The Weather Research and Forecasting mesoscale model coupled to a multilayer urban canopy parameterization was used to evaluate the evolution of a 3-day heat wave in New York City, New York, during the summer of 2010. Results from three simulations with different degrees of urban modeling complexity and one with an absence of urban surfaces are compared with observations. To improve the city morphology representation, building information was assimilated and the land cover land-use classification was modified. The thermal and drag effects of buildings represented in the multilayer urban canopy model improve simulations over urban regions, giving better estimates of the surface temperature and wind speed. The accuracy of the simulation is further assessed against more simplified urban parameterizations models. The nighttime excessive cooling shown by the Building Energy Parameterization is compensated for when the Building Energy Model is activated. The turbulent kinetic energy is vertically distributed when using the multilayer scheme with a maximum at the average building height, whereas turbulence production is confined to a few meters above the surface when using the simplified scheme. Evidence for the existence of horizontal roll vortices is presented, and the impact that the horizontal resolution and the time step value have on their formation is assessed.

Hong Kong is one of the most high‐rise and highly compact cities in the world. The urban land surface is highly heterogeneous, which creates low‐level convergence zones in urban areas, particularly the Kowloon Peninsula. The low‐level convergence zone is due to the combined effect of urban heat island circulation (UHIC) and sea‐land breeze circulation (SLBC) under weak northeasterly synoptic flow. To study the impacts of anthropogenic fluxes and built‐up areas on the local circulation, the Weather Research and Forecasting (WRF) mesoscale model is combined with the multilayer urban canopy building effect parameterization/building energy model (BEP/BEM) parameterization to produce a 3 day simulation of an air pollution episode in Hong Kong in September 2012. To better represent the city land surface features, building information is assimilated in the central part of the Kowloon Peninsula. The WRF‐BEP‐BEM model captures the 2 m temperature distribution and local wind rotation reasonably well but overestimates the 10 m wind speed with a mean bias error of 0.70 m/s. A dome‐shaped feature with a high level of moisture is captured in the convergence zones due to intensified UHIC and inflowing SLBC. The anthropogenic heat increases the air temperature by around 0.3°C up to 250 m, which in turn modifies the SLBC. A new drag coefficient based on λP, plan area per unit ground area, is tested. Besides the basic physical characteristics captured by the WRF‐BEP‐BEM model, the stagnation of wind in the lower level convergence zone is better captured by this approach than by the traditional constant value coefficient.

It is well known that rooftop technologies, such as cool roofs (CRs), green roofs (GRs), or rooftop photovoltaic panels (RPVPs) can significantly modify fluxes of energy and momentum in the urban canopy layer (Santamouris, 2014). Their deployment is nowadays largely adopted worldwide, with the aim of improving thermal comfort for citizens and diminishing the energy demand for heating/cooling of buildings (Lai et al., 2019). Therefore, a better understanding of the physical mechanisms driving the

A mechanical drag coefficient formulation was implemented into the Building Effect Parameterization + Building Energy Model system coupled with the mesoscale Weather Research Forecasting model to improve the representation of the wind speed in complex urban environments. Previously, this formulation had been assessed only against spatially-averaged results from computational fluid dynamical simulations in idealized urban configurations. The main objective is to evaluate its performance over a real city. The introduction of a drag coefficient that varies with the building plan-area fraction increases the accuracy of the mesoscale model in predicting surface wind speed in complex urban environments (i.e. New York City) particularly in areas with tall buildings. Additionally, a methodology to implement local building information and a new land-cover land-use distribution is proposed that improves the representation of the urban morphology.

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