Title: Improving Urban Representation in High-Resolution WRF-CAMx Model and Evaluating the Effects on PBL and Ozone Prediction
Institution(s) Represented: University of Houston (Wang, Flynn)
Lead PI: Yuxuan Wang
AQRP Project Manager: Elena McDonald-Buller
TCEQ Project Liaison: Gabriel Lee
Awarded Budget: $192,960
Abstract
The Weather Research and Forecasting (WRF) model and the Comprehensive Air Quality Model with Extensions (CAMx), as used in Texas State Implementation Plan (SIP) configuration, represent the entire urban landscape of the Houston-Galveston-Brazoria (HGB) area with a single “Urban and Built-Up” category with uniform building height, surface roughness, and thermal storage across all urban grid cells within the HGB domain. As photochemical air quality models continue to increase their resolutions to kilometer and sub-kilometer scales, such a simple treatment of urban heterogeneity imposes a fundamental limit on our ability to capture the complexity of urban boundary-layer processes that directly influence and escalate the development of ozone. To address these limitations, this AQRP project aims at improving urban representations in the km-scale WRF-CAMx model through the integration of urban classification, urban morphology, and urban vegetation, which will lead to improvements in the urban planetary boundary layer (PBL) and ozone for the HGB region. In addition, Galveston Bay will be distinguished from the Gulf of America as a separate surface category to enable physically realistic representations of thermal structure and turbulence over coastal waters. Using observations from recent (2021-2023) field campaigns, which sampled the diversified landscapes of the HGB via mobile laboratories, the project will evaluate how combined refinements to urban morphological heterogeneity, urban vegetation, and different water surfaces reduce systematic biases in the PBL and ozone across the HGB region.
Specifically, the project’s objectives are to answer the following scientific questions:
- Urban classification: How does replacing the default single urban land-use category with 10 diversified Local Climate Zones (LCZs) improve the simulation of meteorological variables, PBL, ozone, and its precursors across the HGB region?
- Urban morphology and vegetation: To what extent does integrating spatially continuous urban morphology (e.g., building heights) and LCZ-specific, high-resolution urban vegetation parameters (e.g., LAI) enhance the simulation of mechanical drag, vertical mixing, dry deposition, and emissions of biogenic volatile organic compounds (BVOCs), and thereby improve the prediction of meteorological variables, PBL, ozone, and its precursors across the HGB region?
- Water body characterization: How do distinct thermal and physical representations of Galveston Bay and the Gulf of America influence the prediction of sea/bay-breeze evolution, marine PBL, and land-water pollutant transport across the HGB region?
- Integrated impacts: Does the combined refinement of urban surface characteristics (morphology and vegetation) and marine/coastal surface boundaries reduce the systematic ozone predictability gap more effectively than isolated adjustments to individual model components?
The project specifically targets the AQRP Research Priorities 2026-2027: Photochemical air quality models with the goal of improving model performance in urban planetary boundary layer height and ozone at the km scale. The urban focus of the project will lead to improvements in the SIP modeling of the HGB. The delivery of new modeling approaches and input data to improve urban classification, urban morphology, and urban vegetation representations in WRF-CAMX will be transferable to air quality modeling of other urban areas in Texas.
Technical Reports:
