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1.
  • 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.
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2.
  • 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. 
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3.
  • 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.
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4.
  • 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. 
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5.
  • 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
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6.
  • Coners, Heinz, et al. (författare)
  • Evapotranspiration and water balance of high-elevation grassland on the Tibetan Plateau
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 533, s. 557-566
  • Tidskriftsartikel (refereegranskat)abstract
    • High-elevation grasslands of the Cyperaceae Kobresia pygmaea cover nearly half a million km2 on the Tibetan Plateau. As a consequence of climate change, precipitation patterns in this monsooninfluenced region may change with possible consequences for grassland productivity. Yet, not much is known about the water cycle in this second largest alpine ecosystem of the world. We measured the evapotranspiration of a high-elevation Kobresia pasture system at 4400 m a.s.l. in the south-eastern part of the plateau in two summers using three different approaches, weighable micro-lysimeters, eddy covariance measurements, and water balance modeling with the soil–plant–atmosphere transfer model SEWAB. In good agreement among the three approaches, we found ET rates of 4–6 mm d-1 in moist summer periods (June–August) and 2mmd-1 in dry periods, despite the high elevation and a leaf area index of only 1. Measured ET rates were comparable to rates reported from alpine grasslands at 1500–2500 m a.s.l. in temperate mountains, and also matched ET rates of managed lowland grasslands in the temperate zone. At the study site with 430 mm annual precipitation, low summer rainfall reduced ET significantly and infiltration into the subsoil occurred only in moist periods. Our results show that the evapotranspiration of high-elevation grasslands at 4400 m can be as high as in lowland grasslands despite large elevational changes in abiotic and biotic drivers of ET, and periodic water shortage is likely to influence large parts of the Tibetan Kobresia pastures.
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7.
  • Cvetkovic, Vladimir, et al. (författare)
  • Global sensitivity analysis of groundwater transport
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 531
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we address the model and parametric sensitivity of groundwater transport using the Lagrangian-Stochastic Advection-Reaction (LaSAR) methodology. The 'attenuation index' is used as a relevant and convenient measure of the coupled transport mechanisms. The coefficients of variation (CV) for seven uncertain parameters are assumed to be between 0.25 and 3.5, the highest value being for the lower bound of the mass transfer coefficient k0. In almost all cases, the uncertainties in the macro-dispersion (CV = 0.35) and in the mass transfer rate k0 (CV = 3.5) are most significant. The global sensitivity analysis using Sobol and derivative-based indices yield consistent rankings on the significance of different models and/or parameter ranges. The results presented here are generic however the proposed methodology can be easily adapted to specific conditions where uncertainty ranges in models and/or parameters can be estimated from field and/or laboratory measurements.
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8.
  • Cvetkovic, Vladimir, et al. (författare)
  • Tracer travel and residence time distributions in highly heterogeneous aquifers : Coupled effect of flow variability and mass transfer
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707.
  • Tidskriftsartikel (refereegranskat)abstract
    • The driving mechanism of tracer transport in aquifers is groundwater flow which is controlled by the heterogeneity of hydraulic properties. We show how hydrodynamics and mass transfer are coupled in a general analytical manner to derive a physically-based (or process-based) residence time distribution for a given integral scale of the hydraulic conductivity; the result can be applied for a broad class of linear mass transfer processes. The derived tracer residence time distribution is a transfer function with parameters to be inferred from combined field and laboratory measurements. It is scalable relative to the correlation length and applicable for an arbitrary statistical distribution of the hydraulic conductivity. Based on the derived residence time distribution, the coefficient of variation and skewness of residence time are illustrated assuming a log-normal hydraulic conductivity field and first-order mass transfer. We show that for a low Damkohler number the coefficient of variation is more strongly influenced by mass transfer than by heterogeneity, whereas skewness is more strongly influenced by heterogeneity.
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9.
  • Fischer, Benjamin M. C., et al. (författare)
  • Spatial variability in the isotopic composition of rainfall in a small headwater catchment and its effect on hydrograph separation
  • 2017
  • Ingår i: Journal of Hydrology. - : ELSEVIER SCIENCE BV. - 0022-1694 .- 1879-2707. ; 547, s. 755-769
  • Tidskriftsartikel (refereegranskat)abstract
    • Isotope hydrograph separation (IHS) is a valuable tool to study runoff generation processes. To perform an IHS, samples of baseflow (pre-event water) and streamflow are taken at the catchment outlet. For rainfall (event water) either a bulk sample is collected or it is sampled sequentially during the event. For small headwater catchment studies, event water samples are usually taken at only one sampling location in or near the catchment because the spatial variability in the isotopic composition of rainfall is assumed to be small. However, few studies have tested this assumption. In this study, we investigated the spatiotemporal variability in the isotopic composition of rainfall and its effects on IHS results using detailed measurements from a small pre-alpine headwater catchment in Switzerland. Rainfall was sampled sequentially at eight locations across the 4.3 km(2) Zwackentobel catchment and stream water was collected in three subcatchments (0.15, 0.23, and 0.70 km(2)) during ten events. The spatial variability in rainfall amount, average and maximum rainfall intensity and the isotopic composition of rainfall was different for each event. There was no significant relation between the isotopic composition of rainfall and total rainfall amount, rainfall intensity or elevation. For eight of the ten studied events the temporal variability in the isotopic composition of rainfall was larger than the spatial variability in the rainfall isotopic composition. The isotope hydrograph separation results, using only one rain sampler, varied considerably depending on which rain sampler was used to represent the isotopic composition of event water. The calculated minimum pre-event water contributions differed up to 60%. The differences were particularly large for events with a large spatial variability in the isotopic composition of rainfall and a small difference between the event and pre-event water isotopic composition. Our results demonstrate that even in small catchments the spatial variability in the rainfall isotopic composition can be significant and has to be considered for IHS studies. Using data from only one rain sampler can result in significant errors in the estimated pre-event water contributions to streamflow.
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10.
  • Galfi, Helen, et al. (författare)
  • Indicator bacteria and associated water quality constituents in stormwater and snowmelt from four urban catchments
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 539, s. 125-140
  • Tidskriftsartikel (refereegranskat)abstract
    • SummaryFour indicator bacteria were measured in association with physico-chemical constituents and selected inorganics during rainfall, baseflow and snowmelt periods in storm sewers of four urban catchments in a northern Swedish city. The variation patterns of coliforms, E. coli, enterococci and C. perfringens concentrations were assessed in manually collected grab samples together with those of phosphorus, nitrogen, solids, and readings of pH, turbidity, water conductivity, temperature and flow rates to examine whether these constituents with variation patterns similar to those of indicator bacteria, and to exclude the constituents with less similarity. In the reduced data set, the similarities were quantified by the clustering correlation analysis. Finally, the positive/negative relationships found between indicator bacteria and the identified associated constituent groups were described by multilinear regressions. In the order of decreasing concentrations, coliforms, E. coli and enterococci were found in the highest mean concentrations during both rainfall and snowmelt generated runoff. Compared to dry weather baseflow, concentrations of these three indicators in stormwater were 10 (snowmelt runoff) to 102 (rain runoff) times higher. C. perfringens mean concentrations were practically constant regardless of the season and catchment. The type and number of variables associated with bacteria depended on the degree of catchment development and the inherent complexity of bacteria sources. The list of variables associated with bacteria included the flow rate, solids with associated inorganics (Fe and Al) and phosphorus, indicating similar sources of constituents regardless of the season. On the other hand, bacteria were associated with water temperature only during rain periods, and somewhat important associations of bacteria with nitrogen and pH were found during the periods of snowmelt. Most of the associated constituents were positively correlated with bacteria responses, but conductivity, with two associated inorganics (Si and Sr), was mostly negatively correlated in all the catchments. Although the study findings do not indicate any distinct surrogates to indicator bacteria, the inclusion of the above identified constituents (flow rate, solids and total phosphorus for all seasons, water temperature for rainfall runoff, and total nitrogen and pH for snowmelt only) in sanitary surveys of northern climate urban catchments would provide additional insight into indicator bacteria sources and their modelling.
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11.
  • Gavric, Snezana, et al. (författare)
  • Measurement and conceptual modelling of retention of metals (Cu, Pb, Zn) in soils of three grass swales
  • 2019
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 574, s. 1053-1061
  • Tidskriftsartikel (refereegranskat)abstract
    • Grass swales are important elements of the urban green infrastructure that convey and attenuate urban runoff and improve its quality mostly through stormwater infiltration into, and retention of conveyed pollutants by, swale soils. The retention of metals by grass swales was addressed in this study investigating the enrichment of swale soils by three common traffic-related metals: Cu, Pb and Zn. Three swales of various characteristics (L1, L2, L3) were selected for study and their soils were sampled by coring the top 30 cm and dividing the cores into 5 cm thick layers. Cumulative metal burdens were compared to those modelled by the proprietary StormTac Web model, which estimates annual loads of specific constituents for the given land uses and stormwater treatment. The comparisons of measured (MBm) and simulated (MBs) metal burdens retained by swales showed that the measured values exceed the simulated ones, as described by average ratios MBs/MBm = 0.64, 0.50 and 0.59, for swales L1, L2 and L3, respectively. The measured burdens were calculated after subtracting the native soil metal concentrations, assumed equal to those found in the deepest sampled layer, 25–30 cm below the surface. The results suggest the feasibility of assessing performance of grass swales by modelling metal (Cu, Pb, Zn) retention by swales, however for older facilities considered for rehabilitation, the simulated results should be supplemented by soil chemistry sampling.
