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  • 1.
    Ahlberg, Jesper
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Distributed snow modelling integrating ground penetrating radar data for improved runoff predictions in a Swedish mountain basin2009In: EGU General Assembly 2009, 2009Conference paper (Other academic)
    Abstract [en]

    Operational forecasts of snow melt runoff in Sweden are currently running with precipitation and temperature as the main input variables and calibrated with runoff data, and there is an interest to make better use of new measurement systems for distributed snow data. At the same time, various data assimilation techniques are becoming more frequently used in hydrological modeling, in order to reduce uncertainties related to both model structure errors and errors in input and calibration data. Thus, it is important to address not only what type of snow data that can be used to improve the model predictions, but also what type of input data and model structures that are optimal in relation to the available snow data. The objective of this study is to investigate to what extent the runoff predictions can be improved by assimilation of temporal and spatially distributed snow data, and if the improvements depend on the choice of model structures, for instance the use of energy balance or day-degree snow models. In order to achieve these objectives a new distributed snow model has been implemented into the hydrological modeling framework HYSS/HYPE. This model can easily be setup with either an energy balance model or a day-degree model for the snow pack calculations, and it is easy to run the model with different spatial resolutions. In the fully distributed case, snow drift processes are implicitly included in the model through a precipitation distribution model, based on topographical information and wind direction. The model was applied to a mountain basin in northern Sweden used for hydropower production, where extensive snow measurements were taken during the last two winters 2007-2009. A climate station is located at the outlet of the regulation lake, including automated point measurements of snow depth, snow mass (snow pillow), snow wetness and snow temperature. Distributed snow cover data was sampled using ground-penetrating radar from snow mobiles. Measurements were taken at the time of the maximum snow cover, providing a data set with snow depth, snow density, snow water equivalent along 20 km long transects in representative areas of the basin. The precipitation distribution model was calibrated using the distributed SWE data from the GPR measurements. Application of the calibrated model to previous years without available snow data show that the runoff predictions was improved compared to calibrations without the distributed snow data, however the improvements were larger for the energy balance compared to the day-degree model. Further developments will include assimilation of the temporal and spatial snow data to adjust the distribution of various input variables, for instance air temperature and wind speed.

  • 2.
    Ahlberg, Jesper
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Snow melt runoff simulations using ensemble Kalman filter assimilation of distributed snow data2010Conference paper (Other academic)
  • 3.
    Aullón Alcaine, Anna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Geochemistry and Ecotechnology.
    Bhattacharya, Prosun
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Geochemistry and Ecotechnology.
    Jacks, Gunnar
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Geochemistry and Ecotechnology.
    Schulz, C.
    Universidad Nacional de la Pampa, Argentina.
    Bundschuh, Jochen
    University of Southern Queensland, Australia.
    Thunvik, Roger
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Mörth, Carl-Magnus
    Stockholms Universitet, Institutionen för geologiska vetenskaper.
    Geogenic arsenic and fluoride in shallow aquifers of northeastern La Pampa, Argentina: mobility constraints2013Conference paper (Other academic)
    Abstract [en]

    High concentrations of geogenic arsenic (As) and fluoride (F-) in groundwater have been reported at elevated concentrations in different parts of the Chaco-Pampean Plain, in Argentina, where more than 2 million people may be exposed to high levels of these toxic elements through drinking water. Groundwater from the shallow aquifer is far exceeding the permissible WHO Standard limits of 10 μg/L for As and 1.5 mg/L for fluoride, as well as the Argentinean Standard limit of 50 μg/L for As. Geogenic As results due to the weathering of ash originated by volcanic eruptions from the Andean Cordillera and transported by wind and deposited along with the sediments and also as discrete layers and lenses over large geographical area containing around 90% of rhyolitic glass. Groundwater is hosted in a sandy silty interconnected system of aquifers and aquitards within the The Pampean aquifer. A total of 44 groundwater samples were collected from the shallow aquifers in NE of La Pampa province. Two rural areas covering an area of 600km2 in Quemú Quemú (QQ) and 300km2 in Intendente Alvear (IA) were investigated in the present study. Groundwater was circum-neutral to alkaline (pH 7.43-9.18), predominantly oxidizing (Eh ~0.24 V) with widely variable EC range (456-11,400 μS/cm). The major cation dissolved in groundwater was Na+, while the predominant anions were HCO3-, Cl- and SO42-, respectively. Water type in QQ was mostly Na-HCO3- while in IA, the composition differed between Na-HCO3- and Na-Cl-SO42- water types. Groundwater composition showed high degree of mineralization and high salinity evidenced by high EC. In discharge areas, high evaporation rates result in high salinity of shallow groundwater and visible salts incrustations on the surface of the lakes. Elevated concentrations of NO3- and PO43- observed in some wells indicated possible anthropogenic contamination. Total As concentration in groundwater from QQ ranged from 5.58 to 535 μg/L, where 94% of the wells exceeded the WHO standard limit for safe drinking water of 10 μg/L, and 56% of the wells exceeded the old Argentine standard limit of 50 μg/L. F- concentrations revealed heterogeneity and high concentrations in some wells (0.5-14.2 mg/L), 78% of samples in QQ study area exceeded the WHO standard limit of 1.5 mg/L. Under oxidizing conditions and neutral to alkaline pH, arsenate (AsV) species predominated, mainly in HAsO42- forms. As "hotspots" indicated locally contamination and correlated positively with F-, HCO3-, B and V and showed negative correlation with salinity, dissolved Fe, Al and Mn. The mechanisms involved in the mobilization of As in the shallow aquifers are controlled by the rise of pH, variations in Eh conditions and the presence of competitor ions (HCO3-, PO43-, Si, V oxyanions). Geochemical processes like adsorption/desorption, precipitation/dissolution and redox reactions may trigger to As mobilization in the shallow aquifers of La Pampa region.

  • 4. Blomqvist, Göran
    et al.
    Riehm, Mats
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    ROAD SURFACE WETNESS AS AFFECTED BY EVAPORATION, SURFACE RUNOFF AND TRAFFIC SPLASHINGManuscript (preprint) (Other academic)
    Abstract [en]

    Road surface wetness governs the fate of pollutants on the road surface. The wetness is also important for estimating the risk of ice formation during winters. The road surface water is affected by evaporation, run-off and traffic induced splash and spray. Increased knowledge of how these processes govern the road surface water and how they could be modelled would help to improve the possibility to abate problems with raised levels of air pollutants, as well as traffic safety issues by facilitating optimization of the use of anti- and de-icing chemicals. The aim of this study was to use a modeling tool in order to differentiate between three processes governing the loss of wetness from the road surface within a cross section of a road during two different climatic scenes (winter and spring). Two new measurement techniques were used for detailed measurements of road surface wetness across a road to validate the model. It could be concluded that the changes in wetness on the road can be simulated from general simple weather and traffic information. Furthermore, the wetness across the road is very heterogeneous and can be described by a distribution of regulating parameter values. The presented model application has a potential for real time application on roads and within a region and also for predictions of future conditions by using weather forecast data.

  • 5. Feiccabrino, James
    et al.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Lundberg, Angela
    Surface-based precipitation phase determination methods in hydrological models2013In: Hydrology Research, ISSN 1998-9563, Vol. 44, no 1, p. 44-57Article in journal (Refereed)
    Abstract [en]

    We compared solid and liquid precipitation mass output from three categories of common model precipitation phase determination schemes (PPDS) to the recorded precipitation phase in a set of 45 years of 3-hour manual meteorological observations from 19 Swedish meteorological stations. In the first category of rain/snow thresholds, it was found that rain/snow air temperature threshold (ATT) is a better precipitation phase indicator than a rain/snow dew point temperature threshold. When a rain/snow ATT of 0.0 degrees C (a default value used in some recent models) was replaced by 1.0 degrees C, misclassified precipitation was reduced by almost one half. A second category of PPDS use two ATTs, one snow and one rain, with a linear decrease in snow fraction between. This category identified precipitation phase better than a rain/snow ATT at 17 stations. Using all observations from all the meteorological stations, a final category using an air-temperature-dependent snow probability curve resulted in slightly lower misclassified precipitation mass at 13 of the 19 stations. However, schemes from the linear decrease in snow fraction category had the lowest misclassified precipitation mass at four meteorological stations.

  • 6.
    Granlund, Nils
    et al.
    Luleå University of Technology.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Lundberg, Angela
    Luleå University of Technology.
    Snow Salinity Influence on the Relationship between Electrical: Conductivity of Snow and Snow Wetness2009In: 65th Annual Eastern Snow Conference, 2009Conference paper (Other academic)
  • 7.
    Granlund, Nils
    et al.
    Luleå University of Technology.
    Lundberg, Angela
    Luleå University of Technology.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Ahlberg, Jesper
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Wetterhall, Fredrik
    Sveriges Meteorologiska och Hydrologiska Institut.
    Towards better predictions of snow melt runoffs: Measuring Snow Depth and Density Using Ground Penetrating Radar2009Conference paper (Other academic)
    Abstract [en]

    Snow melt runoff predictions by hydrological models are essential for efficient hydropower production in the Scandinavian countries, similar to many areas with a substantial amount of snow precipitation. Operational models in Sweden are currently based on precipitation and temperature as the main input variables and calibrated with runoff data, but there is an interest to make better use of new measurement systems for distributed snow data, especially the total amount of snow in the catchment area of interest. The main objective of our project is to investigate the potential improvements in runoff predictions in relation to the choice of model structure and measurement systems, as well as measurement accuracy. This involves comparing different methods for estimating the total amount of snow in a catchment area as well as improving their accuracy. Here we present the result of such comparison based on data from case studies conducted in Sweden. Our approach involves automated single point measurements over a long period in combination with high resolution distributed measurements over a large area during critical periods. Stationary measurements are performed at a snow measurement station, with snow density and wetness estimated with a low-frequency impedance sensor band, snow depth measured using an ultrasonic depth gauge, and temperature measured at several (fixed) snow depths and at the snow surface. The station, located at Lake Korsvattnet in Swedish mountains, operates continuously during the whole winter season. Measurements of snow depth and density over large lateral distances are performed using multi-offset ground penetrating radar (GPR) operated from a snow mobile. These measurements are conducted once a year, in late winter, when the amount of snow is expected to reach its maximum before snow melt begins. Since 2007 and during the duration of the project, yearly measurements have been and will be taken in two Swedish mountain basins important for hydropower, Lake Korsvattnet and Lake Kultsjön. The radar system used is a multi-channel RAMAC/GPR system with shielded 800 and 1600 MHz antennas. The antennas are attached to a snow mobile sledge forming an array, which allows us to use the common midpoint method to calculate both radar propagation velocity and two-way travel time of radar pulses. For dry snow this gives snow density and depth via an empirical formula establishing the relationship between electrical permittivity (i.e. propagation velocity) and snow density. Note that for wet snow additional information about liquid water content in snow is required, which can be estimated, for example, from radar wave attenuation. However, for the purpose of this presentation we assume that the snow is dry. The results of GPR measurements taken from a snow mobile are compared with results obtained by two other methods. The first comparison is with manual measurements taken with traditional snow tubes along a 1000 m measurement profile at the area of Lake Korsvattnet. In this case a log-linear relationship between snow depth and density is used to interpret GPR data (note that this relationship is obtained from analysis of radar data itself). The other comparison is with GPR measurements taken from a helicopter along a 12 km transect in the area of Lake Kultsjön.

