| 1. |
- Chrysoulakis, N, et al.
(författare)
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7E.3: Urban Energy Balance from Space: the URBANFLUXES Project
- 2018
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Ingår i: 10th International Conference on Urban Climate/14th Symposium on the Urban Environment, New York, US, August 2018.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The H2020-Space project URBANFLUXES investigated the potential of Copernicus Sentinels to retrieve the key components of the Urban Energy Budget (UEB). The Discrete Anisotropic Radiative Transfer (DART) model was used to estimate the net all-wave radiation fluxes. The storage heat flux was determined using the Element Surface Temperature Method (ESTM) after being modified to use satellite observations. Turbulent sensible and latent heat fluxes were estimated with the Aerodynamic Resistance Method (ARM). The fluxes were evaluated with in-situ flux measurements in London, Basel and Heraklion. URBANFLUXES prepared the ground for further innovative exploitation of Earth Observation data in climate variability studies scales and emerging applications (sustainable urban planning, mitigation technologies) to benefit climate change mitigation and adaptation. The wide range of data produced (e.g. land cover, vegetation phenology, surface morphology) have a much large possible applications. This project website (http://urbanfluxes.eu) provides more detailed information.
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| 2. |
- Eliasson, Ingegärd, 1961, et al.
(författare)
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Wind fields and turbulence statistics in an urban street canyon
- 2006
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 40:1, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- This is the first paper of a long-term measurement campaign to explore wind, temperature, radiation and energy fieldswithin an urban canyon. A canyon and a rooftop mast were installed in a canyon with an aspect ratio (Height/Width)of 2.1 in Goteborg, Sweden. A number of instruments including sonic anemometers, radiometers and thermocoupleswere mounted in vertical profiles and across the width of the canyon. The experimental set-up, the characteristics of thecanyon flow pattern and mean and turbulence statistics with respect to above canyon flow are examined using datacollected under clear-sky conditions in summer and autumn 2003. Results show that under cross-canyon (within 601 oforthogonal) flow, a single helical vortex exists. High temporal resolution analysis suggests that eddies frequentlypenetrate the shear stress layer at the canyon top disrupting established flow patterns. A combination of complexbuilding roof shapes and local topography may contribute to this effect by maintaining a high degree of turbulence. Theprofile of mean wind speed within the canyon and the relation with that above canyon depends on the ambient flowdirection in relation to the canyon long axis. Turbulence statistics show results similar to other field studies, withturbulence kinetic energy and vertical mixing greatest toward the windward wall.
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| 3. |
- Evyatar, E, et al.
(författare)
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Incorporating spatial and temporal variations of advected moisture in the canyon air temperature (CAT) model.
- 2009
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Ingår i: ICUC7 Proceedings.
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Konferensbidrag (refereegranskat)abstract
- CAT (Canyon Air Temperature) is a parametric model that predicts site-specific air temperature in an urban street canyon for extended periods on the basis of data from a reference station in the region. A method is described for incorporating spatial and temporal variations in advected moisture, allowing application of the model with no prior knowledge of moisture availability in the area. The revised model is tested against data from field experiments in Gothenburg and Adelaide, in all seasons and in a variety of atmospheric conditions.
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| 4. |
- Jonsson, P., et al.
(författare)
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Longwave incoming radiation in the Tropics: results from field work in three African cities
- 2006
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Ingår i: Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 85:3-4, s. 185-201
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates differences in longwave incoming radiation (L down arrow) within and between three African cities, Dar es Salaam (Tanzania), Ouagadougou (Burkina Faso), and Gaborone (Botswana), during the dry season, and evaluates the performance of a model to simulate these fluxes. In each city, direct observations of L down arrow, shortwave incoming radiation (K down arrow), air temperature, air humidity, and total suspended particle (TSP) concentration for three land uses (CBD, green residential, and traditional residential) were taken. The observed L down arrow flux decreases with increasing latitude, and temperature becomes an increasingly important factor in governing L down arrow variations further from the Equator. Humidity, as well as particle loading, differs significantly between the three cities. Differences between observed and modelled epsilon(sky) for rural stations near all cities showed a clear diurnal variation, with maximum differences of 0.08 between day and night. This diurnal difference was incorporated in the model and, for urban areas the model overestimates L down arrow by around 25m(-2). However, this model performs equally well regardless of the land use considered in any of the cities. The residual (difference between observed and modelled urban L down arrow) did not show any correlation with particulate pollution. However, the difference between observed and calculated epsilon(sky) is around 0.05 higher in Ouagadougou compared to the other cities, likely due to the heavy dust load observed here. It is concluded that tropical urban longwave radiation is not dramatically different from the mid latitudes.
