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Boreal land surface water and heat balance: Modelling soil-snow-vegetation-atmosphere behaviour
KTH, Superseded Departments, Land and Water Resources Engineering.
2002 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The water and heat exchange in thesoil-snow-vegetation-atmosphere system was studied in order toimprove the quantitative knowledge of land surface processes.In this study, numerical simulation models and availabledatasets representing arable land, sub-alpine snowpack, andboreal forest were evaluated at both diurnal and seasonaltimescales.

Surface heat fluxes, snow depth, soil temperatures andmeteorological conditions were measured at an agriculturalfield in central Sweden during three winters and two summersfrom 1997 to 2000 within the WINTEX project. A one-dimensionalsimulation model (COUP) was used to simulate the water and heatbalance of the field. Comparison of simulated and measured heatfluxes in winter showed that parameter values governing theupper boundary condition were more important for explainingmeasured fluxes than the formulation of the internal mass andheat balance of the snow cover. The assumption of steady stateheat exchange between the surface and the reference height wasinadequate during stable atmospheric conditions. Independentestimates of the soil heat and water balance together with thecomparison of simulated and measured surface heat fluxes showedthat the eddy-correlation estimates of latent heat fluxes fromthe arable field were on average 40 % too low.

The ability of a multi-layered snowpack model (SNTHERM) tosimulate the layered nature of a sub-alpine snowpack wasevaluated based on a dataset from Switzerland. The modelsimulated the seasonal development of snow depth and densitywith high accuracy. However, the models ability to reproducethe strong observed snowpack layering was limited by theneglection of the effect of snow microstructure on snowsettling, and a poor representation of water redistributionwithin the snowpack.

The representation of boreal forest in the land surfacescheme used within a weather forecast (ECMWF) model was testedwith a three-year dataset from the NOPEX forest site in centralSweden. The new formulation with separate energy balances forvegetation and the soil/snow beneath the tree cover improvedthe simulation of seasonal and diurnal variations in latent andsensible heat flux. Further improvements of simulated latentheat fluxes were obtained when seasonal variation in vegetationproperties was introduced. Application of the COUP model withthe same dataset showed that simulation of evaporation fromintercepted snow contributed to a better agreement with themeasured sensible heat flux above forests, but also indicatedthat the measurements might have underestimated latent heatflux. The winter sensible heat flux above the forest wasfurther improved if an upper limit of the aerodynamicresistance of 500 s m-1 was applied for stable conditions.

A comparison of the water and heat balance of arable landand forest confirmed the general knowledge of the differencesbetween these two surface types. The forest contributed withconsiderably more sensible heat flux to the atmosphere than thearable land in spring and summer due to the lower albedo andrelatively less latent heat flux. Latent heat flux from theforest was higher in winter due to the evaporation ofintercepted snow and rain. The net radiation absorbed by theforest was 60 % higher than that absorbed by the arable land,due to the lower surface albedo in winter.

Key words:soil; snow; land surface heat exchange;forest; arable land; eddy-correlation.

Place, publisher, year, edition, pages
Stockholm: KTH , 2002. , xii, 26 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1002
Keyword [en]
soil, snow, land surface heat exchange, forest, arable land, eddy-correlation
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3406ISBN: 91-7283-360-2 (print)OAI: oai:DiVA.org:kth-3406DiVA: diva2:9202
Public defence
2002-10-04, 00:00
Note
QC 20100614Available from: 2002-09-23 Created: 2002-09-23 Last updated: 2010-06-14Bibliographically approved
List of papers
1. The surface energy balance of a snow cover: comparing measurements to two different simulation models
Open this publication in new window or tab >>The surface energy balance of a snow cover: comparing measurements to two different simulation models
2001 (English)In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 70, no 1-4, 81-96 p.Article in journal (Refereed) Published
Abstract [en]

