<p>Winter fog is a defining feature of the Indo-Gangetic Plains; however, its characteristics appear to be evolving in rapidly urbanizing regions. This study investigates long-term changes in winter fog over Delhi, one of the fastest-growing megacities in the world, using 20 years (2006–2025) of METAR observations from Indira Gandhi International (IGI) Airport. Fog events are classified into general, shallow, moderate, and dense categories based on visibility thresholds, and their diurnal evolution and inter-decadal variability are examined. All fog categories exhibit a pronounced nocturnal cycle associated with radiation fog, forming after sunset, peaking during late night to pre-dawn hours, and dissipating rapidly after sunrise. However, a consistent decline in both frequency and persistence of fog is observed in the recent decade (2016–2025) compared to 2006–2015. Reductions are most prominent for shallow and moderate fog, while dense fog events also show a noticeable decrease in peak occurrence and duration during core winter months. To explore potential links between fog variability and land-surface change, land-use/land-cover transformations in the surrounding region were analysed revealing rapid urban expansion, with built-up area more than doubling over the study period and substantial reductions in agricultural and fallow land. This transition from moisture-rich, radiatively efficient surfaces to impervious urban structures is likely to influence nocturnal cooling, near-surface moisture availability, and boundary-layer mixing, all of which are important factors governing radiation fog formation and persistence. The observed reductions in fog frequency and duration are consistent with these changes. Although the observed fog decline coincides with substantial land-use/land-cover transformation, the potential contributions of synoptic variability, aerosol characteristics, and broader climatic influences were not explicitly quantified. Overall, the results suggest a transition toward a less persistent and generally weaker winter fog regime over Delhi during the recent decade. The observed changes have important implications for urban climate, air quality interactions, and aviation operations in rapidly developing megacities.</p>