| 1. |
- Reynolds, Eduardo, et al.
(författare)
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Robustness of flood-model calibration using single and multiple events
- 2019
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Ingår i: Hydrological Sciences Journal. - Oxon : Taylor & Francis. - 0262-6667 .- 2150-3435. ; 65:5, s. 842-853
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Tidskriftsartikel (refereegranskat)abstract
- Lack of discharge data for model calibration is challenging for flood prediction in ungauged basins. Since establishment and maintenance of a permanent discharge station is resource demanding, a possible remedy could be to measure discharge only for a few events. We tested the hypothesis that a few flood-event hydrographs in a tropical basin would be sufficient to calibrate a bucket-type rainfall-runoff model, namely the HBV model, and proposed a new event-based calibration method to adequately predict floods. Parameter sets were chosen based on calibration of different scenarios of data availability, and their ability to predict floods was assessed. Compared to not having any discharge data, flood predictions improved already when one event was used for calibration. The results further suggest that two to four events for calibration may considerably improve flood predictions with regard to accuracy and uncertainty reduction, whereas adding more events beyond this resulted in small performance gains.
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| 2. |
- Seibert, Jan, et al.
(författare)
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Linking soil- and stream-water chemistry based on a Riparian Flow-Concentration Integration Model
- 2009
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Ingår i: Hydrology and earth system sciences. - : Copernicus Publications. - 1607-7938 .- 1027-5606. ; 13:12, s. 2287-2297
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Tidskriftsartikel (refereegranskat)abstract
- The riparian zone, the last few metres of soil through which water flows before entering a gaining stream, has been identified as a first order control on key aspects of stream water chemistry dynamics. We propose that the distribution of lateral flow of water across the vertical profile of soil water chemistry in the riparian zone provides a conceptual explanation of how this control functions in catchments where matrix flow predominates. This paper presents a mathematical implementation of this concept as well as the model assumptions. We also present an analytical solution, which provides a physical basis for the commonly used power-law flow-load equation. This approach quantifies the concept of riparian control on stream-water chemistry providing a basis for testing the concept of riparian control. By backward calculation of soil-water-chemistry profiles, and comparing those with observed profiles we demonstrate that the simple juxtaposition of the vertical profiles of water flux and soil water chemistry provides a plausible explanation for observed variations in stream water chemistry of several major stream components such as Total Organic Carbon (TOC), magnesium, calcium and chloride. The "static" implementation of the model structure presented here provides a basis for further development to account for seasonal influences and hydrological hysteresis in the representation of hyporheic, riparian, and hillslope processes.
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| 3. |
- Teutschbein, Claudia, 1985-, et al.
(författare)
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Evaluation of different downscaling techniques for hydrological climate-change impact studies at the catchment scale
- 2011
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 37:9-10, s. 2087-2105
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Tidskriftsartikel (refereegranskat)abstract
- Hydrological modeling for climate-change impact assessment implies using meteorological variables simulated by global climate models (GCMs). Due to mismatching scales, coarse-resolution GCM output cannot be used directly for hydrological impact studies but rather needs to be downscaled. In this study, we investigated the variability of seasonal streamflow and flood-peak projections caused by the use of three statistical approaches to downscale precipitation from two GCMs for a meso-scale catchment in southeastern Sweden: (1) an analog method (AM), (2) a multi-objective fuzzy-rule-based classification (MOFRBC) and (3) the Statistical DownScaling Model (SDSM). The obtained higher-resolution precipitation values were then used to simulate daily streamflow for a control period (1961-1990) and for two future emission scenarios (2071-2100) with the precipitation-streamflow model HBV. The choice of downscaled precipitation time series had a major impact on the streamflow simulations, which was directly related to the ability of the downscaling approaches to reproduce observed precipitation. Although SDSM was considered to be most suitable for downscaling precipitation in the studied river basin, we highlighted the importance of an ensemble approach. The climate and streamflow change signals indicated that the current flow regime with a snowmelt-driven spring flood in April will likely change to a flow regime that is rather dominated by large winter streamflows. Spring flood events are expected to decrease considerably and occur earlier, whereas autumn flood peaks are projected to increase slightly. The simulations demonstrated that projections of future streamflow regimes are highly variable and can even partly point towards different directions.
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| 4. |
- Viviroli, D., et al.