  • 8.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Measurements of snow water equivalent using multiple-offset ground-penetrating radar2006In: , 2006Conference paper (Other academic)
    Abstract [en]

    Ground-penetrating radar (GPR) measurements of snow water equivalent depend onaccurate information of the radar wave propagation velocity in the snow cover, aswell as on the relationship between the dielectric constant and snow density. This paperevaluates a simplified procedure to derive snow water equivalent from GPR traveltime data only, using multiple-offset GPR antennas arranged in an array. The dielectricconstant and the depth of the snow cover are determined by multi-channel measurementsusing several combinations of transmitter and receiver antennas in the array,based on basic common-mid-point principles. This set-up enables continuous determinationof both snow cover depth and snow density along the measurement profile,which reduces the uncertainties due to spatial variation of snow density. The measurementsystem is evaluated using manual snow depth and snow density measurements attwo sites in northern Sweden during winter 2004/2005. Results show that the spatialvariation of both snow depth and snow density were improved with the multi-offsetmeasurements compared to the use of a single channel measurement.

  • 9.
    Gustafsson, David
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Ahlberg, Jesper
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Granlund, Nils
    Luleå University of Technology.
    Lindström, Göran
    Sveriges meteorologiska och hydrologiska institut.
    Wetterhall, Fredrik
    Sveriges meteorologiska och hydrologiska institut.
    Lundberg, Angela
    Luleå University of Technology.
    Distribuerade system för förbättrade snö- och avrinningsprognoser. Integration i hydrologiska modeller: Delrapport 12009Report (Other academic)
  • 10.
    Gustafsson, David
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Granlund, Nils
    Luleå University of Technology.
    Lundberg, Angela
    Luleå University of Technology.
    Multi-offset impulse radar for snow water equivalent measurements2008In: Proceedings of the 65th Annual Meeting of Eastern Snow Conference, 2008Conference paper (Other academic)
  • 11.
    Gustafsson, David
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Gärdenäs, Annemieke
    Department of Soil and Environment, Swedish University of Agricultural Sciences.
    Eckersten, Henrik
    Department of Ecology and Crop Production, Swedish University of Agricultural Sciences.
    Simulated carbon and water processes of forest ecosystems in Forsmark and Oskarshamn during a 100-year period2006Report (Other academic)
  • 12.
    Gustafsson, David
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Magnusson, Jan
    WSL Swiss Federal Institute for Snow and Avalanche Research.
    Granlund, Nils
    Luleå University of Technology.
    Impulse radar measurements of snow interception: laboratory tests and field application to a forest stand in northern Sweden2009Conference paper (Other academic)
    Abstract [en]

    Snow melt runoff is a dominating water resource in many alpine and high latitude regions. Therefore, hydrological model predictions and information on the amount of snow are important for efficient management of for instance hydropower production. Snow interception and evaporation of snow from forest canopies is known to reduce the snow cover accumulation in forest areas compared to open areas, but there is a need for better process understanding in order to improve the model predictions. The exchange of heat and water between snow cover, canopy, and atmosphere involve many processes that can be difficult to observe at the relevant scales. Particularly, the snow interception storage is difficult to observe on a forest stand level compared with snow cover development and forest evaporation. In this study, a new application of ground penetrating impulse radar (GPR) to measure the total amount, spatial distribution and phase of the interception storage in the forest canopy is presented. The propagation velocity and frequency dependent attenuation of a broadband impulse radar wave can be used to give a direct estimate of the complex effective dielectric permittivity. The real part of the effective dielectric permittivity, estimated from the propagation velocity alone, can be used to estimate either the mass of liquid water or the mass of dry snow on the canopy if a suitable mixing formula for the effective permittivity is known. However, to separate between liquid and frozen interception additional information that we intend to get from the attenuation is needed. It has been shown for snow that the liquid water content can be estimated from the imaginary component of the effective permittivity alone. Thus, the contribution from liquid water to the real component can be subtracted, and the remaining fraction depended only on the amount of frozen snow. Laboratory experiments were performed with a GPR system, measuring the propagation velocity and frequency dependent attenuation through a sample of Norway spruce branches loaded with different amount of liquid water and snow. The results were used to establish empirical mixing formulas relating imaginary and real components of the effective dielectric permittivity to the volumetric fraction of liquid and frozen water. The obtained formulas were tested in a field application in northern Sweden, in a homogeneous stand dominated by Norway spruce. The mass of snow stored in the tree canopies were measured in two ways: firstly by measuring the weight of a single tree scaled to a forest stand average and secondly using impulse radar measurements through a small section of the forest. The transmitting and receiving antennas were placed in two small towers, separated horizontally by 15 m. The amount of intercepted snow determined from the radar measurements compared well with the measurements from the single tree weighing lysimeter, especially during cold conditions. Systematic differences were observed in situations with melting snow on the trees, when the estimation of liquid water content was overestimated by the frequency attenuation method. However, this might be due to a combination of uncertainties in the mixing models and inadequate corrections for drift in the measurement system. Overall, the results were promising and showed that impulse radar can be used to study snow interception.

  • 13.
    Gustafsson, David
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Magnusson, Jan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Grelle, Achim
    Swedish University of Agricultural Sciences.
    Lundberg, Angela
    Luleå University of Technology.
    Impact of snow interception on water and energy balance of a forest stand in northern Sweden: combining measurements with impulse radar and eddy-correlation with numerical modelling2007Conference paper (Other academic)
  • 14.
    Gustafsson, David
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Sommer, Wolfram
    Sommer Mess- Systemtechnique, Austria.
    Measurement of liquid water content in snow and its applications in snow hydrological modeling2010Conference paper (Other academic)
  • 15.
    Gustafsson, David
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Stähli, Manfred
    WSL Swiss Federal Institute for Forest Snow and Landscape Research.
    Lundberg, Angela
    Luleå University of Technology.
    A Multi-criteria parameterisation of a numerical forest snow processes model: analysis of parameter uncertainty and governing processes2006In: , 2006Conference paper (Other academic)
  • 16.
    Gärdenäs, Annemieke
    et al.
    Department of Soil and Environment, Swedish University of Agricultural Sciences.
    Eckersten, Henrik
    Department of Ecology and Crop Production, Swedish University of Agricultural Sciences.
    Reinlert, André
    Dept. of Physical Geography and Ecosystems Analysis, Lund University.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Ekström, Per-Anders
    Facilia AB.
    Avila, Rodolfo
    Facilia AB.
    Greger, Maria
    Dept. of Botany, Stockholm University.
    Tracey - a simulation model of trace element fluxes in soil-plant system for long-term assessment of a radioactive groundwater contamination2009Report (Other academic)
  • 17.
    Gärdenäs, Annemieki
    et al.
    Department of Soil and Environment, Swedish University of Agricultural Sciences.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Karltun, Erik
    Department of Soil and Environment, Swedish University of Agricultural Sciences.
    Klemendtsson, Leif
    Department of Plant and Environmental Sciences, Gothenburg University.
    Lehtonen, Aleksi
    Finnish Forest Research Institute, Vantaa, Finland.
    Ortiz, Carina
    Department of Soil and Environment, Swedish University of Agricultural Sciences.
    Palosuo, Taru
    MTT Agrifood Research, Helsinki, Finland.
    Svensson, Magnus
    Department of Soil and Environment, Swedish University of Agricultural Sciences.
    Estimating soil carbon stock changes by process-based models and soil inventories: uncertainties and complementarities2011In: Soil Carbon in Sensitive European Ecosystems: From Science to Land Management / [ed] Robert Jandl, Mirco Rodehiero and Mats Olsson, Oxford: Wiley-Blackwell, 2011Chapter in book (Refereed)
    Abstract [en]

