Characterizing the Effects of Coastal Urban Land Cover on the Spatiotemporal and Microphysical Properties of Convective Cells in Houston, Texas

Coastal urban areas are increasingly vulnerable to extreme weather events, yet the complex interactions between urban landscapes and coastal meteorological processes remain poorly understood. This knowledge gap hinders accurate weather forecasting and effective urban planning in these rapidly growing regions. This study examines the impact of urban environments on convective cell characteristics in Houston's coastal region to address critical questions about how cities modify convective processes in coastal settings. In this study, Houston was divided into upwind, urban, and downwind regions based on the prevailing south-southeasterly flow, and we analyzed 22,372 convective cell tracks from KHGX NEXRAD observations for the summer of 2022. Dual-polarization radar variables were also analyzed using contoured frequency by altitude diagrams to investigate microphysical processes. This comprehensive approach allowed for a detailed examination of urban effects on convection initiation and the evolution of convective cells and precipitation patterns.

Our findings revealed regional variations in convective cell properties. The upwind region, dominated by sea breeze effects and a maritime airmass, exhibited smaller cells (42.5 km²) with moderate precipitation. The urban area showed approximately double the cell initiation frequency compared to the upwind region, and had larger cell areas (45.5 km²). The downwind region demonstrated the highest precipitation efficiency on a per cell basis (30 mm/cell) despite the lower cell density, suggesting a prolonged urban effect on convective processes. Microphysical analysis using dual-polarization radar variables revealed distinct regional variations in hydrometeor characteristics. The upwind region showed a predominance of smaller, more uniform raindrops (ZDR < 2.5 dB). Urban-influenced cells exhibited broader distributions of Z and ZDR, indicating greater variability in drop sizes and more effective collision-coalescence processes. The downwind region maintained larger droplets (ZDR up to 3.5 dB) and showed evidence of continued ice processes aloft, suggesting persistent urban effects on precipitation formation.

This study reveals significant urban influences on convective cell characteristics and microphysics in coastal environments, with effects persisting beyond the immediate urban area. These findings enhance our understanding of urban-coastal interactions in convective processes and provide crucial insights for improving numerical models for coastal regions.