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  • 51.
    Metzger, Christine
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. Karlsruhe Institute for Technology, Germany.
    Nilsson, Mats B.
    Peichl, Matthias
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Parameter interactions and sensitivity analysis for modelling carbon heat and water fluxes in a natural peatland, using CoupModel v52016In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 9, no 12, p. 4313-4338Article in journal (Refereed)
    Abstract [en]

    In contrast to previous peatland carbon dioxide (CO2) model sensitivity analyses, which usually focussed on only one or a few processes, this study investigates interactions between various biotic and abiotic processes and their parameters by comparing CoupModel v5 results with multiple observation variables. Many interactions were found not only within but also between various process categories simulating plant growth, decomposition, radiation interception, soil temperature, aerodynamic resistance, transpiration, soil hydrology and snow. Each measurement variable was sensitive to up to 10 (out of 54) parameters, from up to 7 different process categories. The constrained parameter ranges varied, depending on the variable and performance index chosen as criteria, and on other calibrated parameters (equifinalities). Therefore, transferring parameter ranges between models needs to be done with caution, especially if such ranges were achieved by only considering a few processes. The identified interactions and constrained parameters will be of great interest to use for comparisons with model results and data from similar ecosystems. All of the available measurement variables (net ecosystem exchange, leaf area index, sensible and latent heat fluxes, net radiation, soil temperatures, water table depth and snow depth) improved the model constraint. If hydraulic properties or water content were measured, further parameters could be constrained, resolving several equifinalities and reducing model uncertainty. The presented results highlight the importance of considering biotic and abiotic processes together and can help modellers and experimentalists to design and calibrate models as well as to direct experimental set-ups in peatland ecosystems towards modelling needs.

  • 52.
    Nickman, Alireza
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Lyon, Steve W.
    Olofsson, Bo
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Kalantari, Zahra
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    The impact of roads on hydrological responses: A case study in SwedenManuscript (preprint) (Other academic)
    Abstract [en]

    A method engaged for simulating and assessing the alterations excreted by road topography within watersheds and estimating the road effects on hydrologic responses. The method uses Geographic Information System (GIS) to allocate and eliminate roads from the elevation data. HEC-HMS was used to model surface and near surface hydrological responses of watersheds with roads and without roads in response to three storms with different intensities. A detailed study of the simulated flow duration curves showed differences between 20 watersheds for three different storms based on a digital elevation data with and without roads. To compare flow duration curves, L-moment ratios were calculated and their variation compared. An increase in peak flow and reduced delay occurred with increased storm intensity. Variations of the L-moment ratios were larger in larger watersheds. However, the impact of the roads was much smaller and only possible to identify by detailed examination of statistical descriptors. The results are useful to gain a better estimating of the effect of road topography in hydrological processes and responses especially in high storm intensities.

  • 53.
    Nickman, Alireza
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Lyon, Steve W.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Olofsson, Bo
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Simulating the impact of roads on hydrological responses: examples from Swedish terrain2016In: Hydrology Research, ISSN 1998-9563, Vol. 47, no 4, p. 767-781Article in journal (Refereed)
    Abstract [en]

    In this study, the potential impacts of road topography on hydrologic responses at the watershed scale were simulated. The method considered used a geographic information system to identify road embankment locations and subsequently remove them from the baseline elevation data. Starting from both the 'with' and 'without' road elevation model, the surface and near-surface hydrological responses for 20 watersheds in Sweden were modeled in HEC-HMS under three different storm intensities. Flow duration curves (FDCs) were used to compare hydrologic responses for the different modeling scenarios under the various storm intensities. Specifically, L-moment ratios of the FDCs were calculated and their variation compared. Results showed an increase in peak flow amounts and reduction in time to peak with increased storm intensity. In addition, variations of the L-moment ratios were larger in larger watersheds. However, the impact of the roads on the modeled hydrologic responses was much smaller than anticipated and only identifiable through detailed examination of the L-moment statistical descriptors. Our findings not only highlight the potential impacts of road topography on watershed-scale hydrology (especially concerning high intensity storms) but also provide a methodology for detecting the even rather small changes that could manifest, for example, under coupled road network and climatic changes.