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12.
  • Gebrehiwot, Solomon Gebreyohannis, et al. (författare)
  • Is observation uncertainty masking the signal of land use change impacts on hydrology?
  • 2019
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 570, s. 393-400
  • Tidskriftsartikel (refereegranskat)abstract
    • Analysis of hydrological impacts of land use change raises questions about whether, and how much, such impacts are misrepresented because of errors in river flow observations. In this paper, land use change impacts (represented by changes in watershed storage) and different ranges of discharge measurement error are compared to assess how errors in discharge measurement can potentially mask a land use change impact. Using a watershed from the Ethiopian highlands to exemplify this, we simulated five different levels of land use change impacts with five levels of watershed storage reductions (from 10% to 50% change) and the associated time series of runoff. Different levels of observation error were then introduced into these artificial time series. Comparison was made between every pair, i.e. a time series derived from a certain level of land use change (storage reduction) versus a time series corresponding to a given level of observation error, using a step-change t-test. Significant step-changes between pairs define the detectability of land use change impact. The analysis was made for the entire 30-year time series as well as for the most extreme annual weather conditions. The results showed that for the average year and wettest year, 75% or more error in observed discharge masks the maximum simulated land use change impact on hydrology. In dry years, a 50% error in discharge is enough to mask the same impact. Knowing (and improving) the level of data quality contributes to a better understanding of hydrological uncertainties and improves the precision in assessing land use change impacts. Both of these are essential elements in water resources development planning.
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13.
  • Ghosh, Devanita, et al. (författare)
  • Characterization and microbial utilization of dissolved lipid organic fraction in arsenic impacted aquifers (India)
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 527, s. 221-233
  • Tidskriftsartikel (refereegranskat)abstract
    • The coupled role of organic matter (OM) and microbial activity is widely acknowledged in arsenic (As) biogeochemical cycling in sedimentary environments. However, little is known about OM characteristics particularly the dissolved fraction in the Bengal Delta Plain aquifers – one of the worst As impacted regions in the world. Ongoing investigations in As-rich aquifers in Nadia district (West Bengal, India) indicate presence of arsenite As(III) oxidizing bacterial communities in the Grey Sand Aquifers (GSA), but absent in Brown Sand Aquifers (BSA). In this study, we investigate the key differences in dissolved organic carbon (DOC) characteristics and its relationship with differences in elemental concentrations, distribution of biomarkers, and utilization of DOC by in situ microbial communities in BSA and GSA. We demonstrate a new approach using ENVIâ„¢ C-18 DSK discs to pre-concentrate DOC from large volumes of water, and further extract the OM and separate it into different lipid fractions using the solid phase extraction technique. The aquifers show marked heterogeneity in terms of their DOC characteristics and elemental profiles irrespective of their grey or brown color. DOC indicates variable inputs of terrestrial derived OM sources, and OM derived from decomposition and/or microbial cellular components. DOC in the aquifers consist of predominantly n-alkanoic acids (∌80%) followed by n-alkanes and n-alcohols. The GSAs indicate high iron (Fe) and manganese (Mn) concentrations, and presence of mature petroleum derived hydrocarbons in DOC. BSA has comparatively lower concentrations of Fe and Mn, and shows absence of mature hydrocarbons in DOC. Experiments in presence of indigenous bacteria from groundwater with DOC lipid extracts as the sole carbon source indicate higher growth in the GSA samples implying preferential use of DOC. The potential availability of DOC in these aquifers can influence the community composition of indigenous heterotrophic microbial flora, which in turn can affect elemental cycles including that of As.
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14.
  • Girons Lopez, Marc, 1986-, et al. (författare)
  • Influence of Hydro-Meteorological Data Spatial Aggregation on Streamflow Modelling
  • 2016
  • Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 541, s. 1212-1220
  • Tidskriftsartikel (refereegranskat)abstract
    • Data availability is important for virtually any purpose in hydrology. While some parts of the world continue to be under-monitored, other areas are experiencing an increased availability of high-resolution data. The use of the highest available resolution has always been preferred and many efforts have been made to maximize the information content of data and thus improve its predictive power and reduce the costs of maintenance of hydrometric sensor networks. In the light of ever-increasing data resolution, however, it is important to assess the added value of using the highest resolution available. In this study we present an assessment of the relative importance of hydro-meteorological data resolution for hydrological modelling. We used a case study with high-resolution data availability to investigate the influence of using models calibrated with different levels of spatially aggregated meteorological input data to estimate streamflow for different periods and at different locations. We found site specific variations, but model parameterizations calibrated using sub-catchment specific meteorological input data tended to produce better streamflow estimates, with model efficiency values being up to 0.35 efficiency units higher than those calibrated with catchment averaged meteorological data. We also found that basin characteristics other than catchment area have little effect on the performance of model parameterizations applied in different locations than the calibration site. Finally, we found that using an increased number of discharge data locations has a larger impact on model calibration efficiency than using spatially specific meteorological data. The results of this study contribute to improve the knowledge on assessing data needs for water management in terms of adequate data type and level of spatial aggregation.
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15.
  • Granath, Gustaf (författare)
  • Post-fire ecohydrological conditions at peatland margins in different hydrogeological settings of the Boreal Plain
  • 2017
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 548, s. 741-753
  • Tidskriftsartikel (refereegranskat)abstract
    • In the Boreal Plain of Canada, the margins of peatland ecosystems that regulate solute and nutrient fluxes between peatlands and adjacent mineral uplands are prone to deep peat burning. Whether post-fire carbon accumulation is able to offset large carbon losses associated with the deep burning at peatland margins is unknown. For this reason, we examined how post-fire hydrological conditions (i.e. water table depth and periodicity, soil tension, and surface moisture content) and depth of burn were associated with moss recolonization at the peatland margins of three sites. We then interpreted these findings using a hydrogeological systems approach, given the importance of groundwater in determining conditions in the soil-plant-atmosphere continuum in peatlands. Peatland margins dominated by local groundwater flow from adjacent peatland middles were characterized by dynamic hydrological conditions that, when coupled with lowered peatland margin surface elevations due to deep burning, produced two common hydrological states: 1) flooding during wet periods and 2) rapid water table declines during dry periods. These dynamic hydrological states were unfavorable to peatland moss recolonization and bryophytes typical of post-fire recovery in mineral uplands became established. In contrast, at a peatland margin where post-fire hydrological conditions were moderated by larger-scale groundwater flow, flooding and rapid water table declines were infrequent and, subsequently, greater peatland-dwelling moss recolonization was observed. We argue that peatland margins poorly connected to larger-scale groundwater flow are not only prone to deep burning but also lags in post-fire moss recovery. Consequently, an associated reduction in post-fire peat accumulation may occur and negatively affect the net carbon sink status and ecohydrological and biogeochemical function of these peatlands. (C) 2017 Elsevier B.V. All rights reserved.
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16.
  • Grech-Madin, Charlotte, 1992-, et al. (författare)
  • Negotiating Water across Levels : A Peace and Conflict “Toolbox” for Water Diplomacy
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 559, s. 100-109
  • Tidskriftsartikel (refereegranskat)abstract
    • As a key policy tool, water diplomacy offers greater political engagement in the cooperative management of shared water. A range of initiatives has been dedicated to this end, almost invariably oriented around the interactions of nation states. Crucially, however, practitioners of water diplomacy also need to address water governance at sub-state levels. As a political, multi-level, and normative field, peace and conflict research offers a pluralism of approaches designed to bring actors together at all levels. Drawing upon this research, this paper offers new focal points for water diplomacy that can enhance its policy effectiveness and enrich its underlying academic current. More specifically, it presents three hitherto undervalued tools for water diplomacy: at the interstate level, to uncover the rich body of political norms that bind states to shared understandings of acceptable practice around water. At the intrastate level, to incorporate ethnography of water users and civil society groups’ responses to state-led waterworks projects, and at the communal level to employ disaggregated georeferenced data on water resources in conflict-prone areas. Taken together, these analytical tools provide a multi-faceted political gauge of the dynamics of water diplomacy, and add vital impetus to develop water diplomacy across multiple levels of policy engagement.
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17.