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| 5. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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3D modelling of vegetation within a 2D model – evaluation and application
- 2012
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Ingår i: The Eight International Conference on Urban Climates.. ; :abstract nr 180
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The SOlar and LongWave Environmental Irradiance Geometry (SOLWEIG) model simulates spatial variations of 3D radiation fluxes and mean radiant temperature (Tmrt) as well as shadow patterns in complex urban settings. Here, a new vegetation scheme is presented and evaluated. A new shadow casting algorithm for complex vegetation structures makes it possible to obtain continuous images of shadow patterns and sky view factors taking both buildings and vegetation into account. The model is evaluated using 5 days of integral radiation measurements at two sites within a square surrounded by low-rise buildings and vegetation in Göteborg, Sweden (57°N). There is good agreement between modelled and observed values of Tmrt. Furthermore, SOLWEIG is used to examine vegetation and building morphology characteristics through a north-south LiDAR transect across the megacity of London. It is shown that the contribution of vegetation to the shadowing and reduction of Tmrt at ground level is higher during summer than in autumn. The results from these simulations highlight that vegetation can be most effective at reducing heat stress within dense urban environments in summer. The daytime average Tmrt is found to be lowest in the densest urban environments due to shadowing; foremost from buildings but also from trees. It is clearly shown that this method could be used to quantify the influence of vegetation on Tmrt within the urban environment. The results presented in this paper highlight a number of possible climate sensitive planning practices for urban areas at the local scale.
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| 6. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Influence of ground surface characteristics on the mean radiant temperature in urban areas
- 2016
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Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 60:9, s. 1439-1452
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Tidskriftsartikel (refereegranskat)abstract
- The effect of variations in land cover on mean radiant temperature (T-mrt) is explored through a simple scheme developed within the radiation model SOLWEIG. Outgoing longwave radiation is parameterised using surface temperature observations on a grass and an asphalt surface, whereas outgoing shortwave radiation is modelled through variations in albedo for the different surfaces. The influence of ground surface materials on T-mrt is small compared to the effects of shadowing. Nevertheless, altering ground surface materials could contribute to a reduction in T-mrt to reduce the radiant load during heat-wave episodes in locations where shadowing is not an option. Evaluation of the new scheme suggests that despite its simplicity it can simulate the outgoing fluxes well, especially during sunny conditions. However, it underestimates at night and in shadowed locations. One grass surface used to develop the parameterisation, with very different characteristics compared to an evaluation grass site, caused T-mrt to be underestimated. The implications of using high temporal resolution (e.g. 15 minutes) meteorological forcing data under partly cloudy conditions are demonstrated even for fairly proximal sites.
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| 7. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Nature of vegetation and building morphology characteristics across a city: Influence on shadow patterns and mean radiant temperatures in London
- 2011
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Ingår i: Urban Ecosystems. - : Springer Science and Business Media LLC. - 1083-8155 .- 1573-1642. ; 14:4, s. 617-634
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Tidskriftsartikel (refereegranskat)abstract
- Vegetation and building morphology characteristics are investigated at 19 sites on a north-south LiDAR transect across the megacity of London. Local maxima of mean building height and building plan area density at the city centre are evident. Surprisingly, the mean vegetation height (zv3) is also found to be highest in the city centre. From the LiDAR data various morphological parameters are derived as well as shadow patterns. Continuous images of the effects of buildings and of buildings plus vegetation on sky view factor (SVF) are derived. A general reduction of SVF is found, indicating the importance of including vegetation when deriving SVF in urban areas. The contribution of vegetation to the shadowing at ground level is higher during summer than in autumn. Using these 3D data the influence on urban climate and mean radiant temperature (Tmrt) is calculated with SOLWEIG. The results from these simulations highlight that vegetation can be most effective at reducing heat stress within dense urban environments in summer. The daytime average Tmrt is found to be lowest in the densest urban environments due to shadowing, foremost from buildings but also from trees. It is clearly shown that this method could be used to quantify the influence of vegetation on Tmrt within the urban environment. The results presented in this paper highlight a number of possible climate sensitive planning practices for urban areas at the local scale (i.e. 102- 5×10^3 m).
