Large Eddy Simulation and Study of the Urban Boundary Layer

Based on a pseudo-spectral large eddy simulation (LES) model, an LES model with an anisotropy turbulent kinetic energy (TKE) closure model and an explicit multi-stage third-order Runge-Kutta scheme is established. The modeling and analysis show that the LES model can simulate the planetary boundary layer (PBL) with a uniform underlying surface under various stratifications very well. Then, similar to the description of a forest canopy, the drag term on momentum and the production term of TKE by subgrid city buildings are introduced into the LES equations to account for the area-averaged effect of the subgrid urban canopy elements and to simulate the meteorological fields of the urban boundary layer (UBL). Numerical experiments and comparison analysis show that: (1) the result from the LES of the UBL with a proposed formula for the drag coefficient is consistent and comparable with that from wind tunnel experiments and an urban subdomain scale model; (2) due to the effect of urban buildings, the wind vel

Delineation of urban growth boundary based on FLUS model under the perspective of land use evaluation in hilly mountainous areas

With rapid economic development,the size of urban land in China is expanding dramatically.The Urban Growth Boundary(UGB)is an expandable spatial boundary for urban construction in a certain period in order to control the urban sprawl.Reasonable delineation of UGB can inhibit the disorderly spread of urban space and guide the normal development of the city.It is of practical significance for the construction of green urban space.The study utilizes GIS technology to establish a land construction suitability evaluation system for Nankang city,which is experiencing rapid urban expansion,and outlines the preliminary UGB under the future land use simulation(FLUS)model.At the same time,considering the coupled coordination of"Production-Living-Ecological Space",and based on the suitability evaluation,we revised the preliminary UGB by combining the advantages of the patch-generating land use simulation(PLUS)model and the convex hull model to delineate the final UGB.The results show that:1)the comprehensive score of the evaluation of the suitability of the construction of land from high to low shows the distribution of the center of the city to the surrounding circle type spread,the center of the city has the highest suitability score.The results of convex hull model show that the urban expansion type of Nankang is epitaxial.In the future,the urban expansion will mainly occur in the northern part of the city.The PLUS model predicts an increase of 3359.97 hm^(2)of construction land in Nankang by 2035,of which 2022.97 hm^(2)is urban construction land.2)The FLUS model has a prediction accuracy of 86.3%and delineates a preliminary UGB area of 9215.07 hm^(2).3)We used the results of the construction suitability evaluation,PLUS model simulation results,and convex hull model predictions to revise the originally delineated UGB.The final delineated UGB area is 8895.67 hm^(2)and it is capable of meeting the future development of the study area.The results of the delineation can promote sustainable urban development,and the delineation methodology can provide a reference basis for the preparation of territorial spatial planning.

Development vs.conservation in limited urban sprawl:An integrated framework for resolving the urban boundary dilemma in China

The strategic delineation of the urban development boundary(UDB)is an effective initiative for efficient land resource allocation and for facilitating planned urban development.To align with sustainable development objectives,UDB definitions have evolved to reconcile urban development with ecological preservation.This study presents a UDB delineation framework from an integrated perspective that incorporates both demand-oriented and comprehensive constraints.Specifically,the urban construction land demand area was estimated based on population projections,meanwhile,the ecological red line(ERL)was delineated and integrated into the evaluation of the construction land suitability.Subsequently,with the demand area as the simulation target and unsuitable areas as comprehensive constraints,the UDB was delineated by simulating future land use patterns.The proposed framework was applied to Wuhan,a rapidly urbanizing city in central China,where the delineation of the UDB serves the dual purpose of managing the rapid expansion of built-up land and achieving a harmonious balance between urban development imperatives and ecological protection goals.Moreover,based on the results and analysis,policy implications for the rational spatial planning of Wuhan were proposed,encompassing the spatial patterns and scientific decision-making in ecological conservation and urban development.The results demonstrate that the efficacy of adopting a comprehensive perspective in delineating UDB effectively reconciles the competing needs of urban development and conservation.The framework and the policy insights derived in this study could inform spatial planning efforts not only in Wuhan but also in other cities facing the dilemma of urban development and ecological protection.

Urban Heat Island and Boundary Layer Structures under Hot Weather Synoptic Conditions:A Case Study of Suzhou City,China

A strong urban heat island （UHI） appeared in a hot weather episode in Suzhou City during the period from 25 July to 1 August 2007. This paper analyzes the urban heat island characteristics of Suzhou City under this hot weather episode. Both meteorological station observations and MODIS satellite observations show a strong urban heat island in this area. The maximum UHI intensity in this hot weather episode is 2.2℃, which is much greater than the summer average of 1.0℃ in this year and the 37–year （from 1970 to 2006） average of 0.35℃. The Weather Research and Forecasting （WRF） model simulation results demonstrate that the rapid urbanization processes in this area will enhance the UHI in intensity, horizontal distribution, and vertical extension. The UHI spatial distribution expands as the urban size increases. The vertical extension of UHI in the afternoon increases about 50 m higher under the year 2006 urban land cover than that under the 1986 urban land cover. The conversion from rural land use to urban land type also strengthens the local lake-land breeze circulations in this area and modifies the vertical wind speed field.