  • Haaf, Ezra, 1985, et al. (författare)
  • An inter-comparison of similarity-based methods for organisation and classification of groundwater hydrographs
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 559, s. 222-237
  • Tidskriftsartikel (refereegranskat)abstract
    • Classification and similarity based methods, which have recently received major attention in the field of surface water hydrology, namely through the PUB (prediction in ungauged basins) initiative, have not yet been applied to groundwater systems. However, it can be hypothesised, that the principle of ‘‘similar systems responding similarly to similar forcing” applies in subsurface hydrology as well. One fundamental prerequisite to test this hypothesis and eventually to apply the principle to make ‘‘predictions for ungauged groundwater systems” is efficient methods to quantify the similarity of groundwater system responses, i.e. groundwater hydrographs. In this study, a large, spatially extensive, as well as geologically and geomorphologically diverse dataset from Southern Germany and Western Austria was used, to test and compare a set of 32 grouping methods, which have previously only been used individually in localscale studies. The resulting groupings are compared to a heuristic visual classification, which serves as a baseline. A performance ranking of these classification methods is carried out and differences in homogeneity of grouping results were shown, whereby selected groups were related to hydrogeological indices and geological descriptors. This exploratory empirical study shows that the choice of grouping method has a large impact on the object distribution within groups, as well as on the homogeneity of patterns captured in groups. The study provides a comprehensive overview of a large number of grouping methods, which can guide researchers when attempting similarity-based groundwater hydrograph classification.
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18.
  • Haghighatafshar, Salar, et al. (författare)
  • Hydroeconomic optimization of mesoscale blue-green stormwater systems at the city level
  • 2019
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 578
  • Tidskriftsartikel (refereegranskat)abstract
    • The development of tools to help cities and water utility authorities communicate and plan for long-term sustainable solutions is of utmost importance in the era of a changing and uncertain climate. This study introduces a hybrid modeling concept for the cosimulation of mesoscale blue-green stormwater systems and conventional urban sewer networks. The hybrid model successfully introduces the retention/detention effects of mesoscale blue-green stormwater systems to the hydraulic dynamics of the sewer network. The cosimulation package was further facilitated with a cost-oriented multiobjective optimization algorithm. The aim of the scalar multiobjective optimization was to minimize the total cost comprising both flooding costs and action costs – both parameters solely representing the financial components of cost – through optimal placement of mesoscale blue-green systems of optimal size. The suggested methodology provides a useful platform for sustainable management of the existing sewer networks in cities from a hydroeconomic perspective.
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19.
  • Islam, M. M.Majedul, et al. (författare)
  • Modelling of river faecal indicator bacteria dynamics as a basis for faecal contamination reduction
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 563, s. 1000-1008
  • Tidskriftsartikel (refereegranskat)abstract
    • To improve microbial water quality and to prevent waterborne disease outbreaks, knowledge on the fate and transport of contaminants and on the contributions from different faecal sources to the total contamination is essential. The fate and transport of faecal indicators E. coli and enterococci within the Betna River in Bangladesh were simulated using a coupled hydrodynamic and water quality model. The hydrodynamic model for the river was set up, calibrated and validated with water level and discharge in our earlier study. In this study, the hydrodynamic model was further validated using measured water temperature and salinity and coupled with the water quality module. Bacterial load data from various faecal sources were collected and used as input in the water quality model. The model output corresponded very well with the measured E. coli and enterococci concentrations in the river; the Root Mean Square Error and the Nash-Sutcliffe efficiency for Log10-transformed concentrations were found to be 0.23 (Log10CFU/100 ml) and 0.84 for E. coli, and 0.19 (Log10CFU/100 ml) and 0.86 for enterococci, respectively. Then, the sensitivity of the model was tested by removing one process or forcing at a time. These simulations revealed that the microbial decay, the upstream concentrations and the discharge of untreated wastewater were the primary factors controlling the concentrations in the river, while wind and the contribution from the diffuse sources (i.e. urban and agricultural runoff) were unlikely to have a major influence. Finally, the model was applied to investigate the influence of wastewater treatment on the bacteria concentrations. This revealed that wastewater treatment would result in a considerable improvement of the microbial water quality of the Betna River. This paper demonstrates the application of a comprehensive state-of-art model in a river in a data-poor tropical area. The model can potentially be applied to other watersheds and can help in formulating solutions to improve the microbial water quality.
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20.
  • Johansson, Emma, et al. (författare)
  • Data evaluation and numerical modeling of hydrological interactions between active layer, lake and talik in a permafrost catchment, Western Greenland
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 527, s. 688-703
  • Tidskriftsartikel (refereegranskat)abstract
    • This study investigates annual water balance conditions and their spatiotemporal variability under a wide variety of atmospheric driving conditions in the periglacial permafrost catchment of Two Boat Lake in Western Greenland. The study uses and combines a comprehensive hydrological multi-parameter dataset measured at the site with site conceptualization and numerical model development, application and testing. The model result reproduces measured lake and groundwater levels, as well as observations made by time-lapse cameras. The results highlights the importance of numerical modeling that takes into account and combines evapotranspiration with other surface and subsurface hydrological processes at various depths, in order to quantitatively understand and represent the dynamics and complexity of the interactions between meteorology, active layer hydrology, lakes, and unfrozen groundwater below permafrost in periglacial catchments. Regarding these interactions, the water flow between the studied lake and a through talik within and beneath it is found to be small compared to other water balance components. The modeling results show that recharge and discharge conditions in the talik can shift in time, while the lake and active layer conditions in the studied catchment are independent of catchment-external landscape features, such as the unfrozen groundwater system below the permafrost and the nearby continental-scale ice sheet.
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21.
  • Karlsen, Reinert, 1983-, et al. (författare)
  • The role of landscape properties, storage and evapotranspiration on variability in streamflow recessions in a boreal catchment
  • 2019
  • Ingår i: Journal of Hydrology. - : ELSEVIER SCIENCE BV. - 0022-1694 .- 1879-2707. ; 570, s. 315-328
  • Tidskriftsartikel (refereegranskat)abstract
    • Streamflow recession analysis provides valuable insights into catchment functioning that can be related to runoff generation, storage retention and baseflow dynamics. As an integrated characteristic, recession analysis is particularly useful in catchment comparison studies to help explain drivers of spatial and temporal variability in hydrological behavior. Here, five years of hourly streamflow data from 14, partly nested, catchments within a 68 km(2) boreal forest landscape in Northern Sweden were used to explore spatiotemporal variation in hydrological processes through recession analysis. The aim of this study was to better understand spatial variation in runoff generation and storage-discharge dynamics across the landscape, as well as the relation to landscape properties. Due to high collinearity between variables, partial least square regression was used to quantify the associations between recession characteristics and catchment properties, as well as to identify key variables controlling recession behavior. We analyzed recession characteristics using both an aggregated approach including all recession data and individual recession events. The analyses based on individual recession events, indicated that catchment topography, quantified by indices such as mean slope or elevation above the stream network, is a primary control on the recession behavior during relatively high flows, whereas catchment area gains importance when flows are relatively low. The proportion of sediment and deep soils also controlled recession behavior. Furthermore, we found that recession characteristics are influenced by both evapotranspiration (ET) and proxies of antecedent catchment storage, but that the patterns were different depending on catchment properties. ET was less influential in catchments with deeper soils and larger catchment area. Shifts in recession rates were primarily related to variation in storage, with faster streamflow recessions occurring during periods with low storage. The results demonstrate the influence of catchment properties on recession behavior, and we found great value in analyzing individual recession events for an increased understanding of spatial and temporal recession characteristics. When recession properties were lumped together, the relationships to catchment characteristics were obscured. This indicates the value of more detailed analyses, at least under the strongly seasonal hydroclimatic conditions of this site.
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22.
  • Khazaei, Bahram, et al. (författare)
  • Climatic or regionally induced by humans? Tracing hydro-climatic and land-use changes to better understand the Lake Urmia tragedy
  • 2019
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 569, s. 203-217
  • Tidskriftsartikel (refereegranskat)abstract
    • Lake Urmia-a shallow endemic hypersaline lake in northwest Iran-has undergone a dramatic decline in its water level (WL), by about 8 m, since 1995. The primary cause of the WL decline in Lake Urmia has been debated in the scientific literature, regarding whether it has been predominantly driven by atmospheric climate change or by human activities in the watershed landscape. Using available climate, hydrological, and vegetation data for the period 1981-2015, this study analyzes and aims to explain the lake desiccation based on other observed hydro-climatic and vegetation changes in the Lake Urmia watershed and classical exploratory statistical methods. The analysis accounts for the relationships between atmospheric climate change (precipitation P, temperature T), and hydrological (soil moisture SM, and WL) and vegetation cover (VC; including agricultural crops and other vegetation) changes in the landscape. Results show that P, T, and SM changes cannot explain the sharp decline in lake WL since 2000. Instead, the agricultural increase of VC in the watershed correlates well with the lake WL change, indicating this human-driven VC and associated irrigation expansion as the dominant human driver of the Lake Urmia desiccation. Specifically, the greater transpiration from the expanded and increasingly irrigated agricultural crops implies increased total evapotranspiration and associated consumptive use of water (inherently related to the irrigation and water diversion and storage developments in the watershed). Thereby the runoff from the watershed into the lake has decreased, and the remaining smaller inflow to the lake has been insufficient for keeping up the previous lake WL, causing the observed WL drop to current conditions.
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23.
