Urban Boundary Layer Height Research Articles

An urban thermal tool chain to simulate summer thermal comfort in passive urban buildings

This paper presents a simulation tool chain for the prediction of thermal comfort in passive urban buildings during summer and under heat wave conditions. The tool chain encompasses EnergyPlus building energy model and the Urban Weather Generator and UrbaWind tools to consider the impacts of the urban environment on building loads. This chain of tools is computationally efficient and does not require notable expertise for the simulations. To assess its accuracy, this simulation results are compared to in situ measurements. This paper describes the measurement setup, analyzes the measurement results and reveals a satisfactory model accuracy through a comparison to the measurement data. The average nighttime urban heat island between July and September 2020 reached 2.31 °C in the city of Lyon. Not considering the urban heat island effect (employing rural weather files) in urban thermal simulations could induce a 1 °C bias in indoor air temperature predictions. This could also result in overpredicting the cooling potential of natural ventilation during summer. Key parameters of the simulation accuracy are identified. These are the action schedule of occupants in regard to opening devices (shutters, windows and doors) and the urban boundary layer height at night.

Refined urban canopy parameters and their impacts on simulation of urbanization-induced climate change

Changes in land cover and urban canopy structure caused by urbanization have important effects on regional climate. In this study, the Weather Research and Forecasting model is used to explore the influences of urbanization on local climate change in Guangzhou, a core city in the rapid urbanization region of the Pearl River Delta of China. Global Land Cover data from 2000 and 2018 are adopted to represent urban expansion, and urban canopy parameters (UCPs) established by a novel method are incorporated to represent changes in urban density. Model results reveal that the updated land cover and refined UCPs describe the surface information more accurately. The 10-m wind speed is reduced by 1–4 m/s and the 2-m air temperature is increased by 2–4 °C in urban areas, which brings the simulation results closer to observations. In terms of surface energy balance, upward longwave radiation is increased by 14.3 W/m2 and the land surface temperature is increased by 0–25 k; hence the net all-wave radiation is decreased by 15.6 W/m2. Meanwhile, the urban boundary layer height is increased by 192.2 m on average, but along with the decreased mean wind speed, the boundary layer ventilation is reduced by 500–3500 m2/s.

Evaluation of urban surface parameterizations in the WRF model using measurements during the Texas Air Quality Study 2006 field campaign

Abstract. The performance of different urban surface parameterizations in the WRF (Weather Research and Forecasting) in simulating urban boundary layer (UBL) was investigated using extensive measurements during the Texas Air Quality Study 2006 field campaign. The extensive field measurements collected on surface (meteorological, wind profiler, energy balance flux) sites, a research aircraft, and a research vessel characterized 3-dimensional atmospheric boundary layer structures over the Houston-Galveston Bay area, providing a unique opportunity for the evaluation of the physical parameterizations. The model simulations were performed over the Houston metropolitan area for a summertime period (12–17 August) using a bulk urban parameterization in the Noah land surface model (original LSM), a modified LSM, and a single-layer urban canopy model (UCM). The UCM simulation compared quite well with the observations over the Houston urban areas, reducing the systematic model biases in the original LSM simulation by 1–2 °C in near-surface air temperature and by 200–400 m in UBL height, on average. A more realistic turbulent (sensible and latent heat) energy partitioning contributed to the improvements in the UCM simulation. The original LSM significantly overestimated the sensible heat flux (~200 W m−2) over the urban areas, resulting in warmer and higher UBL. The modified LSM slightly reduced warm and high biases in near-surface air temperature (0.5–1 °C) and UBL height (~100 m) as a result of the effects of urban vegetation. The relatively strong thermal contrast between the Houston area and the water bodies (Galveston Bay and the Gulf of Mexico) in the LSM simulations enhanced the sea/bay breezes, but the model performance in predicting local wind fields was similar among the simulations in terms of statistical evaluations. These results suggest that a proper surface representation (e.g. urban vegetation, surface morphology) and explicit parameterizations of urban physical processes are required for accurate urban atmospheric numerical modeling.