using it in practical hydrology.
  •  
13.
  • Persson, Magnus, et al. (författare)
  • Estimating soil solution electrical conductivity from time domain reflectometry measurements using neural networks
  • 2003
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 273:1-4, s. 249-256
  • Tidskriftsartikel (refereegranskat)abstract
    • Time domain reflectometry (TDR) is a widely used method for measuring the dielectric constant (K-a) and bulk electrical conductivity (sigma(a)) in soils. The TDR measured sigma(a) and K-a can be used to calculate the soil solution electrical conductivity, sigma(w.) The sigma(w), in turn, can be related to the concentration of an ionic tracer. Several models of the sigma(w)-sigma(a)-K-a relationship can be found in the literature. Most of these models require extensive calibration experiments in order to obtaining best-fit parameters. In this paper, we attempt to model the sigma(w)-sigma(a)-K-a relationship using neural networks (NN). We used TDR measured K-a and sigma(a) along with five different soil physical parameters (sand, silt, clay, and organic matter content and bulk density) measured in nine different soil types using three different sigma(w) levels in each soil type. In total, 2953 K-a and sigma(a) measurements were obtained. The NN estimated sigma(w) was found to have a root mean square error (RMSE) of 0.05-0.13 dS m(-1) for the nine different soil types whereas the RMSE of two traditional sigma(w)-sigma(a)-K-a models was 0.12-0.87 dS m(-1). Furthermore, the traditional models exhibited larger errors for low sigma(a) and K-a, whereas the NN estimated sigma(w) did not show any trend in the errors. A sensitivity analysis showed that the NN model was more sensitive to small changes in sigma(a) compared to K-a. Of the five soil physical parameters, the silt and clay content affected the sigma(w)-sigma(a)-K-a relationship the most. The results presented shows that using NN, the sigma(w)-sigma(a)-K-a relationship can be predicted using soil physical parameters without need for elaborate soil specific calibration experiments. (C) 2003 Elsevier Science B.V. All rights reserved.
  •  
14.
  • Persson, Magnus, et al. (författare)
  • Estimating transport parameters in an undisturbed soil column using time domain reflectometry and transfer function theory
  • 1998
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 205:3-4, s. 232-247
  • Tidskriftsartikel (refereegranskat)abstract
    • Modelling solute transport in the unsaturated zone is a complex problem given the inherent soil heterogeneity. Using time domain reflectometry (TDR) as described in this paper can improve data quality to be used in predictive models. The TDR technique requires appropriate calibration if it is to be used for solute concentration measurements under constant and varying water content. Two ways of determining the parameters in the relationship between bulk soil electrical conductivity, σa, soil solution electrical conductivity, σw and volumetric water content, θ, were used. Among the two calibration methods tested here, the one which involved eluting the soil with several pore volumes of water of known electrical conductivity under transient flow conditions in an undisturbed soil column gave a linear σw−σa−θ relationship with depth dependent parameters. The other calibration method involved the use of disturbed soil under static conditions and resulted in a curvilinear σw−σa−θ relationship. The former calibration was subsequently used to determine solute concentrations in breakthrough experiments. Two solute transport experiments were carried out in the same undisturbed soil column; one for steady-state and one for transient flow condition. Parameters of the convective log normal transfer function (CLT) model were determined using time-integral-normalized resident concentrations. It was shown that the stochastic-convective approach described the experimental data well. Horizontal heterogeneity was more important during the transient experiment, where the topsoil was periodically ponded during a short period, than in the steady-state experiment, where unsaturated conditions were maintained throughout the experiment. This increased heterogeneity during transient flow was also reflected by the fact that preferential solute flow was only observed in the column's outlet under transient conditions.
  •  
15.
  • Persson, Magnus, et al. (författare)
  • Modeling plot scale dye penetration by a diffusion limited aggregation (DLA) model
  • 2001
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 250:1-4, s. 98-105
  • Tidskriftsartikel (refereegranskat)abstract
    • Solute transport in the unsaturated zone often occurs in preferential How paths. There are several reasons for this, e.g., water repellency, the occurrence of fissures and cracks, animal borrows, decomposed root threads etc. The resulting How patterns often display a fractal resemblance which is difficult to predict using conventional transport models. A way to preserve the fractal property of observed data is to use the diffusion limited aggregation (DLA) model concept. In the present paper we use dye infiltration data to further develop the DLA model concept as applied to solute movement in soils. The DLA model is first calibrated against detailed field observations of dye infiltration. The model is shown to give a good description of observed mean and variance of dye penetration. After this, the calibrated model is verified against independent data from a nearby plot. The model is shown to reproduce observed dye patterns in a satisfactory way also at the verification plot.
  •  
16.
  • Persson, Magnus, et al. (författare)
  • Water application frequency effects on steady state solute transport parameters
  • 1999
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 225:3-4, s. 140-154
  • Tidskriftsartikel (refereegranskat)abstract
    • In many studies, data from transient or quasi steady-state solute transport experiments are modeled using steady-state models. Few investigations, however, have been carried out to verify the validity of this approach. In this paper, we study the effects of water application frequency on the parameters derived using steady-state models. Bromide transport was studied in an undisturbed soil column of loamy sand exhibiting fingered flow. Four solute displacement experiments were carried out under quasi steady-state flow conditions. The mean water flux in all experiments was 1.42 cm d−1, but water was applied at different time intervals for each; that is one, two, three, or six times daily. Water content and solute concentration were measured following an in situ calibration, using time domain reflectometry (TDR) probes at nine different depths. The TDR probes were placed in two alternate directions, with every second probe being orthogonal to the first. The convective–dispersive (CDE) and the convective log-normal transfer function (CLT) models were fitted to the solute transport data. The CDE model best described the solute transport. The dispersivity decreased when water was applied more often. The decrease can largely be attributed to lesser variability of the water flux velocity, especially in one of the probe directions. The mass recovery was about 40% for all depths and did not change with the differing intervals between water applications. Solute transport heterogeneity was also constant during the experiments. These observations lead to the conclusion that preferential flow paths in this soil were consistent and independent of application frequency.
  •  
17.
  • Sander, Mikkel, et al. (författare)
  • The relationship between annual varve thickness and maximum annual discharge (1909-1971)
  • 2002
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 263:1-4, s. 23-35
  • Tidskriftsartikel (refereegranskat)abstract
    • Annually laminated (varved) sediments from the River Angermanalven, mid-central Sweden, have been used to construct an annual 2000-year long record of varve thickness. Maximum daily annual discharge and mean varve thickness for the years 1909-1971 are significantly correlated (r = 0.87). A relationship between maximum daily annual discharge for the observed period (1909-1971) and varve thickness was determined. The return time of two exceptionally thick varves in the 2000-year long record at the years 658 and 492 AD were estimated and their likelihood estimated based on a Gumbel frequency analysis. (C) 2002 Elsevier Science B.V. All rights reserved.