  • 54. Norman, Josefine
    et al.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Farahbakhshazad, Neda
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Butterbach-Bahl, Klaus
    Li, Changsheng
    Klemedtsson, Leif
    Simulation of NO and N2O emissions from a spruce forest during a freeze/thaw event using an N-flux submodel from the PnET-N-DNDC model integrated to CoupModel2008In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 216, no 1, p. 18-30Article in journal (Refereed)
    Abstract [en]

    The amount of nitrogen gases (N2O, No and N-2) emitted from forest soils depends on interactions between soil properties, climatic factors and soil management. To increase the understanding of nitrogen processes in soil ecosystems, two dynamic models, CoupModel (coupled heat and mass transfer model for soil-plant-atmosphere systems) and the denitrification-decomposition (DNDC) model were selected. Both are dynamic models with different submodels for soil, vegetation, hydrology and climate system. CoupModel has a higher degree of detail on soil physical and abiotic components, whereas the DNDC model contains details of microbiological processes involved in production of nitrogen gases. To improve the previous simple submodel of nitrogen emission in CoupModel, we included a submodel corresponding to the forest version of DNDC containing photosynthesis/evapotranspiration-nitrogen (PnET-N-DNDC model). The nitrogen (N) and carbon

  • 55. Nylinder, Josefine
    et al.
    Stenberg, Maria
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Klemedtsson, Asa Kasimir
    Weslien, Per
    Klemedtsson, Leif
    Modelling uncertainty for nitrate leaching and nitrous oxide emissions based on a Swedish field experiment with organic crop rotation2011In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 141, no 1-2, p. 167-183Article in journal (Refereed)
    Abstract [en]

    High uncertainties are common in detailed quantification of the N budget of agricultural cropping systems. The process-based CoupModel, integrated with the parameter calibration method known as Generalized likelihood uncertainty estimation (GLUE), was used here to define parameter values and estimate an N budget based on experimental data from an organic farming experiment in south-west Sweden. Data on nitrate (NO3-) leaching and nitrous oxide (N2O) emissions were used as a basis for quantifying N budget pools. A complete N budget with uncertainties associated with the different components of the N cycle compartments for two different fields (B2 and B4) is presented. Simulated N2O emissions contributed 1-2% of total N output, which corresponded to 7% and 8.7% of total N leaching for B2 and B4, respectively. Measured N2O emissions contributed 3.5% and 10.3% of total N leaching from B2 and B4, respectively. Simulated N inputs (deposition, plant N fixation and fertilisation) and outputs (emissions, leaching and harvest) showed a relatively small range of uncertainty, while the differences in N storage in the soil exhibited a larger range of uncertainty. One-fifth of the GLUE-calibrated parameters had a significant impact on simulated NO3- leaching and/or N2O emissions data. Emissions of N2O were strongly associated with the nitrification process. The high degree of equifinality indicated that a simpler model could be calibrated to the same field data.

  • 56.
    Pourfathali Kasmaei, Leila
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Drip versus surface irrigation in long term environmental modelling of soil-water-plant exposed to saline water2012In: Sustainable Irrigation and Drainage IV: Management, Technologies and Policies, WIT Press, 2012, p. 87-99Conference paper (Refereed)
    Abstract [en]

    A physically based soil-water storage model with two surface and drip irrigation scenarios in response to saline water was used in the semi-arid Gordonia district in South Africa. The model (CoupModel) consists of several different modules that couples mass and energy flow models with dynamic biotic models of plant and its environment. The simulation period accounted for non-productive water losses, salt accumulation in root zone, and salt transport to below aquifer via deep percolation. The monitoring of biomass production with respect to water consumption and soil osmotic pressure indicted a decline in crop yield due to the water and salt stresses. The drip scenario had a better functionality in terms of the water wastage as the soil evaporation decreased by 40%. However, the productive water consumption decreased by 20% due to insufficient leaching fraction while salt accumulation increased drastically in the entire root zone. We found that salt could be flushed out from the root zone by more leaching but the water wastage increases as well as increasing the possibility of salinization beneath aquifer. The soil-water and plant ecosystem responds differently to salinity in different water management practices. Salt as a source of pollution can either stabilizes the soil by accumulation in the root zone causing anthropogenic soil desertification or can percolate it to beneath the aquifer resulting to long-term salinization. The findings of our study could sever to improve different management schemes in similar semi-arid regions.

