Development and Evaluation of a New Urban Parameterization in the Weather Research and Forecasting (WRF) Model

In mesoscale Weather Research and Forecasting (WRF) model, several urban-modeling options exist, such as Single-layer Urban Canopy Model, Building Effect Parameterization, and Building Energy Model. However, these models have limitations in terms of the choice of land surface models (LSMs) and planetary boundary layer (PBL) schemes, the associated computational expenses, and other constraints. Recently, Dy et al. (2019, ) included the urban-momentum drag effect for wind-speed modeling by developing a new multilayer model based on a modified nonlocal Asymmetric Convective Model version-2 (ACM2) PBL scheme. This urban-based ACM2 (UACM) has demonstrated a significantly improved ability over the base-ACM2 (BACM) to predict wind speed near the urban ground surface and shown an inflection point at roof level in the vertical profile of horizontal wind. In this study, urban thermal and moisture components are introduced into the Pleim-Xiu (PX) LSM and coupled with UACM. The diurnal variation in street, walls, and roof-surface temperatures is modeled using the two-layer force-restore algorithm. Simple radiation treatment is considered to account for shadowing on streets based on the solar zenith angle and building morphology. Heat and moisture flux evolution are considered explicitly on all urban surfaces. The advantages of this novel UACM are simple formulation, more efficient execution, and its requirement for only a few fundamental urban morphological parameters. The idealized and real urban data case WRF simulations are performed over the Pearl River Delta region in southern China to test the new UACM. The computationally efficient UACM is expected to perform faster for operational forecasting runs.

Automated summary

In this study, a new multilayer model based on a modified nonlocal Asymmetric Convective Model version-2 (ACM2) PBL scheme, called urban-based ACM2 (UACM), is introduced to the WRF model. It has demonstrated improved ability to predict wind speed near the urban ground surface. Urban thermal and moisture components are introduced into the Pleim-Xiu (PX) LSM and coupled with UACM. The advantages of this novel UACM are simple formulation, more efficient execution, and its requirement for only a few fundamental urban morphological parameters.