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| 8. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Sunlit fractions on urban facets – Impact of spatial resolution and approach
- 2015
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Ingår i: Urban Climate. - 2212-0955. ; 12, s. 65-84
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Tidskriftsartikel (refereegranskat)abstract
- The extent of the surface area sunlit is critical for radiative energy exchanges and therefore for a wide range of applications that require urban land surface models (ULSM), ranging from human comfort to weather forecasting. Here a computationally demanding shadow casting algorithm is used to assess the capability of a simple single-layer urban canopy model, which assumes an infinitely long rotating canyon (ILC), to reproduce sunlit areas on roofs, walls and roads over central London. Results indicate that the sunlit road areas are well-represented but somewhat smaller using an ILC, while sunlit roofs areas are consistently larger, especially for dense urban areas. The largest deviations from real world sunlit areas are for roofs during mornings and evenings. Sunlit fractions on walls are overestimated using an ILC during mornings and evenings are found. The implications of these errors are dependent on the application targeted. For example, (independent of albedo) ULSMs used in numerical weather prediction applying ILC representation of the urban form will overestimate outgoing shortwave radiation from roofs due to the overestimation of sunlit fraction of the roofs. Complications of deriving height to width ratios from real world data are also discussed.
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| 9. |
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| 10. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Urban Multi-scale Environmental Predictor (UMEP): An integrated tool for city-based climate services
- 2018
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Ingår i: Environmental Modelling and Software. - : Elsevier BV. - 1364-8152. ; 99, s. 70-87
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 The Authors UMEP (Urban Multi-scale Environmental Predictor), a city-based climate service tool, combines models and tools essential for climate simulations. Applications are presented to illustrate UMEP's potential in the identification of heat waves and cold waves; the impact of green infrastructure on runoff; the effects of buildings on human thermal stress; solar energy production; and the impact of human activities on heat emissions. UMEP has broad utility for applications related to outdoor thermal comfort, wind, urban energy consumption and climate change mitigation. It includes tools to enable users to input atmospheric and surface data from multiple sources, to characterise the urban environment, to prepare meteorological data for use in cities, to undertake simulations and consider scenarios, and to compare and visualise different combinations of climate indicators. An open-source tool, UMEP is designed to be easily updated as new data and tools are developed, and to be accessible to researchers, decision-makers and practitioners.
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| 11. |
- Lindberg, Fredrik, 1974, et al.
(författare)
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Urban storage heat flux variability explored using satellite, meteorological and geodata
- 2020
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Ingår i: Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 141, s. 271-184
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Tidskriftsartikel (refereegranskat)abstract
- The storage heat flux (Delta Q(S)) is the net flow of heat stored within a volume that may include the air, trees, buildings and ground. Given the difficulty of measurement of this important and large flux in urban areas, we explore the use of Earth Observation (EO) data. EO surface temperatures are used with ground-based meteorological forcing, urban morphology, land cover and land use information to estimate spatial variations of Delta Q(S) in urban areas using the Element Surface Temperature Method (ESTM). First, we evaluate ESTM for four "simpler" surfaces. These have good agreement with observed values. ESTM coupled to SUEWS (an urban land surface model) is applied to three European cities (Basel, Heraklion, London), allowing EO data to enhance the exploration of the spatial variability in Delta Q(S). The impervious surfaces (paved and buildings) contribute most to Delta Q(S). Building wall area seems to explain variation of Delta Q(S) most consistently. As the paved fraction increases up to 0.4, there is a clear increase in Delta Q(S). With a larger paved fraction, the fraction of buildings and wall area is lower which reduces the high values of Delta Q(S).