  • 57.
    Reihm, Mats
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Gustavsson, Torbjörn
    Bogren, Jörgen
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Detection of road ice formation by high frequency infrared temperature measurementsManuscript (preprint) (Other academic)
  • 58.
    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.

  • 59.
    Riehm, Mats
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Gustavsson, Torbjörn
    Bogren, Jörgen
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Ice formation detection on road surfaces using infrared thermometry2012In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 83-84, p. 71-76Article in journal (Refereed)
    Abstract [en]

    Ice formation on roads causes hazardous conditions due to reduction of road surface friction. Forecasting, detecting and preventing ice formation are therefore of high importance for winter road maintenance personnel. Advanced sensors for detecting road ice exist, but there is a demand for more cost-effective technologies. A method for detection of road surface ice formation based on remote temperature measurements with infrared thermometers is presented. Freezing events were detected based on the temperature dynamics that result from the exothermic reaction as water freezes. Experimental measurements in a climate chamber and in field conditions showed that ice formation often causes a distinct temperature pattern, which could easily be identified and distinguished from other temperature fluctuations. The method is promising as a cost-effective technique suitable for several applications in cold regions where detection of ice formation is important.

  • 60. Senapati, N.
    et al.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Smith, P.
    Chabbi, A.
    Modelling heat, water and carbon fluxes in mown grassland under multi-objective and multi-criteria constraints2016In: Environmental Modelling & Software, ISSN 1364-8152, E-ISSN 1873-6726, Vol. 80, p. 201-224Article in journal (Refereed)
    Abstract [en]

    A Monte Carlo-based calibration and uncertainty assessment was performed for heat, water and carbon (C) fluxes, simulated by a soil-plant-atmosphere system model (CoupModel), in mown grassland. Impact of different multi-objective and multi-criteria constraints was investigated on model performance and parameter behaviour. Good agreements between hourly modelled and measurement data were obtained for latent and sensible heat fluxes (R2 = 0.61, ME = 0.48 MJ m-2 day-1), soil water contents (R2 = 0.68, ME = 0.34%) and carbon-dioxide flux (R2 = 0.60, ME = -0.18 g C m-2 day-1). Multi-objective and multi-criteria constraints were efficient in parameter conditioning, reducing simulation uncertainty and identifying critical parameters. Enforcing multi-constraints separately on heat, water and C processes resulted in the highest model improvement for that specific process, including some improvement too for other processes. Imposing multi-constraints on all groups of variables, associated with heat, water and C fluxes together, resulted in general effective parameters conditioning and model improvement.

  • 61. Stahli, M.
    et al.
    Nyberg, L.
    Mellander, P. E.
    Jansson, Per-Erik.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Bishop, K. H.
    Soil frost effects on soil water and runoff dynamics along a boreal transect: 2. Simulations2001In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 15, no 6, p. 927-941Article in journal (Refereed)
    Abstract [en]

    A physically based SVAT-model was rested with soil and snow physical measurements, as well as runoff data fr om an 8600 m(2) catchment in northern Sweden in order to quantify the influence of soil frost on spring snowmelt runoff in a moderately sloped, boreal forest. The model was run as an array of connected profiles cascading to the brook. For three winter seasons (1995-98) it was able to predict the onset and total accumulation of the runoff with satisfactory accuracy. Surface runoff was identified as only a minor fraction of the total runoff occurring during short periods in connection with ice blocking of the water-conducting pores. Little surface runoff, though, does not mean that soil frost is unimportant for spring runoff. Simulations without frost routines systematically underestimated the total accumulated runoff. The possibility of major frost effects appearing in response to specific combinations of weather conditions were also tested. Different scenarios of critical initial conditions for the winter, e.g, high water saturation and delayed snow accumulation leading to an increased frost penetration, were tested. These showed that under special circumstances there is potential for increased spring runoff due to soil frost.