Study on Effects of Building Morphology on Urban Boundary Layer Using an Urban Canopy Model

An urban canopy model is incorporated into the Nanjing University Regional Boundary Layer Model. Temperature simulated by the urban canopy model is in better agreement with the observation, especially in the night time, than that simulated by the traditional slab model. The coupled model is used to study the effects of building morphology on urban boundary layer and meteorological environment by changing urban area, building height, and building density. It is found that when the urban area is expanded, the urban boundary layer heat flux, thermal turbu- lence, and the turbulent momentum flux and kinetic energy all increase or enhance, causing the surface air temperature to rise up. The stability of urban atmospheric stratification is affected to different extent at different times of the day. When the building height goes up, the aerodynamic roughness height, zero plane displacement height of urban area, and ratio of building height to street width all increase. Therefore, the increase in building height results in the decrease of the surface heat flux, urban surface temperature, mean wind speed, and turbulent kinetic energy in daytime. While at night, as more heat storage is released by higher buildings, thermal turbulence is more active and surface heat flux increases, leading to a higher urban temperature. As the building density increases, the aerodynamic roughness height of urban area decreases, and the effect of urban canopy on radiation strengthens. The increase of building density results in the decrease in urban surface heat flux, momentum flux, and air temperature, the increase in mean wind speed, and the weakening of turbulence in the daytime. While at night, the urban temperature increases due to the release of more heat storage.

Numerical Study of Winter Urban Boundary Layer Structure over Beijing Area

Based on the successful simulation of a typical winter urban boundary layer(UBL) process over Beijing area during the Beijing City Air Pollution Experiment (BECAPEX) in 2001by the use of MM5 coupled with urban canopy parameterization, a series of simulation experiments areperformed to investigate the effects of urban influence, surrounding terrain, and different extentof urbanization on urban boundary layer structures over Beijing area. The results of factorseparation experiments of urban influence indicate that the total effect of urban influence, whichis the synthetic effect of urban infrastructure on thermal and dynamic structures of atmosphere, isresponsible for the formation of main UBL features over Beijing area. Meanwhile, the relativeimportance of thermal and mechanical factors of urban infrastructure and interaction between thermaland mechanical factors for the formation and evolution of UBL over the Beijing area are alsoexplored. The results show that, during nighttime, mechanical factors are responsible for maincharacteristics of nocturnal urban boundary layer such as elevated inversion layer over downtownarea, smaller wind speed and stronger turbulent kinetic energy (TKE) and its behavior with peak atthe top of canopy layer, whereas in the daytime, thermal factors play dominant role in the structureof UBL, such as the intensity of mixed layer and temperature in the lower atmosphere in urban area.The interaction between mechanical and thermal factors plays an important role in the formation andevolution of UBL, but its specific characteristics of mechanisms are complex. The results ofsurrounding terrain experiment show that terrain surrounding Beijing area not only determines thecharacteristic of prevailing airflow over Beijing area, but also has obvious effect on thermalstructure of UBL, such as the distribution of elevated inversion and urban heat island, and makesthem with special localization feature. The results of different extent urbanization experiment showthat with the increase in the density and height of buildings in Beijing area, wind speed woulddecrease and TKE increase. Meanwhile, the bottom of nocturnal elevated inversion would increase indowntown area, and the intensity of urban heat island would strengthen, and even probably is obviousin the daytime.

An Analytical Study on the Urban Boundary Layer

A two-layer model based on the linearized time-independent atmospheric dynamical equations is proposed in this paper. The analytical solutions of the vertical, the horizontal motions and the potential temperature field induced by the anthropogenic source of urban surface heating are obtained, therefore the heat island circulation existing in unstable boundary layer is verified theoretically. From the analytical solutions, some conclusions can be drawn. (1) The vertical motion induced by urban heat island consists of two parts, namely, the cross-hill wave and the lee wave; (2) The cross-hill wave only exists in the unstable boundary layer, and varies with height according to exponential function law; (3) The vertical motion induced by heat island reaches the maximum at the top of the unstable boundary layer; (4) The wave generated by heat island not only propogates to the downwind district but also travels to the upwind area; (5) γ≠0 is not the necessary condition of the lee wave generation.

