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  • 51.
    Rasmus, Sirpa
    et al.
    University of Helsinki.
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Biogeofysik.
    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 Forests2008Konferansepaper (Annet vitenskapelig)
    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.

  • 52. Rasmus, Sirpa
    et al.
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Mark- och vattenteknik.
    Lundell, Robin
    Saarinen, Timo
    Observations and snow model simulations of winter energy balance terms within and between different coniferous forests in southern boreal Finland2016Inngår i: Hydrology Research, ISSN 1998-9563, Vol. 47, nr 1, s. 201-216Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Variation of canopy properties between different forest types is seldom taken into account in hydrological and climate models, and consideration of variation inside a forest is normally omitted. In this work, three data sets on near surface energy balance terms (incoming shortwave and longwave radiation; air and snow-soil interface temperatures) were collected in the southern boreal coniferous zone in Finland during three winters below different types of forest canopies. The aim was to evaluate the ability of a snow mass and energy balance model with a canopy module to reproduce the observed differences in below-canopy incoming radiations and snow-soil interface temperature. Clear differences were seen between pine and spruce forest sites (higher snow-soil interface temperatures and incoming shortwave fluxes, and lower incoming longwave fluxes at the pine site). Differences were also observed between the sparse and dense pine canopy locations. Canopy parameter values had a great effect on the quality of the model simulations. The combination of optically obtained leaf area index (LAI) values with a needle clumping correction and either optical or empirical sky view fraction (SVF) values as a canopy parameterization gave better correspondence to observations than the use of uncorrected effective LAI and any SVF.

  • 53. 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, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik (flyttat 20130630), Biogeofysik.
    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)2009Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 54. Staehli, Manfred
    et al.
    Jonas, Tobias
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Miljögeokemi och ekoteknik.
    The role of snow interception in winter-time radiation processes of a coniferous sub-alpine forest2009Inngår i: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 23, nr 17, s. 2498-2512Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The radiation balance in forests is modified by the presence of a (temporally snow-covered) canopy much more than it is in open areas. The primary effects of the forest canopy are absorption of incoming shortwave radiation, as well as absorption and emission of Ion-wave radiation. In this study, data from a mobile net radiation sensor moving along a 10-m bar in a coniferous sub-alpine stand of central Switzerland were analysed to assess the role of intercepted snow in comparison with other governing factors for winter-time radiation processes in a coniferous sub-alpine forest. The four winters investigated (2003-2007) covered a broad range of weather and snow conditions including several periods with intercepted snow lasting up to 19 days. For cloudless days, the data show that canopy albedo is elevated by the presence of intercepted snow. For transmissivity, the impact of intercepted snow is less distinct. Our analysis showed that the fraction of diffuse radiation and solar elevation are the main factors affecting shortwave transmissivity. Only after compensating for these effects, could intercepted snow be associated with increased transmissivities. Part of this analysis was carried out with the help of a physically based radiative transfer model. The model results suggest that multiple reflections are relevant to understanding the complex interactions between the factors affecting transmissivity. Finally, snow interception load can be derived reasonably well (R-2 = 0.65) from radiation measurements in this sub-alpine forest.

  • 55. Stahli, M.
    et al.
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Miljögeokemi och ekoteknik.
    Long-term investigations of the snow cover in a subalpine semi-forested catchment2006Inngår i: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 20, nr 2, s. 411-428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To improve spring runoff forecasts from subalpine catchments, detailed spatial simulations of the snow cover in this landscape is obligatory. For more than 30 years, the Swiss Federal Research Institute WSL has been conducting extensive snow cover observations in the subalpine watershed Alptal (central Switzerland). This paper summarizes the conclusions from past snow studies in the Alptal valley and presents an analysis of 14 snow courses located at different exposures and altitudes, partly in open areas and partly in forest. The long-term performance of a physically based numerical snow-vegetation-atmosphere model (COUP) was tested with these snow-course measurements. One single parameter set with meteorological input variables corrected to the prevailing local conditions resulted in a convincing snow water equivalent (SWE) simulation at most sites and for various winters with a wide range of snow conditions. The snow interception approach used in this study was able to explain the forest effect on the SWE as observed on paired snow courses. Finally, we demonstrated for a meadow and a forest site that a successful simulation of the snowpack yields appropriate melt rates.

  • 56. Stähli, M.
    et al.
    Stacheder, M.
    Gustafsson, David
    WSL Swiss Fed. Inst. Snow/Avalanche, Flüelastrasse, Switzerland.
    Schlaeger, S.
    Schneebeli, M.
    Brandelik, A.
    A new in-situ sensor for large-scale snow cover monitoring2004Inngår i: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 38, s. 273-278Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new in situ sensor for the simultaneous measurement of snow water equivalent, snow density and liquid-water content is presented in this paper. The system consists of radio frequency transmission lines of up to 25 in length cast in a flat PVC band, which can be set up either horizontally to monitor single snow-layer properties or sloping from a mast to the soil surface to determine vertical snowpack properties. The dielectric coefficient along the flat-band cable is measured with a time-domain reflectometer at high frequencies, and with a low-frequency impedance analyzer. The performance of the sensor system was tested during two winter seasons (2001-03) at the high-alpine test site Weissfluhjoch, Davos, Switzerland. The cable suspension and set-up of the sloping cable was shown to be critical with regard to stability and the formation of unwanted air gaps along the cable. Overall, the sensing system proved quite robust and produced results in agreement with manual snowpack observations.

  • 57.
    Stähli, Manfred
    et al.
    WSL Swiss Federal Institute for Forest, Snow and Landscape Research.
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Biogeofysik.
    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 representation2006Konferansepaper (Annet vitenskapelig)
  • 58. Sundström, Nils
    et al.
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Mark- och vattenteknik.
    Kruglyak, Andrey
    Lundberg, Angela
    Field evaluation of a new method for estimation of liquid water content and snow water equivalent of wet snowpacks with GPR2013Inngår i: Hydrology Research, ISSN 1998-9563, Vol. 44, nr 4, s. 600-613Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Estimates of snow water equivalent (SWE) with ground-penetrating radar can be used to calibrate and validate measurements of SWE over large areas conducted from satellites and aircrafts. However, such radar estimates typically suffer from low accuracy in wet snowpacks due to a built-in assumption of dry snow. To remedy the problem, we suggest determining liquid water content from path-dependent attenuation. We present the results of a field evaluation of this method which demonstrate that, in a wet snowpack between 0.9 and 3 m deep and with about 5 vol% of liquid water, liquid water content is underestimated by about 50% (on average). Nevertheless, the method decreases the mean error in SWE estimates to 16% compared to 34% when the presence of liquid water in snow is ignored and 31% when SWE is determined directly from two-way travel time and calibrated for manually measured snow density.

  • 59.
    Svensson, Magnus
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik.
    Jansson, Per-Erik
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik.
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik.
    Berggren Kleja, Dan
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik.
    Langvall, Ola
    Lindroth, Anders
    Bayesian calibration of a model describing carbon, water and heat fluxes for a Swedish boreal forest stand.2008Inngår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 213, nr 3-4, s. 331-344Artikkel i tidsskrift (Annet vitenskapelig)
    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

  • 60. Zhang, Linus
    et al.
    Gustafsson, David
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
    Editorial: 'The Nordic Hydrology Model' - Linking science and practice2016Inngår i: Hydrology Research, ISSN 1998-9563, Vol. 47, nr 4, s. 671-671Artikkel i tidsskrift (Fagfellevurdert)
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