  •  
18.
  • Zhang, Tielin, et al. (författare)
  • Temporal patterns and spatial scale of soil water variability in a small humid catchment
  • 1988
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 104:1-4, s. 111-128
  • Tidskriftsartikel (refereegranskat)abstract
    • Temporal and spatial variability of soil water content on mainly two different scales is visualized by means of correlation analyses. The soil water data were collected at seven sites for a period of about ten years. The spatial variability of soil water in the unsaturated zone is illustrated and discussed from the aspects of interdepth, intersite and temporal changes respectively. The results in terms of the correlation structure show an increase in spatial variability when depth increases. Three soil layers with different patterns of variability are identified: 0-60, 60-140, and 140-240 cm. It is concluded that the mean time series values of the soil water content do not differ significantly within horizontal distances of about 10-20m. For distances of about 1100m this variation may be more than 5% by volume in absolute values. Higher spatial variability is noted during the summer period (May-September).
  •  
19.
  • Öhrström, Pernilla, et al. (författare)
  • Field-scale variation of preferential flow as indicated from dye coverage
  • 2002
  • Ingår i: Journal of Hydrology. - 0022-1694. ; 257:1-4, s. 164-173
  • Tidskriftsartikel (refereegranskat)abstract
    • Field investigations were performed in semiarid Tunisia to investigate spatial variability of preferential pathways in catchment- and plot-scales. A rainfall simulator with dye was used to simulate effects of a 20-year rainstorm. After infiltration into six one-meter square plots, vertical 2.5-cm thick soil sections were excavated, and dye penetrations were photographed, The results show that different catchment physiographic areas (nose, slope, and hollow) displayed significantly different responses to the infiltrating dye. Nose and hollow areas exhibited larger susceptibility to preferential flow. Here. infiltrated dye was transported to greater depths. Slopes had fewer deep cracks and fissures. The dye distribution within each plot was also investigated. The variability of the dye patterns increased with scale. Cross-correlations and power spectrum analyses indicated that the preferential pathways were randomly distributed. The power-law behavior of the dye patterns' spectral density suggested scale invariance and the possibility of random cascade modeling. (C) 2002 Elsevier Science B.V. All rights reserved.
  •  
20.
  • Grelle, A., et al. (författare)
  • Evaporation components of a boreal forest : variations during the growing season
  • 1997
  • Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 197:1-4, s. 70-87
  • Tidskriftsartikel (refereegranskat)abstract
    • To improve the understanding of interactions between the boreal forest and the climate system as a key issue for global climate change, the water budget of a mixed pine and spruce forest in central Sweden was estimated by measurements of the water flux components and the total evaporation flux during the period 16 May-31 October 1995. Total evaporation was measured using eddy correlation and the components were obtained using measurements of precipitation, throughfall, tree transpiration, and forest floor evaporation. On a daily basis, tree transpiration was the dominant evaporation component during the vegetation period. However, it could be efficiently blocked by a wet canopy associated with large interception evaporation. The accumulated total evaporation was 399 mm, transpiration was 243 mm, forest floor evaporation was 56 mm and interception evaporation was 74 mm. The accumulated sum of interception, transpiration, and floor evaporation was 51 mm larger than the actual measured total evaporation. This difference was mainly attributed to the fact that transpiration was measured in a rather dense 50-year-old stand while total evaporation represented the average conditions of older, roughly 100-year-old stands. To compare eddy-correlation measurements with small-scale measurements of evaporation components, a source area analysis was made to select the flux data that give the best representation of the investigated stand. Especially under stable atmospheric conditions the requirements for surface homogeneity were very high and extreme care had to be taken to be aware of the flux source areas. Canopy water storage was determined by two methods: by the water balance of the canopy, which gave a result of 3.3 mm; and by the so-called minimum method based on plots of throughfall versus precipitation, which gave a much lower value of 1.5 mm. Seasonal interception evaporation constituted 30% of the precipitation.
  •  
21.
  • Halldin, Sven, et al. (författare)
  • NOPEX - a northern hemisphere climate processes land surface experiment
  • 1998
  • Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 212-213, s. 172-187
  • Tidskriftsartikel (refereegranskat)abstract
    • The interface between land surfaces and the atmosphere is a key area in climate research, where lack of basic knowledge prevents us from reducing the considerable uncertainties about predicted changes. Boreal forests play an important, but not well known, role in the global hydrological and biogeochemical cycles. NOPEX (a NOrthern hemisphere climate Processes land surface EXperiment) is devoted to the study of land surface-atmosphere interaction in a northern European forest-dominated landscape. The main NOPEX region represents the southern edge of the boreal zone. It consists of a highly heterogeneous landscape, with forests, mires, agricultural land and lakes. A second study site, in northern Finland, representing the northern edge of the boreal zone, will be introduced into NOPEX in connection with its coming winter-time field activities. Field activities, dominating the initial phase of NOPEX, are conceived to strike a balance between the need to cover multi-annual observations and the resources required to carry out measurements covering all relevant spatial scales. The long-term data collection activities, the Continuous Climate Monitoring (CCM), form the backbone of the field programme. A suite of Concentrated Field Efforts (CFEs) covering periods of summer, spring and winter brings together scientists from more then 20 countries during month-long campaigns. CFEs have been carried out in May-June 1994 and April-July 1995. A third, winter-time CFE is planned for 1998-99. The System for Information in NOPEX (SINOP) is the database which forms a backbone for modelling and analysis work, dominating the second stage of NOPEX. A series of PhD courses are run in parallell to the research activities. Analysis and modelling are done in four interacting areas, including local-scale processes, meso-scale surface-atmosphere coupling and remote sensing techniques. The fourth area, regionalization methods, aims at bringing the previous three together in order to provide improved parameterization schemes for exchange of energy, momentum, water and CO2 between land and atmosphere in hydrological and meteorological models from the meso to the global scale. 
  •  
22.
  • Johnsson, Holger, et al. (författare)
  • Surface runoff and soil water percolation as affected by snow and soil frost
  • 1991
  • Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 122:1-4, s. 141-159
  • Tidskriftsartikel (refereegranskat)abstract
    • A coupled soil water and heat model was used to study the influence of soil frost and snow on infiltration and drainage flow in an agricultural field in central Sweden. An analogy between freezing/thawing and drying/wetting was assumed for the soil frost submodel. Model simulations were evaluated against measurements of total soil water content, unfrozen water content, soil temperature and drainage water-flow. The influences of soil frost and spatial variation in snow cover were studied by simulation of possible extreme situations in the field. The model accurately described the dynamics of soil temperature and water contents; however, infiltration and field drainage flow were considerably underestimated and delayed by about three weeks under frozen conditions. A model simulation, discounting the effects of soil frost, overestimated the drain response. An attempt at simulating the field variation in snow cover by assuming possible 'sink points' for snowmelt, explained part of the deviations between simulated and measured drain flows. A basis for a new model formulation of the infiltration and percolation processes in frozen soil is proposed in which two water-flow domains are assumed, one low-flow domain in the fine pores, smaller than those filled with ice, and one high-flow domain in the large air-filled pores. This allows the simulation of rapid infiltration in large ice-free pores and drainage flow under frozen conditions as well as the resulting redistribution of ice from smaller to larger pores.
