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Modeling the Seasonality of Carbon, Evapotranspiration and Heat Processes for Cold Climate Conditions
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
2010 (English)Licentiate 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.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , x, 13 p.
Series
Trita-LWR. LIC, ISSN 1650-8629 ; 2045
Keyword [en]
net ecosystem exchange (NEE), sensible and latent heat fluxes, photosynthesis, respiration, nitrogen turnover, Scots pine forest, bare soil, cold climate, soil physical characteristics, CoupModel, GLUE
National Category
Other Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-26918ISBN: 978-91-7415-826-7 (print)OAI: oai:DiVA.org:kth-26918DiVA: diva2:372901
Presentation
2010-12-17, V3, KTH, Teknikringen 76, Stockholm, 13:15 (English)
Opponent
Supervisors
Note
QC 20101206Available from: 2010-12-06 Created: 2010-11-29 Last updated: 2010-12-06Bibliographically approved
List of papers
1. Modelling temperature, moisture and surface heat balance in the bare soil under seasonal frost conditions in China
Open this publication in new window or tab >>Modelling temperature, moisture and surface heat balance in the bare soil under seasonal frost conditions in China
2011 (English)In: European Journal of Soil Science, ISSN 1351-0754, E-ISSN 1365-2389, Vol. 62, no 6, 780-796 p.Article in journal (Refereed) Published
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.

Keyword
FROZEN SOIL; WATER-CONTENT; CALIBRATION; FREEZE; LAND; THAW; FOREST; SCALE; FLOW
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-27036 (URN)10.1111/j.1365-2389.2011.01397.x (DOI)000297206100002 ()2-s2.0-81855228878 (Scopus ID)
Note
QC 20101206. Updated from submitted to published, 20120316. Previous title: Model for temperature, moisture and surface heat balance in the bare soil with seasonal frost conditions in ChinaAvailable from: 2010-12-06 Created: 2010-12-06 Last updated: 2017-12-12Bibliographically approved
2. Modeling seasonal courses of carbon fluxes and evaportranspiration in response to low temperature and moisture in a boreal scots pine ecosystem
Open this publication in new window or tab >>Modeling seasonal courses of carbon fluxes and evaportranspiration in response to low temperature and moisture in a boreal scots pine ecosystem
2011 (English)In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 222, 3103-3119 p.Article in journal (Refereed) Published
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.

Keyword
Net ecosystem exchange (NEE), Sensible and latent heat fluxes, Photosynthesis, Respiration, Scots pine forest, CoupModel, Generalized likelihood uncertainty estimation (GLUE)
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:kth:diva-27038 (URN)10.1016/j.ecolmodel.2011.05.023 (DOI)000295071400010 ()2-s2.0-80051939835 (Scopus ID)
Note
QC 20101206 Uppdaterad från submitted till published 20110921Available from: 2010-12-06 Created: 2010-12-06 Last updated: 2017-12-12Bibliographically approved

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