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| 12. |
- Lordian, Thomas, et al.
(författare)
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Local-Scale Urban Meteorological Parameterization Scheme (LUMPS): longwave radiation parameterization and seasonality related developments
- 2011
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Ingår i: Journal of Applied Meteorology and Climatology. - 1558-8424 .- 1558-8432. ; 50, s. 185-202
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments to the Local-scale Urban Meteorological Parameterization Scheme (LUMPS), a simple model able to simulate the urban energy balance are presented. The major development is the coupling of LUMPS to the Net All-Wave Radiation Parameterization (NARP). Others include that the model now accounts for: changing availability of water at the surface; seasonal variations of active vegetation; and the anthropogenic heat flux; while maintaining the need for only commonly available meteorological observations and basic surface characteristics. The incoming component of the longwave radiation (L↓) in NARP is improved through a simple relation derived using cloud cover observations from a ceilometer collected in central London. The new L↓ formulation is evaluated with two independent multi-year datasets (Łódź, Poland and Baltimore, USA) and compared to alternatives that include: the original NARP and a simpler one using the U. S. National Climatic Data Center cloud observation database as input. The performance for the surface energy balance fluxes is assessed using a two year dataset (Łódź). Results have an overall RMSE
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| 13. |
- Loridan, Thomas, et al.
(författare)
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High Resolution Simulation of the Variability of Surface Energy Balance Fluxes Across Central London with Urban Zones for Energy Partitioning
- 2013
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Ingår i: Boundary-Layer Meteorology. - : Springer Netherlands. - 0006-8314 .- 1573-1472. ; 147:3, s. 493-523
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Tidskriftsartikel (refereegranskat)abstract
- The parameterization of surface heat-flux variability in urban areas relies on adequate representation of surface characteristics. Given the horizontal resolutions (e.g. ≈ 0.1–1 km) currently used in numerical weather prediction (NWP) models, properties of the urban surface (e.g. vegetated/built surfaces, street-canyon geometries) often have large spatial variability. Here, a new approach based on Urban Zones to characterize Energy partitioning (UZE) is tested within a NWP model (Weather Research and Forecasting model; WRF v3.2.1) for Greater London. The urban land-surface scheme is the Noah/Single-Layer Urban Canopy Model (SLUCM). Detailed surface information (horizontal resolution 1 km) in central London shows that the UZE offers better characterization of surface properties and their variability compared to default WRF-SLUCM input parameters. In situ observations of the surface energy fluxes and near-surface meteorological variables are used to select the radiation and turbulence parameterization schemes and to evaluate the land-surface scheme and choice of surface parameters. For radiative fluxes, improved performance (e.g. > 25 W m −2 root-mean-square error reduction for the net radiation) is attained with UZE parameters compared to the WRF v3.2.1 default for all three methods from the simplest to the most detailed. The UZE-based spatial fluxes reproduce a priori expectations of greater energy storage and less evaporation in the dense city centre compared to the residential surroundings. Problems in Noah/SLUCM partitioning of energy between the daytime turbulent fluxes are identified with the overestimation of the turbulent sensible heat and underestimation of the turbulent latent heat fluxes.
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| 14. |
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| 15. |
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| 16. |
- Offerle, Brian, 1967, et al.