  •  
23.
  • Jonsson, K., et al. (författare)
  • Hyporheic exchange of reactive and conservative solutes in streams - tracer methodology and model interpretation
  • 2003
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 278:04-jan, s. 153-171
  • Tidskriftsartikel (refereegranskat)abstract
    • A transient storage model is evaluated using results from a tracer experiment, where a conservative and a reactive tracer (H-3 and Cr-51(III)) were injected simultaneously and monitored in stream water and bed sediment. About 76% of the chromium was lost from the stream water on the reach 30 km downstream of the injection point directly after the passage of the pulse in the flowing water. The bed sediment hosted the main part of the retained chromium. The time to washout 75% of the maximum solute uptake in the sediment was similar to 85 times longer for chromium than for tritium (i.e. similar to 45 days). It was possible to describe the sediment-water exchange with a diffusive flux formulation that could be evaluated using tritium breakthrough curves in the stream water or the tritium inventory breakthrough curves in the sediment. This experiment revealed further that observations of chromium concentrations in the sediment were essential for the quantifying of sorption properties, as it was not possible to catch accurately the time scale of sorption within the duration of the breakthrough curves in the stream water. There was a clear need for a rate-limited description of the sorption of chromium in the sediment. We found that a first-order kinetic description of the sorption process could acceptably describe the breakthrough curves in both the stream water and the bed sediment.
  •  
24.
  • Jonsson, Karin, et al. (författare)
  • Hyporheic Exchange of Reactive and Conservative Solutes in Streams - Tracer Methodology and Model Interpretation
  • 2003
  • Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 278:1-4, s. 153-171
  • Tidskriftsartikel (refereegranskat)abstract
    • A transient storage model is evaluated using results from a tracer experiment, where a conservative and a reactive tracer (3H and 51Cr(III)) were injected simultaneously and monitored in stream water and bed sediment. About 76% of the chromium was lost from the stream water on the reach 30 km downstream of the injection point directly after the passage of the pulse in the flowing water. The bed sediment hosted the main part of the retained chromium. The time to washout 75% of the maximum solute uptake in the sediment was ∼85 times longer for chromium than for tritium (i.e. ∼45 days). It was possible to describe the sediment-water exchange with a diffusive flux formulation that could be evaluated using tritium breakthrough curves in the stream water or the tritium inventory breakthrough curves in the sediment. This experiment revealed further that observations of chromium concentrations in the sediment were essential for the quantifying of sorption properties, as it was not possible to catch accurately the time scale of sorption within the duration of the breakthrough curves in the stream water. There was a clear need for a rate-limited description of the sorption of chromium in the sediment. We found that a first-order kinetic description of the sorption process could acceptably describe the breakthrough curves in both the stream water and the bed sediment.
  •  
25.
  • Lundberg, Angela, et al. (författare)
  • Evaporation of intercepted snow : measurement and modelling
  • 1998
  • Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 206:3-4, s. 151-163
  • Tidskriftsartikel (refereegranskat)abstract
    • Snow storage on a coniferous forest canopy was measured using γ-ray attenuation and tree weighing systems, along with measurements of throughfall, using two plastic sheet net rainfall gauges. Meteorological parameters were measured with an automatic weather station. Estimates of evaporation of intercepted snow show an average rate of 0.24 mm h-1 and a maximum cumulative total of 3.9 mm in 7 h. Comparison with evaporation determined by a combination method with two different estimates of aerodynamic resistance (the "standard" rain aerodynamic resistance raL and a snow aerodynamic resistance raS-an order of magnitude larger than raL) showed that raL overestimated the evaporation by a factor of 2.6, whereas raS gave fair agreement with the measured evaporation. A multilayer model may be needed to take into account the variations of latent heat source area. Using the long-term measurements of the weight of snow on a single tree the total interception evaporation was estimated to be of the order 200 mm year-1.
  •  
26.
  • Lundberg, Angela (författare)
  • Evaporation of intercepted snow : review of existing and new measurement methods
  • 1993
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 151:2-4, s. 267-290
  • Tidskriftsartikel (refereegranskat)abstract
    • Knowledge of the annual water balance within a catchment is still hampered by an insufficient understanding of winter conditions. The least known term of the winter water balance is evaporation - particularly that from intercepted snow. Methods to measure interception and evaporation are reviewed. Undisturbed meteorological conditions, high time resolution and continuous measurements of intercepted mass were taken as criteria for an ideal method. The ideal method should work during periods of melt and sublimation and above rough forest surfaces. None of the existing methods fulfils all the criteria. Most traditional hydrological methods to estimate winter-time evaporation, such as runoff and snow-course studies, non-weighing lysimeters, and precipitation and throughfall measurements, produce too little information to distinguish the causes of the observed changes. Among micrometeorological methods, only the eddy-correlation technique is suitable, and should be used in combination with interception measurements. Of the methods primarily designed to quantify interception, i.e. collection of intercepted snow, visual or photographic observations, displacement transducers, weighing of branches and trees and gamma-ray attenuation, only the last two yield continuous interception records. In combination with continuous measurements of throughfall and drip, these methods can be used to study the evaporation process. The gamma-ray method can be used to measure whole-canopy losses, whereas the other two methods deal only with losses from a branch or a single tree. The weighing-lysimeter technique produces the same information as the method of weighing a cut tree but employs a more complex set-up. The weighing-tree method combined with measurement of drip is one of the current methods that is most suitable for process studies. A new device for this purpose is presented, which differs from earlier designs by allowing a continuous weighing of drip in a tray of 2m width placed around the tree. The tray was fastened to the tree with wires and was automatically raised and lowered, thus allowing continuous measurements of both intercepted mass (with the tray raised) and evaported mass (with the tray lowered). A maximum evaporation rate of 0.3 mm h-1 was recorded with this device on 22-23 March 1990 at a site close to Luleå in northern Sweden. This maximum value was measured when wet snow was present, and confirmed earlier reports of high evaporation rates. The maximum evaporated mass during 24 h was 3.3 mm.
  •  
27.
  •  
28.
