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Urban microclimate and surface hydrometeorological processes
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The urban near surface atmosphere is of great concern since it affects the climate to which an increasing amount of people are immediately exposed. This study investigated the microclimate in central Stockholm in terms of the thermal conditions in the 0-2.5 m air layer and the water and heat exchange processes at different types of surfaces found within the urban environment. The main objective was to improve our understanding of the urban small-scale climate system.

The urban microclimate was measured in terms of vertical air temperature profiles along a horizontal transect running through a vegetated park and its built-up surroundings during three clear and relatively calm summer days. The results showed that the air temperature at 1.2 m height within the park was 0.5 to 1.5 K lower than in the surrounding city blocks, and that the thermal stratification was generally stable (increasing temperature with height) in the park and unstable (decreasing temperature with height) in the built-up areas. In addition, there were a few examples of temperature gradients orientated in different directions within the lowest 2.5 m air layer, indicating horizontal advection between the park and the built-up areas. Climate conditions simulated with a three-dimensional microclimate model agreed well with observations and the model was therefore assumed to provide reasonable representations of important climate processes such as surface-air energy exchange processes. However, there were some discrepancies between observations and simulations that are discussed in terms of differences in real and modelled heat storage processes and wind conditions. Processes that need to be included for a more precise model description of areas such as the Stockholm environment include dynamic heat storage in buildings and dynamic wind forcing during the course of the simulation.

A soil-vegetation-atmosphere transfer model was used to study soil water transport, the surface energy balance of an asphalt surface, and the impact of urban climate on evapotranspiration. Based on model calibration to field measurements of soil water content in a till catchment outside Stockholm, new parameter values were estimated that can be used for water flow modelling of till soils. The heat fluxes of an asphalt surface were reliably simulated without knowledge of site-specific calibration and the model was useful in identifying problems with energy balance closure based on measurements only. Simulations of ‘urban’ modifications to the forcing climate conditions demonstrated that increased air temperature, and thereby increased vapour pressure deficit, had most effect on evapotranspiration from tall vegetation, while increased long-wave radiation raised grass evapotranspiration the most.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , viii, 24 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1027
Keyword [en]
CoupModel, ENVI-met, roughness sub-layer, urban heat island
National Category
Physical Geography
Identifiers
URN: urn:nbn:se:kth:diva-3879ISBN: 91-7178-295-8 (print)OAI: oai:DiVA.org:kth-3879DiVA: diva2:9852
Public defence
2006-03-24, Sal D3, Lindstedtsvägen 5, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100901Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2010-09-01Bibliographically approved
List of papers
1. Preferential water flow in a glacial till soil
Open this publication in new window or tab >>Preferential water flow in a glacial till soil
2005 (English)In: Nordic Hydrology, ISSN 0029-1277, Vol. 36, no 1, 1-11 p.Article in journal (Refereed) Published
Abstract [en]

Measured and simulated response of runoff during snowmelt has suggested that preferential water flow occurs as part of the infiltration process in glacial till. However, only a few quantitative studies have been presented. TDR measurements of soil water content were performed during the growing period in a till slope (7-10%) outside Stockholm. Soil cores were used to determine the water retention curve and the saturated hydraulic conductivity. A physically based one-dimensional model was used to simulate soil water dynamics in the slope. Two simulation approaches were used: a strict one-domain Darcian approach and a two-domain approach accounting for a bypass of the matrix flow system. The measured response of soil water content occurred within the first few hours after rainfall. This was best represented by the two-domain approach, while the response for the one-domain approach was significantly delayed with time and depth. The general behaviour of the soil water content throughout the season was, however, best simulated with a one-domain approach. The results indicated that preferential flow patterns through the unsaturated zone does not need to be considered to describe the seasonal pattern in glacial till soil. However, the results also point out that the purpose of the simulation is decisive when choosing a simulation approach, depending on whether the general soil water content over the season or the instant behaviour immediately after rainfall is of major interest.

Keyword
infiltration, macropore, runoff; two-domain, unsaturated
National Category
Physical Geography
Identifiers
urn:nbn:se:kth:diva-5472 (URN)000228802600001 ()2-s2.0-18144387575 (Scopus ID)
Note
QC 20100901Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2012-02-08Bibliographically approved
2. Heat balance of an asphalt surface: observations and physically-based simulations
Open this publication in new window or tab >>Heat balance of an asphalt surface: observations and physically-based simulations
2006 (English)In: Meteorological Applications, ISSN 1350-4827, E-ISSN 1469-8080, Vol. 13, no 2, 203-212 p.Article in journal (Refereed) Published
Abstract [en]

A physically-based 1-D beat and mass transfer model was tested to estimate the beat fluxes of an asphalt surface. The model was run for two summer months for a road test site in southwest Sweden. Parameters for thermal properties, surface runoff, radiation and turbulent transfer were obtained from a description of the road stratification and from the literature. Coefficients of determination (r(2)) 0.94, 0.93 and 0.97 were obtained when simulated results were compared with observations of net radiation, beat flow below the surface and surface temperature respectively, all with slope coefficients close to unity. In addition, simulation results elucidated the robe of water vapour transport through the asphalt-soil profile and its effect on the latent beat flow from the surface. Problems were identified with closure of the beat balance in measurements based on discrepancy between simulated and observed sensible heat flux.

Keyword
CoupModel, energy balance, road, transport, bare-soil, numerical-model, temperature, parameterization, evaporation, prediction, moisture, ice
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-15795 (URN)10.1017/s1350482706002179 (DOI)000238662200008 ()2-s2.0-33748130507 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Simulating impact on evapotranspiration vegetated surfaces
Open this publication in new window or tab >>Simulating impact on evapotranspiration vegetated surfaces
(English)Manuscript (Other academic)
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-5474 (URN)
Note
QC 20100901Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2010-09-01Bibliographically approved
4. Near surface climate in an urban vegetated park and its surroundings
Open this publication in new window or tab >>Near surface climate in an urban vegetated park and its surroundings
2007 (English)In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 89, no 34, 185-193 p.Article in journal (Refereed) Published
Abstract [en]

Near surface climate was observed through temperature profiling from the surface to 2.47 m height in an urban vegetated park and its surroundings in central Stockholm, Sweden. Measurements were conducted during three summer days by mobile traverses. Air temperature differences between the built-up area and the park were in the range of 0.5-0.8°C during the day and reached a maximum of 2°C at sunset. The thermal stratification of the air was mainly stable in the park and unstable in the built-up area. Inverse air temperature profiles in the park were less stable in open than in shady areas, and close to neutral at midday. The most unstable air was found in the north-south orientated canyons in the early afternoon. Possible heat advection from the surroundings, and thus uncoupling between the surface and the air, was identified through temperature gradients pointing at different directions within the 2.47 m profile. Examples at midday indicated that warm air advected as far as 150 m into the park.

Keyword
heat islands, temperature, cities, energy, areas
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:kth:diva-5475 (URN)10.1007/s00704-006-0259-z (DOI)000247417400005 ()2-s2.0-34347374875 (Scopus ID)
Note
QC 20100901Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2017-11-21Bibliographically approved
5. The urban-park climate system: Testing the dynamic behaviour of a small-scale numerical model
Open this publication in new window or tab >>The urban-park climate system: Testing the dynamic behaviour of a small-scale numerical model
(English)Manuscript (Other academic)
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:kth:diva-5476 (URN)
Note
QC 20100901Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2010-09-01Bibliographically approved

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