scholarly journals Energetics of Urban Canopies: A Meteorological Perspective

J ◽  
2021 ◽  
Vol 4 (4) ◽  
pp. 645-663
Author(s):  
Edson Marciotto ◽  
Marcos Vinicius Bueno de de Morais
Keyword(s):  
Boundary Layer ◽  
Urban Heat Island ◽  
Urban Areas ◽  
Numerical Models ◽  
Urban Canopy ◽  
Urban Heat Island Intensity ◽  
Heat Island ◽  
Local Flow ◽  
Urban Climatology ◽  
Urban Heat

The urban climatology consists not only of the urban canopy temperature but also of wind regime and boundary layer evolution among other secondary variables. The energetic input and response of urbanized areas is rather different to rural or forest areas. In this paper, we outline the physical characteristics of the urban canopy that make its energy balance depart from that of vegetated areas and change local climatology. Among the several canopy characteristics, we focus on the aspect ratio h/d and its effects. The literature and methods of retrieving meteorological quantities in urban areas are reviewed and a number of physical analyzes from conceptual or numerical models are presented. In particular, the existence of a maximum value for the urban heat island intensity is discussed comprehensively. Changes in the local flow and boundary layer evolution due to urbanization are also discussed. The presence of vegetation and water bodies in urban areas are reviewed. The main conclusions are as follows: for increasing h/d, the urban heat island intensity is likely to attain a peak around h/d≈4 and decrease for h/d>4; the temperature at the pedestrian level follows similar behavior; the urban boundary layer grows slowly, which in combination with low wind, can worsen pollution dispersion.

scholarly journals Opposite Effects of Aerosols on Daytime Urban Heat Island Intensity between Summer and Winter

2020 ◽  
Author(s):  
Wenchao Han ◽  
Zhanqing Li ◽  
Fang Wu ◽  
Yuwei Zhang ◽  
Jianping Guo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Urban Heat Island ◽  
Planetary Boundary Layer ◽  
Urban Areas ◽  
Urban Heat Island Intensity ◽  
Heat Island ◽  
Different Seasons ◽  
Urban Heat ◽  
The Impact

Abstract. The urban heat island intensity (UHII) is the temperature difference between urban areas and their rural surroundings. It is commonly attributed to changes in the underlying surface structure caused by urbanization. Air pollution caused by aerosol particles can affect the UHII by changing the surface energy balance and atmospheric thermodynamic structure. By analyzing satellite data and ground-based observations collected from 2001 to 2010 at 35 cities in China and using the WRF-Chem model, we found that aerosols have very different effects on daytime UHII in different seasons: reducing the UHII in summer, but increasing the UHII in winter. The seasonal contrast in the spatial distribution of aerosols between the urban centers and the suburbs lead to a spatial discrepancy in aerosol radiative effect (SD-ARE). Additionally, different stability of the planetary boundary layer induced by aerosol is closely associated with a dynamic effect (DE) on the UHII. SD-ARE reduces the amount of radiation reaching the ground and changes the vertical temperature gradient, whereas DE increases the stability of the planetary boundary layer and weakens heat release and exchange between the surface and the PBL. Both effects exist under polluted conditions, but their relative roles are opposite between the two seasons. It is the joint effects of the SD-ARE and the DE that drive the UHII to behave differently in different seasons, which is confirmed by model simulations. In summer, the UHII is mainly affected by the SD-ARE, and the DE is weak, and the opposite is the case in winter. This finding sheds a new light on the impact of the interaction between urbanization-induced surface changes and air pollution on urban climate.

The urban heat island of London, an empirical model

2019 ◽  
Vol 40 (3) ◽  
pp. 290-295 ◽  
Author(s):  
Geoff Levermore ◽  
John Parkinson
Keyword(s):  
Urban Heat Island ◽  
Empirical Model ◽  
Urban Areas ◽  
Urban Heat Island Intensity ◽  
Weather Data ◽  
Rural Site ◽  
City Centre ◽  
Heat Island ◽  
Data Set ◽  
Urban Heat

