| 61. |
- Gong, Lebing, et al.
(författare)
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Global-scale river routing-an efficient time-delay algorithm based on HydroSHEDS high-resolution hydrography
- 2011
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 25:7, s. 1114-1128
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Tidskriftsartikel (refereegranskat)abstract
- Coupling of global hydrologic and atmospheric models is difficult because of the highly nonlinear hydrological processes to be integrated at large scales. Aggregation of high-resolution data into low-resolution spatial distribution functions is one way to preserve information and account for the nonlinearity. We used HydroSHEDS, presently the most highly resolved (3 '') global hydrography available, to provide accurate control on global river routing through a computationally efficient algorithm. The high resolution of HydroSHEDS allowed discrimination of river-channel pixels, and time-delay distributions were calculated for all such pixels. The distributions were aggregated into network-response functions (NRFs) for each low-resolution cell using an algorithm originally developed for the 1-km-resolution HYDRO1k hydrography. The large size of HydroSHEDS required a modification in algorithm to maintain computational efficiency. The new algorithm was tested with a high-quality local and a more uncertain global weather dataset to identify whether improved routing would provide a gain when weather data quality was limiting. The routing was coupled to the WASMOD-M runoff-generation model to evaluate discharge from the Dongjiang River and the Willamette River basins. The HydroSHEDS-based routing, compared with the HYDRO1k-based routing, provided a small gain in model efficiency, for local and global weather data and for both test basins. The HydroSHEDS-based routing, contrary to the HYDRO1k-based routing, provided physically realistic wave velocities. The most stable runoff-generation parameter values were achieved when HydroSHEDS was used to derive the NRFs. Routing was computed in two steps: first, a preparatory calculation which was a one-time effort and second, the routing during each simulation. The computational efficiency was four to five orders of magnitude better for the simulation step than that for the preparatory step.
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| 62. |
- Granlund, Nils, et al.
(författare)
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Laboratory study of the influence of salinity on the relationship between electrical conductivity and wetness of snow
- 2010
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Ingår i: Hydrological Processes. - : John Wiley & Sons. - 0885-6087 .- 1099-1085. ; 24:14, s. 1981-1984
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Tidskriftsartikel (refereegranskat)abstract
- Snow water equivalent of a snowpack can be estimated using ground-penetrating radar from the radar wave two-way travel time. However, such estimates often have low accuracy when the snowpack contains liquid water. If snow wetness is known, it is possible to take it into account in the estimates; it is therefore desirable to be able to determine snow wetness from already available radar data. Our approach is based on using radar wave attenuation, and it requires that the relationship between electrical conductivity and wetness of snow should be known. This relationship has been tentatively established in previous laboratory experiments, but only for a specific liquid water salinity and radar frequency. This article presents the results of new laboratory experiments conducted to investigate if and how this relationship is influenced by salinity. In each experiment, a certain amount of snow was melted and a known amount of salt (different for different experiments) was added to the water. Water salinity was measured, and the water was added step-wise to a one-meter thick snowpack, with radar measurements taken between additions of water. Our experiments have confirmed the earlier established linear relationship between electrical conductivity and wetness of snow, and they allow us to suggest that the influence of liquid water salinity on electrical conductivity is negligible when compared to the influence of liquid water content in snow.
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| 63. |
- Grip, Harald
(författare)
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Sweden's first forest hydrology field study 1905-1926: contemporary relevance of inherited conclusions and data from the Rokliden Hillslope
- 2015
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 29, s. 3616-3631
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Tidskriftsartikel (refereegranskat)abstract
- During the last decades of the 19th century, a great worry arose about forest landscape paludification in Northern Sweden. This was the original impetus for forest hydrological research in Sweden, and the Swedish Institute of Experimental Forestry established the first field research site in 1905 at Rokliden, close to Pitea in North Sweden. It comprised 8.64ha located 2km down a 3-km-long gently sloping (similar to 4%), north facing Norway spruce covered till slope, interspersed with small mires. By 1931, it was concluded that paludification was not spreading across Northern Sweden at an appreciable rate. Within the Rokliden research site, 22 groundwater wells were installed and levels measured weekly until 1926. A map with 0.5m equidistance, ten vegetation classes, and soil profiles was established. Groundwater flow velocity was estimated by tracing added sodium chloride. Hydraulic conductivity was measured on undisturbed soil cores, while mechanical and chemical analyses were carried out on other samples. Groundwater was collected and analysed for dissolved compounds including oxygen. Hydrology was found important for soil types and vegetation development. The necessary profile drainage for podzol soil development was identified as vein drainage at the bedrock surface. Modern measurements in the re-established groundwater observation network and re-analysis of old data confirmed the plausibility of these original conclusions. Partial catchment area could explain rates of both groundwater level rise and recession. Revisiting this field study reveals that many issues in contemporary hillslope hydrology were already established a century ago, even though the provenance of that knowledge is not generally recognized. Copyright (c) 2014 John Wiley & Sons, Ltd.