    In this chapter, four examples of scientific questions and challenges in which process-oriented modelling could provide a useful contribution for accounting soil organic carbon (SOC) stocks and changes are presented. These challenges include cases i) when measurements are either time-consuming and/or expensive or there are methodological limitations; ii) an attempt to verify the national soil inventory estimates through comparison with process-based model estimates; iii) prediction of the potential impact on SOC changes due to land-use change; and iv) a comparison of different scenarios for mitigating GHG-emissions. We found that the use of process-based models offers a complementary way to account SOC change and provides an option for assessing the potential impact of climate and land-use change on SOC stocks. However, uncertainty in model estimates is inherent and needs to be communicated. Progress has been made in the assessment of uncertainty and there is growing awareness of how this uncertainty can be communicated. Suggestions for collaborative approaches are presented in order to reduce the uncertainties.

  • 18. Hollesen, J.
    et al.
    Elberling, B.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Future active layer dynamics and carbon dioxide production from thawing permafrost layers in Northeast Greenland2011In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, no 2, p. 911-926Article in journal (Refereed)
    Abstract [en]

    Thawing permafrost and the resulting mineralization of previously frozen organic carbon (C) is considered an important future feedback from terrestrial ecosystems to the atmosphere. Here, we use a dynamic process oriented permafrost model, the CoupModel, to link surface and subsurface temperatures from a moist permafrost soil in High-Arctic Greenland with observed heat production and carbon dioxide (CO2) release rates from decomposition of previously frozen organic matter. Observations show that the maximum thickness of the active layer at the end of the summer has increased 1 cm yr-1 since 1996. The model is successfully adjusted and applied for the study area and shown to be able to simulate active layer dynamics. Subsequently, the model is used to predict the active layer thickness under future warming scenarios. The model predicts an increase of maximum active layer thickness from today 70 to 80-105 cm as a result of a 2-6 degrees C warming. An additional increase in the maximum active layer thickness of a few centimetres may be expected due to heat production from decomposition of organic matter. Simulated future soil temperatures and water contents are subsequently used with measured basal soil respiration rates in a respiration model to predict the corresponding depth-integrated CO2 production from permafrost layers between 0.7 and 2 m below the surface. Results show an increase from present values of < 40 g C m-2 yr-1 to between 120 and 213 g C m-2 yr-1 depending on the magnitude of predicted warming. These rates are more than 50% of the present soil CO2 efflux measured at the soil surface. Future modelling accounting for snow, vegetation and internal biological heat feedbacks are of interest in order to test the robustness of the above predictions and to describe the entire ecosystem response.

  • 19.
    Jansson, Per-Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Karlberg, Louise
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Theory and practice of coupled heat and mass transfer model for soil-plant-atmosphere system2009Book (Refereed)
  • 20.
    Karlberg, Louise
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Modelling carbon and water flows in terrestrial ecosystems in the boreal zone: Examples from Oskarshamn2006Report (Other academic)
  • 21. Lina, Nordin
    et al.
    Riehm, Mats
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Gustavsson, Torbjörn
    Bogren, Jörgen
    Road surface wetness variations: Measurements and effects for winter road maintenance2013In: Journal of transportation engineering, ISSN 0733-947X, E-ISSN 1943-5436, Vol. 139, no 8, p. 787-796Article in journal (Refereed)
    Abstract [en]

    Road wetness is a critical parameter when it comes to preventing road slipperiness. It has so far been difficult to measure, but new measurement techniques on the market make it useful to investigate the savings opportunities within road maintenance operations. The present study tests a new sensor mounted on a road maintenance vehicle run in a maintenance district in central Sweden. The sensor that measures road surface water depth is connected to a global positioning system (GPS) system and a global system for mobile communications (GSM) phone modem. Potential savings are calculated based on the measured road surface water depth and on the amount of applied salt needed to lower the freezing point to a certain degree. The results indicate variations in water depth along the measured roads, which implies that the salt concentrations along the roads could also vary. Though the variations were smaller along the tested highway, the calculated savings could still be up to 22%. Despite the many assumptions made in the calculations, considerable savings could potentially be realized by applying such wetness measurements.