  • Koussis, Antonis D., et al. (författare)
  • A correction for Dupuit-Forchheimer interface flow models of seawater intrusion in unconfined coastal aquifers
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 525, s. 277-285
  • Tidskriftsartikel (refereegranskat)abstract
    • Interface flow models that use the Dupuit-Forchheimer (DF) approximation for assessing the freshwater lens and the seawater intrusion in coastal aquifers lack representation of the gap through which fresh groundwater discharges to the sea. In these models, the interface outcrops unrealistically at the same point as the free surface, is too shallow and intersects the aquifer base too far inland, thus overestimating an intruding seawater front. To correct this shortcoming of DF-type interface solutions for unconfined aquifers, we here adapt the outflow gap estimate of an analytical 2-D interface solution for infinitely thick aquifers to fit the 50%-salinity contour of variable-density solutions for finite-depth aquifers. We further improve the accuracy of the interface toe location predicted with depth-integrated DF interface solutions by similar to 20% (relative to the 50%-salinity contour of variable-density solutions) by combining the outflow-gap adjusted aquifer depth at the sea with a transverse-dispersion adjusted density ratio (Pool and Carrera, 2011), appropriately modified for unconfined flow. The effectiveness of the combined correction is exemplified for two regional Mediterranean aquifers, the Israel Coastal and Nile Delta aquifers.
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24.
  • Li, Lu, et al. (författare)
  • Hydrological projections under climate change in the near future by RegCM4 in Southern Africa using a large-scale hydrological model
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 528, s. 1-16
  • Tidskriftsartikel (refereegranskat)abstract
    • This study aims to provide model estimates of changes in hydrological elements, such as EvapoTranspiration (ET) and runoff, in Southern Africa in the near future until 2029. The climate change scenarios are projected by a high-resolution Regional Climate Model (RCM), RegCM4, which is the latest version of this model developed by the Abdus Salam International Centre for Theoretical Physics (ICTP). The hydrological projections are performed by using a large-scale hydrological model (WASMOD-D), which has been tested and customized on this region prior to this study. The results reveal that (1) the projected temperature shows an increasing tendency over Southern Africa in the near future, especially eastward of 25 degrees E, while the precipitation changes are varying between different months and sub-regions; (2) an increase in runoff (and ET) was found in eastern part of Southern Africa, i.e. Southern Mozambique and Malawi, while a decrease was estimated across the driest region in a wide area encompassing Kalahari Desert, Namibia, southwest of South Africa and Angola; (3) the strongest climate change signals are found over humid tropical areas, i.e. north of Angola and Malawi and south of Dem Rep of Congo; and (4) large spatial and temporal variability of climate change signals is found in the near future over Southern Africa. This study presents the main results of work-package 2 (WP2) of the 'Socioeconomic Consequences of Climate Change in Sub-equatorial Africa (SoCoCA)' project, which is funded by the Research Council of Norway.
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25.
  • Lind, Lovisa, et al. (författare)
  • Hydrological and thermal controls of ice formation in 25 boreal stream reaches
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 540, s. 797-811
  • Tidskriftsartikel (refereegranskat)abstract
    • The Northern Hemisphere has a high density of fluvial freshwater ecosystems, many of which become ice-covered during winter. The development and extent of ice have both ecological and socio-economic implications. For example, ice can cause freezing of riparian vegetation and fish eggs as well as influence hydropower production; however, when, where and why ice develops in small streams is not well known. We used observations from 25 stream reaches to study the factors controlling ice development during two consecutive winters, addressing where in the catchment surface or anchor-ice is most likely to develop, how stream morphology influences ice formation, and how climate influences ice processes. Reaches far downstream from lake outlets, or without any upstream lakes, were most prone to develop anchor-ice, but other factors also influenced ice formation. Anchor-ice was most common where water temperature and groundwater inputs were low and stream power high. Given cold air temperature and water supercooling, the in-stream substrate as well as the current velocity were also important for the development of anchor-ice. Climate and substrate seemed to be important factors for the development of surface ice. This study shows that ice processes are substantial during the hydrological year and may therefore have large implications for the ecology and engineering around boreal streams.. The study also demonstrates that ice formation in the studied streams was complex, involving many variables and physical processes. We constructed a conceptual model describing the likelihood for various ice types to develop, based on the large dataset. As such, this model will be useful for practitioners and scientists working in small watercourses in the Northern Hemisphere.
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26.
  • Mahmoudzadeh, Batoul, et al. (författare)
  • Solute transport through fractured rock : Radial diffusion into the rock matrix with several geological layers for an arbitrary length decay chain
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 536, s. 133-146
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper presents a model development to derive a semi-analytical solution to describe reactive solute transport through a single channel in a fracture with cylindrical geometry. The model accounts for advection through the channel, radial diffusion into the adjacent heterogeneous rock matrix comprising different geological layers, adsorption on both the channel surface, and the geological layers of the rock matrix and radioactive decay chain. Not only an arbitrary-length decay chain, but also as many number of the rock matrix layers with different properties as observed in the field can be handled. The solution, which is analytical in the Laplace domain, is transformed back to the time domain numerically e.g. by use of de Hoog algorithm. The solution is verified against experimental data and analytical solutions of limiting cases of solute transport through porous media. More importantly, the relative importance and contribution of different processes on solute transport retardation in fractured rocks are investigated by simulating several cases of varying complexity. The simulation results are compared with those obtained from rectangular model with linear matrix diffusion. It is found that the impact of channel geometry on breakthrough curves increases markedly as the transport distance along the flow channel and away into the rock matrix increase. The effect of geometry is more pronounced for transport of a decay chain when the rock matrix consists of a porous altered layer.
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27.
  • Mazzoleni, Maurizio, et al. (författare)
  • Evaluating precipitation datasets for large-scale distributed hydrological modelling
  • 2019
  • Ingår i: Journal of Hydrology. - : ELSEVIER. - 0022-1694 .- 1879-2707. ; 578
  • Tidskriftsartikel (refereegranskat)abstract
    • We are experiencing a proliferation of satellite derived precipitation datasets. Advantages and limitations of their promising application in hydrological modelling application have been broadly investigated. However, most studies have analysed only the performance of one or few datasets, were limited to selected small-scale case studies or used lumped models when investigating large-scale basins. In this study, we compared the performance of 18 different precipitation datasets when used as main forcing in a grid-based distributed hydrological model to assess streamfiow in medium to large-scale river basins. These datasets are classified as Uncorrected Satellites (Class 1), Corrected Satellites (Class 2) and Reanalysis - Gauges based datasets (Class 3). To provide a broad-based analysis, 8 large-scale river basins (Amazon, Brahmaputra, Congo, Danube, Godavari, Mississippi, Rhine and Volga) having different sizes, hydrometeorological characteristics, and human influence were selected. The distributed hydrological model was recalibrated for each precipitation dataset individually. We found that there is not a unique best performing precipitation dataset for all basins and that results are very sensitive to the basin characteristics. However, a few datasets persistently outperform the others: SM2RAIN-ASCAT for Class 1, CHIRPS V2.0, MSWEP V2.1, and CMORPH-CRTV1.0 for Class 2, GPCC and WFEDEI GPCC for Class 3. Surprisingly, precipitation datasets showing the highest model accuracy at basin outlets do not show the same high performance in internal locations, supporting the use of distributed modelling approach rather than lumped.
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28.
  • Meng, Shuo, et al. (författare)
  • Solute transport along a single fracture with a finite extent of matrix : A new simple solution and temporal moment analysis
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 562, s. 290-304
  • Tidskriftsartikel (refereegranskat)abstract
    • A new simple and robust solution, based on uniform steady-state flow velocity, is developed for the problem of solute transport in a fracture-matrix system with a finite penetration depth of a radioactive contaminant into the rock matrix. The solution is an extension of Liu et al. (2017) to finite penetration depth and an alternative solution strategy to the problem solved by Sudicky et al. (1982). The solution takes the form of a convolution of two functions. The first function describes the probability density function of the residence time distribution of a conservative solute resulting merely from advection and Fickian dispersion. The second function is actually the impulse response of the fracture-matrix system in the case of a plug flow without any hydrodynamic dispersion. As a result, the effects of Fickian dispersion and matrix diffusion on solute transport are decoupled, and thus the resulting breakthrough curve can be analyzed in terms of those two functions. In addition to this, the derived Péclet numbers of those two functions, based on temporal moments, are also found to be associated with the derived Péclet number of the resulting breakthrough curve. By comparing the Péclet numbers of those two functions, the contribution of Fickian dispersion and matrix diffusion to solute spreading is determined in a straightforward way. This can aid to find out the dominating mechanism on solute transport, and therefore the performance of breakthrough curve.
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29.