  • 62.
    Svensson, Magnus
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Berggren Kleja, Dan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Modelling soil C sequestration in spruce forest ecosystems along a Swedish transect based on current conditions2008In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 89, no 1, p. 95-119Article in journal (Refereed)
    Abstract [en]

    The change of current pools of soil C in Norway spruce ecosystems in Sweden were studied using a process-based model (CoupModel). Simulations were conducted for four sites representing different regions covering most of the forested area in Sweden and representing annual mean temperatures from 0.7 degrees C to 7.1 degrees C. The development of both tree layer and field layer (understory) was simulated during a 100-year period using data on standing stock volumes from the Swedish Forest Inventory to calibrate tree growth using different assumptions regarding N supply to the plants. The model successfully described the general patterns of forest stand dynamics along the Swedish climatic transect, with decreasing tree growth rates and increasing field layer biomass from south to north. However, the current tree growth pattern for the northern parts of Sweden could not be explained without organic N uptake and/or enhanced mineralisation rates compared to the southern parts. Depending on the assumption made regarding N supply to the tree, different soil C sequestration rates were obtained. The approach to supply trees with both mineralised N and organic N, keeping the soil C:N ratio constant during the simulation period was found to be the most realistic alternative. With this approach the soils in the northern region of Sweden lost 5 g C m(-2) year(-1), the soils in the central region lost 2 g C m(-2) year(-1), and the soils in the two southern regions sequestered 9 and 23 g C m(-2) year(-1), respectively. In addition to climatic effects, the feedback between C and N turnover plays an important role that needs to be more clearly understood to improve estimates of C sequestration in boreal forest ecosystems.

  • 63.
    Svensson, Magnus
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Gustafsson, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Berggren Kleja, Dan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Langvall, Ola
    Lindroth, Anders
    Bayesian calibration of a model describing carbon, water and heat fluxes for a Swedish boreal forest stand.2008In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 213, no 3-4, p. 331-344Article in journal (Other academic)
    Abstract [en]

    This study quantified major fluxes of carbon (C), heat and water, including uncertainty estimates, in a boreal forest in northern Sweden, using a process-based model (Coup-Model) and Bayesian calibration methodology. Coupled C, water and heat fluxes were described together with estimated uncertainties for all major components of the simulated C budget. Simulated mean gross primary production was 641 +/- 74 gC m(-2) yr(-1), total ecosystem respiration 570 +/- 55 gC m(-2)yr(-1) and net ecosystem productivity 71 +/- 37gCm(-2)yr(-1). Most high-resolution measurements were well described but some interesting exceptions arose between model and measurements, e.g. latent heat flux was overestimated and field layer (understory) root litter production underestimated. Bayesian calibration reduced the assumed prior parameter ranges in 30 of 33 parameters, thus reducing the uncertainty in the estimates. There was a high degree of couplings between different sub-models and processes in the model, highlighting the importance of considering parameters not as singularities but in clusters

  • 64. Talei, Amin
    et al.
    Chua, Lloyd Hock Chye
    Quek, Chai
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Runoff forecasting using a Takagi-Sugeno neuro-fuzzy model with online learning2013In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 488, p. 17-32Article in journal (Refereed)
    Abstract [en]

    A study using local learning Neuro-Fuzzy System (NFS) was undertaken for a rainfall-runoff modeling application. The local learning model was first tested on three different catchments: an outdoor experimental catchment measuring 25 m(2) (Catchment 1), a small urban catchment 5.6 km(2) in size (Catchment 2), and a large rural watershed with area of 241.3 km(2) (Catchment 3). The results obtained from the local learning model were comparable or better than results obtained from physically-based, i.e. Kinematic Wave Model (KWM), Storm Water Management Model (SWMM), and Hydrologiska Byrans Vattenbalan-savdelning (HBV) model. The local learning algorithm also required a shorter training time compared to a global learning NFS model. The local learning model was next tested in real-time mode, where the model was continuously adapted when presented with current information in real time. The real-time implementation of the local learning model gave better results, without the need for retraining, when compared to a batch NFS model, where it was found that the batch model had to be retrained periodically in order to achieve similar results.