On top of climate change and its consequent temperature rises, urban areas have the added burden of the urban heat island (the urban area being warmer than the rural area especially at night under calm, cloud-free conditions). The urban heat island intensity (the difference between the rural air temperature and that in the city centre) can be as large as 10K for the major cities such as London. The urban heat island intensity, consequently, can have a significant effect on the sizing of heating, ventilating and air-conditioning plant and its energy consumption. At present, designers have access to empirical factors for design days only in June, July and August from the Chartered Institution of Building Services Engineers Guide. Or they can use the latest Design Summer Year which implicitly includes the urban heat island intensity. However, the empirical model discussed in this paper allows the designer to add on the hourly urban heat island intensity for central London to any recent year’s hourly weather data set from London Heathrow or Bracknell, a more rural site. The model is similar to one for Manchester, suggesting that the model may well be of application to other UK cities. Practical applications: Most buildings that building services engineers and other building designers are involved with are in urban or city centres. However, the weather data for their designs are based on near-rural weather data, which does not include the urban heat island effect. This paper describes the urban heat island effects that a designer needs to consider and the adjustments that can be made, related to London.

scholarly journals Assessment of Planetary Boundary Layer Parameterizations and Urban Heat Island Comparison: Impacts and Implications for Tracer Transport

2020 ◽  
Vol 59 (10) ◽  
pp. 1637-1653
Author(s):  
Israel Lopez-Coto ◽  
Micheal Hicks ◽  
Anna Karion ◽  
Ricardo K. Sakai ◽  
Belay Demoz ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Urban Heat Island ◽  
Planetary Boundary Layer ◽  
Urban Areas ◽  
Greenhouse Gas Emission ◽  
Sensible Heat Flux ◽  
Heat Island ◽  
Tracer Transport ◽  
Urban Heat ◽  
The Impact

AbstractAccurate simulation of planetary boundary layer height (PBLH) is key to greenhouse gas emission estimation, air quality prediction, and weather forecasting. This paper describes an extensive performance assessment of several Weather Research and Forecasting (WRF) Model configurations in which novel observations from ceilometers, surface stations, and a flux tower were used to study their ability to reproduce the PBLH and the impact that the urban heat island (UHI) has on the modeled PBLHs in the greater Washington, D.C., area. In addition, CO2 measurements at two urban towers were compared with tracer transport simulations. The ensemble of models used four PBL parameterizations, two sources of initial and boundary conditions, and one configuration including the building energy parameterization urban canopy model. Results have shown low biases over the whole domain and period for wind speed, wind direction, and temperature, with no drastic differences between meteorological drivers. We find that PBLH errors are mostly positively correlated with sensible heat flux errors and that modeled positive UHI intensities are associated with deeper modeled PBLs over the urban areas. In addition, we find that modeled PBLHs are typically biased low during nighttime for most of the configurations with the exception of those using the MYNN parameterization, and these biases directly translate to tracer biases. Overall, the configurations using the MYNN scheme performed the best, reproducing the PBLH and CO2 molar fractions reasonably well during all hours and thus opening the door to future nighttime inverse modeling.

Impact of Upstream Urbanization on the Urban Heat Island Effects along the Washington–Baltimore Corridor

2011 ◽  
Vol 50 (10) ◽  
pp. 2012-2029 ◽  
Author(s):  
Da-Lin Zhang ◽  
Yi-Xuan Shou ◽  
Russell R. Dickerson ◽  
Fei Chen
Keyword(s):  
Urban Heat Island ◽  
Urban Areas ◽  
Urban Canopy ◽  
Horizontal Wind ◽  
Dynamical Process ◽  
Heat Island ◽  
Moist Convection ◽  
Land Cover Data ◽  
Urban Heat ◽  
The Impact

AbstractAlthough there has been considerable research on urban heat island (UHI) effects, most of the previous studies have attributed UHI effects to localized, surface processes. In this study, the impact of upstream urbanization on enhanced UHI effects is examined using surface observations and numerical simulations of an extreme UHI event that occurred on 9 July 2007 over Baltimore, Maryland. Under southwesterly wind, Baltimore experienced higher peak surface temperatures and higher pollution concentrations than did the larger urban area of Washington, D.C. Results from a coupled ultrahigh-resolution mesoscale–urban canopy model with 2001 National Land Cover Data show an advective contribution from upstream urbanization to the UHI event. This dynamical process is demonstrated by replacing Baltimore or its upstream urban areas by natural vegetation (in the model), indicating that the UHI effects could be reduced by as much as 25%. An analysis of the urban–bay interaction reveals the importance of horizontal wind direction in determining the intensity of bay breezes and the urban boundary layer structures. In addition, the vertical growth and structures of UHI effects are shown as layered “hot plumes” in the mixed layer with pronounced rising motions, and these plumes can be advected many kilometers downstream. These findings suggest that judicious land use and urban planning, especially in rapidly developing countries, could help to alleviate UHI consequences, including heat stress and smog. They also have important implications for improving the prediction of urban weather, including the initiation of moist convection, air quality, and other environment-related problems.