(författare)
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On the risk of obtaining misleading results by pooling streamflow data for trend analyses
- 2012
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 48, s. W05601-
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Tidskriftsartikel (refereegranskat)abstract
- Floods have broad impacts on nature, society, and the economy. The frequency and intensity of flood events are generally believed to increase with the anticipated changes in temperature and precipitation. Trend analyses are important tools to quantify these changes, but often, they provide inconclusive results, partly because of the limited data availability. One way to overcome this limitation is to pool data from different gauging stations. However, pooling data from different stations may lead to misleading results. For example, using pooled flood data Allamano et al. (2009a) found a considerable increase of flooding risks for Switzerland. Here we demonstrate that the previous finding of increased flooding risks was an artifact of the pooling of stations and the fact that the longer time series came from larger catchments, which tend to have lower values for specific peak flows than smaller catchments. Our results demonstrate the risk of obtaining incorrect statistical conclusions when statistical analyses and data selection are not considered with due care.
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| 5. |
- Teutschbein, Claudia, 1985-, et al.
(författare)
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Is bias correction of regional climate model (RCM) simulations possible for non-stationary conditions?
- 2013
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 17:12, s. 5061-5077
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Tidskriftsartikel (refereegranskat)abstract
- In hydrological climate-change impact studies, regional climate models (RCMs) are commonly used to transfer large-scale global climate model (GCM) data to smaller scales and to provide more detailed regional information. Due to systematic and random model errors, however, RCM simulations often show considerable deviations from observations. This has led to the development of a number of correction approaches that rely on the assumption that RCM errors do not change over time. It is in principle not possible to test whether this underlying assumption of error stationarity is actually fulfilled for future climate conditions. In this study, however, we demonstrate that it is possible to evaluate how well correction methods perform for conditions different from those used for calibration with the relatively simple differential split-sample test.
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| 6. |
- Teutschbein, Claudia, 1985-, et al.
(författare)
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Regional Climate Models for Hydrological Impact Studies at the Catchment Scale : A Review of Recent Modeling Strategies
- 2010
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Ingår i: Geography Compass. - : Wiley. - 1749-8198. ; 4:7, s. 834-860
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Tidskriftsartikel (refereegranskat)abstract
- This article reviews recent applications of regional climate model (RCM) output for hydrological impact studies. Traditionally, simulations of global climate models (GCMs) have been the basis of impact studies in hydrology. Progress in regional climate modeling has recently made the use of RCM data more attractive, although the application of RCM simulations is challenging due to often considerable biases. The main modeling strategies used in recent studies can be classified into (i) very simple constructed modeling chains with a single RCM (S-RCM approach) and (ii) highly complex and computing-power intensive model systems based on RCM ensembles (E-RCM approach). In the literature many examples for S-RCM can be found, while comprehensive E-RCM studies with consideration of several sources of uncertainties such as different greenhouse gas emission scenarios, GCMs, RCMs and hydrological models are less common. Based on a case study using control-run simulations of fourteen different RCMs for five Swedish catchments, the biases of and the variability between different RCMs are demonstrated. We provide a short overview of possible bias-correction methods and show that inter-RCM variability also has substantial consequences for hydrological impact studies in addition to other sources of uncertainties in the modeling chain. We propose that due to model bias and inter-model variability, the S-RCM approach is not advised and ensembles of RCM simulations (E-RCM) should be used. The application of bias-correction methods is recommended, although one should also be aware that the need for bias corrections adds significantly to uncertainties in modeling climate change impacts.
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| 7. |
- Grabs, Thomas, et al.
(författare)
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Riparian zone hydrology and soil water total organic carbon (TOC) : implications for spatial variability and upscaling of lateral riparian TOC exports
- 2012
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 9:10, s. 3901-3916
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater flowing from hillslopes through riparian (near-stream) soils often undergoes chemical transformations that can substantially influence stream water chemistry. We used landscape analysis to predict total organic carbon (TOC) concentration profiles and groundwater levels measured in the riparian zone (RZ) of a 67 km2 catchment in Sweden. TOC exported laterally from 13 riparian soil profiles was then estimated based on the riparian flow-concentration integration model (RIM). Much of the observed spatial variability of riparian TOC concentrations in this system could be predicted from groundwater levels and the topographic wetness index (TWI). Organic riparian peat soils in forested areas emerged as hotspots exporting large amounts of TOC. These TOC fluxes were subject to considerable temporal variations caused by a combination of variable flow conditions and changing soil water TOC concentrations. Mineral riparian gley soils, on the other hand, were related to rather small TOC export rates and were characterized by relatively time-invariant TOC concentration profiles. Organic and mineral soils in RZs constitute a heterogeneous landscape mosaic that potentially controls much of the spatial variability of stream water TOC. We developed an empirical regression model based on the TWI to move beyond the plot scale and to predict spatially variable riparian TOC concentration profiles for RZs underlain by glacial till.
