Pukyong National University

“Moisture Cycles Significantly Influence Urban Climate”: Development of the Next-Generation Urban Climate Model ‘BECLOUD’

- Research team led by Professor Kim Jae-Jin of Pukyong National University develops a next-generation CFD model that precisely simulates urban moisture and phase-change processes

- Published in the international journal <Sustainable Cities and Society>

A research team led by Professor Kim Jae-Jin and master’s student Lee Hyun-Ji from the Major in Environmental Atmospheric Sciences at Pukyong National University has developed a new urban climate model called BECLOUD (Building-rEsolving Computational fLuid dynamics model incorporating Output of Urban moisture and Dynamics), which integrates warm-cloud microphysics into a computational fluid dynamics (CFD) model with building-scale resolution.

The results of this study were published in the March issue of the international journal <Sustainable Cities and Society> (Impact Factor: 12.0), published by Elsevier.

Urban climate research has traditionally focused on analyses centered on heat and momentum, such as urban heat islands (UHI), turbulent structures, and pollutant dispersion. However, in real urban atmospheres, microphysical phase-change processes―including the condensation and evaporation of water vapor and latent heat release―have a significant impact on heat and moisture balances. In particular, under hot and humid summer conditions or during periods before and after rainfall, these phase-change processes can substantially alter local thermal environments and humidity structures.

Conventional mesoscale weather models include cloud microphysics but have limitations in accurately reproducing the complex flow structures at the building scale. In contrast, building-resolving CFD models allow for precise analysis of airflow, but processes such as moisture condensation and phase changes are often treated in a simplified manner.

To overcome these limitations, the research team developed an integrated model that combines warm-cloud microphysical processes―including the phase changes of moisture variables―with microscale turbulent structures formed by building geometries. This approach enables the quantitative simulation of moisture transport, latent heat exchange, localized humidity amplification, and cooling effects within urban spaces at the building scale.

The team confirmed that turbulent mixing and moisture evaporation occurring in densely built areas interact to induce localized changes in the thermal environment, and that this coupled effect strengthens the nonlinearity of urban climate systems. The key implication is that the urban atmosphere should be understood not simply as a heat-transfer system, but as a complex system in which energy and moisture cycles are closely interconnected.

Professor Kim Jae-Jin explained, “This study can be extended to a wide range of applications, including the evaluation of urban thermal environments, analysis of humidity changes before and after precipitation, estimation of urban evapotranspiration, and the analysis of condensation behavior under extreme weather conditions.” He added, “The most significant outcome of this research is that high-resolution urban climate simulation technology can provide a hydrological scientific basis necessary for smart city design and the development of climate adaptation infrastructure.”

This approach also shows strong potential for application in the analysis of Urban Air Mobility (UAM) operating environments. Low-altitude aerial vehicles can be affected not only by average wind speeds, but also by microscale atmospheric phenomena such as turbulence amplification around high-rise buildings, localized moisture condensation, reduced visibility, and potential cloud formation. By simultaneously considering moisture dynamics and phase-change processes at building-scale resolution, this model is expected to serve as a scientific foundation for evaluating vertiport (UAM takeoff and landing site) locations, diagnosing low-altitude weather risks, and establishing operational safety standards.

Professor Kim Jae-Jin’s research team at Pukyong National University conducted this study with support from the Korea Meteorological Administration’s project on developing core technologies for the Korean Urban Air Mobility (K-UAM) safe operation system (RS-2024-00404042). <Pukyong Today>