  • Stålnacke, P., et al. (författare)
  • Trends in nutrient concentrations in Latvian rivers and the response to the dramatic change in agriculture
  • 2003
  • Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 283:1-4, s. 184-205
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years, the use of fertilisers in the Baltic countries (Estonia, Latvia, and Lithuania) has decreased at an unprecedented rate. The import of mineral fertilisers and feed stuff became almost non-existent, and extensive slaughtering of livestock reduced the amount of manure. In Latvia, the purchase of mineral fertilisers decreased by a factor of 15 between 1987 and 1996 and the number of livestock decreased with a factor of almost 4 during the same time period. Such abrupt and comprehensive changes in land use have never before occurred in the history of modern European agriculture. Here, the impact that this dramatic reduction has had on concentrations of nutrients in Latvian rivers is examined. To discern temporal changes, statistical analyses were undertaken on time series of nutrient concentrations and relationships between concentrations and runoff at 12 sampling sites in ten Latvian rivers covering drainage areas from 334 to 64,000 km2. Considering the study period 1987-1998, only four of the 12 sites showed statistically significant downward trends (one-sided test at the 5% level) in the dissolved inorganic nitrogen (DIN = NO3-N + NO2-N + NH4-N) data. There are probably two main explanations for the weak DIN trends. Firstly, long water-transit times in the soilwater and groundwater may have caused substantial time lag between changes in input and output of nitrate in the studied catchments. Secondly, the loss of DIN might have been dominated by mineralisation of large pools of organic nitrogen that have accumulated over several years. These inferences are supported by (i) a hydrograph recession analysis and (ii) indications of DIN transformation processes, presumably denitrification, in smaller streams and channels, based on measurements in small agricultural catchments (1-4 km2) in Estonia and Latvia. Formal testing of trends in phosphorus data revealed that marked drops occurred in riverine concentrations at six sites in 1987-1998. A joint analysis of concentration time series for all sampling sites for 1987-1998 showed weak statistical significance for downward trends in NH4-N, NO 3-N, and DIN (p ? 0.04) and substantial significance for PO 4-P (p < 0.01). Thus, the extensive decrease in agricultural intensity that began in the early 1990s has led to only a slow and limited (especially regarding nitrogen) response in Latvian rivers. The difference noted between nitrogen and phosphorus also suggests that factors other than reduced fertiliser application influenced the inertia of the water quality response. Our findings, along with those obtained in similar studies, show that large cuts in nutrient inputs do not necessarily cause an immediate response, particularly in medium-sized and large catchment areas.
  •  
29.
  • Szöllösi-Nagy, Andras (författare)
  • The discretization of the continuous linear cascade by means of state space analysis
  • 1982
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 58:3-4, s. 223-236
  • Tidskriftsartikel (refereegranskat)abstract
    • In applying digital filtering techniques for hydrological forecasting by means of cascade models a discrete model of the continuous processes involved is necessary. The paper deals with the discretization of the continuous Nash cascade. The principles of state space modelling are used. The continuous state variable model of the Nash cascade together with the computation of the state transition matrix and the impulse response is given. A discrete state variable model is derived whose state and input transition matrices are in a dual relationship. Any different discrete state representations of the continuous Nash cascade are related to each other via a linear transformation. In the limit case the discrete state models are identical with the continuous Nash cascade. The discrete state models are discretely coincident with the continuous model but at the same time consider the dynamic changes in between the sampling points. A numerical example is presented
  •  
30.
  • Achleitner, Stefan, et al. (författare)
  • Analyzing the operational performance of the hydrological models in an alpine flood forecasting system
  • 2012
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 412-413, s. 90-100
  • Tidskriftsartikel (refereegranskat)abstract
    • During recent years a hybrid model has been set up for the operational forecasting of flood discharges in the 6750km 2 Tyrolean part of the River Inn catchment in Austria. The catchment can be characterized as a typical alpine area with large variations in altitude. The paper is focused on the error analysis of discharge forecasts of four main tributary catchments simulated with hydrological water balance models. The selected catchments cover an area of 2230km 2, where the non-glaciated and glaciated parts are modeled using the semi-distributed HQsim and the distributed model SES, respectively.The forecast errors are evaluated as a function of forecast lead time and forecasted discharge magnitude using 14 events from 2007 to 2010. The observed and forecasted precipitation inputs were obtained under operational conditions. The mean relative bias of the forecasted discharges revealed to be constant with regard to the forecast lead time, varying between 0.2 and 0.25 for the different catchments. The errors as a function of the forecasted discharge magnitude showed large errors at lower values of the forecast hydrographs, where errors decreased significantly at larger discharges being relevant in flood forecasting
  •  
31.
  • Ala-aho, P., et al. (författare)
  • Using stable isotopes to assess surface water source dynamics and hydrological connectivity in a high-latitude wetland and permafrost influenced landscape
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 556, s. 279-293
  • Tidskriftsartikel (refereegranskat)abstract
    • Climate change is expected to alter hydrological and biogeochemical processes in high-latitude inland waters. A critical question for understanding contemporary and future responses to environmental change is how the spatio-temporal dynamics of runoff generation processes will be affected. We sampled stable water isotopes in soils, lakes and rivers on an unprecedented spatio-temporal scale along a 1700 km transect over three years in the Western Siberia Lowlands. Our findings suggest that snowmelt mixes with, and displaces, large volumes of water stored in the organic soils and lakes to generate runoff during the thaw season. Furthermore, we saw a persistent hydrological connection between water bodies and the landscape across permafrost regions. Our findings help to bridge the understanding between small and large scale hydrological studies in high-latitude systems. These isotope data provide a means to conceptualise hydrological connectivity in permafrost and wetland influenced regions, which is needed for an improved understanding of future biogeochemical changes.
  •  
32.
  • Ameli, A. A., et al. (författare)
  • Hillslope permeability architecture controls on subsurface transit time distribution and flow paths
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier B.V.. - 0022-1694 .- 1879-2707. ; 543, s. 17-30
  • Tidskriftsartikel (refereegranskat)abstract
    • Defining the catchment transit time distribution remains a challenge. Here, we used a new semi-analytical physically-based integrated subsurface flow and advective–dispersive particle movement model to assess the subsurface controls on subsurface water flow paths and transit time distributions. First, we tested the efficacy of the new model for simulation of the observed groundwater dynamics at the well-studied S-transect hillslope (Västrabäcken sub-catchment, Sweden). This system, like many others, is characterized by exponential decline in saturated hydraulic conductivity and porosity with soil depth. The model performed well relative to a tracer-based estimate of transit time distribution as well as observed groundwater depth–discharge relationship within 30 m of the stream. Second, we used the model to assess the effect of changes in the subsurface permeability architecture on flow pathlines and transit time distribution in a set of virtual experiments. Vertical patterns of saturated hydraulic conductivity and porosity with soil depth significantly influenced hillslope transit time distribution. Increasing infiltration rates significantly decreased mean groundwater age, but not the distribution of transit times relative to mean groundwater age. The location of hillslope hydrologic boundaries, including the groundwater divide and no-flow boundary underlying the hillslope, changed the transit time distribution less markedly. These results can guide future decisions on the degree of complexity that is warranted in a physically-based rainfall–runoff model to efficiently and explicitly estimate time invariant subsurface pathlines and transit time distribution. 
