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.

scholarly journals Advantages of using a fast urban boundary layer model as compared to a full mesoscale model to simulate the urban heat island of Barcelona

2016 ◽  
Vol 9 (12) ◽  
pp. 4439-4450 ◽  
Author(s):  
Markel García-Díez ◽  
Dirk Lauwaet ◽  
Hans Hooyberghs ◽  
Joan Ballester ◽  
Koen De Ridder ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Wind Speed ◽  
Mesoscale Model ◽  
Urban Climate ◽  
Urban Canopy ◽  
Forecast Model ◽  
Heat Island ◽  
Layer Model ◽  
Urban Heat

Abstract. As most of the population lives in urban environments, the simulation of the urban climate has become a key problem in the framework of the climate change impact assessment. However, the high computational power required by high-resolution (sub-kilometre) fully coupled land–atmosphere simulations using urban canopy parameterisations is a severe limitation. Here we present a study on the performance of UrbClim, an urban boundary layer model designed to be several orders of magnitude faster than a full-fledged mesoscale model. The simulations are evaluated with station data and land surface temperature observations from satellites, focusing on the urban heat island (UHI). To explore the advantages of using a simple model like UrbClim, the results are compared with a simulation carried out with a state-of-the-art mesoscale model, the Weather Research and Forecasting Model, which includes an urban canopy model. This comparison is performed with driving data from ERA-Interim reanalysis (70 km). In addition, the effect of using driving data from a higher-resolution forecast model (15 km) is explored in the case of UrbClim. The results show that the performance of reproducing the average UHI in the simple model is generally comparable to the one in the mesoscale model when driven with reanalysis data (70 km). However, the simple model needs higher-resolution data from the forecast model (15 km) to correctly reproduce the variability of the UHI at a daily scale, which is related to the wind speed. This lack of accuracy in reproducing the wind speed, especially the sea-breeze daily cycle, which is strong in Barcelona, also causes a warm bias in the reanalysis driven UrbClim run. We conclude that medium-complexity models as UrbClim are a suitable tool to simulate the urban climate, but that they are sensitive to the ability of the input data to represent the local wind regime. UrbClim is a well suited model for impact and adaptation studies at city scale without high computing requirements, but does not replace the need for mesoscale atmospheric models when the focus is on the two-way interactions between the city and the atmosphere.

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.

An Observational Case Study of Synergies between an Intense Heat Wave and the Urban Heat Island in Beijing

2020 ◽  
Vol 59 (4) ◽  
pp. 605-620 ◽  
Author(s):  
Ning An ◽  
Jingjing Dou ◽  
Jorge E. González-Cruz ◽  
Robert D. Bornstein ◽  
Shiguang Miao ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Urban Heat Island ◽  
Heat Wave ◽  
Apparent Temperature ◽  
Heat Index ◽  
Heat Island ◽  
Canopy Layer ◽  
Urban Heat ◽  
Peak Pattern ◽  
Intense Heat

AbstractThe focus of this study is an intense heat episode that occurred on 9–13 July 2017 in Beijing, China, that resulted in severe impacts on natural and human variables, including record-setting daily electricity consumption levels. This event was observed and analyzed with a suite of local and mesoscale instruments, including a high-density automated weather station network, soil moisture sensors, and ground-based vertical instruments (e.g., a wind profiler, a ceilometer, and three radiometers) situated in and around the city, as well as electric power consumption data and analysis data from the U.S. National Centers for Environmental Prediction. The results show that the heat wave originated from dry adiabatic warming induced by the dynamic downslope and synoptic subsidence. The conditions were aggravated by the increased air humidity during subsequent days, which resulted in historically high records of the heat index (i.e., an index representing the apparent temperature that incorporates both air temperature and moisture). The increased thermal energy and decreased boundary layer height resulted in a highly energized urban boundary layer. The differences between urban and rural thermal conditions throughout almost the entire boundary layer were enhanced during the heat wave, and the canopy-layer urban heat island intensity (UHII) reached up to 8°C at a central urban station at 2300 local standard time 10 July. A double-peak pattern in the diurnal cycle of UHIIs occurred during the heat wave and differed from the single-peak pattern of the decadal average UHII cycles. Different spatial distributions of UHII values occurred during the day and night.