scholarly journals Spatial and Temporal Characteristics of Beijing Urban Heat Island Intensity

2013 ◽  
Vol 52 (8) ◽  
pp. 1803-1816 ◽  
Author(s):  
Ping Yang ◽  
Guoyu Ren ◽  
Weidong Liu
Keyword(s):  
Urban Heat Island ◽  
Urban Areas ◽  
Urban Heat Island Intensity ◽  
Heat Island ◽  
Temporal Characteristics ◽  
Seasonal Basis ◽  
Urban Heat ◽  
The City ◽  
Urban Sites ◽  
Spatial And Temporal Characteristics

AbstractAn hourly dataset of automatic weather stations over Beijing Municipality in China is developed and is employed to analyze the spatial and temporal characteristics of urban heat island intensity (UHII) over the built-up areas. A total of 56 stations that are located in the built-up areas [inside the 6th Ring Road (RR)] are considered to be urban sites, and 8 stations in the suburban belts surrounding the built-up areas are taken as reference sites. The reference stations are selected by using a remote sensing method. The urban sites are further divided into three areas on the basis of the city RRs. It is found that the largest UHII generally takes place inside the 4th RR and that the smallest ones occur in the outer belts of the built-up areas, between the 5th RR and the 6th RR, with the areas near the northern and southern 6th RR experiencing the weakest UHI phenomena. On a seasonal basis, the strongest UHII generally occurs in winter and weak UHII is dominantly observed in summer and spring. The UHII diurnal variations for each of the urban areas are characterized by a steadily strong UHII stage from 2100 local solar time (LST) to 0600 LST and a steadily weak UHII stage from 1100 to 1600 LST, with the periods 0600–1100 LST and 1600–2100 LST experiencing a swift decline and rise, respectively. UHII diurnal variation is seen throughout the year, but the steadily strong UHII stage at night is longer (shorter) and the steadily weak UHII stage during the day is shorter (longer) during winter and autumn (summer and spring).

An Observational and Modeling Study of Characteristics of Urban Heat Island and Boundary Layer Structures in Beijing

2009 ◽  
Vol 48 (3) ◽  
pp. 484-501 ◽  
Author(s):  
Shiguang Miao ◽  
Fei Chen ◽  
Margaret A. LeMone ◽  
Mukul Tewari ◽  
Qingchun Li ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Diurnal Variation ◽  
Urban Heat Island ◽  
Urban Canopy ◽  
Heat Island ◽  
Mountain Valley ◽  
Layer Structures ◽  
Urban Heat ◽  
Convective Rolls

Abstract In this paper, the characteristics of urban heat island (UHI) and boundary layer structures in the Beijing area, China, are analyzed using conventional and Moderate Resolution Imaging Spectroradiometer (MODIS) observations. The Weather Research and Forecasting (WRF) model coupled with a single-layer urban canopy model (UCM) is used to simulate these urban weather features for comparison with observations. WRF is also used to test the sensitivity of model simulations to different urban land use scenarios and urban building structures to investigate the impacts of urbanization on surface weather and boundary layer structures. Results show that the coupled WRF/Noah/UCM modeling system seems to be able to reproduce the following observed features reasonably well: 1) the diurnal variation of UHI intensity; 2) the spatial distribution of UHI in Beijing; 3) the diurnal variation of wind speed and direction, and interactions between mountain–valley circulations and UHI; 4) small-scale boundary layer convective rolls and cells; and 5) the nocturnal boundary layer lower-level jet. The statistical analyses reveal that urban canopy variables (e.g., temperature, wind speed) from WRF/Noah/UCM compare better with surface observations than the conventional variables (e.g., 2-m temperature, 10-m wind speed). Both observations and the model show that the airflow over Beijing is dominated by mountain–valley flows that are modified by urban–rural circulations. Sensitivity tests imply that the presence or absence of urban surfaces significantly impacts the formation of horizontal convective rolls (HCRs), and the details in urban structures seem to have less pronounced but not negligible effects on HCRs.

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