Urban Development Boundary Simulation Based on“Double Evaluation”and FLUS Model

The delimitation of urban development boundaries plays an important role in optimizing the nation land space.“Double evaluation”is one of the important means to study and predict the scale of new construction land in the future and to determine the spatial distribution of urban construction land.This study combines the“double evaluation”with the FLUS(Future Land-Use Simulation)model to study the delimitation of the urban development boundary of Yichang.The results show that:(1)the“double evaluation”method comprehensively considers the carrying capacity of the resource environmental bear and the suitability of urban development;(2)the FLUS model can better couple the“double evaluation”method for Land Use/Land Cover(LULC)suitability evaluation,Land Use/land Cover Change(LUCC)simulation and urban development boundary delineation,and the overall accuracy of the simulation reaches 96%;(3)according to the requirements of relevant national policies,this study divides the urban development boundary of the study area into concentrated construction areas,elastic development areas and special purpose areas.This function-based division can meet the requirements of urban flexible development,ecological protection and urban safety.This research combines the FLUS model,which is widely used in the simulation of LUCC,with the double evaluation method used in China’s new round of land and space planning to obtain the result of the urban development boundary.This result is consistent with the existing plan of the study area.

Spatially Heterogeneous Response of Carbon Storage to Land Use Changes in Pearl River Delta Urban Agglomeration, China

Carbon storage of terrestrial ecosystems plays a vital role in advancing carbon neutrality. Better understanding of how land use changes affect carbon storage in urban agglomeration will provide valuable guidance for policymakers in developing effective regional conservation policies. Taking the Pearl River Delta Urban Agglomeration(PRDUA) in China as an example, we examined the heterogeneous response of carbon storage to land use changes in 1990–2018 from a combined view of administrative units and physical entities. The results indicate that the primary change in land use was due to the expansion of construction land(5897.16 km2). The carbon storage in PRDUA decreased from 767.34 Tg C in 1990 to 725.42 Tg C in 2018 with a spatial pattern of high wings and the low middle. The carbon storage loss was largely attributed to construction land expansion(55.74%), followed by forest degradation(54.81%). Changes in carbon storage showed significant divergences in different sized cities and hierarchical boundaries. The coefficients of geographically weighted regression(GWR) reveal that the alteration in carbon storage in Guangzhou City was more responsive to changes in construction land(-0.11) compared to other cities, while that in Shenzhen was mainly affected by the dynamics of forest land(8.32). The change in carbon storage was primarily influenced by the conversion of farmland within urban extent(5.05) and the degradation of forest land in rural areas(5.82). Carbon storage changes were less sensitive to the expansion of construction land in the urban center, urban built-up area, and ex-urban built-up area, with the corresponding GWR coefficients of 0.19, 0.04, and 0.02. This study necessitates the differentiated protection strategies of carbon storage in urban agglomerations.

Exploring Smart Growth Boundaries of Urban Agglomeration with Land Use Spatial Optimization:A Case Study of Changsha-Zhuzhou-Xiangtan City Group,China

Urban agglomeration is the main spatial organization mode used by the Chinese government to promote the policy of new urbanization strategy.Hence,a better understanding of the urban growth boundary(UGB)has profound theoretical and practical significance regarding sustainable urban development.This study devised a raster-based land use spatial optimization(LUSO)framework,and utilized ant colony optimization(ACO)algorithm to delimit the smart growth boundaries of the Changsha-Zhuzhou-Xiangtan city group(CZTCG)in China.The aim of this study is to design a LUSO model to explore an optimal pattern of urban agglomeration for sustainable growth.Multi growth scenario including a single development center,multipolar development and balanced development patterns are generated by the LUSO model for the year of 2050,and the optimum spatial pattern is chosen based on objectives comparison and the present stage of economic and social development in CZTCG.The main results are listed as the following.1)It is feasible to identify the growth boundaries of the urban agglomeration using the land use spatial optimization model,and the optimal form of the spatial pattern can be defined.2)With the growth trend of the urban agglomeration gradually spreads from a single center to multi-centers and even small towns,the total optimization target performance gradually increases,which means that the traditional pie-shaped development does not meet the maximum comprehensive benefit of the city group.3)Subject to the regional social and economic development stage,absolute fair development or simply developing the central city is not conducive to promoting the coordinated development of the urban agglomeration.Gradient equalization and gradual advancement are the best choice for UGB delineation of urban agglomeration.The findings of this study would be useful to identify the UGB in CZTCG for more sustainable urban development in the future.