We compared two one-dimensional simulation models for heat and water fluxes in the soil-snow-atmosphere system with respect to their mathematical formulations of the surface heat exchange and the snow pack evolution. They were chosen as examples of a simple one-layer snow model and a more detailed multiple-layer snow model (SNTHERM). The snow models were combined with the same one-dimensional model for the heat and water balance of the underlying soil (CoupModel). Data from an arable field in central Sweden (Marsta), covering two years (1997-1999) of soil temperature, snow depth and eddy-correlation measurements were successfully compared with the models. Conditions with a snow pack deeper or shallower than 10cm and bare soil resulted in similar discrepancies. The simulated net radiation and sensible heat flux were in good agreement with that measured during snow-covered periods, except for situations with snowmelt when the downward sensible heat flux was overestimated by 10-20 WM-2. The results showed that the uncertainties in parameter values were more important than the model formulation and that both models were useful in evaluating the limitations and uncertainties of the measurements.

Keyword
LAND, PARAMETERIZATION, TEMPERATURE, RADIATION, WATER, SOIL
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-13341 (URN)10.1007/s007040170007 (DOI)000172271800007 ()
Note
QC 20100614Available from: 2010-06-14 Created: 2010-06-14 Last updated: 2017-12-12Bibliographically approved
2. Boreal-forest surface parameterisation in the ECMWF model: 1D test with NOPEX long-term data.
Open this publication in new window or tab >>Boreal-forest surface parameterisation in the ECMWF model: 1D test with NOPEX long-term data.
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-13342 (URN)
Note
QC 20100614Available from: 2010-06-14 Created: 2010-06-14 Last updated: 2010-06-14Bibliographically approved
3. Factors governing the formation and persistance of layers in a sub-alpine snowpack
Open this publication in new window or tab >>Factors governing the formation and persistance of layers in a sub-alpine snowpack
2004 (English)In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 18, no 7, 1165-1183 p.Article in journal (Refereed) Published
Abstract [en]

The layered structure of a snowpack has a great effect on several important physical processes, such as water movement, reflection of solar radiation or avalanche release. Our aim was to investigate what factors are most important with respect to the formation and persistence of distinct layers in a subalpine environment. We used a physically based numerical one-dimensional model to simulate the development of a snowpack on a subalpine meadow in central Switzerland during one winter season (1998-99). A thorough model validation was based on extensive measurement data including meteorological and snow physical parameters. The model simulated the snow water equivalent and the depth of the snowpack as well as the energy balance accurately. The observed strong layering of the snowpack, however, was not reproduced satisfactorily. In a sensitivity analysis, we tested different model options and parameter settings significant for the formation of snow layers. The neglection of effects of snow microstructure on the compaction rate, and the current description of the water redistribution inside the snowpack, which disregard capillary barrier effects, preferential flow and lateral water flow, were the major limitations for a more realistic simulation of the snowpack layering.

Keyword
snowpack, layering, numerical simulation model, subalpine, physical snoatack model, greenland ice-sheet, energy-balance, numerical-model, boreal forest, cover, water, heat, parameterization, simulation
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-13343 (URN)10.1002/hyp.1398 (DOI)000221218000001 ()2-s2.0-2442452602 (Scopus ID)
Note
QC 20100614Available from: 2010-06-14 Created: 2010-06-14 Last updated: 2017-12-12Bibliographically approved
4. Surface heat and water balance of a boreal arable field: long-term measurements and simulations
Open this publication in new window or tab >>Surface heat and water balance of a boreal arable field: long-term measurements and simulations
(English)Manuscript (preprint) (Other academic)
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-13344 (URN)
Note
QC 20100614Available from: 2010-06-14 Created: 2010-06-14 Last updated: 2010-06-14Bibliographically approved
5. Water and heat balance of the boreal landscape: comparison of forest and arable land.
Open this publication in new window or tab >>Water and heat balance of the boreal landscape: comparison of forest and arable land.
(English)Manuscript (preprint) (Other academic)
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-13345 (URN)
Note
QC 20100614Available from: 2010-06-14 Created: 2010-06-14 Last updated: 2010-06-14Bibliographically approved

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Citation style
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