| 1. |
- Achleitner, Stefan, et al.
(författare)
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Analyzing the operational performance of the hydrological models in an alpine flood forecasting system
- 2012
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 412-413, s. 90-100
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Tidskriftsartikel (refereegranskat)abstract
- During recent years a hybrid model has been set up for the operational forecasting of flood discharges in the 6750km 2 Tyrolean part of the River Inn catchment in Austria. The catchment can be characterized as a typical alpine area with large variations in altitude. The paper is focused on the error analysis of discharge forecasts of four main tributary catchments simulated with hydrological water balance models. The selected catchments cover an area of 2230km 2, where the non-glaciated and glaciated parts are modeled using the semi-distributed HQsim and the distributed model SES, respectively.The forecast errors are evaluated as a function of forecast lead time and forecasted discharge magnitude using 14 events from 2007 to 2010. The observed and forecasted precipitation inputs were obtained under operational conditions. The mean relative bias of the forecasted discharges revealed to be constant with regard to the forecast lead time, varying between 0.2 and 0.25 for the different catchments. The errors as a function of the forecasted discharge magnitude showed large errors at lower values of the forecast hydrographs, where errors decreased significantly at larger discharges being relevant in flood forecasting
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| 2. |
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| 3. |
- Blecken, Godecke-Tobias, et al.
(författare)
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Laboratory study on stormwater biofiltration : nutrient and sediment removal in cold temperatures
- 2010
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 394:3-4, s. 507-514
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Tidskriftsartikel (refereegranskat)abstract
- Stormwater biofilters have the ability to remove nutrients from stormwater. Reliable pollutant removal during the cold season is particularly important due to the comparably high contamination levels. However, the removal performance might be negatively affected by low temperatures. A biofilter column study was conducted in thermostat-controlled climate rooms (at 2, 7 and 20 °C) to investigate the effect of low temperatures on nutrient removal. Phosphorus and suspended solids removal were significantly correlated and consistently very high (typically in excess of 90 and 95%, respectively, at all temperatures). This is important for the successful implementation of biofilters in cold climates since phosphorus is commonly of principal concern, often being the limiting factor for eutrophication in freshwater ecosystems. Unfortunately, nitrogen removal was poor and leaching was shown, which increased with temperature. The increasing nitrate-nitrogen production rates with temperature were well described by the Arrhenius relationship with temperature coefficients Q10 in the range which is typically used to describe temperature effects on nitrification. Thus, temperature effects have to be considered when nitrogen removal is targeted and the biofilter might be exposed to cold temperatures.
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| 4. |
- Bodin, Hristina, et al.
(författare)
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Influence of residence time analyses on estimates of wetland hydraulics and pollutant removal
- 2013
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Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 501, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- Hydraulic tracer studies are frequently used to estimate wetland residence time distributions (RTDs) and ultimately pollutant removal. However, there is no consensus on how to analyse these data. We set out to (i) review the different methods used and (ii) use simulations to explore how the data analysis method influences the quantification of wetland hydraulics and pollutant removal. The results showed that the method influences the water dispersion (N) most strongly and the removal least strongly. The influence increased with decreasing effective volume ratio (e) and N, indicating a greater effect of the method in wetlands with low effective volume and high dispersion. The method of moments with RTD truncation at 3 times the theoretical residence time (t(n)) and tracer background concentration produced the most dissimilar parameters. The most similar parameters values were those for gamma modelling and the method of moments with RTD truncation at tracer background concentration. For correct removal estimates, e was more important than N. However, the results from the literature review and simulations indicated that previously published articles may contain overestimated e and underestimated N values as a result of frequent RTD truncations at 3t(n), when using the method of moments. As a result, the removal rates may also be overestimated by as much as 14% compared to other truncation methods or modelling. Thus, it is recommended that wetland hydraulic tracer studies should use the same method, specifically, RTD truncation. We conclude that the choice of tracer data analysis method can greatly influence the quantifications of wetland hydraulics and removal rate.
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| 5. |
- Breinl, Korbinian, et al.