  • Mineo, Claudio, et al. (författare)
  • The areal reduction factor : A new analytical expression for the Lazio Region in central Italy
  • 2018
  • Ingår i: Journal of Hydrology. - Amsterdam : Elsevier. - 0022-1694 .- 1879-2707. ; 560, s. 471-479
  • Tidskriftsartikel (refereegranskat)abstract
    • For the study and modeling of hydrological phenomena, both in urban and rural areas, a proper estimation of the areal reduction factor (ARF) is crucial. In this paper, we estimated the ARF from observed rainfall data as the ratio between the average rainfall occurring in a specific area and the point rainfall. Then, we compared the obtained ARF values with some of the most widespread empirical approaches in literature which are used when rainfall observations are not available. Results highlight that the literature formulations can lead to a substantial over- or underestimation of the ARF estimated from observed data. These findings can have severe consequences, especially in the design of hydraulic structures where empirical formulations are extensively applied. The aim of this paper is to present a new analytical relationship with an explicit dependence on the rainfall duration and area that can better represent the ARF-area trend over the area case of study. The analytical curve presented here can find an important application to estimate the ARF values for design purposes. The test study area is the Lazio Region (central Italy).
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30.
  • Mondal, Arun, et al. (författare)
  • Intercomparison of trend analysis of Multisatellite Monthly Precipitation Products and Gauge Measurements for River Basins of India
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 565, s. 779-790
  • Tidskriftsartikel (refereegranskat)abstract
    • This study compares the precipitation trend from the gridded rain gauge data collected by India Meteorological Department (IMD) and Multisatellite High Resolution Precipitation Products (HRPPs) including Tropical Rainfall Measurement Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) version 7, Climate Prediction Center Morphing (CMORPH) version 1.0, Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN), and Multi-Source Weighted-Ensemble Precipitation (MSWEP) version 1.1 for the river basins of India. The IMD and HRPPs are of the same spatial resolution (0.25° × 0.25°) and extend from 1998 to 2015. The gridded precipitation datasets are compared for 25 river basins of India. TRMM, CMORPH, PERSIANN, and MSWEP datasets accuracy for the river basins are assessed by comparison with IMD using root mean square error (RMSE) and correlation coefficient (CC) methods. The Mann–Kendall (MK) and modified Mann–Kendall (MMK) tests are applied for analyzing the data trend, and the change is detected by Sen's Slope using all datasets for annual and seasonal time periods. Variation in precipitation is high (>20%) in the northern part of India in all datasets. All these basins located at the elevations above 2000 m. The annual and monsoon trend pattern for TMPA, CMORPH, PERSIANN, and MSWEP matched with IMD data in the north, northwest, and central part in 1–2, 22–25, and parts of 3, 12, and 21 river basins (1998–2015). The calculated results implied that the TMPA precipitation product (in terms of accuracy) and PERSIANN (in terms of annual and monsoon trend) show a better agreement with IMD and they can be used in climate studies and hydrological simulation in locations/river basins where the number of rain gauges is not adequate to quantify the spatial variability of precipitation.
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31.
  • Mård Karlsson, Johanna, et al. (författare)
  • Hydro-climatic and lake change patterns in Arctic permafrost and non-permafrost areas
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 529, s. 134-145
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper investigates patterns of lake-area and hydro-climatic change in Arctic river basins, and possible influence of permafrost change reflected in such patterns. A salient change pattern, emerging across all investigated basins in both permafrost and non-permafrost areas, is an opposite change direction in runoff (R) from that in precipitation (P). To explain this change contrast, an increase (decrease) in relative water-balance constrained evapotranspiration ETwb/P is required where R decreases (increases). Increasing temporal variability of daily river discharge (sdQ) is found in all basins with spatially extensive lake decrease, which also exhibit decrease in ELwb/P. Clear indication of basin-wide permafrost thaw is found in only one basin, and is possible in two more, but unlikely in the largest of the total four investigated permafrost basins.
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32.
  • Nakagawa, Kei, et al. (författare)
  • On the use of coprostanol to identify source of nitrate pollution in groundwater
  • 2017
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 550, s. 663-668
  • Tidskriftsartikel (refereegranskat)abstract
    • Investigation of contaminant sources is indispensable for developing effective countermeasures against nitrate (NO3 −) pollution in groundwater. Known major nitrogen (N) sources are chemical fertilizers, livestock waste, and domestic wastewater. In general, scatter diagrams of δ18O and δ15N from NO3 − can be used to identify these pollution sources. However, this method can be difficult to use for chemical fertilizers and livestock waste sources due to the overlap of δ18O and δ15N ranges. In this study, we propose to use coprostanol as an indicator for the source of pollution. Coprostanol can be used as a fecal contamination indicator because it is a major fecal sterol formed by the conversion of cholesterol by intestinal bacteria in the gut of higher animals. The proposed method was applied to investigate NO3 − pollution sources for groundwater in Shimabara, Nagasaki, Japan. Groundwater samples were collected at 33 locations from March 2013 to November 2015. These data were used to quantify relationships between NO3-N, δ15N-NO3 −, δ18O-NO3 −, and coprostanol. The results show that coprostanol has a potential for source identification of nitrate pollution. For lower coprostanol concentrations (<30 ng L−1) in the nitrate-polluted group, fertilizer is likely to be the predominant source of NO3 −. However, higher concentration coprostanol samples in the nitrate-polluted group can be related to pollution from livestock waste. Thus, when conventional diagrams of isotopic ratios cannot distinguish pollution sources, coprostanol may be a useful tool.
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33.
  • Orth, Rene, et al. (författare)
  • Does model performance improve with complexity? : A case study with three hydrological models
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 523, s. 147-159
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent decades considerable progress has been made in climate model development. Following the massive increase in computational power, models became more sophisticated. At the same time also simple conceptual models have advanced. In this study we validate and compare three hydrological models of different complexity to investigate whether their performance varies accordingly. For this purpose we use runoff and also soil moisture measurements, which allow a truly independent validation, from several sites across Switzerland. The models are calibrated in similar ways with the same runoff data. Our results show that the more complex models HBV and PREVAH outperform the simple water balance model (SWBM) in case of runoff but not for soil moisture. Furthermore the most sophisticated PREVAH model shows an added value compared to the HBV model only in case of soil moisture. Focusing on extreme events we find generally improved performance of the SWBM during drought conditions and degraded agreement with observations during wet extremes. For the more complex models we find the opposite behavior, probably because they were primarily developed for prediction of runoff extremes. As expected given their complexity, HBV and PREVAH have more problems with over-fitting. All models show a tendency towards better performance in lower altitudes as opposed to (pre-) alpine sites. The results vary considerably across the investigated sites. In contrast, the different metrics we consider to estimate the agreement between models and observations lead to similar conclusions, indicating that the performance of the considered models is similar at different time scales as well as for anomalies and long-term means. We conclude that added complexity does not necessarily lead to improved performance of hydrological models, and that performance can vary greatly depending on the considered hydrological variable (e.g. runoff vs. soil moisture) or hydrological conditions (floods vs. droughts). (C) 2015 The Authors. Published by Elsevier B.V.
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34.
  • Peralta Tapia, Andres, et al. (författare)
  • Hydroclimatic influences on non-stationary transit time distributions in a boreal headwater catchment
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 543:A, s. 7-16
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding how water moves through catchments - from the time it enters as precipitation to when it exits via streamflow - is of fundamental importance to understanding hydrological and biogeochemical processes. A basic descriptor of this routing is the Transit Time Distribution (TTD) which is derived from the input-output behavior of conservative tracers, the mean of which represents the average time elapsed between water molecules entering and exiting a flow system. In recent decades, many transit time studies have been conducted, but few of these have focused on snow-dominated catchments. We assembled a 10-year time series of isotopic data (delta O-18 and delta H-2) for precipitation and stream water to estimate the characteristics of the transit time distribution in a boreal catchment in northern Sweden. We applied lumped parameter models using a gamma distribution to calculate the Mean Transit Time (MTT) of water over the entire period of record and to evaluate how inter-annual differences in transit times relate to hydroclimatic variability. The best fit MTT for the complete 10-year period was 650 days (Nash-Sutcliff Efficiency = 0.65), while the best fit inter-annual MTT ranged from 300 days up to 1200 days. Whilst there was a weak negative correlation between mean annual total precipitation and the annual MTT, this relationship was stronger (r(2) = 0.53, p = 0.02) for the annual rain water input. This strong connection between the MTT and annual rainfall, rather than snowmelt, has strong implications for understanding future hydrological and biogeochemical processes in boreal regions, given that predicted warmer winters would translate into a greater proportion of precipitation falling as rain and thus shorter MTT in catchments. Such a change could have direct implications for the export of solutes and pollutants.
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35.