  •  
33.
  • Amvrosiadi, Nino, et al. (författare)
  • Soil moisture storage estimation based on steady vertical fluxes under equilibrium
  • 2017
  • Ingår i: Journal of Hydrology. - : Elsevier B.V.. - 0022-1694 .- 1879-2707. ; 553, s. 798-804
  • Tidskriftsartikel (refereegranskat)abstract
    • Soil moisture is an important variable for hillslope and catchment hydrology. There are various computational methods to estimate soil moisture and their complexity varies greatly: from one box with vertically constant volumetric soil water content to fully saturated-unsaturated coupled physically-based models. Different complexity levels are applicable depending on the simulation scale, computational time limitations, input data and knowledge about the parameters. The Vertical Equilibrium Model (VEM) is a simple approach to estimate the catchment-wide soil water storage at a daily time-scale on the basis of water table level observations, soil properties and an assumption of hydrological equilibrium without vertical fluxes above the water table. In this study VEM was extended by considering vertical fluxes, which allows conditions with evaporation and infiltration to be represented. The aim was to test the hypothesis that the simulated volumetric soil water content significantly depends on vertical fluxes. The water content difference between the no-flux, equilibrium approach and the new constant-flux approach greatly depended on the soil textural class, ranging between ∼1% for silty clay and ∼44% for sand at an evapotranspiration rate of 5 mm·d−1. The two approaches gave a mean volumetric soil water content difference of ∼1 mm for two case studies (sandy loam and organic rich soils). The results showed that for many soil types the differences in estimated storage between the no-flux and the constant flux approaches were relatively small.
  •  
34.
  • Andersson, Lotta, et al. (författare)
  • Impact of climate change and development scenarios on flow patterns in the Okavango River
  • 2006
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 331:1-2, s. 43-57
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper lays the foundation for the use of scenario modelling as a tool for integrated water resource management in the Okavango River basin. The Pitman hydrological model is used to assess the impact of various development and climate change scenarios on downstream river flow. The simulated impact on modelled river discharge of increased water use for domestic use, livestock, and informal irrigation (proportional to expected population increase) is very limited. Implementation of all likely potential formal irrigation schemes mentioned in available reports is expected to decrease the annual flow by 2% and the minimum monthly flow by 5%. The maximum possible impact of irrigation on annual average flow is estimated as 8%, with a reduction of minimum monthly flow by 17%. Deforestation of all areas within a 1 km buffer around the rivers is estimated to increase the flow by 6%. However, construction of all potential hydropower reservoirs in the basin may change the monthly mean flow distribution dramatically, although under the assumed operational rules, the impact of the dams is only substantial during wet years. The simulated impacts of climate change are considerable larger that those of the development scenarios (with exception of the high development scenario of hydropower schemes) although the results are sensitive to the choice of GCM and the IPCC SRES greenhouse gas (GHG) emission scenarios. The annual mean water flow predictions for the period 2020-2050 averaged over scenarios from all the four GCMs used in this study are close to the present situation for both the A2 and B2 GHG scenarios. For the 2050-2080 and 2070-2099 periods the all-GCM mean shows a flow decrease of 20% (14%) and 26% (17%), respectively, for the A2 (B2) GHG scenarios. However, the uncertainty in the magnitude of simulated future changes remains high. The simulated effect of climate change on minimum monthly flow is proportionally higher than the impact on the annual mean flow. © 2006 Elsevier B.V. All rights reserved.
  •  
35.
  • Barron, Jennie (författare)
  • Building climate resilience in degraded agricultural landscapes through water management: A case study of Bundelkhand region, Central India
  • 2020
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 591
  • Tidskriftsartikel (refereegranskat)abstract
    • Rainfall variability and water scarcity continue to hamper the food and income security of smallholder farming systems in poverty-affected regions. Innovations in soil and water management, especially in the drylands, are critical for meeting food security and water productivity targets of Agenda 2030. This study analyzes how rainfed agriculture can be intensified with marginal impact on the landscape water balance. The impact of rainwater harvesting structures on landscape hydrology and associated agricultural services was analyzed in the semi-arid Jhansi district of Bundelkhand region in central India. The Parasai-Sindh pilot watershed was subjected to a 5-year (2012-2016) monitoring of rainfed system improvements in water availability and crop intensification due to surface water storage (haveli system), check dams, and field infiltration structures. Hydrological processes were monitored intensively to analyze the landscape's water balance components. Rainwater harvesting (RWH) structures altered the landscape's hydrology, limiting average surface runoff from 250 mm/year to 150 mm/year over the study period. Groundwater levels increased by 2-5 m (m), alleviating water scarcity issues of the communities in recurring dry years. Nearly 20% of fallow lands were brought under cultivation. Crop yields increased by 10-70% and average household income increased from US$ 960/year to US $ 2700/year compared to that in the non-intervention landscape. The combined soil-water-vegetation efforts strengthened water resilience and environmental systems in agricultural landscape.
  •  
36.
  • Bejarano, Maria Dolores, et al. (författare)
  • Characterizing effects of hydropower plants on sub-daily flow regimes
  • 2017
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 550, s. 186-200
  • Tidskriftsartikel (refereegranskat)abstract
    • A characterization of short-term changes in river flow is essential for understanding the ecological effects of hydropower plants, which operate by turning the turbines on or off to generate electricity following variations in the market demand (i.e., hydropeaking). The goal of our study was to develop an approach for characterizing the effects of hydropower plant operations on within-day flow regimes across multiple dams and rivers. For this aim we first defined ecologically meaningful metrics that provide a full representation of the flow regime at short time scales from free-flowing rivers and rivers exposed to hydropeaking. We then defined metrics that enable quantification of the deviation of the altered short-term flow regime variables from those of the unaltered state. The approach was successfully tested in two rivers in northern Sweden, one free-flowing and another regulated by cascades of hydropower plants, which were additionally classified based on their impact on short-term flows in sites of similar management. The largest differences between study sites corresponded to metrics describing sub-daily flow magnitudes such as amplitude (i.e., difference between the highest and the lowest hourly flows) and rates (i.e., rise and fall rates of hourly flows). They were closely followed by frequency-related metrics accounting for the numbers of within-day hourly flow patterns (i.e., rises, falls and periods of stability of hourly flows). In comparison, between-site differences for the duration-related metrics were smallest. In general, hydropeaking resulted in higher within-day flow amplitudes and rates and more but shorter periods of a similar hourly flow patterns per day. The impacted flow feature and the characteristics of the impact (i.e., intensity and whether the impact increases or decreases whatever is being described by the metric) varied with season. Our approach is useful for catchment management planning, defining environmental flow targets, prioritizing river restoration or dam reoperation efforts and contributing information for relicensing hydropower dams. 
  •  
37.