The Use and Abuse of Economics in Land Use Decision-Making in South Florida: An Industrial Park & Its Alternatives, 2020-2023

This paper reviews the economic methodology used to justify a proposed 357 hectare (800 acre) Industrial Park that would breach the Urban Development Boundary (UDB) in Miami-Dade County, Florida, a boundary that had been established to constrain urban sprawl and protect the surrounding wetlands and farmlands. We will examine the socio-economic setting of the region, the ownership of the farmland parcels designated to become industrial sites, and the misuse of the promoters’ narrow economic analysis. Then we shall explain and compute correctly the likely job creation based on the author’s own survey of recently constructed industrial plants similar to those proposed for this site. Rather than an industrial park, we offer instead a newly-designed multi-purpose Recreational–Ecological–Agricultural Park (REAP) & Nature Preserve which would maintain the integrity of the rural landscape, connect the densely-populated neighborhoods to the mangrove shoreline, and open nature’s treasure chest to urban Miami and the wider public.

Building Morphological Characteristics and Their Effect on the Wind in Beijing

An urban boundary layer model （UBLM） is improved by incorporating the effect of buildings with a sectional drag coefficient and a height-distributed canopy drag length scale. The improved UBLM is applied to simulate the wind fields over three typical urban blocks over the Beijing area with different height-towidth ratios. For comparisons, the wind fields over the same blocks are simulated by an urban sub-domain scale model resolving the buildings explicitly. The wind fields simulated from the two different methods are in good agreement. Then, two-dimensional building morphological characteristics and urban canopy parameters for Beijing are derived from detailed building height data. Finally, experiements are conducted to investigate the effect of buildings on the wind field in Beijing using the improved UBLM.

Diurnal Cycle of Heating and Water Vapor in the Metropolitan Area of Porto in Portugal

In this work, it is investigated the Urban Heat Island (UHI) using conservative thermodynamic variables observed by surface weather stations on the Metropolitan Area of Porto (Oporto) in Portugal, under adiabatic conditions at the surface. These conditions are usually present and associated with the development of a mixture layer into the diurnal Convective Boundary Layer (CBL), which residual layer in the late afternoon defines the initial state for the development of the nocturnal UHI. Both the spatial structure and temporal variation of potential temperature and specific humidity were considered, along the hours and days of the year, from a statistical point of view, resulting in hourly climatology. Details of the hourly evolution of the meteorological variables on the Oporto surface are presented and discussed. Results show a seasonal variation of the potential temperature up to 17°C throughout the year, which is associated with horizontal thermal gradients that can control and trigger mesoscale circulations such as sea-land, urban and valley-mountain breezes.

Modelling of urban growth boundary using geoinformatics

Urban growth boundary(UGB)is a regulatory measure of local government for delineating limits of urban growth over a period of time.Land within the UGB allows urban development,while the land outside of this boundary remains primarily non-urban.The increasing popularity of UGB demands an easy and effective method to design this boundary.This article introduces a new concept,Ideal Urban Radial Proximity(IURP),to designate a spatial UGB using geoinformatics in the digital environment.The Kolkata urban agglomeration was considered to demonstrate this model.Remotely sensed imageries of three temporal instants(years 1975,1990 and 2005)were considered to determine the information on urban extent and growth of the city.These data were then used as inputs to model the UGB for the years 2020 and 2035.The proposed model discourages scattered development and increase in urban growth rate.It preserves urban vegetation,water bodies and any other important non-urban areas within the inner city space.The IURP concept will also be useful to make the cities circular and polycentric urban blobs into a monocentric tract.Apart from the proposed model and derived results,this research also proves the potential of geoinformatics in modelling a UGB.

Turbulent flows over real heterogeneous urban surfaces:Wind tunnel experiments and Reynolds-averaged Navier-Stokes simulations

Wind tunnel experiment and steady-state Reynolds-averaged Navier-Stokes(RANS)approaches are used to examine the urban boundary layer(UBL)development above Kowloon Peninsula,Hong Kong Special Administrative Region(HKSAR).The detailed urban morphology is resolved by computational fluid dynamics(CFD)and is fabricated by 3D-printing(reduced scale)for wind tunnel experiments.Different from the majority existing results based on idealized,homogeneous urban geometries,it was found that the wind and turbulence in the UBL over downtown Kowloon are characterized by the wake behind several high-rise buildings.In particular,local maxima of turbulence kinetic energy(TKE)and shear stress are found at the roof level of those high-rise buildings.In the downstream region where the flows are already adjusted to the urban surfaces,the urban roughness sublayer(URSL)can be further divided into two layers based on the structures of the mixing length/m,effective drag Dx and dispersive stress.In the lower URSL(z<100 m),lm is rather uniform,and the Reynolds stress and dispersive stress are comparable.In the upper URSL(100 m z s 300 m),on the contrary,lm is peaked at the mid-height and the magnitude of dispersive stress is smaller than that of the Reynolds stress(<30%).The effective drag Dx is negligible in the upper URSL.