  • 22.
    Lind, Bo
    et al.
    Swedish Geotechnical Institute, SGI.
    Larsson, L.
    Gustafsson, Jon-Petter
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Geochemistry and Ecotechnology.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Ohlsson, Susanna
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Geochemistry and Ecotechnology.
    Norrman, J.
    Arvidsson, O.
    Arm, M.
    Energiaska som vägbyggnadsmaterial - utlakning och miljöbelastning från en provväg2005Report (Other academic)
  • 23.
    Lundberg, Angela
    et al.
    Luleå University of Technology.
    Granlund, Nils
    Luleå University of Technology.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Review of operational and new ground-based snow measurement methods for Sweden, Norway and Finland2009In: The 65th Annual Meeting of the Eastern Snow Conference, 2009Conference paper (Other academic)
  • 24.
    Lundberg, Angela
    et al.
    Luleå University of Technology.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Sensitivity of snow process simulations to precipitation phase transition method in forested and open areas2009Conference paper (Other academic)
    Abstract [en]

    Modeling of forest snow processes is complicated and especially problematic seems to be the separation of precipitation phase in climates where a large part of the precipitation falls at temperatures near zero degrees Celsius. When the precipitation is classified as snow, the tree crowns can carry an order of magnitude more canopy storage as compared to when the precipitation is classified as rain, and snow in the trees also alters the albedo of the forest while rain does not. Many different schemes for the precipitation phase separation are used by various snow models. Some models use just one air temperature threshold (TR/S) below which all precipitation is assumed to be snow and above which all precipitation is classified as rain. A more common approach for forest snow models is to use two temperature thresholds. The snow fraction (SF) is then set to one below the snow threshold (TS) and to zero above the rain threshold (TR) and SF is assumed to decrease linearly between these two thresholds. Also more sophisticated schemes exist, but three seems to be a lack of agreement on how the precipitation phase separations should be performed. The aim with this study is to use a hydrological model including canopy snow processes to illustrate the sensitivity for different formulations of the precipitation phase separation on a) the simulated maximum snow pack storage b) the interception evaporation loss and c) snow melt runoff. In other words, to investigate of the choice of precipitation phase separation has an impact on the simulated wintertime water balance. Simulations are made for sites in different climates and for both open fields and forest sites in different regions of Sweden from north to south. In general, precipitation phase separation methods that classified snowfall at higher temperatures resulted in a larger proportion of the precipitation lost by interception evaporation as a result of the increased interception capacity. However, the maximum snow accumulation was also increased in some cases due to the overall increased snowfall, depending on canopy density and precipitation and temperature regimes. Results show that the choice of precipitation phase separation method can have an significant impact on the simulated wintertime water balance, especially in forested regions.

  • 25.
    Olofsson, Bo
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Salinization of groundwater in coastal areas2005In: Groundwater under Threat / [ed] Johansson, B., Sellberg, B., The Swedish Research Council Formas , 2005, p. 45-50Chapter in book (Other academic)
  • 26.
    Olofsson, Bo
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Andersson, Erika
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Groundwater quality problems in housing areas in hard rock: an example from eastern Sweden2005In: Proceedings of the Fennoscandian 3rd Regional Workshop on Hardrock Hydrogeology / [ed] Rönkä, E., Niini, H., Suokko, T., Edita Publishing Oy, 2005Conference paper (Refereed)
    Abstract [en]

    The aim of the project was to analyse the infl uence of small-scale sewage treatment on the

    groundwater quality in areas with scarcity of freshwater. The content of chloride, nitrate,

    heterotrophic bacteria and coliforms was analysed in 42 wells at the island of Ramsö, eastern

    Sweden. Statistical analyses were carried out as well as calculations of chloride vulnerability

    and a groundwater balance calculation. The study showed that the groundwater quality

    was affected by the type and location of the sewage systems in various natural conditions

    and that it is possible to develop a model for nitrate contamination on drilled wells taking

    several signifi cant natural and technical factors into consideration.

  • 27.
    Olofsson, Bo
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Lundmark, Annika
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Grundvattenförorening vid trafikolyckor: Utveckling av ny bedömningsmetodik2010Report (Other academic)
  • 28.
    Rasmus, Sirpa
    et al.
    University of Helsinki.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Koivusalo, Harri
    Finnish Forest Research Institute.
    Lauren, Ari
    Finnish Forest REsearch Institute.
    Estimation of Winter Leaf Area Index and Sky View Fraction for Snow Modelling in Boreal Coniferous Forests2008Conference paper (Other academic)
    Abstract [en]

    Leaf area index (LAI) and sky view fraction have an important role in controlling snow interception capacity, throughfall fraction, and canopy radiation transfer in snow energy balance models developed for forest conditions. In most models winter LAI and sky view fraction are provided by the user a priori as model parameters. Because stems, branches and needles are capable of intercepting water, snow and radiation, LAI needs to be defined in terms of the total plant area. Plant area indices (PAI) or winter 'effective' LAI values have been introduced in the snow models. Canopy parameters are typically adopted from literature, where the relationship between the winter LAI and sky view fraction is described with different mathematical functions. Winter LAI and sky view fraction can be measured using optical methods. Optical measurements include radiation transmission observations by plant canopy analysers or analysis of hemispheric photographs. Measurements of tree biomass provide another option for the determination of LAI. Computation of LAI from the biomass is a tempting option, because an estimate of stand biomass can easily be derived from operational forest inventory data. The first objective of this study was to estimate winter LAI and sky view fraction using different methods. Optical and biomass-based approximations of winter LAI and sky view fraction were available from coniferous forests in Scandinavia with different stand density and site latitude. The biomass-based estimate of LAI was found to be comparable with the values derived from the optical measurements in most sites. Heterogeneity of tree species and site fertility, as well as edge effects between different forest compartments caused differences in the LAI estimates in some sites. The second goal was to apply a snow energy balance model (SNOWPACK) to detect, how the differences in the estimated values of the winter LAI and sky view fraction are reflected in simulated snow processes. An increase in LAI and a decrease in the sky view fraction changed the snow surface energy balance by decreasing short-wave radiation input and increasing long wave radiation input. Changes in the studied canopy parameters had a direct impact on snow accumulation through altered throughfall fraction, and an indirect and less visible impact on snowmelt through the changed surface energy balance.