(författare)
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Stochastic generation of multi-site daily precipitation for applications in risk management
- 2013
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 498, s. 23-35
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Tidskriftsartikel (refereegranskat)abstract
- Unlike single-site precipitation generators, multi-site precipitation generators make it possible to reproduce the space–time variation of precipitation at several sites. The extension of single-site approaches to multiple sites is a challenging task, and has led to a large variety of different model philosophies for multi-site models. This paper presents an alternative semi-parametric multi-site model for daily precipitation that is straightforward and easy to implement. Multi-site precipitation occurrences are simulated with a univariate Markov process, removing the need for individual Markov models at each site. Precipitation amounts are generated by first resampling observed values, followed by sampling synthetic precipitation amounts from parametric distribution functions. These synthetic precipitation amounts are subsequently reshuffled according to the ranks of the resampled observations in order to maintain important statistical properties of the observation network. The proposed method successfully combines the advantages of non-parametric bootstrapping and parametric modeling techniques. It is applied to two small rain gauge networks in France (Ubaye catchment) and Austria/Germany (Salzach catchment) and is shown to well reproduce the observations. Limitations of the model relate to the bias of the reproduced seasonal standard deviation of precipitation and the underestimation of maximum dry spells. While the lag-1 autocorrelation is well reproduced for precipitation occurrences, it tends to be underestimated for precipitation amounts. The model can generate daily precipitation amounts exceeding the ones in the observations, which can be crucial for risk management related applications. Moreover, the model deals particularly well with the spatial variability of precipitation. Despite its straightforwardness, the new concept makes a good alternative for risk management related studies concerned with producing daily synthetic multi-site precipitation time series.
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| 6. |
- Bring, Arvid, et al.
(författare)
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Hydro-climatic changes and their monitoring in the Arctic : Observation-model comparisons and prioritization options for monitoring development
- 2013
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 492, s. 273-280
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic undergoes particularly large and rapid hydro-climatic changes, and information on hydrological responses to these changes is crucial to plan for societal adaptation. We investigate hydro-climatic change severity and monitoring in 14 major hydrological basins across the pan-Arctic, in view of different possible strategies for their monitoring prioritization. Results show that the current distribution of monitoring density in these basins is more relevant for so far observed precipitation changes than for observed temperature changes, or for projected future temperature and precipitation changes. Furthermore, present and projected future hot-spots of greatest hydro-climatic change differ spatially, so that major spatial shifts must occur in the future among the different Arctic basins in order for observations and climate model projections to converge with regard to hydro-climatic change severity. Also temporally, observation-model convergence requires that important change direction shifts occur in major Arctic basins, which have currently decreasing precipitation while model projections imply future increasing precipitation within them. Different prioritization options for rational development of hydro-climatic monitoring can be argued for based on the present results. The divergent prioritization options imply a need for an explicit strategy for achieving certain information goals, which must be selected from a larger set of different possible goals based on societal importance.
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| 7. |
- Cheng, Qin-Bo, et al.
(författare)
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Improvement and comparison of likelihood functions for model calibration and parameter uncertainty analysis within a Markov chain Monte Carlo scheme
- 2014
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 519:Part B, s. 2202-2214
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Tidskriftsartikel (refereegranskat)abstract
- Summary In this study, the likelihood functions for uncertainty analysis of hydrological models are compared and improved through the following steps: (1) the equivalent relationship between the Nash–Sutcliffe Efficiency coefficient (NSE) and the likelihood function with Gaussian independent and identically distributed residuals is proved; (2) a new estimation method of the Box–Cox transformation (BC) parameter is developed to improve the effective elimination of the heteroscedasticity of model residuals; and (3) three likelihood functions—NSE, Generalized Error Distribution with BC (BC-GED) and Skew Generalized Error Distribution with BC (BC-SGED)—are applied for SWAT-WB-VSA (Soil and Water Assessment Tool – Water Balance – Variable Source Area) model calibration in the Baocun watershed, Eastern China. Performances of calibrated models are compared using the observed river discharges and groundwater levels. The result shows that the minimum variance constraint can effectively estimate the BC parameter. The form of the likelihood function significantly impacts on the calibrated parameters and the simulated results of high and low flow components. SWAT-WB-VSA with the NSE approach simulates flood well, but baseflow badly owing to the assumption of Gaussian error distribution, where the probability of the large error is low, but the small error around zero approximates equiprobability. By contrast, SWAT-WB-VSA with the BC-GED or BC-SGED approach mimics baseflow well, which is proved in the groundwater level simulation. The assumption of skewness of the error distribution may be unnecessary, because all the results of the BC-SGED approach are nearly the same as those of the BC-GED approach.
