Urbanisation-induced cloud enhancement over Greater Kuala Lumpur: Evidence from satellite data and WRF-UCM model

A comprehensive understanding of urban cloud dynamics is crucial, as changes in local cloud patterns impact energy and water cycles. Given the relatively limited research on urban cloud formation compared to urban precipitation, particularly in Southeast Asian cities, this study provides critical insights into the effects of urbanization on cloud formation over Greater Kuala Lumpur (GKL). Using Himawari-8 satellite observations (2016–2021) and Weather Research and Forecasting (WRF) model simulations incorporating a single-layer Urban Canopy Model (UCM), this study conducts a comprehensive analysis of urban cloudiness during the southwest monsoon (dry season, JJA) and northeast monsoon (wet season, DJF). Satellite observations reveal that urban areas in GKL consistently exhibit greater daytime cloud cover than the surrounding rural regions. At 15:00 local time (LT), peak urban cloudiness is 1.22 times greater than in rural areas during JJA and 1.24 times greater during DJF. These differences are primarily attributed to increased absorption of solar radiation and the urban heat island (UHI) effect, which enhance surface heating and convective activity. Numerical experiments further elucidate the mechanisms underlying this urban cloud enhancement. Urban areas exhibit significantly higher sensible heat fluxes (SH), with peak SH values reaching 1.4 times those of rural areas during both JJA and DJF. Consequently, the urban boundary layer height (PBLH) is consistently elevated, with average differences reaching approximately 530 m at 16:00 LT in DJF and 520 m at 18:00 LT in JJA. The diurnal evolution of PBLH closely follows SH variations, peaking around 15:00 LT. Enhanced boundary layer growth over urban regions fosters greater cloud fraction between 17:00 and 19:00 LT, reinforcing satellite-derived evidence of increased urban cloudiness. By integrating statistical and numerical approaches, this study enhances the understanding of urban cloud dynamics in tropical megacities, providing valuable insights for improving weather and climate predictions in rapidly urbanizing regions.