(författare)
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Surface heating in relation to air temperature, wind and turbulence in an urban street canyon
- 2007
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Ingår i: Boundary-Layer Meteorology. - : Springer Science and Business Media LLC. - 0006-8314 .- 1573-1472. ; 122:2, s. 273-292
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Tidskriftsartikel (refereegranskat)abstract
- Wind and temperature measurements from within and above a deep urban canyon (height/width = 2.1) were used to examine the thermal structure of air within the canyon, exchange of heat with the overlying atmosphere, and the possible impacts of surface heating on within-canyon air flow. Measurements were made over a range of seasons and primarily analysed for sunny days. This allowed the study of temperature differences between opposing canyon walls and between wall and air of more than 15 degrees C in summer. The wall temperature patterns follow those of incoming solar radiation loading with a secondary daytime effect from the longwave exchange between the walls. In winter, the canyon walls receive little direct solar radiation, and temperature differences are largely due to anthropogenic heating of the building interiors. Cool air from aloft and heated air from canyon walls is shown to circulate within the canyon under cross-canyon flow. Roofs and some portions of walls heat up rapidly on clear days and have a large influence on heat fluxes and the temperature field. The magnitude and direction of the measured turbulent heat flux also depend strongly on the direction of flow relative to surface heating. However, these spatial differences are smoothed by the shear layer at the canyon top. Buoyancy effects from the heated walls were not seen to have as large an impact on the measured flow field as has been shown in numerical experiments. At night canyon walls are shown to be the source of positive sensible heat fluxes. The measurements show that materials and their location, as well as geometry, play a role in regulating the heat exchange between the urban surface and atmosphere.
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| 17. |
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| 18. |
- Offerle, Brian, 1967, et al.
(författare)
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Urban modification of the surface energy balance in the West African Sahel: Ouagadougou, Burkina Faso
- 2005
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 18:19, s. 3983-3995
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Tidskriftsartikel (refereegranskat)abstract
- Surface-atmosphere energy exchanges in Ouagadougou, Burkina Faso, located in the West African Sahel, were investigated during February 2003. Basic knowledge of the impact of land cover changes on local climate is needed to understand and forecast the impacts of rapid urbanization predicted for the region. Previously collected data showed a large dry season urban heat island (UHI), which dramatically decreased with the onset of the rainy season and corresponding changes to the natural land cover thermal and radiative properties. Observations of local-scale energy balance fluxes were made over a residential district; and building surface temperatures were measured in three separate locations. Net all-wave radiation showed an increase with urbanization owing to the higher albedo, lower heat capacity, and thermal conductivity of the bare dry soil compared to the urbanized surface. The combination of material and geometry resulted in a decrease in albedo toward the urban center. Despite the higher albedo, surface temperatures of bare undisturbed soil could exceed surface temperatures in the residential area and urban center by 15 degrees-20 degrees C due to differences in thermal characteristics. Turbulent heat exchange measured over a residential area was dominated by sensible heat flux. Latent heat fluxes were greater than expected from the amount of vegetation but in accordance with water use in the area. An urban land surface scheme reproduced fluxes in agreement with measurements. The results point toward an intensification of the dry season urban heat island in Ouagadougou, given increased urbanization.
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| 19. |
- Onomura, Shiho, 1985, et al.
(författare)
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Meteorological forcing data for urban outdoor thermal comfort models from a coupled convective boundary layer and surface energy balance scheme
- 2015
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Ingår i: Urban Climate. - : Elsevier BV. - 2212-0955. ; 11, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- Site-specific meteorological forcing appropriate for applications such as urban outdoor thermal comfort simulations can be obtained using a newly coupled scheme that combines a simple slab convective boundary layer (CBL) model and urban land surface model (ULSM) (here two ULSMs are considered). The former simulates daytime CBL height, air temperature and humidity, and the latter estimates urban surface energy and water balance fluxes accounting for changes in land surface cover. The coupled models are tested at a suburban site and two rural sites, one irrigated and one unirrigated grass, in Sacramento, U.S.A. All the variables modelled compare well to measurements (e.g. coefficient of determination = 0.97 and root mean square error = 1.5 °C for air temperature). The current version is applicable to daytime conditions and needs initial state conditions for the CBL model in the appropriate range to obtain the required performance. The coupled model allows routine observations from distant sites (e.g. rural, airport) to be used to predict air temperature and relative humidity in an urban area of interest. This simple model, which can be rapidly applied, could provide urban data for applications such as air quality forecasting and building energy modelling, in addition to outdoor thermal comfort.
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| 20. |
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