  • Pietroń, Jan, et al. (författare)
  • Model analyses of the contribution of in-channel processes to sediment concentration hysteresis loops
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 527, s. 576-589
  • Tidskriftsartikel (refereegranskat)abstract
    • Sediment concentration (SC)-water discharge (Q) relations in rivers are typically governed by multiple and relatively complex processes. Due to hysteresis effects, sediment discharges can differ for similar or equivalent water discharges, which causes scatter in empirical datasets and may decrease the predictive power of SC rating curves. Such hysteresis effects must therefore be understood and accounted for to make dependable predictions for river system management. The overall objectives of this study are to develop modelling approaches suitable for reproducing and predicting hysteresis effects at larger scales and to investigate the possible contribution of in-channel processes (erosion and deposition) to sediment concentration hysteresis loops. To investigate relevant field-scale conditions, we develop a one-dimensional dynamic sediment transport model of the downstream Tuul River (northern Mongolia), investigating in-channel processes along a 141 km stretch during a hydrological year. The results show that the present modelling approach can reproduce both anti-clockwise and clockwise hysteresis effects. Importantly, in-channel processes alone can cause considerable anti-clockwise hysteresis effects without being reinforced by catchment processes such as hillslope erosion. Such specific contributions from in-channel processes introduced data scatter into the sediment rating curves, decreasing their R-2-values from unity to approximately 0.5 to 0.6. More generally, possible changes in the number or magnitude of high-flow events, caused by climatic or other anthropogenic factors, could influence total sediment deposition, which was primarily found to occur during relatively short high-flow events. Such potential changes also have important implications for the possible spreading of polluted sediments.
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36.
  • Pool, Sandra, et al. (författare)
  • Prediction of hydrographs and flow-duration curves in almost ungauged catchments : Which runoff measurements are most informative for model calibration?
  • 2017
  • Ingår i: Journal of Hydrology. - : ELSEVIER SCIENCE BV. - 0022-1694 .- 1879-2707. ; 554, s. 613-622
  • Tidskriftsartikel (refereegranskat)abstract
    • Applications of runoff models usually rely on long and continuous runoff time series for model calibration. However, many catchments around the world are ungauged and estimating runoff for these catchments is challenging. One approach is to perform a few runoff measurements in a previously fully ungauged catchment and to constrain a runoff model by these measurements. In this study we investigated the value of such individual runoff measurements when taken at strategic points in time for applying a bucket-type runoff model (HBV) in ungauged catchments. Based on the assumption that a limited number of runoff measurements can be taken, we sought the optimal sampling strategy (i.e. when to measure the streamflow) to obtain the most informative data for constraining the runoff model. We used twenty gauged catchments across the eastern US, made the assumption that these catchments were ungauged, and applied different runoff sampling strategies. All tested strategies consisted of twelve runoff measurements within one year and ranged from simply using monthly flow maxima to a more complex selection of observation times. In each case the twelve runoff measurements were used to select 100 best parameter sets using a Monte Carlo calibration approach. Runoff simulations using these 'informed' parameter sets were then evaluated for an independent validation period in terms of the Nash-Sutcliffe efficiency of the hydrograph and the mean absolute relative error of the flow-duration curve. Model performance measures were normalized by relating them to an upper and a lower benchmark representing a well-informed and an uninformed model calibration. The hydrographs were best simulated with strategies including high runoff magnitudes as opposed to the flow-duration curves that were generally better estimated with strategies that captured low and mean flows. The choice of a sampling strategy covering the full range of runoff magnitudes enabled hydrograph and flow-duration curve simulations close to a well-informed model calibration. The differences among such strategies covering the full range of runoff magnitudes were small indicating that the exact choice of a strategy might be less crucial. Our study corroborates the information value of a small number of strategically selected runoff measurements for simulating runoff with a bucket-type runoff model in almost ungauged catchments.
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37.
  • Reynolds, Eduardo, et al. (författare)
  • Sub-daily runoff predictions using parameters calibrated on the basis of data with a daily temporal resolution
  • 2017
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 550, s. 399-411
  • Tidskriftsartikel (refereegranskat)abstract
    • Concentration times in small and medium-sized basins (similar to 10-1000 km(2)) are commonly less than 24 h. Flood-forecasting models are thus required to provide simulations at high temporal resolutions (1 h-6 h), although time-series of input and runoff data with sufficient lengths are often only available at the daily temporal resolution, especially in developing countries. This has led to study the relationships of estimated parameter values at the temporal resolutions where they are needed from the temporal resolutions where they are available. This study presents a methodology to treat empirically model parameter dependencies on the temporal resolution of data in two small basins using a bucket-type hydrological model, HBV-light, and the generalised likelihood uncertainty estimation approach for selecting its parameters. To avoid artefacts due to the numerical resolution or numerical method of the differential equations within the model, the model was consistently run using modelling time steps of one-hour regardless of the temporal resolution of the rainfall-runoff data. The distribution of the parameters calibrated at several temporal resolutions in the two basins did not show model parameter dependencies on the temporal resolution of data and the direct transferability of calibrated parameter sets (e.g., daily) for runoff simulations at other temporal resolutions for which they were not calibrated (e.g., 3 h or 6 h) resulted in a moderate (if any) decrease in model performance, in terms of Nash-Sutcliffe and volume-error efficiencies. The results of this study indicate that if sub-daily forcing data can be secured, flood forecasting in basins with sub-daily concentration times may be possible with model-parameter values calibrated from long time series of daily data. Further studies using more models and basins are required to test the generality of these results.
  •  
38.
  • Rujner, Hendrik, 1983-, et al. (författare)
  • High-resolution modelling of the grass swale response to runoff inflows with Mike SHE
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 562, s. 411-422
  • Tidskriftsartikel (refereegranskat)abstract
    • The feasibility of simulating the hydrological response of a grass swale to runoff inflows was examined using the hydrological model Mike SHE and the available input data from 12 irrigation events mimicking runoff from block rainfalls. The test swale channel had a trapezoidal cross-section, bottom slope of 1.5%, length of 30 m, and was built in loamy fine sand. The irrigation events consisted in releasing two equal constant inflows to the swale: a concentrated longitudinal flow at the upstream end and a distributed lateral inflow along the swale side slope adjacent to the contributing drainage area. The total inflows approximated runoff from two events with return periods of 2 months and 3 years, respectively, for durations of 30 min. Irrigation experiments were done for two states of the initial soil moisture, dry or wet antecedent moisture conditions (AMC). Mike SHE has been extensively used on catchments of various sizes, but rarely for small stormwater management facilities and their detailed topography investigated in this study. The latter application required high spatial and temporal resolutions, with computational cells of 0.2 × 0.2 m and time steps as short as 0.6 s to avoid computational instabilities. For dominant hydrological processes, the following computational options in Mike SHE were chosen: Soil infiltration – the van Genuchten equation, unsaturated zone flow – the one-dimensional Richards equation, and overland flow – the diffusive wave approximation of the St. Venant equations. For study purposes, the model was calibrated for single events representing one of four combinations of low and high inflows, and dry and wet AMC, and then applied to the remaining 11 events. This was complemented by calibration for two events, representing high inflow on wet AMC and low inflow in dry AMC. The goodness of fit was statistically assessed for observed and simulated peak flows, hydrograph volumes, Nash-Sutcliffe model efficiencies (NSE), and soil water content (SWC) in swale soil layers. The best fit (NSE > 0.8) was obtained for high inflows and wet AMC (i.e., when the primary swale function is flow conveyance); the least fit was noted for low inflows and dry AMC, when the primary swale function is flow attenuation. Furthermore, this observation indicates the overall importance of correct modelling of the soil infiltration. The effects of spatial variation of SWC on the swale discharge hydrograph could not be confirmed from simulation results, but high topographical accuracy was beneficial for reproducing well the locations of the observed water ponding. No significant increases in simulated SWC at 0.3 m or greater depths were noted, which agreed with field observations. Overall, the results indicated that Mike SHE was effective in process-oriented small-scale modelling of grass swale flow hydrographs.
  •  
39.
  • Scaini, Anna, et al. (författare)
  • Velocity and celerity dynamics at plot scale inferred from artificial tracing experiments and time-lapse ERT
  • 2017
  • Ingår i: Journal of Hydrology. - : ELSEVIER SCIENCE BV. - 0022-1694 .- 1879-2707. ; 546, s. 28-43
  • Tidskriftsartikel (refereegranskat)abstract
    • The relationship between tracer velocities and wave or wetting front celerities is essential to understand water flowing from hillslopes to the stream. The connection between maximum velocity and celerities estimated by means of experimental techniques has not been explored. To assess the pattern of infiltrating water front and dominant flow direction, we performed sprinkling experiments at a trenched plot in the Weierbach catchment in Luxembourg. Maximum velocities and wetting front celerities were inferred at different depths using artificial tracers, soil moisture measurements (TDR), and geophysical techniques. The flow direction was predominantly vertical within the observed plot, with almost no lateral flow observed until depths of 2-3 m; shallow trench flow was intermittent and associated with preferential flow. Average celerity estimates using TDR and geophysical techniques were equal to 707 +/- 234 mm h(-1) and 971 +/- 625 mm h(-1), respectively. Vertical maximum velocity estimates were tracer-dependent and had very variable ranges: 109.3 +/- 89.3 mm h(-1) (Cl-), 177.8 +/- 199.1 mm h(-1) (Br-), and 604.1 +/- 610.7 mm h(-1) (Li+). Preferential flow processes were inferred from maximum velocities apparently greater than celerities and scattered trench flow with highly variable tracer concentrations. The high variability between maximum velocities of different tracers indicated a complex pattern of tracer movement through the soil, not captured by celerity values alone. Our study demonstrated the importance to assess both velocities and celerities to understand flow dynamics in response to sprinkling while information on the wetting front alone would have missed important preferential flow processes.