  • Bergion, Viktor, 1986, et al. (författare)
  • Hydrological modelling in a drinking water catchment area as a means of evaluating pathogen risk reduction
  • 2017
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 544, s. 74-85
  • Tidskriftsartikel (refereegranskat)abstract
    • Waterborne outbreaks of gastrointestinal diseases are of great concern to drinking water producers and can give rise to substantial costs to the society. The World Health Organisation promotes an approach where the emphasis is on mitigating risks close to the contamination source. In order to handle microbial risks efficiently, there is a need for systematic risk management. In this paper we present a framework for microbial risk management of drinking water systems. The framework incorporates cost-benefit analysis as a decision support method. The hydrological Soil and Water Assessment Tool (SWAT) model, which was set up for the Stäket catchment area in Sweden, was used to simulate the effects of four different mitigation measures on microbial concentrations. The modelling results showed that the two mitigation measures that resulted in a significant (p
  •  
38.
  • Beven, Keith (författare)
  • A manifesto for the equifinality thesis
  • 2006
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 320:1-2, s. 18-36
  • Tidskriftsartikel (refereegranskat)abstract
    • This essay discusses some of the issues involved in the identification and predictions of hydrological models given some calibration data. The reasons for the incompleteness of traditional calibration methods are discussed. The argument is made that the potential for multiple acceptable models as representations of hydrological and other environmental systems (the equifinality thesis) should be given more serious consideration than hitherto. It proposes some techniques for an extended GLUE methodology to make it more rigorous and outlines some of the research issues still to be resolved. (c) 2005 Elsevier Ltd All rights reserved.
  •  
39.
  • Beven, Keith J, et al. (författare)
  • Comment on “Hydrological forecasting uncertainty assessment: Incoherence of the GLUE methodology” by Pietro Mantovan and Ezio Todini
  • 2007
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 338:3-4, s. 315-318
  • Tidskriftsartikel (refereegranskat)abstract
    • This comment is a response to the criticisms of the GLUE methodology by [Mantovan, P., Todini, E., 2006. Hydrological forecasting uncertainty assessment: Incoherence of the GLUE methodology, J. Hydrology, 2006]. In this comment it is shown that the formal Bayesian identification of models is a special case of GLUE that can be used where the modeller is prepared to make very strong assumptions about the nature of the modelling errors. For the hypothetical study of Mantovan and Todini, exact assumptions were assumed known for the formal Bayesian identification, but were then ignored in the application of GLUE to the same data. We show that a more reasonable application of GLUE to this problem using similar prior knowledge shows that gives equally coherent results to the formal Bayes identification. In real applications, subject to input and model structural error it is suggested that the coherency condition of MT06 cannot hold at the single observation level and that the choice of a formal Bayesian likelihood function may then be incoherent. In these (more interesting) cases, GLUE can be coherent in the application of likelihood measures based on blocks of data, but different choices of measures and blocks effectively represent different beliefs about the information content of data in real applications with input and model structural errors.
  •  
40.
  • Beven, Keith, et al. (författare)
  • So just why would a modeller choose to be incoherent?
  • 2008
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 354:1-4, s. 15-32
  • Tidskriftsartikel (refereegranskat)abstract
    • This article provides an extended response to the criticisms of the GLUE methodology by Mantovan and Todini [Mantovan, P., Todini, E., 2006. Hydrological forecasting uncertainty assessment: incoherence of the GLUE methodology. J. Hydrol. 330, 368-381]. It is shown that the formal Bayesian identification of models is a special case of GLUE that can be used where the modeller is prepared to make very strong assumptions about the nature of the modelling errors. Under such assumptions, GLUE can be coherent in the sense of Manotvan and Todini. In real applications, however, with multiple sources of uncertainty including model structural error, their strong definition of coherence is shown to be inapplicable to the extent that the choice of a format likelihood function based on a simple error structure may be an incoherent choice. It is demonstrated by some relatively minor modifications of their hypothetical example that misspecification of the error model and the non-stationarities associated with the presence of input error and model structural error in the Bayes approach will then produce well-defined but incorrect parameter distributions. This empirical result is quite independent of GLUE, but the flexibility of the GLUE approach may then prove to be an advantage in providing more coherent and robust choices of model evaluation in these cases and, by analogy, in other non-ideal cases for real applications. At the current time it is difficult to make a reasoned choice between methods of uncertainty estimation for real applications because of a lack of understanding of the real information content of data in conditioning models.
  •  
41.
  •  
42.
  • Bhunya, Pradeep, et al. (författare)
  • Flood analysis using generalized logistic models in partial duration series
  • 2012
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 420, s. 59-71
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract in Undetermined As a generalization of the commonly assumed Poisson distribution (PD) used to estimate the annual number of peaks over threshold in partial duration series (PDS) model, the negative binomial (NB) distribution is proposed in this study. Instead of generalized pareto distribution (GPD) and exponential distribution (ED) models popularly applied to predict the probability of the exceedances of peak over threshold, the performance of the general logistic distribution (GLD) models is analyzed. Two different models for analyzing extreme hydrologic events are compared, based on, PDS and annual maximum series (AMS), respectively. The performance of the two models in terms of uncertainty of T-year event estimator [q(T)] is evaluated in the cases of estimation with the method of moments (MOMs), maximum likelihood (ML), and probability weighted moments (PWMs). The annual maximum distribution corresponding to a PDS model with Poisson distributed count of peaks above threshold and GLD for flood exceedances was found to be an extreme value type I (EV1) distribution. The comparison between PDS and AMS is made using ratio of variance of the T-year event estimates, which is derived analytically after checking the reliability of the expressions with Monte Carlo simulations. The results reveal that the AMS/NB-GLD and PDS/GLD models using PWM estimation method give least variance of flood estimates with the PDS model giving marginally better results. From the overall results, it was observed that the Poisson distribution performs better, where the difference between mean (mu) and variance of counts of threshold exceedances is small otherwise the NB distribution is found to be efficient when used in combination with generalized logistic distribution in the PDS model, and this is more prominent for it mu < 1.4. Hence, in such cases when the PDS data have a mean less than this, the AMS/NB-GLD and PDS/GLD should be a better model for q(T) estimation as compared to PDS/ED.
  •  
43.
  •  
44.