  • 29.
    Riehm, Mats
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Measurements for winter road maintenance2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Winter road maintenance activities are crucial for maintaining the accessibility and traffic safety of the road network at northerly latitudes during winter. Common winter road maintenance activities include snow ploughing and the use of anti-icing agents (e.g. road salt, NaCl). Since the local weather is decisive in creating an increased risk of slippery conditions, understanding the link between local weather and conditions at the road surface is critically important. Sensors are commonly installed along roads to measure road weather conditions and support road maintenance personnel in taking appropriate actions. In order to improve winter road maintenance, more precise information about road surface conditions is essential. In this thesis, different methods for estimation of road weather are developed, discussed and tested. The methods use the principles of infrared thermometry, image analysis and spectroscopy to describe ice formation, snow accumulation and road surface wetness in specific patches or along road sections. In practical applications, the methods could be used for better planning of snow clearing operations, forecasting of ice formation and spreading of road salt. Implementing the proposed methods could lead to lower maintenance costs, increased traffic safety and reduced environmental impact.

  • 30.
    Riehm, Mats
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Blomqvist, Michael
    Gustavsson, Torbjörn
    Bogren, Jörgen
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    IMAGE PROCESSING AS A METHOD FOR DETERMINING ROAD SNOW ACCUMULATIONManuscript (preprint) (Other academic)
    Abstract [en]

    Snowfall often causes limitations for road transportation and large efforts are devoted to snow removal. Snow that falls on a road surface often melts due to the surface being warmer than the air under some circumstances. Melting of snow can also be induced by use of road salt. Consequently, snow measurements by precipitation sensors along roads may indicate thicker snow depths than are actually present on the roads. A method for determining the onset time of snow accumulation on roads based on a combination of precipitation measurements and image processing is presented. The method detects whether the snow accumulates rather than melts. It can be used to calculate accumulated snow depth, a more accurate measurement than using precipitation sensors alone. The method was tested over one winter and showed potential to improve the description of snow accumulation in a road network, which could lead to more efficient planning of snow removal.

  • 31. Rutter, Nick
    et al.
    Essery, Richard
    Pomeroy, John
    Altimir, Nuria
    Andreadis, Kostas
    Baker, Ian
    Barr, Alan
    Bartlett, Paul
    Boone, Aaron
    Deng, Huiping
    Douville, Herve
    Dutra, Emanuel
    Elder, Kelly
    Ellis, Chad
    Feng, Xia
    Gelfan, Alexander
    Goodbody, Angus
    Gusev, Yeugeniy
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Hellstroem, Rob
    Hirabayashi, Yukiko
    Hirota, Tomoyoshi
    Jonas, Tobias
    Koren, Victor
    Kuragina, Anna
    Lettenmaier, Dennis
    Li, Wei-Ping
    Luce, Charlie
    Martin, Eric
    Nasonova, Olga
    Pumpanen, Jukka
    Pyles, R. David
    Samuelsson, Patrick
    Sandells, Melody
    Schaedler, Gerd
    Shmakin, Andrey
    Smirnova, Tatiana G.
    Staehli, Manfred
    Stoeckli, Reto
    Strasser, Ulrich
    Su, Hua
    Suzuki, Kazuyoshi
    Takata, Kumiko
    Tanaka, Kenji
    Thompson, Erin
    Vesala, Timo
    Viterbo, Pedro
    Wiltshire, Andrew
    Xia, Kun
    Xue, Yongkang
    Yamazaki, Takeshi
    Evaluation of forest snow processes models (SnowMIP2)2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, no 6Article in journal (Refereed)
    Abstract [en]

    Thirty-three snowpack models of varying complexity and purpose were evaluated across a wide range of hydrometeorological and forest canopy conditions at five Northern Hemisphere locations, for up to two winter snow seasons. Modeled estimates of snow water equivalent (SWE) or depth were compared to observations at forest and open sites at each location. Precipitation phase and duration of above-freezing air temperatures are shown to be major influences on divergence and convergence of modeled estimates of the subcanopy snowpack. When models are considered collectively at all locations, comparisons with observations show that it is harder to model SWE at forested sites than open sites. There is no universal "best'' model for all sites or locations, but comparison of the consistency of individual model performances relative to one another at different sites shows that there is less consistency at forest sites than open sites, and even less consistency between forest and open sites in the same year. A good performance by a model at a forest site is therefore unlikely to mean a good model performance by the same model at an open site (and vice versa). Calibration of models at forest sites provides lower errors than uncalibrated models at three out of four locations. However, benefits of calibration do not translate to subsequent years, and benefits gained by models calibrated for forest snow processes are not translated to open conditions.

  • 32.
    Skeppström, Kirlna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Olofsson, Bo
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Analysis of causes of increased radon concentration in groundwater using GIS and multivariate statistics2005In: Proceedings of the Fennoscandian 3rd Rerional Workshop on Hardrock Hydrogeology / [ed] Rönkä, E., Niini, H., Suokko, T., Helsinki: Edita Publishing Oy, 2005, p. 62-67Conference paper (Refereed)
    Abstract [en]

    High radon concentration in drilled wells contributes to an increased risk of radiation and is therefore a health threat. This preliminary study focuses on 1,460-drilled wells in Stockholm County in Sweden and involves the use of GIS to investigate the infl uence of soil, bedrock, fracture zone, elevation, landuse and slope of a terrain on the radon content in drilled wells at a regional level. Statistical analyses of data were performed, using Kruskal-Wallis ANOVA by ranks and the multivariate statistical method of Principal Component Analysis (PCA). The project has so far shown that 8% of analysed wells exceed the Swedish regulatory limit of 1000 Bq/l while 26% of the 1460 wells have a radon concentration greater than 500 Bq/l. In addition it was found that bedrock, topography and the use of the well clearly affect the radon content.