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| 8. |
- Dahlke, Helen E., et al.
(författare)
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Dissecting the variable source area concept - Subsurface flow pathways and water mixing processes in a hillslope
- 2012
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 420, s. 125-141
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Tidskriftsartikel (refereegranskat)abstract
- This study uses an instrumented (trenched) 0.5 ha hillslope in the southern tier of New York State, USA, to provide new data and insights on how variable source areas and associated flow pathways form and combine to connect rainfall with downstream water flows across a hillslope. Measurements of water fluxes in the trench, upslope water table dynamics, surface and bedrock topography, and isotopic and geochemical tracers have been combined for a four-dimensional (space-time) characterization of subsurface storm flow responses. During events with dry antecedent conditions infiltrating rainwater was found to percolate through a prevailing fragipan layer to deeper soil layers, with much (33-71%) of the total discharge of the hillslope originating from deeper water flow below the fragipan. During storm events with wet antecedent conditions and large rainfall amounts, shallow lateral flow of event and pre-event water above the fragipan occurred and was one magnitude greater than the deeper water flow contribution. Spatial surface and subsurface water quality observations indicate that water from a distance of up to 56 m contributed runoff from the hillslope during storm events. In addition, mobilization of total dissolved phosphorus (TDP) with subsurface flow played a greater role than with overland or near-surface flow. During all events TDP loads were highest in the total discharge during peak flows (8-11.5 kg ha(-1) d(-1)), except during the largest storm event, when TDP concentrations were highly diluted. These results have implications for strategies to protect streams and other downstream water recipients from waterborne nutrient and pollutant loading.
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| 9. |
- Dargahi, Bijan, et al.
(författare)
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Combined 3D Hydrodynamic and Watershed Modelling of Lake Tana, Ethiopia
- 2011
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 398:1-2, s. 44-64
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Tidskriftsartikel (refereegranskat)abstract
- The growing high demand for lake Tana water portends a disturbing future. The main objective of this paper is to make a contribution to the development of a sustainable use of the water of Lake Tana. A fully three-dimensional hydrodynamic model was combined with a watershed model and together, these models were successfully validated for the year 2006. The flow structure is characterized by large recirculation and secondary flow regions. Secondary flows are induced by hydrodynamic instabilities occurring at the interfaces of layers with a velocity gradient and the interaction with the irregularities of the bed. The weak stratification process in Lake Tana is characterized by a classic summer profile, which is more pronounced during January-February. Mixing processes in the lake are controlled by wind, the mixing energy induced by both river inflows and the lake outlet, and convective mixing due to the negative buoyancy. An alarming fall of the water levels in Lake Tana was found in response to the planned water withdrawal. The long flushing time (19 months) will not allow a fast decay of contaminated materials released into the lake. The flow structure will not be significantly modified by the planned water withdrawal but the flushing time will decrease. The hydrodynamics of Lake Tana resemble a closed system similar to a shallow reservoir with an overflow type outlet. The implication is that the lake is vulnerable to changes in external conditions and sustainable use of the water resource of the lake will require awareness of this vulnerability. The combined watershed and hydrodynamic models would be effective tools to achieve this awareness. It is also necessary to address the impact of climate change on the fate of the lake. These are all difficult challenges that need to be addressed to safeguard the sensitive eco-system of the area.
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| 10. |
- Destouni, Georgia, et al.
(författare)
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Screening long-term variability and change of soil moisture in a changing climate
- 2014
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 516, s. 131-139
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Tidskriftsartikel (refereegranskat)abstract
- Soil moisture is an essential component of water variability and change in the landscape. This paper develops a conceptual and analytical framework for linking hydro-climatic change at the surface and soil-groundwater conditions in the subsurface, and quantifying long-term development of soil moisture statistics in a changing climate. Soil moisture is evaluated both in the unsaturated zone and over a fixed soil depth that may also include a variable groundwater table. Long-term variability and change of soil moisture are assessed for a hydro-climatic observation record that extends over the whole 20th century in a major Swedish drainage basin. Frequencies of particularly dry and wet soil moisture events are investigated for different 20-year climatic periods. Results show major increase in the frequency of dry events from the beginning to the end of the 20th century. This indicates increased risk for hydrological and agricultural drought even though the risk for meteorological drought, in terms of precipitation, has decreased in the region. The developed quantification framework can also be used to screen future scenarios of soil moisture change under projected climate change.
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