  •  
40.
  • Seibert, Jan (författare)
  • What is the best time to take stream isotope samples for event-based model calibration?
  • 2019
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 577
  • Tidskriftsartikel (refereegranskat)abstract
    • Environmental tracer data, such as the stable water isotopic composition of streamwater and precipitation, are valuable for understanding runoff generation processes and calibrating hydrological models. Despite recent technical advancements, the collection and analysis of streamwater and precipitation samples still involve significant costs and efforts. Consequently, it is useful to study how many samples need to be collected as a basis for model calibration and what the most informative sampling times are. In previous studies, we used the Birkenes hydrological model and synthetic data to explore the value of a few stream isotope samples for event-based model calibration. Our results showed that the information from two or three selected isotope samples, and particularly a sample taken during the falling limb of the hydrograph, improved model performance significantly compared to calibration against streamflow data only. In this follow-up study, we used a unique Swiss dataset with high-frequency isotope measurements of precipitation and streamwater during six rainfall-runoff events to determine which stream isotope samples were most informative for model calibration. Several benchmarks were used to judge model validation performance. Our results showed that for 83% of the 42 possible combinations of calibration and validation events two strategically selected streamwater samples improved model performance compared to the lower benchmark when only stream stage data were used for calibration. The most informative samples also improved the calibration of a mixing-related parameter. When the model was calibrated and validated for the same event, the most informative samples for model calibration were those from the early part of the falling limb, which confirmed the results of the previous studies with synthetic data. Pre-event isotope samples were more informative when the model was calibrated for one event and then validated against other events or all events combined. Our results suggest that relatively inexpensive event-based data for model calibration can be obtained for so-far ungauged catchments by placing a water level logger in the stream and collecting precipitation isotope data and a few streamflow samples. These samples should preferably include a pre-event sample and a sample from the early falling limb. However, similar analyses for a wider range of sites and events, in combination with a selection of models with different structures and assumptions, are needed to confirm these results and to optimise sampling strategies further.
  •  
41.
  • Seibert, Jan (författare)
  • Your work is my boundary condition! Challenges and approaches for a closer collaboration between hydrologists and hydrogeologists
  • 2019
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 571, s. 235-243
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrologists and hydrogeologists both study the flux and storage of water with the numerous interactions and feedback mechanisms of surface water and groundwater. Traditionally however, focus, models and scales of the studies differ. In this commentary, situations are illustrated where boundary conditions that each discipline assumes, preserves and actively uses, can and have to be overcome. These situations occur when the domain of one discipline cannot be separated from the other one because of existing interaction and feedback mechanisms at the boundaries. Highlighted are especially these boundary conditions, where closer collaboration between catchment hydrologists and hydrogeologists would be most useful. Often such collaborations would be relatively straight-forward and rather requiring an increased awareness than novel methods.
  •  
42.
  • Seidl, R., et al. (författare)
  • Linking scientific disciplines: Hydrology and social sciences
  • 2017
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 550, s. 441-452
  • Tidskriftsartikel (refereegranskat)abstract
    • The integration of interdisciplinary scientific and societal knowledge plays an increasing role in sustain ability science and more generally, in global change research. In the field of water resources, interdisciplinarity has long been recognized as crucial. Recently, new concepts and ideas about how to approach water resources management more holistically have been discussed. The emergence of concepts such as socio-hydrology indicates the growing relevance of connections between social and hydrological disciplines. In this paper, we determine how well social sciences are integrated with hydrological research by using two approaches. First, we conducted a questionnaire survey with a sample of hydrology researchers and professionals (N = 353) to explore current opinions and developments related to interdisciplinary collaboration between hydrologists and social scientists. Second, we analyzed the disciplinary composition of author teams and the reference lists of articles pertaining to the socio-hydrology concept. We conclude that interdisciplinarity in water resources research is on a promising track but may need to mature further in terms of its aims and methods of integration. We find that current literature pays little attention to the following questions: What kind of interdisciplinarity do different scholars want? What are social scientists' preferred roles and knowledge from a hydrology perspective? (C) 2017 Elsevier B.V. All rights reserved.
  •  
43.
  • Shahkarami, Pirouz, 1986-, et al. (författare)
  • Radionuclide migration through fractured rock for arbitrary-length decay chain: Analytical solution and global sensitivity analysis : new
  • 2015
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 520, s. 448-460
  • Tidskriftsartikel (refereegranskat)abstract
    • This study presents an analytical approach to simulate nuclide migration through a channel in a fracture accounting for an arbitrary-length decay chain. The nuclides are retarded as they diffuse in the porous rock matrix and stagnant zones in the fracture. The Laplace transform and similarity transform techniques are applied to solve the model. The analytical solution to the nuclide concentrations at the fracture outlet is governed by nine parameters representing different mechanisms acting on nuclide transport through a fracture, including diffusion into the rock matrices, diffusion into the stagnant water zone, chain decay and hydrodynamic dispersion. Furthermore, to assess how sensitive the results are to parameter uncertainties, the Sobol method is applied in variance-based global sensitivity analyses of the model output. The Sobol indices show how uncertainty in the model output is apportioned to the uncertainty in the model input. This method takes into account both direct effects and interaction effects between input parameters. The simulation results suggest that in the case of pulse injections, ignoring the effect of a stagnant water zone can lead to significant errors in the time of first arrival and the peak value of the nuclides. Likewise, neglecting the parent and modeling its daughter as a single stable species can result in a significant overestimation of the peak value of the daughter nuclide. It is also found that as the dispersion increases, the early arrival time and the peak time of the daughter decrease while the peak value increases. More importantly, the global sensitivity analysis reveals that for time periods greater than a few thousand years, the uncertainty of the model output is more sensitive to the values of the individual parameters than to the interaction between them. Moreover, if one tries to evaluate the true values of the input parameters at the same cost and effort, the determination of priorities should follow a certain sequence.
  •  
44.
  • Shahkarami, Pirouz, 1986-, et al. (författare)
  • The effect of stagnant water zones on retarding radionuclide transport in fractured rocks : An extension to the Channel Network Model
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 540, s. 1122-1135
  • Tidskriftsartikel (refereegranskat)abstract
    • An essential task of performance assessment of radioactive waste repositories is to predict radionuclide release into the environment. For such a quantitative assessment, the Channel Network Model and the corresponding computer program, CHAN3D, have been used to simulate radionuclide transport in crystalline bedrocks. Recent studies suggest, however, that the model may tend to underestimate the rock retarding capability, because it ignores the presence of stagnant water zones, STWZs, situated in the fracture plane. Once considered, the STWZ can provide additional surface area over which radionuclides diffuse into the rock matrix and thereby contribute to their retardation.The main objective of this paper is to extend the Channel Network Model and its computer implementation to account for diffusion into STWZs and their adjacent rock matrices.In the first part of the paper, the overall impact of STWZs in retarding radionuclide transport is investigated through a deterministic calculation of far-field releases at Forsmark, Sweden. Over the time-scale of the repository safety assessments, radionuclide breakthrough curves are calculated for increasing STWZ width. It is shown that the presence of STWZs enhances the retardation of most long-lived radionuclides except for 36Cl and 129I.The rest of the paper is devoted to the probabilistic calculation of radionuclide transport in fractured rocks. The model that is developed for transport through a single channel is embedded into the Channel Network Model and new computer codes are provided for the CHAN3D. The program is used to (I) simulate the tracer test experiment performed at Äspö HRL, STT-1 and (II) investigate the short- and long-term effect of diffusion into STWZs. The required data for the model are obtained from detailed hydraulic tests in boreholes intersecting the rock mass where the tracer tests were made.The simulation results fairly well predict the release of the sorbing tracer 137Cs. It is found that over the short time-scale of the tracer experiment, the effect of diffusion into STWZs is not as pronounced as that of matrix diffusion directly from the flow channel, and the latter remains the main retarding mechanism. Predictions for longer time-scale, tens of years and more, show that the effect of STWZs becomes strong and tends to increase with transport time. It is shown that over the long times of interest for safety assessment of radioactive waste repositories, STWZs can substantially contribute to radionuclide retardation, though for the short time-scales the impact is not very strong and is not expected to affect the results of short-term field experiments.
  •  
45.