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.

scholarly journals Radon-based technique for the analysis of atmospheric stability – a case study from Central Poland

Nukleonika ◽  
2018 ◽  
Vol 63 (2) ◽  
pp. 47-54 ◽  
Author(s):  
Agnieszka Podstawczyńska ◽  
Scott D. Chambers
Keyword(s):  
Wind Speed ◽  
Temperature Gradient ◽  
Urban Heat Island ◽  
Urban Heat Island Intensity ◽  
Heat Island ◽  
Vertical Temperature Gradient ◽  
Mixing State ◽  
Vertical Temperature ◽  
Near Surface ◽  
Urban Heat

Abstract An economical and easy-to-implement technique is outlined by which the mean nocturnal atmospheric mixing state (“stability”) can be assessed over a broad (city-scale) heterogeneous region solely based on near-surface (2 m above ground level [a.g.l.]) observations of the passive tracer radon-222. The results presented here are mainly based on summer data of hourly meteorological and radon observations near Łodź, Central Poland, from 4 years (2008–2011). Behaviour of the near-surface wind speed and vertical temperature gradient (the primary controls of the nocturnal atmospheric mixing state), as well as the urban heat island intensity, are investigated within each of the four radon-based nocturnal stability categories derived for this study (least stable, weakly stable, moderately stable, and stable). On average, the most (least) stable nights were characterized by vertical temperature gradient of 1.1 (0.5)°C·m−1, wind speed of ~0.4 (~1.0) m·s−1, and urban heat island intensity of 4.5 (0.5)°C. For sites more than 20 km inland from the coast, where soils are not completely saturated or frozen, radon-based nocturnal stability classification can significantly enhance and simplify a range of environmental research applications (e.g. urban climate studies, urban pollution studies, regulatory dispersion modelling, and evaluating the performance of regional climate and pollution models).

scholarly journals A tree-planting decision support tool for urban heat island mitigation

2019 ◽  
Author(s):  
Zoey Werbin ◽  
Leila Heidari ◽  
Sarabeth Buckley ◽  
Paige Brochu ◽  
Lindsey Butler ◽  
...  
Keyword(s):  
Urban Heat Island ◽  
Web Application ◽  
Tree Mortality ◽  
Urban Canopy ◽  
Urban Trees ◽  
Tree Planting ◽  
Heat Island ◽  
Support Tool ◽  
Mortality And Morbidity ◽  
Urban Heat

AbstractHeat poses an urgent threat to public health in cities, as the urban heat island (UHI) effect can amplify exposures, contributing to high heat-related mortality and morbidity. Urban trees have the potential to mitigate by providing substantial cooling, as well as co-benefits such as reductions in energy consumption. The City of Boston has attempted to expand its urban canopy, yet maintenance costs and high tree mortality have hindered successful canopy expansion. Here, we present an interactive web application called “Right Place, Right Tree - Boston” that aims to support informed decision-making for planting new trees. To highlight priority regions for canopy expansion, we developed a Boston-specific Heat Vulnerability Index (HVI) and present this alongside maps of summer temperatures. We also provide information about tree pests and diseases, suitability of species for various conditions, land ownership, maintenance tips, and alternatives to tree planting.

The Influence of Synoptic Pattern and Atmospheric Boundary Layer on PM10 and Urban Heat Island

2013 ◽  
Vol 22 (5) ◽  
pp. 796-807 ◽  
Author(s):  
Guang-Xing He ◽  
Chuck Wah Francis Yu ◽  
Chan Lu ◽  
Qi-Hong Deng
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Urban Heat Island ◽  
Heat Island ◽  
Synoptic Pattern ◽  
Urban Heat
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