  • 65. van Oijen, M.
    et al.
    Cameron, D. R.
    Butterbach-Bahl, K.
    Farahbakhshazad, Neda
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Kiese, R.
    Rahn, K. -H
    Werner, C.
    Yeluripati, J. B.
    A Bayesian framework for model calibration, comparison and analysis: Application to four models for the biogeochemistry of a Norway spruce forest2011In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 151, no 12, p. 1609-1621Article in journal (Refereed)
    Abstract [en]

    Four different parameter-rich process-based models of forest biogeochemistry were analysed in a Bayesian framework consisting of three operations: (1) Model calibration, (2) Model comparison, (3) Analysis of model-data mismatch. Data were available for four output variables common to the models: soil water content and emissions of N(2)O, NO and CO(2). All datasets consisted of time series of daily measurements. Monthly averages and quantiles of the annual frequency distributions of daily emission rates were calculated for comparison with equivalent model outputs. This use of the data at model-appropriate temporal scale, together with the choice of heavy-tailed likelihood functions that accounted for data uncertainty through random and systematic errors, helped prevent asymptotic collapse of the parameter distributions in the calibration. Model behaviour and how it was affected by calibration was analysed by quantifying the normalised RMSE and r(2) for the different output variables, and by decomposition of the MSE into contributions from bias, phase shift and variance error. The simplest model, BASFOR, seemed to underestimate the temporal variance of nitrogenous emissions even after calibration. The model of intermediate complexity. DAYCENT, simulated the time series well but with large phase shift. COUP and MoBiLE-DNDC were able to remove most bias through calibration. The Bayesian framework was shown to be effective in improving the parameterisation of the models, quantifying the uncertainties in parameters and outputs, and evaluating the different models. The analysis showed that there remain patterns in the data - in particular infrequent events of very high nitrogenous emission rate - that are unexplained by any of the selected forest models and that this is unlikely to be due to incorrect model parameterisation.

  • 66.
    Van Quang, Pham
    et al.
    An Giang University.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Geochemistry and Ecotechnology.
    Development and description of soil compaction on orchard soils in the Mekong Delta (Vietnam)2008In: Scientific Research and Essays, ISSN 1992-2248, E-ISSN 1992-2248, Vol. 3, no 10, p. 500-504Article in journal (Refereed)
    Abstract [en]

    The study conducted in the Vietnamese Mekong Delta (VMD) was to examine soil degradation and soil compaction in fruit tree plantations due to the impact of agricultural activities. The specific objective was to elucidate the impact of soil compaction on current and future production. Fruit trees are one of the most important components for the development of the delta. The plantation areas have increased rapidly over the recent years (from 117,000 ha in 1996 to 300,000 ha by the year 2006). Fruit trees in this region are usually grown on raised beds to avoid submergence due to annual flood. Most of the soils of raised beds are alluvial and perturbed from the natural soils. Studies on the raised beds have recognized trends of soil compaction during ageing of the raised beds. However, there are many uncertainties and consequently a need for further investigations exists, to improve the knowledge and understanding of soil processes in the region.