  • 33.
    Skeppström, Kirlna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Olofsson, Bo
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Radon in groundwater: Analysis of causes and development of a prediction methodology2006In: FoU-seminarium vid SGU 14–15 mars 2006: Dokumentation, Uppsala: Sveriges Geologisa Undersökning , 2006, p. 20-23Conference paper (Other academic)
  • 34.
    Snickars, Folke
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Mattsson, Lars-Göran
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics. KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Olofsson, Bo
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Sustainable urban flows and networks: Theoretical and practical aspects of infrastructure development and planning2013In: Sustainable Stockholm: Exploring Urban Sustainability in Europe's Greenest City / [ed] Jonathan Metzger, Rader Olsson Amy, Routledge, 2013, p. 102-128Chapter in book (Refereed)
  • 35.
    Stähli, Manfred
    et al.
    WSL Swiss Federal Institute for Forest, Snow and Landscape Research.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Hardmeier, Marco
    WSL Swiss Federal Institute for Forest, Snow, and Landscape Research.
    Schleppi, Patrick
    WSL Swiss Federal Institute for Forest, Snow, and Landscape Research.
    Sensitivity of simulated snow water equivalent and snowmelt runoff to spatial forest representation2006Conference paper (Other academic)
  • 36.
    Wu, Sihong
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Impact of cold climate on boreal ecosystem processes: exploring data and model uncertainties2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The impact of cold climate on physical and biological processes, especially the role of air and soil temperature in recovering photosynthesis and transpiration in boreal forests, was investigated in a series of studies. A process-based ecosystem model (CoupModel) considering atmospheric, soil and plant components was evaluated and developed using Generalized Likelihood Uncertainty Estimation (GLUE) and detailed measurements from three different sites. The model accurately described the variability in measurements within days, within years and between years. The forcing environmental conditions were shown to govern both aboveground and belowground processes and regulating carbon, water and heat fluxes. However, the various feedback mechanisms between vegetation and environmental conditions are still unclear, since simulations with one model assumption could not be rejected when compared with another.

    The strong interactions between soil temperature and moisture processes were indicated by the few behavioural models obtained when constrained by combined temperature and moisture criteria. Model performance on sensible and latent heat fluxes and net ecosystem exchange (NEE) also indicated the coupled processes within the system. Diurnal and seasonal courses of eddy flux data in boreal conifer ecosystems were reproduced successfully within defined ranges of parameter values. Air temperature was the major limiting factor for photosynthesis in early spring, autumn and winter, but soil temperature was a rather important limiting factor in late spring. Soil moisture and nitrogen showed indications of being more important for regulating photosynthesis in the summer period. The need for systematic monitoring of the entire system, covering both soil and plant components, was identified as a subject for future studies. The results from this modelling work could be applied to suggest improvements in management of forest and agriculture ecosystems in order to reduce greenhouse gas emissions and to find adaptations to future climate conditions.

  • 37.
    Wu, Sihong
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Modeling the Seasonality of Carbon, Evapotranspiration and Heat Processes for Cold Climate Conditions2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The productivity of agricultural and forest ecosystems in regions at higher latitudes is to a large extent governed by low temperature and moisture conditions. Environmental conditions are acting both above- and below-ground and regulating carbon fluxes and evapotranspiration. However, the understanding of various feedbacks between vegetation and environmental conditions is still unclear. In this thesis, two studies were conducted to understand the physical and biological processes. In the first study, the aim was to simulate soil temperature and moisture dynamics in the bare soil with seasonal frost conditions in China. In the second study, the aims were to model seasonal courses of carbon and evapotranspiration and to examine the responses of photosynthesis, transpiration and respiration on environmental conditions in a boreal Scots pine ecosystem in Finland. In both studies the CoupModel was applied to simulate the dynamic responses of the systems. Both sites represented investigations from which a high number of measurements were available. To understand to what extent the data could be used to increase the understanding of the systems, the Generalized Likelihood Uncertainty Estimation (GLUE) was applied. The GLUE method was useful to reduce basic uncertainties with respect to parameter ranges, model structures and measurements.

    The strong interactions between soil temperature and moisture processes have indicated by a few behavioral models obtained when constrained by combined temperature and moisture criteria. Model performance on sensible and latent heat fluxes and net ecosystem exchange (NEE) also indicated the coupled processes within the system. Seasonal and diurnal courses were reproduced successfully with reduced parameter ranges. However, uncertainties on what is the most general regulation for transpiration and NEE are still unclear and need further systematic investigations.

  • 38.
    Wu, Sihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Modelling soil temperature and moisture and corresponding seasonality of photosynthesis and transpiration in a boreal spruce ecosystemManuscript (preprint) (Other academic)
  • 39.
    Wu, Sihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Kolari, Pasi
    Department of Forest Ecology, University of Helsinki, Finland.
    Modeling seasonal courses of carbon fluxes and evaportranspiration in response to low temperature and moisture in a boreal scots pine ecosystem2011In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 222, p. 3103-3119Article in journal (Refereed)
    Abstract [en]

    Environmental conditions act above and below ground, and regulate carbon fluxes and evapotranspiration. The productivity of boreal forest ecosystems is strongly governed by low temperature and moisture conditions, but the understanding of various feedbacks between vegetation and environmental conditions is still unclear. In order to quantify the seasonal responses of vegetation to environmental factors, the seasonality of carbon and heat fluxes and the corresponding responses for temperature and moisture in air and soil were simulated by merging a process-based model (CoupModel) with detailed measurements representing various components of a forest ecosystem in Hyytiälä, southern Finland. The uncertainties in parameters, model assumptions, and measurements were identified by generalized likelihood uncertainty estimation (GLUE). Seasonal and diurnal courses of sensible and latent heat fluxes and net ecosystem exchange (NEE) of CO2 were successfully simulated for two contrasting years. Moreover, systematic increases in efficiency of photosynthesis, water uptake, and decomposition occurred from spring to summer, demonstrating the strong coupling between processes. Evapotranspiration and NEE flux both showed a strong response to soil temperature conditions via different direct and indirect ecosystem mechanisms. The rate of photosynthesis was strongly correlated with the corresponding water uptake response and the light use efficiency. With the present data and model assumptions, it was not possible to precisely distinguish the various regulating ecosystem mechanisms. Our approach proved robust for modeling the seasonal course of carbon fluxes and evapotranspiration by combining different independent measurements. It will be highly interesting to continue using long-term series data and to make additional tests of optional stomatal conductance models in order to improve our understanding of the boreal forest ecosystem in response to climate variability and environmental conditions.