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| 64. |
- Gustafsson, David, et al.
(författare)
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Factors governing the formation and persistance of layers in a sub-alpine snowpack
- 2004
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 18:7, s. 1165-1183
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Tidskriftsartikel (refereegranskat)abstract
- The layered structure of a snowpack has a great effect on several important physical processes, such as water movement, reflection of solar radiation or avalanche release. Our aim was to investigate what factors are most important with respect to the formation and persistence of distinct layers in a subalpine environment. We used a physically based numerical one-dimensional model to simulate the development of a snowpack on a subalpine meadow in central Switzerland during one winter season (1998-99). A thorough model validation was based on extensive measurement data including meteorological and snow physical parameters. The model simulated the snow water equivalent and the depth of the snowpack as well as the energy balance accurately. The observed strong layering of the snowpack, however, was not reproduced satisfactorily. In a sensitivity analysis, we tested different model options and parameter settings significant for the formation of snow layers. The neglection of effects of snow microstructure on the compaction rate, and the current description of the water redistribution inside the snowpack, which disregard capillary barrier effects, preferential flow and lateral water flow, were the major limitations for a more realistic simulation of the snowpack layering.
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| 65. |
- Hailemariam, F. M., et al.
(författare)
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Investigating the influence of minor hydraulic structures on modeling flood events in lowland areas
- 2014
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Ingår i: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 28:4, s. 1742-1755
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Tidskriftsartikel (refereegranskat)abstract
- Flood inundation models have been recognized to be a valuable tool to reproduce flow dynamics in a given area and support decision-making processes on flood management measures. In many cases, in the simulation of flood events, only the main river channel and the associated structures are represented within the model. However, during flood events involving lowland areas, the minor drainage network - and the associated hydraulic structures - may have an important role in conveying flow and determining which areas will be flooded. The objective of this study is to investigate whether - and to what extent - small hydraulic structures in drainage networks have an influence in flooding on lowland areas. The case study for this research is the 1990 flood event which occurred in the lowland plain of the Reno River, in Northern Italy. The study area is mainly used for agricultural purposes and has a drainage system with several small bridges and culverts. The influence of the minor hydraulic structures on flood dynamics was analyzed through a combined use of one-dimensional (1D) and two-dimensional (2D) hydraulic models. First, a number of detailed and simplified approaches to represent hydraulic structures in the computational grids were analyzed by means of the HECRAS 1D model. Second, these approaches were implemented and tested in several 2D simulations of the flood event. The simulated inundation extents and flood levels were then compared with the observed data and with each other. The analysis of results showed that simplified schematizations were sufficient to obtain good model predictions of peak inundation extent and flood levels, at least for the present case study. Moreover, the influence of the structures on the peak flood inundation extent and flood levels was found to be limited, whereas it showed to be more significant during the drainage phase of the flood.
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| 66. |
- Hasselquist, Niles, et al.
(författare)
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Canopy cover effects on local soil water dynamics in a tropical agroforestry system: Evaporation drives soil water isotopic enrichment
- 2018
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 32, s. 994-1004
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Tidskriftsartikel (refereegranskat)abstract
- Despite the widely held assumption that trees negatively affect the local water budget in densely planted tree plantations, we still lack a clear understanding of the underlying processes by which canopy cover influences local soil water dynamics in more open, humid tropical ecosystems. In this study, we propose a new conceptual model that uses a combination of stable isotope and soil moisture measurements throughout the soil profile to assess potential mechanisms by which evaporation (of surface soil water and of canopy-intercepted rainfall) affects the relationship between surface soil water isotopic enrichment (lc-excess) and soil water content. Our conceptual model was derived from soil water data collected under deciduous and evergreen plants in a shade grown coffee agroforestry system in Costa Rica. Reduced soil moisture under shade trees during the drier season, coinciding when these trees were defoliated, was largely the result of increase soil water evaporation as indicated by the positive relationship between soil water content and lc-excess of surface soil water. In contrast, the evergreen coffee shrubs had a higher leaf area index during the drier season, leading to enhanced rainfall interception and a negative relationship between lc-excess and soil water content. During the wet season, there was no clear relationship between soil water content and between lc-excess of surface soil water. Greater surface soil water under coffee during the dry season may, in part, explain greater preferential flow under coffee compared with under trees in conditions of low rainfall intensities. However, with increasing rainfall intensities during the wet season, there was no obvious difference in preferential flow between the two canopy covers. Results from this study indicate that our new conceptual model can be used to help disentangling the relative influence of canopy cover on local soil water isotopic composition and dynamics, yet also stresses the need for additional measurements to better resolve the underlying processes by which canopy structure influences local water dynamics.
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| 67. |
- Hiroshiro, Y, et al.