  • Bhunya, P.K., et al. (författare)
  • Suitability of Gamma, Chi-square, Weibull, and Beta distributions as synthetic unit hydrographs
  • 2007
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 334:1-2, s. 28-38
  • Tidskriftsartikel (refereegranskat)abstract
    • Most available methods for synthetic unit hydrograph (SUH) derivation involve manual, subjective fitting of a hydrograph through a few data points. Because of this tedious procedure, the generated unit hydrograph is often left unadjusted for unit runoff volume. During recent decades, use of probability distribution functions (pdfs) in developing SUH has received much attention because of its similarity with unit hydrograph properties. In this study, the potential of four popular pdfs, i.e., two-parameter Gamma, three-parameter Beta, two-parameter Weibull, and one-parameter Chi-square distribution to derive SUH have been explored. Simple formulae are derived using analytical and numerical schemes to compute the distribution parameters, and their validity is checked with simulation of field data. The Gamma and Chi-square distributions behave analogously, and the Beta distribution approximates a Gamma distribution in a limiting case. Application to field data shows that the Beta and Weibull distributions are more flexible in hydrograph prediction than the Gamma, Chi-square, Gray [Gray, D.M., 1961. Synthetic hydrographs for small drainage areas. In: Proceedings of the ASCE, 87, HY4, pp. 33-54], SCS [SCS, 1957. Use of Storm and Watershed Characteristics in Synthetic Hydrograph Analysis and Application: V. Mockus. US Dept. of Agriculture, Soil Conservation Service, Washington, DC], and Snyder [Synder, F.F., 1938. Synthetic unit hydrographs. Trans. Am. Geophys. Union 19, 447-454] methods. A sensitivity analysis of pdf parameters on peak flow estimates of an UH indicated that Gamma and Chi-square distributions overestimate the peak flow value, for any overestimation in its parameter estimates. However, for the Beta and Weibull distributions a reverse trend was observed. Both were found to behave similarly at higher @a (ratio of time to base and time to peak of UH) values. Further, an analogous triangular hydrograph approach was used to express the mean and variance of the UH in terms of time base and time to peak of the UH. This enabled a simple parameter estimation equation involving only time base and time to peak of the UH. Although the validity of this equation could not be evaluated with a proper amount of data, the results give an indication of the relationship between pdf and statistical properties of the UH to be further elaborated in future research.
  •  
45.
  • Bikse, Janis, et al. (författare)
  • Assessing automated gap imputation of regional scale groundwater level data sets with typical gap patterns
  • 2023
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 620
  • Tidskriftsartikel (refereegranskat)abstract
    • Large groundwater level (GWL) data sets are often patchy with hydrographs containing continuous gaps and irregular measurement frequencies. However, most statistical time series analyses require regular observations, thus hydrographs with larger gaps are routinely excluded from further analysis despite the loss of coverage and representativity of an initially large data set. Missing values can be filled in with different imputation methods, yet the challenge is to assess the imputation performance of automated methods. Assessment of such methods tends to be carried out on randomly introduced missing values. However, large GWL data sets are commonly dominated by more complex patterns of missing values with longer contiguous gaps. This study presents a new artificial gap introduction approach (TGP- typical gap patterns) that improves our understanding of automated imputation performance by mimicking typical gap patterns found in regional scale groundwater hydrographs. Imputation performance of machine learning algorithm missForest and imputePCA is then compared with commonly applied linear interpolation to prepare a gapless daily GWL data set for the Baltic states (Estonia, Latvia, Lithuania). We observed that imputation performance varies among different gap patterns, and performance for all imputation algorithms declined when infilling previously unseen extremes and hydrographs influenced by groundwater abstraction. Further, missForest algorithm substantially outperformed other methods when infilling contiguous gaps (up to 2.5 years), while linear interpolation performs similarly for short random gaps. The TGP approach can be of use to assess the complexity of missing observation patterns in a data set and its value lies in assessing the performance of gap filling methods in a more realistic way. Thus the approach aids the appropriate selection of imputation methods, a task not limited to groundwater level time series alone. The study further provides insights into region-specific data peculiarities that can assist groundwater analysis and modelling.
  •  
46.
  • Bishop, Kevin, et al. (författare)
  • Effect of DEM-smoothing and -aggregation on topographically-based flow directions and catchment boundaries
  • 2021
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 602
  • Tidskriftsartikel (refereegranskat)abstract
    • It is generally assumed that, in humid climates, the groundwater table is a subdued copy of the surface topography. However, the general groundwater table is unlikely to be affected by the microtopography as seen in high-resolution Digital Elevation Models (DEMs). So far, there has been little guidance on the best resolution DEM to use to determine the shape of the water table or the direction of shallow groundwater flow in headwater catchments. We, therefore, looked at the effects of DEM-smoothing and -aggregation on the calculated flow directions and derived catchment boundaries, and identified areas and landscape features for which the calculated flow directions are particularly sensitive to DEM smoothing or aggregation. For > 40 % of the area of the Krycklan study catchment, the calculated flow directions depend strongly on the degree of smoothing or aggregation of the DEM. The four main landscape features for which DEM smoothing or aggregation strongly affected the calculated flow directions were: local slopes in the opposite direction of the general slope, flat areas, ridges, and incised streambanks. To determine the effects of the changing flow directions on the derived catchment boundaries for the smoothed and aggregated DEMs, we calculated the drainage area for 40 locations, representing the outlets of catchments of varying sizes. The shape and size of the catchments of first-order streams were most affected by the processing of the DEM. These streams were often almost completely smoothed out during the DEM preprocessing steps. These shifts in catchment boundaries and drainage area would have a large effect on the water balance. This study thus highlights the need to carefully consider the effects of DEM smoothing or -aggregation on the calculated flow directions and drainage areas.
  •  
47.
  • Blecken, Godecke-Tobias, et al. (författare)
  • Laboratory study on stormwater biofiltration : nutrient and sediment removal in cold temperatures
  • 2010
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 394:3-4, s. 507-514
  • Tidskriftsartikel (refereegranskat)abstract
    • Stormwater biofilters have the ability to remove nutrients from stormwater. Reliable pollutant removal during the cold season is particularly important due to the comparably high contamination levels. However, the removal performance might be negatively affected by low temperatures. A biofilter column study was conducted in thermostat-controlled climate rooms (at 2, 7 and 20 °C) to investigate the effect of low temperatures on nutrient removal. Phosphorus and suspended solids removal were significantly correlated and consistently very high (typically in excess of 90 and 95%, respectively, at all temperatures). This is important for the successful implementation of biofilters in cold climates since phosphorus is commonly of principal concern, often being the limiting factor for eutrophication in freshwater ecosystems. Unfortunately, nitrogen removal was poor and leaching was shown, which increased with temperature. The increasing nitrate-nitrogen production rates with temperature were well described by the Arrhenius relationship with temperature coefficients Q10 in the range which is typically used to describe temperature effects on nitrification. Thus, temperature effects have to be considered when nitrogen removal is targeted and the biofilter might be exposed to cold temperatures.
  •  
48.