  • 40.
    Wu, Sihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Physics.
    Kolari, Pasi
    The role of air and soil temperature in the seasonality of photosynthesis and transpiration in a boreal Scots pine ecosystem2012In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 156, p. 85-103Article in journal (Refereed)
    Abstract [en]

    Photosynthesis and transpiration in boreal forests are restricted by air temperature (T a) and soil temperature (T s), especially in spring after the dormant period, but the extent to which the recovery process is regulated these factors is still uncertain. To examine the role of air temperature and soil temperature, years with three types of typical patterns of temperature rises were identified from 13 years of continuous flux measurements for a Scots pine ecosystem in Hyytiälä, southern Finland. By combining a process-based ecosystem model (CoupModel) with an uncertainty estimation procedure (GLUE), the role of regulating factors was explored and 45 of 51 parameters were found to have reduced uncertainty after calibration. Air temperature was the major limiting factor for photosynthesis in early spring, autumn and winter, but soil temperature was a rather important limiting factor in late spring. Especially during warm spring with a large delay of soil temperature rise both water uptake and photosynthesis was strongly reduced due to low soil temperature. Soil moisture and nitrogen showed indications of being more important for regulating photosynthesis in the summer period. It proved possible to replace the soil temperature acclimation function on photosynthesis and transpiration with a corresponding air temperature function only during warm years with a small delay between T a and T s. Fluxes of photosynthesis and transpiration showed a sensitivity to the carbon footprint representation, as expected from the high spatial variability in soil temperature during the spring of a warm year with a large delay between T a and T s.

  • 41.
    Wu, Sihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Zhang, X. Y.
    Hailun Experimental Station, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, China.
    Modelling temperature, moisture and surface heat balance in the bare soil under seasonal frost conditions in China2011In: European Journal of Soil Science, ISSN 1351-0754, E-ISSN 1365-2389, Vol. 62, no 6, p. 780-796Article in journal (Refereed)
    Abstract [en]

    Soil heat and moisture processes are interconnected, especially during low temperatures. To examine the interaction between soil temperature and moisture under freeze-thaw cycles, a physical process-based model (CoupModel) coupled with uncertainty analysis was applied to 3-year measurements under seasonal frost conditions from a site in the black soil belt of northeast China. The uncertainty in parameters and measurements was described by general likelihood uncertainty estimation (GLUE). To identify the degree of linkage between soil temperature and moisture, three criteria were applied to them separately or together. The most sensitive parameters among 26 site-specific parameters were closely related to soil heat, soil evaporation and freeze-thaw processes. Soil temperature was simulated with less uncertainty than soil moisture. Soil temperature measurements had the potential to improve model performance for soil water content, whereas soil moisture measurements demonstrated a trade-off effect when finding a model with good performance for both temperature and moisture. During winter conditions the uncertainty ranges of soil temperature were most pronounced, probably because of the greater complexity of soil properties during the freeze-thaw process and the uncertainty caused by snow properties. The largest uncertainty ranges of both soil water content and soil water storage were found mainly in the deep soil layers. The simulated surface heat fluxes are an important output of the model and it is of great value to compare them with the results from regional climate models and micrometeorological measurements.

  • 42.
    Zhang, Wenxin
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Long-term Trend of Evapotranspiration in Sweden Affected by Climate Change or Land-use Change.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Evapotranspiration (ET) is an essential component of water cycle as it is an interlinkage between atmosphere, vegetation and soil surface in terms of energy and water balance. However, whether potential ET has the same tendency to change as actual ET and how ET trend (based on the difference between precipitation and runoff) is directly driven by dominant meteorological factors alone or combined with ecosystem‘s feedbacks to climate change (like land-use change) is still under the discussion. In this report, five ET parameterizations within two rainfall-runoff models [Coupled Heat and Mass Transfer Model (CoupModel) and Hydrologiska Byråns Vattenbalansavdelning (HBV)] have been set up based on six subcatchments of Sweden. The scenario derived from CoupModel shows that the trend of ET is affected by the change of land-use, where soil evaporation tends to shift to transpiration and interception evaporation. However, HBV model produces the other scenario: the trend of ET is merely the consequence of meteorological factors. Increased ET is contributed by increased interception evaporation due to the increased precipitation. After identifying the time split of changing ET trends, a dynamic simulation constructed both from HBV and CoupModel indicate that the increased total ET is primarily from increased ET in winter time. More and more interceptive water loss and transpiration resulted from land-use change due to more vegetation. On the other hand, land-use change is also a feed back to climate change. Transpiration controlled by the mechanism of stomata and water uptake controlled by reduction of soil moisture is highly related to variations of climatic conditions.

  • 43.
    Zhao, Zhihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Evaluation of hydrodynamic dispersion parameters in fractured rocks2010In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 2, p. 243-254Article in journal (Refereed)
    Abstract [en]

    A numerical procedure to determine the equivalent hydrodynamic dispersion coefficients and Péclet number (Pe) of a fractured rock is presented using random walk particle tracking method. The geometrical effects of fracture system on hydrodynamic dispersion are studied. The results obtained from the proposed method agree well with those of empirical models, which are the scale-dependent hydrodynamic dispersion coefficients in an asymptotic or exponential form. A variance case is added to investigate the influence of longitudinal hydrodynamic dispersion in individual fractures on the macro-hydrodynamic dispersion at the fracture network scale, and its influence is demonstrated with a verification example. In addition, we investigate the influences of directional flow and stress conditions on the behavior of hydrodynamic dispersion in fracture networks. The results show that the magnitudes of the hydrodynamic dispersion coefficients are relatively smaller when the flow direction is parallel to the dip directions of fracture sets. Compressive stresses significantly reduce hydrodynamic dispersion. However, the remaining questions are: (1) whether the deformed fracture network under high stress conditions may make the scale-dependent hydrodynamic dispersion coefficients have asymptotic or exponential forms, and (2) what the conditions for existence of a welldefined equivalent hydrodynamic dispersion tensor are. They need to be further investigated.

1 - 43 of 43
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