  • 67.
    Van Quang, Pham
    et al.
    An Giang University.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Geochemistry and Ecotechnology.
    thi Guong, Vo
    Can Tho University.
    Soil physical properties during different development stage of fruit orchards2012In: Journal of Soil Science and Environmental Management, ISSN 2141-2391, Vol. 3, no 12, p. 308-319Article in journal (Refereed)
    Abstract [en]

    In the Mekong Delta (MD), fruit trees are usually grown on raised-beds to avoid submergence due to annual flooding. The soils are mostly alluvial and disarranged from the natural soils. The soil may beadversely impacted temporally, particularly with its physical properties. The study was conducted on 10 citrus plantations in Hau Giang province, MD, to illustrate if the covariance between clay content andage can be separated from the impact of soil ageing on compaction; we further discuss the design of how to make an investigation where only age is the analyzed event that age has a covariance with the spatial scale. Soil sampling was done in the dry season 2010 at two soil depths for each raised-bed toanalyze soil physical properties. Soil texture can be classified as silty-clay soil. The bulk density of topsoils ranged from 0.76 to 1.18 g cm-3 and slightly lower than subsoils; 0.85 to 1.24 g cm-3. Saturated hydraulic conductivity spanned the range from 2.04 to 5.43 m day-1 for topsoils and significantly higher than in subsoils; 1.4 to 5.5 m day-1. Organic matter was in the range of 4.4 to 12.2% for topsoils and significantly higher than in subsoils; 3.0 to 9.6%. A significant tendency of soil degradation with aging was found. Clay content showed a covariance with age of raised-beds counteracting the compaction processes. The high clay content for the aged raised-bed may have been hiding some of the compaction process. The relation between age and soil degradation was seen for the larger pore sizes within the water retention curve.

  • 68.
    Van Quang, Pham
    et al.
    An Giang University.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Environmental Geochemistry and Ecotechnology.
    van Khoa, Le
    Can Tho University.
    Soil Penetration Resistance and Its Dependence on Soil Moisture and Age of the Raised-Beds in the Mekong Delta, Vietnam2012In: International Journal of Engineering Research and Development, ISSN 2278-067X, Vol. 4, no 8, p. 87-96Article in journal (Refereed)
    Abstract [en]

    The research was conducted on 10 citrus plantations at Hau Giang province in the Mekong delta, Vietnam during one year with a portable electronic penetrometerto understand the impact of moisture on the soil compaction. Soil penetration resistance (PR) was measured in the depth of 0-80 cm depth and soil samples also taken at each 10 cm depth from the soil surface to the water level for soil moisture measurement. The results showed that PR increased as a function ofraised-bed’s age and it could be reached to a high degree by soil moisture variability during the season. The sensitivity of PR to soil moisture decreases with the age of raised-beds while the soil moisture represented an increasing tendency with the age of raised-beds. Relationship between PR and soil moisture are explained betterby the volumetric water content than the corresponding soil water potential expressed as pF values. The measurements of soil PR determined by the previous results, which are obtained from soil, core samples with the dry bulk density and water retention curves were calculated and analyzed. Using the PR data will be very useful; it is a complementary and important information for identification the soil structure and soil moisture content. Without such processing of PR measurements, the values of the PR measurements will be limited and not indicated for soil compaction. To minify soil compaction on the raised-beds, all the pressure and mechanical activities should not be done in the soil surface, specially in the wet condition. Organic fertilizers and Biocharcan be considered as soil conditioners and recommended to applied in orchard for improving soil properties.

  • 69. Widén, Elin
    et al.
    Jansson, Per-Erik
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Espeby, Bengt
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Olofsson, Bo
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Estimations of the water flows to Lake Hällefjärd and Lake Eckarfjärden, Northern Uppland2004Report (Refereed)
  • 70. Wu, J.
    et al.
    Jansson, Per- Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    van der Linden, L.
    Pilegaard, K.
    Beier, C.
    Ibrom, A.
    Modelling the decadal trend of ecosystem carbon fluxes demonstrates the important role of functional changes in a temperate deciduous forest2013In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 260, p. 50-61Article in journal (Refereed)
    Abstract [en]