(författare)
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Hydrogeochemical properties of a salinity-affected coastal aquifer in western Japan
- 2006
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Ingår i: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 20:6, s. 1425-1435
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Tidskriftsartikel (refereegranskat)abstract
- Coastal groundwater aquifers are often exposed to heavy pumping and consequently to risks of saltwater intrusion. In many cases, however, the observed increase in groundwater salinity can only be partly explained by actual saltwater intrusion from the sea. Other salinity-increasing processes may also significantly contribute to the total salt content of the groundwater. This paper describes a geochemical investigation that was carried out to investigate recent salinity increases in groundwater for the Motooka coastal area in Fukuoka, Japan. A strong increase in electrical conductivity at 15-20 m depth was observed, corresponding to the freshwater and saltwater interface. Oxidation-reduction potentials observed in deeper groundwater were low, indicating long residence time for the groundwater. These results, together with hydrogen-oxygen isotope ratio analysis, indicated that the deeper groundwater is affected by seawater. Consequently, observed tritium concentration in the shallow groundwater system was higher than that of the deeper groundwater system, and a C-14 isotope dating of shell samples collected at 2 m depth indicated an age of about 2000 years. The overall results suggest that the aquifer was originally below the current sea floor and that deeper saline groundwater is not mixed with the shallower fresh groundwater. The deeper groundwater is, therefore, mainly affected by old seawater. In other words, modern saltwater intrusion has not yet occurred even if some wells contain saline water. The study shows that, even though coastal aquifers are heavily pumped, the reason for the rise in groundwater salinity may not necessarily be due to seawater intrusion. Further geochemical and hydrological investigations will be necessary to identify the underlying mechanisms. Copyright (c) 2006 John Wiley & Sons, Ltd.
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| 68. |
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| 69. |
- Hubbard, K. A., Jr., et al.
(författare)
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Evaluating nitrate uptake in a Rocky Mountain stream using labelled N-15 and ambient nitrate chemistry
- 2010
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 24:23, s. 3322-3336
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Tidskriftsartikel (refereegranskat)abstract
- Background aqueous chemistry and N-15(nitrate) tracer injection methods were used to calculate in-stream nitrate uptake metrics at Red Canyon Creek, a third-order stream in the Rocky Mountains in the state of Wyoming, United States. 'Net' nitrate uptake lengths, which reflect both nitrate uptake and regeneration, and 'gross' nitrate uptake lengths, which exclude re-mineralization, were quantified separately from background nitrate chemistry and N-15 labelling tracer data, respectively. Gross nitrate uptake lengths, from tracer injections of N-15 labelled nitrate, ranged from 502 to 3140 m. Net nitrate uptake lengths, from background nitrate chemistry downstream of a point source, ranged from 1170 to 4330 m. Diurnal changes in uptake lengths suggest the importance of nitrate utilization by autotrophs in the stream and benthic zone. The differences between net and gross nitrate uptake lengths along lower reaches of Red Canyon Creek allowed us to estimate the nitrate regeneration rate, which was 0.056-0.080 mu mol m(-2) s(-1) during the day and 0.0062-0.0083 mu mol m(-2) s(-1) at night. Spatial patterns of streambed pore water chemistry indicate those areas of the hyporheic zone where denitrification was likely occurring. Permanent log dams generated stronger redox gradients in the hyporheic zone than areas with transient beaver dams. By combining isotopically labelled nitrate additions, estimates of uptake from background aqueous nitrate chemistry and characterization of redox conditions in the hyporheic zone, we were able to determine the nitrate regeneration rate and the redox processes responsible for nitrogen cycling in the hyporheic zone. Copyright. (C) 2010 John Wiley & Sons, Ltd.
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| 70. |
- Jin, Y H, et al.
(författare)
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Detection of ENSO-influence on the monthly precipitation in South Korea
- 2005
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Ingår i: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 19:20, s. 4081-4092
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Tidskriftsartikel (refereegranskat)abstract
- During the latest several decades, there has been considerable interest in revealing the relationship between El Nino-southern oscillation (ENSO) and hydro-meteorological variables. The oscillation is characterized by a simple index, the southern oscillation index (SOI). However, thus far, there is little evidence for the influence of ENSO in Korea and Japan. The influence of ENSO has also been studied in South Korea, but the estimated results are still qualitative and show an indirect relationship between ENSO and hydro-meteorological variables. In this study we use simple approaches to reveal the quantitative and direct correlation between SOI and the monthly precipitation at five stations distributed over South Korea. The monthly precipitation data are transformed into nonexceedance probability time series because the data cannot be normally distributed by applying the usual transformations. The SOI is classified into five categories according to their values. Additionally, to detect the nonlinear relationship between categorized SOI and nonexceedance probability of the monthly precipitation, we use Kendall's tau, a nonparametric test. Significant correlations between the categorized SOI and the transformed precipitation are detected. Generally, the monthly precipitation is influenced by a La Nina event with a lag time of 4 months for southern coastal areas and a lag time of 5 months for middle to high regions in South Korea.
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