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| 8. |
- Hakala, Kirsti, et al.
(författare)
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Hydrological Modeling of Climate Change Impacts
- 2019
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Ingår i: Encyclopedia of Water. - : John Wiley & Sons. - 9781119300755 - 9781119300762
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Bokkapitel (refereegranskat)abstract
- Hydrological climate change impact modeling is a commonly used approach to quantify potential future changes in streamflow. In this article, we present an introduction to the main steps involved in the production of such streamflow projections. We review commonly used modeling approaches to quantify climate change impacts on water resources, describe the main sources of uncertainty in hydrological projections and how to characterize them, and discuss best practices. The supplementary material includes a guide to perform typical data processing tasks involved in the production of hydrological projections. We also provide material to support teaching activities related to hydrological climate change impact modeling. The goal of this article is to support studies on climate change impacts on hydrological systems by providing guidance on working with the climate-hydrology modeling chain.
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| 9. |
- Amvrosiadi, Nino, et al.
(författare)
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Water storage dynamics in a till hillslope : the foundation for modeling flows and turnover times
- 2017
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Ingår i: Hydrological Processes. - : John Wiley and Sons Ltd. - 0885-6087 .- 1099-1085. ; 31:1, s. 4-14
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Tidskriftsartikel (refereegranskat)abstract
- Studies on hydrology, biogeochemistry, or mineral weathering often rely on assumptions about flow paths, water storage dynamics, and transit times. Testing these assumptions requires detailed hydrometric data that are usually unavailable at the catchment scale. Hillslope studies provide an alternative for obtaining a better understanding, but even on such well-defined and delimited scales, it is rare to have a comprehensive set of hydrometric observations from the water divide down to the stream that can constrain efforts to quantify water storage, movement, and turnover time. Here, we quantified water storage with daily resolution in a hillslope during the course of almost an entire year using hydrological measurements at the study site and an extended version of the vertical equilibrium model. We used an exponential function to simulate the relationship between hillslope discharge and water table; this was used to derive transmissivity profiles along the hillslope and map mean pore water velocities in the saturated zone. Based on the transmissivity profiles, the soil layer transmitting 99% of lateral flow to the stream had a depth that ranged from 8.9 m at the water divide to under 1 m closer to the stream. During the study period, the total storage of this layer varied from 1189 to 1485 mm, resulting in a turnover time of 2172 days. From the pore water velocities, we mapped the time it would take a water particle situated at any point of the saturated zone anywhere along the hillslope to exit as runoff. Our calculations point to the strengths as well as limitations of simple hydrometric data for inferring hydrological properties and water travel times in the subsurface.
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| 10. |
- Beck, Hylke E., et al.
(författare)
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Global Fully Distributed Parameter Regionalization Based on Observed Streamflow From 4,229 Headwater Catchments
- 2020
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Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 125:17
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Tidskriftsartikel (refereegranskat)abstract
- All hydrological models need to be calibrated to obtain satisfactory streamflow simulations. Here we present a novel parameter regionalization approach that involves the optimization of transfer equations linking model parameters to climate and landscape characteristics. The optimization was performed in a fully spatially distributed fashion at high resolution (0.05 degrees), instead of at lumped catchment scale, using an unprecedented database of daily observed streamflow from 4,229 headwater catchments (<5,000 km(2)) worldwide. The optimized equations were subsequently applied globally to produce parameter maps for the entire land surface including ungauged regions. The approach was evaluated using the Kling-Gupta efficiency (KGE) and a gridded version of the hydrological model HBV. Tenfold cross validation was used to evaluate the generalizability of the approach and to obtain an ensemble of parameter maps. For the 4,229 independent validation catchments, the regionalized parameters yielded a median KGE of 0.46. The median KGE improvement (relative to uncalibrated parameters) was 0.29, and improvements were obtained for 88% of the independent validation catchments. These scores compare favorably to those from previous large catchment sample studies. The degree of performance improvement due to the regionalized parameters did not depend on climate or topography. Substantial improvements were obtained even for independent validation catchments located far from the catchments used for optimization, underscoring the value of the derived parameters for poorly gauged regions. The regionalized parameters-available via -should be useful for hydrological applications requiring accurate streamflow simulations.
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