    Temperate forests are globally important carbon sinks and stocks. Trends in net ecosystem exchange have been observed in a Danish beech forest and this trend cannot be entirely attributed to changing climatic drivers. This study sought to clarify the mechanisms responsible for the observed trend, using a dynamic ecosystem model (CoupModel) and model data fusion with multiple constraints and model experiments. Experiments with different validation datasets showed that a multiple constraints model data fusion approach that included the annual tree growth, the seasonal canopy development, the latent and sensible heat fluxes and the CO2 fluxes decreased the parameter uncertainty considerably compared to using CO2 fluxes as validation data alone. The fitted model was able to simulate the observed carbon fluxes well (R-2 = 0.8, mean error = 0.1 g C m(-2) d(-1)) but did not reproduce the decadal (1997-2009) trend in carbon uptake when global parameter estimates were used. Annual parameter estimates were able to reproduce the decadal scale trend; the yearly fitted posterior parameters (e.g. the light use efficiency) indicated a role for changes in the ecosystem functional properties. A possible role for nitrogen demand during mast years is supported by the inter-annual variability in the estimated parameters. The inter-annual variability of photosynthesis parameters was fundamental to the simulation of the trend in carbon fluxes in the investigated beech forest and this demonstrates the importance of functional change in carbon balance.

  • 71. Wu, M.
    et al.
    Ran, Y.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Chen, P.
    Tan, X.
    Zhang, W.
    Global parameters sensitivity analysis of modeling water, energy and carbon exchange of an arid agricultural ecosystem2019In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 271, p. 295-306Article in journal (Refereed)
    Abstract [en]

    Agricultural ecosystems are important for regulating terrestrial hydrological and carbon cycles. Hydrological and carbon processes in agricultural ecosystem models are complex due to interactions between parameters. It is therefore crucial to identify parameter sensitivity before a process-based model is applied for simulations and predictions of water, energy and carbon fluxes in agricultural ecosystems. In this study, we investigated the sensitivity and equifinality of the CoupModel parameters in modeling an arid agricultural ecosystem in northwestern China. In total, 27 model parameters were analyzed using a global parameters sensitivity analysis approach and a combination of multiple in situ and remotely sensed data sets. Among the five major model processes, we found that the energy balance process account for much of the importance in the model, followed by soil hydrology, plant growth, soil heat, and soil carbon processes. Meanwhile, parameters from the plant growth process exhibited higher equifinalities than other processes. We found that net ecosystem exchange (NEE) is controlled by soil heat, soil hydrology and energy balance processes, which is mainly due to a high equifinality (0.91) between the parameters g max (maximal stomatal conductance) and V cmax (maximal carboxylation rate). The equifinalities between different parameters result in a trade-off in model performance metrics (i.e. determination coefficient R 2 and mean error ME) in the water, energy and carbon balance simulations. We revealed that daytime and yearly accumulated eddy fluxes (sensible heat H s , latent heat LE and NEE) can constrain the model parameters better. Remotely sensed data were also promising as additional constraints on soil water contents and energy fluxes. This study introduced a systematic global parameter sensitivity analysis approach together with the equifinality identification in an ecosystem model. The approach proposed here is applicable to other studies and the equifinalities detected in this study can be important implications for modelling arid agricultural ecosystems. Additional exploration on remotely sensed data in constraining the model from different aspects are highly recommended in modeling agricultural ecosystems. © 2019 Elsevier B.V.

  • 72.
    Wu, Mousong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Tan, X.
    Wu, J.
    Huang, J.
    Simulations of water and heat dynamics in a seasonally frozen soil using field data to improve understanding,Manuscript (preprint) (Other academic)
  • 73.
    Wu, Mousong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. Wuhan University, China.
    Tan, Xiao
    Huang, Jiesheng
    Wu, Jingwei
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Solute and water effects on soil freezing characteristics based on laboratory experiments2015In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 115, p. 22-29Article in journal (Refereed)
    Abstract [en]

    Laboratory experiments were conducted to study effects of water and solute on soil freezing using TDR and temperature sensor combination methods. ANOVA methods were applied for analyzing significance for solute influences on soil freezing characteristic curve (SFCC). Results showed that higher initial water content influenced the SFCC by increasing liquid water content at the same temperature due to more water connection with soil pores, and adsorbed by soil particles. ANOVA results showed solute content and solute type all had significant effects (P < 0.001 to P < 0.5) on soil freezing processes. And solute in soil resulted in a lower freezing point of soil, which made more liquid water co-exist with ice at negative temperatures. And solute concentration condensing due to liquid water decline would also impede soil freezing processes by decreasing osmotic potential. Due to the physical and chemical process of soil solution, different ions also presented some differences in SFCC parameter estimation. Based on a trial and error method, a prediction model was also built, and it behaved well in predicting SFCC under different water and solute conditions.