  • Bodin, Hristina, et al. (författare)
  • Influence of residence time analyses on estimates of wetland hydraulics and pollutant removal
  • 2013
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 501, s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydraulic tracer studies are frequently used to estimate wetland residence time distributions (RTDs) and ultimately pollutant removal. However, there is no consensus on how to analyse these data. We set out to (i) review the different methods used and (ii) use simulations to explore how the data analysis method influences the quantification of wetland hydraulics and pollutant removal. The results showed that the method influences the water dispersion (N) most strongly and the removal least strongly. The influence increased with decreasing effective volume ratio (e) and N, indicating a greater effect of the method in wetlands with low effective volume and high dispersion. The method of moments with RTD truncation at 3 times the theoretical residence time (t(n)) and tracer background concentration produced the most dissimilar parameters. The most similar parameters values were those for gamma modelling and the method of moments with RTD truncation at tracer background concentration. For correct removal estimates, e was more important than N. However, the results from the literature review and simulations indicated that previously published articles may contain overestimated e and underestimated N values as a result of frequent RTD truncations at 3t(n), when using the method of moments. As a result, the removal rates may also be overestimated by as much as 14% compared to other truncation methods or modelling. Thus, it is recommended that wetland hydraulic tracer studies should use the same method, specifically, RTD truncation. We conclude that the choice of tracer data analysis method can greatly influence the quantifications of wetland hydraulics and removal rate.
  •  
49.
  • Breinl, Korbinian, et al. (författare)
  • Stochastic generation of multi-site daily precipitation for applications in risk management
  • 2013
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 498, s. 23-35
  • Tidskriftsartikel (refereegranskat)abstract
    • Unlike single-site precipitation generators, multi-site precipitation generators make it possible to reproduce the space–time variation of precipitation at several sites. The extension of single-site approaches to multiple sites is a challenging task, and has led to a large variety of different model philosophies for multi-site models. This paper presents an alternative semi-parametric multi-site model for daily precipitation that is straightforward and easy to implement. Multi-site precipitation occurrences are simulated with a univariate Markov process, removing the need for individual Markov models at each site. Precipitation amounts are generated by first resampling observed values, followed by sampling synthetic precipitation amounts from parametric distribution functions. These synthetic precipitation amounts are subsequently reshuffled according to the ranks of the resampled observations in order to maintain important statistical properties of the observation network. The proposed method successfully combines the advantages of non-parametric bootstrapping and parametric modeling techniques. It is applied to two small rain gauge networks in France (Ubaye catchment) and Austria/Germany (Salzach catchment) and is shown to well reproduce the observations. Limitations of the model relate to the bias of the reproduced seasonal standard deviation of precipitation and the underestimation of maximum dry spells. While the lag-1 autocorrelation is well reproduced for precipitation occurrences, it tends to be underestimated for precipitation amounts. The model can generate daily precipitation amounts exceeding the ones in the observations, which can be crucial for risk management related applications. Moreover, the model deals particularly well with the spatial variability of precipitation. Despite its straightforwardness, the new concept makes a good alternative for risk management related studies concerned with producing daily synthetic multi-site precipitation time series.
  •  
50.
  • Bring, Arvid, et al. (författare)
  • Hydro-climatic changes and their monitoring in the Arctic : Observation-model comparisons and prioritization options for monitoring development
  • 2013
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 492, s. 273-280
  • Tidskriftsartikel (refereegranskat)abstract
    • The Arctic undergoes particularly large and rapid hydro-climatic changes, and information on hydrological responses to these changes is crucial to plan for societal adaptation. We investigate hydro-climatic change severity and monitoring in 14 major hydrological basins across the pan-Arctic, in view of different possible strategies for their monitoring prioritization. Results show that the current distribution of monitoring density in these basins is more relevant for so far observed precipitation changes than for observed temperature changes, or for projected future temperature and precipitation changes. Furthermore, present and projected future hot-spots of greatest hydro-climatic change differ spatially, so that major spatial shifts must occur in the future among the different Arctic basins in order for observations and climate model projections to converge with regard to hydro-climatic change severity. Also temporally, observation-model convergence requires that important change direction shifts occur in major Arctic basins, which have currently decreasing precipitation while model projections imply future increasing precipitation within them. Different prioritization options for rational development of hydro-climatic monitoring can be argued for based on the present results. The divergent prioritization options imply a need for an explicit strategy for achieving certain information goals, which must be selected from a larger set of different possible goals based on societal importance.
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-50 av 327
Typ av publikation
tidskriftsartikel (325)
forskningsöversikt (2)
Typ av innehåll
refereegranskat (317)
övrigt vetenskapligt/konstnärligt (10)
Författare/redaktör
Berndtsson, Ronny (27)
Seibert, Jan (15)
Destouni, Georgia (15)
Chen, Deliang, 1961 (13)
Bishop, Kevin (11)
Laudon, Hjalmar (11)
visa fler...
Duan, Zheng (11)
Wörman, Anders (8)
Singh, V. P. (8)
Bhattacharya, Prosun (7)
Santos, Isaac R. (7)
Liu, Longcheng (7)
Bengtsson, Lars (6)
Persson, Magnus (6)
Di Baldassarre, Giul ... (6)
Zhang, Wenxin (6)
Lyon, Steve W. (6)
Chen, Xi (6)
Beven, Keith (6)
Seibert, Jan, 1968- (5)
Kalantari, Zahra (5)
Bertacchi Uvo, Cinti ... (5)
Jiang, T. (5)
Teutschbein, Claudia ... (5)
Zhang, Q. (4)
Seibert, J., 1968- (4)
Jarsjö, Jerker (4)
Viklander, Maria (4)
Neretnieks, Ivars (4)
Moreno, Luis (4)
Barthel, Roland, 196 ... (4)
Niemczynowicz, Janus ... (4)
Li, Lu (4)
Larson, Magnus (3)
Bishop, Kevin, 1960- (3)
Bundschuh, Jochen (3)
Marsalek, Jiri (3)
Lundberg, Angela (3)
Mukherjee, Abhijit (3)
Andersson, Lotta (3)
Nakagawa, Kei (3)
Grabs, T.homas J., 1 ... (3)
Hughes, Denis (3)
Xia, Jun (3)
Halldin, S (3)
Fang, Keyan (3)
Haaf, Ezra, 1985 (3)
Jansson, Per-Erik. (3)
Singh, Vijay P. (3)
Sokolova, Ekaterina, ... (3)
visa färre...
Lärosäte
Uppsala universitet (100)
Lunds universitet (72)
Kungliga Tekniska Högskolan (45)
Stockholms universitet (40)
Sveriges Lantbruksuniversitet (32)
Göteborgs universitet (29)
visa fler...
Luleå tekniska universitet (13)
Umeå universitet (10)
Linköpings universitet (9)
Chalmers tekniska högskola (9)
Linnéuniversitetet (2)
RISE (2)
Karlstads universitet (2)
Högskolan Väst (1)
Örebro universitet (1)
Karolinska Institutet (1)
visa färre...
Språk
Engelska (327)
Forskningsämne (UKÄ/SCB)
Naturvetenskap (234)
Teknik (90)
Lantbruksvetenskap (24)
Samhällsvetenskap (14)
Medicin och hälsovetenskap (1)

År

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy