Abstract
Previous studies have noted that cities enhance cloud cover, but the mechanisms of urban morphological types on cloud formation remain elusive. Observations of cloud climatology from 44 major U.S. cities show that cloud enhancement increases with the street-canyon aspect ratio and decreases with building density. Here, to explain these observations, we conducted numerical experiments using urban morphology-resolving large-eddy simulations. In these simulations, urban and rural surfaces retain their respective heat-flux differences, while the moisture sources and background atmospheric water vapor are prescribed to be identical, allowing us to isolate the morphological controls on moist convection. Results show that urban morphology influences cloud formation through two mechanisms: taller buildings intensify urban-breeze circulations at the urban-rural interface, while denser buildings, acting as momentum sinks, reduce vertical turbulent transport at the urban core. These vertical motions modify the transport of moisture in the urban atmospheric boundary layer, causing different cloud amounts across different urban morphology. This study highlights the mechanistic link between urban form, vertical motions, and cloud enhancement, thus providing a basis for city-specific boundary-layer convective parameterizations in large-scale weather and climate models.
Data availability
The Python data post-processing scripts used in this study are available on Zenodo at https://doi.org/10.5281/zenodo.17683735. The full original LES output data are not publicly available due to their large size. The cloud cover is obtained from MODIS cloud masks (MYD35_L2 C6.1) from 2002 to 2020. The LCZ map is derived from multiple Earth Observation datasets.
Code availability
The FastEddy® model is publicly available via github: https://github.com/NCAR/FastEddy-model, with the urban capabilities utilized in this study incorporated starting with version 4.0.
References
United Nations. World Urbanization Prospects: The 2018 Revision. Online Edition (UN, 2018).
Qian, Y. et al. Urbanization impact on regional climate and extreme weather: current understanding, uncertainties, and future research directions. Adv. Atmos. Sci. 39, 819–860 (2022).
Liu, J. & Niyogi, D. Meta-analysis of urbanization impact on rainfall modification. Sci. Rep. 9, 7301 (2019).
Oke, T. R. The energetic basis of the urban heat island. Q. J. R. Meteorol. Soc. 108, 1–24 (1982).
Manoli, G. et al. Magnitude of urban heat islands largely explained by climate and population. Nature 573, 55–60 (2019).
Theeuwes, N. E., Barlow, J. F., Teuling, A. J., Grimmond, C. S. B. & Kotthaus, S. Persistent cloud cover over mega-cities linked to surface heat release. Npj Clim. Atmos. Sci. 2, 15 (2019).
Betts, A. K., Ball, J. H., Beljaars, A. C., Miller, M. J. & Viterbo, P. A. The land surface-atmosphere interaction: A review based on observational and global modeling perspectives. J. Geophys. Res. Atmos. 101, 7209–7225 (1996).
Ek, M. & Holtslag, A. Influence of soil moisture on boundary layer cloud development. J. Hydrometeorol. 5, 86–99 (2004).
Manoli, G. et al. Soil–plant–atmosphere conditions regulating convective cloud formation above southeastern US pine plantations. Glob. Chang. Biol. 22, 2238–2254 (2016).
Vo, T. T., Hu, L., Xue, L., Li, Q. & Chen, S. Urban effects on local cloud patterns. Proc. Natl. Acad. Sci. 120, e2216765120 (2023).
Collier, C. G. The impact of urban areas on weather. Q. J. R. Meteorol. Soc. 132, 1–25 (2006).
Oke, T. R., Mills, G., Christen, A. & Voogt, J. A. Urban climates (Cambridge University Press, 2017).
Angevine, W. M. et al. Urban–rural contrasts in mixing height and cloudiness over Nashville in 1999. J. Geophys. Res. Atmos. 108, https://doi.org/10.1029/2001JD001061 (2003).
Hidalgo, J., Pigeon, G. & Masson, V. Urban-breeze circulation during the CAPITOUL experiment: observational data analysis approach. Meteorol. Atmos. Phys. 102, 223–241 (2008).
Hidalgo, J., Masson, V. & Gimeno, L. Scaling the daytime urban heat island and urban-breeze circulation. J. Appl. Meteorol. Climatol. 49, 889–901 (2010).
Ryu, Y.-H., Baik, J.-J. & Han, J.-Y. Daytime urban breeze circulation and its interaction with convective cells. Q. J. R. Meteorol. Soc. 139, 401–413 (2013).
Huang, X. & Song, J. Urban moisture and dry islands: spatiotemporal variation patterns and mechanisms of urban air humidity changes across the globe. Environ. Res. Lett. 18, 103003 (2023).
Fan, Y., Hunt, J. C. R. & Li, Y. Buoyancy and turbulence-driven atmospheric circulation over urban areas. J. Environ. Sci. 59, 63–71 (2017).
Braham Jr, R. R., Semonin, R., Auer, A., Changnon Jr, S., Hales, J. Summary of urban effects on clouds and rain. in Metromex: A Review and Summary 141–152 (Springer, 1981).
Shepherd, J., Stallins, J., Jin, M. & Mote, T. Urbanization: impacts on clouds, precipitation, and lightning. Urban Ecosyst. Ecol. 55, 1–28 (2010).
Qu, Y., Milliez, M., Musson-Genon, L. & Carissimo, B. Numerical study of the thermal effects of buildings on low-speed airflow taking into account 3D atmospheric radiation in urban canopy. J. Wind Eng. Ind. Aerodyn. 104, 474–483 (2012).
Stewart, I. D. & Oke, T. R. Local climate zones for urban temperature studies. Bull. Am. Meteorol. Soc. 93, 1879–1900 (2012).
Carpentieri, M. & Robins, A. G. Influence of urban morphology on air flow over building arrays. J. Wind Eng. Ind. Aerodyn. 145, 61–74 (2015).
Lee, S.-H. & Park, S.-U. A vegetated urban canopy model for meteorological and environmental modelling. Bound.-Layer. Meteorol. 126, 73–102 (2008).
Li, Q., Bou-Zeid, E., Grimmond, S., Zilitinkevich, S. & Katul, G. Revisiting the relation between momentum and scalar roughness lengths of urban surfaces. Q. J. R. Meteorol. Soc. 146, 3144–3164 (2020).
Li, Q. & Bou-Zeid, E. Contrasts between momentum and scalar transport over very rough surfaces. J. Fluid Mech. 880, 32–58 (2019).
Cui, Y., Xiao, S., Giometto, M. G. & Li, Q. Effects of urban surface roughness on potential sources of microplastics in the atmospheric boundary layer. Bound. Layer. Meteorol. 186, 425–453 (2023).
Arnfield, A. J. Two decades of urban climate research: a review of turbulence, exchanges of energy and water, and the urban heat island. Int. J. Climatol. 23, 1–26 (2003).
Omidvar, H., Bou-Zeid, E., Li, Q., Mellado, J.-P. & Klein, P. Plume or bubble? Mixed-convection flow regimes and city-scale circulations. J. Fluid Mech. 897, A5 (2020).
Li, Q., Yang, J. & Yang, L. Impact of urban roughness representation on regional hydrometeorology: An idealized study. J. Geophys. Res. Atmos. 126, e2020JD033812 (2021).
Cui, Y., Xiao, S., Hu, L., Zhao, Y. & Li, Q. Mixed convection in an idealized coastal urban environment with momentum and thermal surface heterogeneities. J. Geophys. Res. Atmos. 129, e2023JD039502 (2024).
Garratt, J. R. The atmospheric boundary layer. Earth Sci. Rev. 37, 89–134 (1994).
Lin, M., Hang, J., Li, Y., Luo, Z. & Sandberg, M. Quantitative ventilation assessments of idealized urban canopy layers with various urban layouts and the same building packing density. Build. Environ. 79, 152–167 (2014).
Jing, Y. et al. Quantitative city ventilation evaluation for urban canopy under heat island circulation without geostrophic winds: Multi-scale CFD model and parametric investigations. Build. Environ. 196, 107793 (2021).
Muñoz-Esparza, D. et al. Inclusion of building-resolving capabilities into the FastEddy® GPU-LES model using an immersed body force method. J. Adv. Model. Earth Syst. 12, e2020MS002141 (2020).
Sauer, J. A. & Muñoz-Esparza, D. The FastEddy® resident-GPU accelerated large-eddy simulation framework: model formulation, dynamical-core validation and performance benchmarks. J. Adv. Model. Earth Syst. 12, e2020MS002100 (2020).
Muñoz-Esparza, D., Sauer, J. A., Jensen, A. A., Xue, L. & Grabowski, W. W. The FastEddy® resident-GPU accelerated large-eddy simulation framework: Moist dynamics extension, validation and sensitivities of modeling non-precipitating shallow cumulus clouds. J. Adv. Model. Earth Syst. 14, e2021MS002904 (2022).
Demuzere, M., Argüeso, D., Zonato, A. & Kittner, J. W2W: a Python package that injects WUDAPT’s local climate zone information in WRF. J. Open Source Softw. 7, 4432 (2022).
Du, B., Ge, M., Zeng, C., Cui, G. & Liu, Y. Influence of atmospheric stability on wind-turbine wakes with a certain hub-height turbulence intensity. Phys. Fluids 33, 055111 (2021).
Cheesewright, R. Natural Convection from a Vertical Plane Surface, Ph.D. thesis, Queen Mary University of London (1966).
Meng, Y. & Hibi, K. Turbulent measurments of the flow field around a high-rise building. Wind Eng. JAWE 1998, 55–64 (1998).
Zu, G. & Lam, K. M. Simultaneous measurement of wind velocity field and wind forces on a square tall building. Adv. Struct. Eng. 21, 2241–2258 (2018).
Hong, S.-Y., Noh, Y. & Dudhia, J. A new vertical diffusion package with an explicit treatment of entrainment processes. Mon. Weather Rev. 134, 2318–2341 (2006).
Han, J.-Y., Baik, J.-J. & Khain, A. P. A numerical study of urban aerosol impacts on clouds and precipitation. J. Atmos. Sci. 69, 504–520 (2012).
Zhang, Q., Quan, J., Tie, X., Huang, M. & Ma, X. Impact of aerosol particles on cloud formation: aircraft measurements in China. Atmos. Environ. 45, 665–672 (2011).
Trachte, K., Rollenbeck, R. & Bendix, J. Nocturnal convective cloud formation under clear-sky conditions at the eastern Andes of south Ecuador. J. Geophys. Res. Atmos. 115, https://doi.org/10.1029/2010JD014146 (2010).
Li, R., Sun, T., Ghaffarian, S., Tsamados, M. & Ni, G. GLAMOUR: GLobAl building MOrphology dataset for URban hydroclimate modelling. Sci. Data 11, 618 (2024).
Cui, Y., Hu, L., Wang, Z. & Li, Q. Urban nocturnal cooling mediated by bluespace. Theor. Appl. Climatol. 146, 277–292 (2021).
Rutledge, S. A. & Hobbs, P. The mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones. VIII: A model for the “seeder-feeder” process in warm-frontal rainbands. J. Atmos. Sci. 40, 1185–1206 (1983).
Flatau, P. J., Walko, R. L. & Cotton, W. R. Polynomial fits to saturation vapor pressure. J. Appl. Meteorol. (1988-2005) 31, 1507–1513 (1992).
Chan, S. T. & Leach, M. J. A validation of FEM3MP with Joint Urban 2003 data. J. Appl. Meteorol. Climatol. 46, 2127–2146 (2007).
Deardorff, J. W. Stratocumulus-capped mixed layers derived from a three-dimensional model. Bound.-layer. Meteorol. 18, 495–527 (1980).
Lilly, D. K. On the application of the eddy viscosity concept in the inertial sub-range of turbulence. NCAR report. https://doi.org/10.5065/D67H1GGQ (University Corporation for Atmospheric Research, 1966).
Jiang, G.-S. & Shu, C.-W. Efficient implementation of weighted ENO schemes. J. Comput. Phys. 126, 202–228 (1996).
Wicker, L. J. & Skamarock, W. C. Time-splitting methods for elastic models using forward time schemes. Mon. weather Rev. 130, 2088–2097 (2002).
Kotthaus, S. & Grimmond, C. S. B. Energy exchange in a dense urban environment–Part I: temporal variability of long-term observations in central London. Urban Clim. 10, 261–280 (2014).
Piringer, M. et al. Investigating the surface energy balance in urban areas–recent advances and future needs. Water, Air Soil Pollut. Focus 2, 1–16 (2002).
Siebesma, A. P. et al. A large eddy simulation intercomparison study of shallow cumulus convection. J. Atmos. Sci. 60, 1201–1219 (2003).
Holland, J. Z. & Rasmusson, E. M. Measurements of the atmospheric mass, energy, and momentum budgets over a 500-kilometer square of tropical ocean. Mon. Weather Rev. 101, 44–55 (1973).
Ashkenazy, Y. & Yizhaq, H. The diurnal cycle and temporal trends of surface winds. Earth Planet. Sci. Lett. 601, 117907 (2023).
Thunis, P. & Bornstein, R. Hierarchy of mesoscale flow assumptions and equations. J. Atmos. Sci. 53, 380–397 (1996).
Kusaka, H., Nishi, A., Mizunari, M. & Yokoyama, H. Urban impacts on the spatiotemporal pattern of short-duration convective precipitation in a coastal city adjacent to a mountain range. Q. J. R. Meteorol. Soc. 145, 2237–2254 (2019).
Ackerman, S. A. et al. Cloud detection with MODIS. Part II: validation. J. Atmos. Ocean. Technol. 25, 1073–1086 (2008).
An, N. & Wang, K. A comparison of MODIS-derived cloud fraction with surface observations at five SURFRAD sites. J. Appl. Meteorol. Climatol. 54, 1009–1020 (2015).
Kotarba, A. Z. A comparison of MODIS-derived cloud amount with visual surface observations. Atmos. Res. 92, 522–530 (2009).
Demuzere, M. et al. Combining expert and crowd-sourced training data to map urban form and functions for the continental US. Sci. Data 7, 264 (2020).
Zhang, W. et al. CONUS-wide LCZ map and Training Areas, figshare. https://doi.org/10.6084/M9.FIGSHARE.11416950 (2020).
Dai, C. et al. Determining boundary-layer height from aircraft measurements. Bound. layer. Meteorol. 152, 277–302 (2014).
Acknowledgements
Q.L. acknowledges support from the US National Science Foundation (NSF-CAREER-2143664, NSF-AGS-2028633, NSF-CBET-2028842). Q.L., J.A., and L.H. acknowledge funding support from the NASA Interdisciplinary Research in Earth Science (IDS)(80NSSC20K1263). Q.L. acknowledges computational resources from the National Center for Atmospheric Research (UCOR-0049 and UCOR-0083). We also appreciate the valuable discussions and insights provided by Dr. Ruidong Li of Tsinghua University.
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Y.C. and Q.L. designed and conceptualized this research. D.M. and J.S. developed the LES code, designed the LES setup, and run the simulation. L.H. provided the observational dataset. Y.C. analyzed the numerical and observational dataset and developed the analytical models. Y.C. produced the visualizations, and wrote the manuscript draft. Y.C., S.C., L.X., D.M., J.S., L.H., J.A., and Q.L. revised the manuscript.
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Cui, Y., Chen, S., Xue, L. et al. Local cloud enhancement associated with urban morphology: evidence from observations and idealized large-eddy simulations. Nat Commun (2026). https://doi.org/10.1038/s41467-026-68986-0
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DOI: https://doi.org/10.1038/s41467-026-68986-0