  • 74.
    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)
  • 75.
    Wu, Sihong
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Modelling soil temperature and moisture and corresponding seasonality of photosynthesis and transpiration in a boreal spruce ecosystem2013In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 17, no 2, p. 735-749Article in journal (Refereed)
    Abstract [en]

    Recovery of photosynthesis and transpiration is strongly restricted by low temperatures in air and/or soil during the transition period from winter to spring in boreal zones. The extent to which air temperature (T-a) and soil temperature (T-s) influence the seasonality of photosynthesis and transpiration of a boreal spruce ecosystem was investigated using a process-based ecosystem model (CoupModel) together with eddy covariance (EC) data from one eddy flux tower and nearby soil measurements at Knottasen, Sweden. A Monte Carlo-based uncertainty method (GLUE) provided prior and posterior distributions of simulations representing a wide range of soil conditions and performance indicators. The simulated results showed sufficient flexibility to predict the measured cold and warm Ts in the moist and dry plots around the eddy flux tower. Moreover, the model presented a general ability to describe both biotic and abiotic processes for the Norway spruce stand. The dynamics of sensible heat fluxes were well described by the corresponding latent heat fluxes and net ecosystem exchange of CO2. The parameter ranges obtained are probably valid to represent regional characteristics of boreal conifer forests, but were not easy to constrain to a smaller range than that produced by the assumed prior distributions. Finally, neglecting the soil temperature response function resulted in fewer behavioural models and probably more compensatory errors in other response functions for regulating the seasonality of ecosystem fluxes.

  • 76.
    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.

  • 77.
    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.

  • 78.
    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.

  • 79. Zhang, Shulan
    et al.
    Loevdahl, Lars
    Grip, Harald
    Jansson, Per-Erik
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Tong, Yanan
    Modelling the effects of mulching and fallow cropping on water balance in the Chinese Loess Plateau2007In: Soil & Tillage Research, ISSN 0167-1987, E-ISSN 1879-3444, Vol. 93, no 2, p. 283-298Article in journal (Refereed)
    Abstract [en]

    To improve water use efficiency on drylands it is essential to understand the mechanisms affecting water balance partitioning in arable land ecosystems. A field experiment was conducted, from October 2001 to October 2004, to evaluate the effects of field management regimes on water balance and water use efficiency in a winter wheat (Triticum aestivum L.) system in the Loess Plateau, China. The field management regimes tested were: (i) conventional agricultural management (winter wheat followed by a ploughed summer fallow); (ii) conventional management plus a fallow crop used as green manure; (iii) application of wheat straw mulch (0.8 kg m(-2)), which was retained throughout the year (no summer ploughing). A process-oriented ecosystem model (CoupModel) was calibrated with field measurements of soil water contents, leaf area indices, plant heights and crop yields, then used to generate comparative simulations of the water balance partitioning under the wheat straw mulch, fallow crop and conventional management regimes. The simulations indicated that during the experimental period mulching increased soil water storage by 5-8%, decreased soil evaporation by 11-13%, and increased wheat transpiration by 2-5% compared with the conventional management regime, thus increasing the wheat yield and water use efficiency. Furthermore, water reached deeper horizons under mulching than under conventional practice, resulting in 15% more deep percolation in a wet year. The simulation results also indicated that growing green manure during the fallow period decreased soil water storage, leading to lower wheat yields. Mulching proved to be an efficient measure for increasing yields, and possibly contributed to groundwater recharge.

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