  • Sikorska, A. E., et al. (författare)
  • Effective precipitation duration for runoff peaks based on catchment modelling
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 556, s. 510-522
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite precipitation intensities may greatly vary during one flood event, detailed information about these intensities may not be required to accurately simulate floods with a hydrological model which rather reacts to cumulative precipitation sums. This raises two questions: to which extent is it important to preserve sub-daily precipitation intensities and how long does it effectively rain from the hydrological point of view? Both questions might seem straightforward to answer with a direct analysis of past precipitation events but require some arbitrary choices regarding the length of a precipitation event. To avoid these arbitrary decisions, here we present an alternative approach to characterize the effective length of precipitation event which is based on runoff simulations with respect to large floods. More precisely, we quantify the fraction of a day over which the daily precipitation has to be distributed to faithfully reproduce the large annual and seasonal floods which were generated by the hourly precipitation rate time series. New precipitation time series were generated by first aggregating the hourly observed data into daily totals and then evenly distributing them over sub-daily periods (n hours). These simulated time series were used as input to a hydrological bucket-type model and the resulting runoff flood peaks were compared to those obtained when using the original precipitation time series. We define then the effective daily precipitation duration as the number of hours n, for which the largest peaks are simulated best. For nine mesoscale Swiss catchments this effective daily precipitation duration was about half a day, which indicates that detailed information on precipitation intensities is not necessarily required to accurately estimate peaks of the largest annual and seasonal floods. These findings support the use of simple disaggregation approaches to make usage of past daily precipitation observations or daily precipitation simulations (e.g. from climate models) for hydrological modeling at an hourly time step.
  •  
46.
  • Sikorska, A. E., et al. (författare)
  • Value of different precipitation data for flood prediction in an alpine catchment : A Bayesian approach
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 556, s. 961-971
  • Tidskriftsartikel (refereegranskat)abstract
    • Flooding induced by heavy precipitation is one of the most severe natural hazards in alpine catchments. To accurately predict such events, accurate and representative precipitation data are required. Estimating catchment precipitation is, however, difficult due to its high spatial, and, in the mountains, elevation-dependent variability. These inaccuracies, together with runoff model limitations, translate into uncertainty in runoff estimates. Thus, in this study, we investigate the value of three precipitation datasets, commonly used in hydrological studies, i.e., station network precipitation (SNP), interpolated grid precipitation (IGP) and radar-based precipitation (RBP), for flood predictions in an alpine catchment. To quantify their effects on runoff simulations, we perform a Bayesian uncertainty analysis with an improved description of model systematic errors. By using periods of different lengths for model calibration, we explore the information content of these three datasets for runoff predictions. Our results from an alpine catchment showed that using SNP resulted in the largest predictive uncertainty and the lowest model performance evaluated by the Nash–Sutcliffe efficiency. This performance improved from 0.674 to 0.774 with IGP, and to 0.829 with RBP. The latter two datasets were also much more informative than SNP, as half as many calibration data points were required to obtain a good model performance. Thus, our results show that the various types of precipitation data differ in their value for flood predictions in an alpine catchment and indicate RBP as the most useful dataset.
  •  
47.
  • Skrzypek, Grzegorz, et al. (författare)
  • Groundwater seepage controls salinity in a hydrologically terminal basin of semi-arid northwest Australia
  • 2016
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 542, s. 627-636
  • Tidskriftsartikel (refereegranskat)abstract
    • Very small groundwater outflows have the potential to significantly impact the hydrochemistry and salt accumulation processes of notionally terminal basins in arid environments. However, this limited groundwater outflow can be very difficult to quantify using classical water budget calculations due to large uncertainties in estimates of evaporation and evapotranspiration rates from the surface of dry lake beds. In this study, we used a dimensionless time evaporation model to estimate the range of groundwater outflow required to maintain salinity levels observed at the Fortescue Marsh (FM), one of the largest wetlands of semi-arid northwest Australia (∼1100 km2). The groundwater outflow from aquifers underlying the FM to the Lower Fortescue catchment is constrained by an extremely low hydraulic gradient of <0.0001 and a small ‘alluvial outlet’ of 0.35 km2 because of relatively high bedrock elevation. However, FM groundwater salinity is far below saturation with respect to halite (TDS < 160 g/L), episodic flood water is fresh to brackish, and salt efflorescences are very sparse and evident only when the FM is dry. We show that if the FM was 100% “leakage free” i.e., a true terminal basin, groundwater would have achieved halite saturation (>300 g/L) after ∼45 ka. We calculated that only a very small seepage of ∼2G L/yr (∼0.03% of the FM water volume) is sufficient to maintain current salinity conditions. The minimum time required to develop the current hydrochemical groundwater composition under the FM ranges from ∼60 to ∼165 ka. We conclude that a dimensionless time evaporation model versus inflow over outflow ratio model is likely more suitable than classical water budget calculations for determining outflow from large saline lakes and to estimate groundwater seepage from hydrologically terminal basins.
  •  
48.
  • Skrzypek, Grzegorz, et al. (författare)
  • Unique stable isotope signatures of large cyclonic events as a tracer of soil moisture dynamics in the semiarid subtropics
  • 2019
  • Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 578
  • Tidskriftsartikel (refereegranskat)abstract
    • Evaporative flux from soils in arid and semi-arid climates can be very high and may substantially reduce soil moisture retained between infrequent rainfall events. Direct measurement of the evaporative losses from soils is technically challenging. However, environmental tracers such as water stable hydrogen and oxygen isotope composition can be used to calculate evaporation rates if the initial signature of the infiltrating rainwater is distinct from the signature of residual soil moisture. Large tropical cyclones typically result in rainfall events of large volume and very negative δ18O signatures that are significantly lower than the signatures of more frequent and smaller rainfall events. These very negative stable isotope signatures are retained in the soil and can be used to understand the depth of water infiltration, retention and subsequent rate of evaporation from the soil. At our study site in dry subtropical northwest Australia, we repeatedly sampled rainwater and soil moisture prior to, during and after tropical Cyclones Heidi and Lua in 2012. Site inundation from Cyclone Heidi (rainfall 213 mm, δ18O −17.6‰) replenished soil moisture in the unsaturated zone for several months, completely replacing soil moisture down to depths of ~3.5 m and contributing to groundwater recharge. The transient momentary evaporative losses from wet soil at the time of sampling varied between 0.21 and 0.60 mm × day−1 (equivalent to 76 to 220 mm × yr−1 recalculated as an annual rate). During the prolonged dry period between cyclones, evaporative losses decreased to between 8 and 30 mm × yr−1. Mean long-term groundwater recharge for the study site was low (<6 mm × yr−1). Recharge is primarily driven by infrequent but high-volume cyclones that are an important source of soil moisture and an essential water source for vegetation in this semi-arid environment. However, variation in lithology, position in the landscape and time since the last inundation contribute to highly heterogeneous patterns of δ18O in the vadose zone, which complicates upscaling observations from a local to a regional scale model of evaporative demand.
  •  
49.
  • Sterte, Elin Jutebring, et al. (författare)
  • Groundwater-surface water interactions across scales in a boreal landscape investigated using a numerical modelling approach
  • 2018
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 560, s. 184-201
  • Tidskriftsartikel (refereegranskat)abstract
    • Groundwater and surface-water interactions are regulated by catchment characteristics and complex inter- and intra-annual variations in climatic conditions that are not yet fully understood. Our objective was to investigate the influence of catchment characteristics and freeze-thaw processes on surface and groundwater interactions in a boreal landscape, the Krycklan catchment in Sweden. We used a numerical modelling approach and sub-catchment evaluation method to identify and evaluate fundamental catchment characteristics and processes. The model reproduced observed stream discharge patterns of the 14 sub-catchments and the dynamics of the 15 groundwater wells with an average accumulated discharge error of 1% (15% standard deviation) and an average groundwater-level mean error of 0.1 m (0.23 m standard deviation). We show how peatland characteristics dampen the effect of intense rain, and how soil freeze-thaw processes regulate surface and groundwater partitioning during snowmelt. With these results, we demonstrate the importance of defining, understanding and quantifying the role of landscape heterogeneity and sub-catchment characteristics for accurately representing catchment hydrological functioning.
  •  
50.
  • Su, Ye, et al. (författare)
  • Geochemical responses of forested catchments to bark beetle infestation : Evidence from high frequency in-stream electrical conductivity monitoring
  • 2017
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 550, s. 635-649
  • Tidskriftsartikel (refereegranskat)abstract
    • Under the present conditions of climate warming, there has been an increased frequency of bark beetle induced tree mortality in Asia, Europe, and North America. This study analyzed seven years of high frequency monitoring of in-stream electrical conductivity (EC), hydro-climatic conditions, and vegetation dynamics in four experimental catchments located in headwaters of the Sumava Mountains, Central Europe. The aim was to determine the effects of insect-induced forest disturbance on in-stream EC at multiple timescales, including annual and seasonal average conditions, daily variability, and responses to individual rainfall events. Results showed increased annual average in-stream EC values in the bark beetle-infected catchments, with particularly elevated EC values during baseflow conditions. This is likely caused by the cumulative loading of soil water and groundwater that discharge excess amounts of substances such as nitrogen and carbon, which are released via the decomposition of the needles, branches, and trunks of dead trees, into streams. Furthermore, we concluded that infestation-induced changes in event-scale dynamics may be largely responsible for the observed shifts in annual average conditions. For example, systematic EC differences between baseflow conditions and event flow conditions in relatively undisturbed catchments were essentially eliminated in catchments that were highly disturbed by bark beetles. These changes developed relatively rapidly after infestation and have long-lasting (decadal-scale) effects, implying that cumulative impacts of increasingly frequent bark beetle outbreaks may contribute to alterations of the hydrogeochemical conditions in more vulnerable mountain regions.
  •  
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