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Urban Land Surface Effects on Summertime Clouds and Moist Convection in Houston Under Different Synoptic Conditions.

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Title: Urban Land Surface Effects on Summertime Clouds and Moist Convection in Houston Under Different Synoptic Conditions.
Authors: Liu, Ye1 (AUTHOR) ye.liu@pnnl.gov, Qian, Yun1 (AUTHOR) yun.qian@pnnl.gov, Kaul, Colleen M.1 (AUTHOR), Gaudet, Brian J.1 (AUTHOR), Berg, Larry K.1 (AUTHOR), Feng, Zhe1 (AUTHOR), Varble, Adam C.1 (AUTHOR), Tai, Sheng‐Lun1 (AUTHOR), Feng, Ya‐Chien1 (AUTHOR), Yang, Zhao1 (AUTHOR), Chakraborty, T. C.1 (AUTHOR), Fast, Jerome D.1 (AUTHOR)
Source: Journal of Geophysical Research. Atmospheres. 4/16/2026, Vol. 131 Issue 7, p1-21. 21p.
Subject Terms: *Atmospheric circulation, *Urban heat islands, *Cities & towns, Cloudiness, Convective clouds, Metropolitan areas, Heat convection
Geographic Terms: Houston (Tex.)
Abstract: Urban landscapes modify cloud formation and convection through complex thermodynamic and aerodynamic processes; however, their influence under different synoptic regimes remains poorly understood. This study investigates the impact of the Houston metropolitan area on summertime cloud cover and convective cell characteristics using a combination of satellite observations, radar data, and high‐resolution process‐based modeling. We isolate urban effects by comparing model simulations with realistic urban land cover against hypothetical scenarios where all urban areas are replaced by rural vegetation. Results reveal that Houston's land cover consistently enhances cloud fraction and convective activity relative to surrounding rural areas, altered by large‐scale meteorological forcing. Under weakly forced conditions, enhanced surface heat flux primarily contributes to driving low‐level convergence and vertical ascent, leading to over 8% cloud fraction increase between 2 and 6 km over the city. Under strongly forced conditions, urban influences manifest differently depending on cloud type. For non‐convective clouds, the city acts as a barrier that decelerates and lifts moist southerly inflow, increasing low cloud cover over the urban core, while decreasing it downwind the city. For convective clouds, both synoptic ascent and urbanization modulate moisture redistribution and cloud structure, producing modest cloud enhancement over the city and slight suppression over the downwind area. Urbanization exerts small changes in the intensity of the convective cells; however, it significantly decreases their duration and traveling distance. This work highlights the importance of accounting for land surface heterogeneity in modeling clouds and precipitation and demonstrates that urban impacts on clouds are highly regime‐dependent. Plain Language Summary: Urban areas can change local weather by modifying heat, moisture, and wind patterns. This study explores how Houston affects cloud formation in summer. Using satellite and radar data with high‐resolution weather model simulations, the research compares the current Houston landscape to a version where the city is replaced by natural land cover. The goal is to understand how the combined effects of buildings, roads, and heat from the city surface change clouds under different weather conditions. Houston increases cloud cover and convective activity, especially on calm days with little large‐scale weather influence. Heat from the city warms the air, drawing moisture from nearby rural areas. This moisture is lifted over the city, forming taller clouds and triggering storms that are stronger, longer lasting, and produce more rainfall than in rural areas. On days with strong winds or passing systems, the urban effect is smaller but noticeable, as buildings block or redirect winds. The effect depends on the time of day, with the largest impact on the afternoon. These findings highlight the need to consider urbanization in weather prediction. Future work will explore how building designs and surfaces can help manage these impacts. Key Points: Houston's urban surface increases summer cloud cover and convective activity, especially under weak synoptic conditionsUrban heating drives moisture convergence and updrafts that enhance cloud depth, convective intensity, and rainfall near the cityDominant urban effects vary by synoptic regime, generally mechanical under strong meteorological forcing and thermodynamics under weak forcing [ABSTRACT FROM AUTHOR]
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Database: GreenFILE
Description
Abstract:Urban landscapes modify cloud formation and convection through complex thermodynamic and aerodynamic processes; however, their influence under different synoptic regimes remains poorly understood. This study investigates the impact of the Houston metropolitan area on summertime cloud cover and convective cell characteristics using a combination of satellite observations, radar data, and high‐resolution process‐based modeling. We isolate urban effects by comparing model simulations with realistic urban land cover against hypothetical scenarios where all urban areas are replaced by rural vegetation. Results reveal that Houston's land cover consistently enhances cloud fraction and convective activity relative to surrounding rural areas, altered by large‐scale meteorological forcing. Under weakly forced conditions, enhanced surface heat flux primarily contributes to driving low‐level convergence and vertical ascent, leading to over 8% cloud fraction increase between 2 and 6 km over the city. Under strongly forced conditions, urban influences manifest differently depending on cloud type. For non‐convective clouds, the city acts as a barrier that decelerates and lifts moist southerly inflow, increasing low cloud cover over the urban core, while decreasing it downwind the city. For convective clouds, both synoptic ascent and urbanization modulate moisture redistribution and cloud structure, producing modest cloud enhancement over the city and slight suppression over the downwind area. Urbanization exerts small changes in the intensity of the convective cells; however, it significantly decreases their duration and traveling distance. This work highlights the importance of accounting for land surface heterogeneity in modeling clouds and precipitation and demonstrates that urban impacts on clouds are highly regime‐dependent. Plain Language Summary: Urban areas can change local weather by modifying heat, moisture, and wind patterns. This study explores how Houston affects cloud formation in summer. Using satellite and radar data with high‐resolution weather model simulations, the research compares the current Houston landscape to a version where the city is replaced by natural land cover. The goal is to understand how the combined effects of buildings, roads, and heat from the city surface change clouds under different weather conditions. Houston increases cloud cover and convective activity, especially on calm days with little large‐scale weather influence. Heat from the city warms the air, drawing moisture from nearby rural areas. This moisture is lifted over the city, forming taller clouds and triggering storms that are stronger, longer lasting, and produce more rainfall than in rural areas. On days with strong winds or passing systems, the urban effect is smaller but noticeable, as buildings block or redirect winds. The effect depends on the time of day, with the largest impact on the afternoon. These findings highlight the need to consider urbanization in weather prediction. Future work will explore how building designs and surfaces can help manage these impacts. Key Points: Houston's urban surface increases summer cloud cover and convective activity, especially under weak synoptic conditionsUrban heating drives moisture convergence and updrafts that enhance cloud depth, convective intensity, and rainfall near the cityDominant urban effects vary by synoptic regime, generally mechanical under strong meteorological forcing and thermodynamics under weak forcing [ABSTRACT FROM AUTHOR]
ISSN:2169897X
DOI:10.1029/2025JD045131