| 1. |
- Bin Ashraf, Faisal, et al.
(författare)
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Changes in short term river flow regulation and hydropeaking in Nordic rivers
- 2018
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Quantifying short-term changes in river flow is important in understanding the environmental impacts of hydropower generation. Energy markets can change rapidly and energy demand fluctuates at sub-daily scales, which may cause corresponding changes in regulated river flow (hydropeaking). Due to increasing use of renewable energy, in future hydropower will play a greater role as a load balancing power source. This may increase current hydropeaking levels in Nordic river systems, creating challenges in maintaining a healthy ecological status. This study examined driving forces for hydropeaking in Nordic rivers using extensive datasets from 150 sites with hourly time step river discharge data. It also investigated the influence of increased wind power production on hydropeaking. The data revealed that hydropeaking is at high levels in the Nordic rivers and have seen an increase over the last decade and especially over the past few years. These results indicate that increased building for renewable energy may increase hydropeaking in Nordic rivers.
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| 2. |
- Burman, Anton
(författare)
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Hydraulic Modelling of Dynamics in Regulated Rivers
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Nordic countries hold a significant portion of the European hydropower production. One advantage of hydropower is its ability to store water in reservoirs in times when the energy demand is low. The readjustment of energy production to renewable energy sources, as required by the Paris agreement, like wind power and solar power is likely going to change the role of Nordic hydropower production. Wind power and solar power are both dependent on the current weather conditions, in times when the weather is not favourable, hydropower can be used to stabilize the electricity grid. Since weather can change rapidly so will the discharge from the hydropower plants, causing hydropeaking events. Hydropeaking rapidly changes the flow conditions in proximity to the power plant. Such changes can be detrimental to the downstream habitats in and along the river. The study reach in this work is the bypass reach in Stornorrfors in the Ume River. The open-source hydrodynamic solver Delft3D is used to numerically model the flow in the study reach. To validate the simulations water level measurements have been used. The aim of the thesis is to investigate inherent damping properties in the river reach that can be used to mitigate the influence of hydropeaking scenarios. The influence of parameters such as upstream closing time, manning number distribution and hydropeaking frequency have been investigated. It is shown that the closing time drastically affects the dynamics of the wetted area. The water surface elevation exhibits a hysteresis like behaviour. Inherent damping increases with the downstream coordinate. The frequency of the flow changes affects the areas upstream more than downstream. As a result, potential habitats in the downstream parts of the reach could become more stable if more frequent flow changes occur.
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| 3. |
- Kasurinen, Ville, et al.
(författare)
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Latent heat exchange in the boreal and arctic biomes
- 2014
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 20:11, s. 3439-3456
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Forskningsöversikt (refereegranskat)abstract
- In this study latent heat flux (E) measurements made at 65 boreal and arctic eddy-covariance (EC) sites were analyses by using the Penman-Monteith equation. Sites were stratified into nine different ecosystem types: harvested and burnt forest areas, pine forests, spruce or fir forests, Douglas-fir forests, broadleaf deciduous forests, larch forests, wetlands, tundra and natural grasslands. The Penman-Monteith equation was calibrated with variable surface resistances against half-hourly eddy-covariance data and clear differences between ecosystem types were observed. Based on the modeled behavior of surface and aerodynamic resistances, surface resistance tightly control E in most mature forests, while it had less importance in ecosystems having shorter vegetation like young or recently harvested forests, grasslands, wetlands and tundra. The parameters of the Penman-Monteith equation were clearly different for winter and summer conditions, indicating that phenological effects on surface resistance are important. We also compared the simulated E of different ecosystem types under meteorological conditions at one site. Values of E varied between 15% and 38% of the net radiation in the simulations with mean ecosystem parameters. In general, the simulations suggest that E is higher from forested ecosystems than from grasslands, wetlands or tundra-type ecosystems. Forests showed usually a tighter stomatal control of E as indicated by a pronounced sensitivity of surface resistance to atmospheric vapor pressure deficit. Nevertheless, the surface resistance of forests was lower than for open vegetation types including wetlands. Tundra and wetlands had higher surface resistances, which were less sensitive to vapor pressure deficits. The results indicate that the variation in surface resistance within and between different vegetation types might play a significant role in energy exchange between terrestrial ecosystems and atmosphere. These results suggest the need to take into account vegetation type and phenology in energy exchange modeling.
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| 4. |
- Kasurinen, Ville, et al.
(författare)
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Modeling nonlinear responses of DOC transport in boreal catchments in Sweden
- 2016
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 52:7, s. 4970-4989
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Tidskriftsartikel (refereegranskat)abstract
- Stream water dissolved organic carbon (DOC) concentrations display high spatial and temporal variation in boreal catchments. Understanding and predicting these patterns is a challenge with great implications for water quality projections and carbon balance estimates. Although several biogeochemical models have been used to estimate stream water DOC dynamics, model biases common during both rain and snow melt-driven events. The parsimonious DOC-model, K-DOC, with 10 calibrated parameters, uses a nonlinear discharge and catchment water storage relationship including soil temperature dependencies of DOC release and consumption. K-DOC was used to estimate the stream water DOC concentrations over 5 years for eighteen nested boreal catchments having total area of 68 km2 (varying from 0.04 to 67.9 km2). The model successfully simulated DOC concentrations during base flow conditions, as well as, hydrological events in catchments dominated by organic and mineral soils reaching NSEs from 0.46 to 0.76. Our semimechanistic model was parsimonious enough to have all parameters estimated using statistical methods. We did not find any clear differences between forest and mire-dominated catchments that could be explained by soil type or tree species composition. However, parameters controlling slow release and consumption of DOC from soil water behaved differently for small headwater catchments (less than 2 km2) than for those that integrate larger areas of different ecosystem types (10–68 km2). Our results emphasize that it is important to account for nonlinear dependencies of both, soil temperature, and catchment water storage, when simulating DOC dynamics of boreal catchments.
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| 5. |
- Lind, Lovisa, et al.
(författare)
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Hydrological and thermal controls of ice formation in 25 boreal stream reaches
- 2016
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Ingår i: Journal of Hydrology. - : Elsevier. - 0022-1694 .- 1879-2707. ; 540, s. 797-811
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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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| 6. |
- Lind, Lovisa, et al.
(författare)
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Hydrological and thermal controls of ice formation in 25 boreal stream reaches
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The Northern Hemisphere has a high density of fluvial freshwater ecosystems, many of which become ice-covered during winter. The formation 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 poorly described. Data from 25 stream reaches were used to study the factors controlling ice formation during two consecutive winters. We addressed 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 away from lake outlets were most prone to form anchor ice, but many other factors also influenced ice formation. We found that anchor-ice was most common where water temperature and groundwater input were low and stream power high. The in-stream substrate was also important for the formation of anchor ice as well as the current velocity, which created turbulence and super-cooled conditions if high enough. We demonstrated that ice formation in the studied streams was complex, involving many variables, thus we constructed a conceptual model describing the likelihood of various ice types to develop, based on our large dataset. To our knowledge, this model is the first to describe the complexity of ice formation in steep boreal streams. As such it will be useful for practitioners and scientists working in small rivers in the Northern Hemisphere.
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| 7. |
- Prowse, Terry, et al.
(författare)
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Arctic Freshwater Ice and Its Climatic Role
- 2011
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 40:Suppl 1, s. 46-52
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Tidskriftsartikel (refereegranskat)abstract
- Freshwater ice dominates the Arctic terrestrial environment and significantly impacts bio-physical and socio-economic systems. Unlike other major cryospheric components that either blanket large expanses (e.g., snow, permafrost, sea ice) or are concentrated in specific locations, lake and river ice are interwoven into the terrestrial landscape through major flow and storage networks. For instance, the headwaters of large ice-covered rivers extend well beyond the Arctic while many northern lakes owe their genesis to broader cryospheric changes. The effects of freshwater ice on climate mostly occur at the local/regional scale, with the degree of influence dependent on the magnitude, timing, location, and duration of ice cover, and the size of the water body. Freshwater-ice formation, growth, decay, and break-up are influenced by climatic variables that control surface heat fluxes, but these differ markedly between lakes and rivers. Despite the importance of freshwater ice, there has been a recent reduction in observational recordings.
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| 8. |
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| 9. |
- Prowse, Terry, et al.
(författare)
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Effects of Changes in Arctic Lake and River Ice
- 2011
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 40:Suppl 1, s. 63-74
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Tidskriftsartikel (refereegranskat)abstract
- Climatic changes to freshwater ice in the Arctic are projected to produce a variety of effects on hydrologic, ecological, and socio-economic systems. Key hydrologic impacts include changes to low flows, lake evaporation regimes and water levels, and river-ice break-up severity and timing. The latter are of particular concern because of their effect on river geomorphology, vegetation, sediment and nutrient fluxes, and sustainment of riparian aquatic habitats. Changes in ice phenology will affect a wide range of related biological aspects of seasonality. Some changes are likely to be gradual, but others could be more abrupt as systems cross critical ecological thresholds. Transportation and hydroelectric production are two of the socio-economic sectors most vulnerable to change in freshwater-ice regimes. Ice roads will require expensive on-land replacements while hydroelectric operations will both benefit and be challenged. The ability to undertake some traditional harvesting methods will also be affected.
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| 10. |
- Prowse, Terry, et al.
(författare)
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Past and Future Changes in Arctic Lake and River Ice
- 2011
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 40:Suppl 1, s. 53-62
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Tidskriftsartikel (refereegranskat)abstract
- Paleolimnological evidence from some Arctic lakes suggests that longer ice-free seasons have been experienced since the beginning of the nineteenth century. It has been inferred from some additional records that many Arctic lakes may have crossed an important ecological threshold as a result of recent warming. In the instrumental record, long-term trends exhibit increasingly later freeze-ups and earlier break-ups, closely corresponding to increasing air temperature trends, but with greater sensitivity at the more temperate latitudes. Broad spatial patterns in these trends are also related to major atmospheric circulation patterns. Future projections of lake ice indicate increasingly later freeze-ups and earlier break-ups, decreasing ice thickness, and changes in cover composition, particularly white-ice. For rivers, projected future decreases in south to north air-temperature gradients suggest that the severity of ice-jam flooding may be reduced but this could be mitigated by changes in the magnitude of spring snowmelt.
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