Impacts of Urbanization on Meteorological Dynamics in Megacities

Urbanization substantially alters surface energy fluxes, boundary-layer structure and urban ventilation, with direct consequences for local climate and air quality. While numerous modelling studies have examined individual cities, a globally consistent framework to compare urban meteorological impacts across megacities is still lacking. Here, we develop a unified WRF-based diagnostic framework, built around radial urban-rural analysis, to quantify urban-induced meteorological modifications in a global catalogue of megacities using month-long simulations for May and October 2024. The set spans a wide range of climatic and geographic settings, including inland megacities (e.g. Delhi, Beijing, Paris, Cairo, Mexico City, Moscow, Dhaka, Tehran, Johannesburg) and coastal megacities (e.g. New York, Barcelona, Tokyo, Shanghai, Lagos, Los Angeles, Mumbai, Istanbul, São Paulo).

The methodology aggregates key meteorological variables such as 2-m air temperature (T_2m), 10-m wind speed (WS10) and planetary boundary-layer height (PBLH), into concentric 5-km rings from 0 to 60 km around each city centre. This radial design explicitly tracks how these meteorological fields evolve from rural surroundings towards the urban core. Urban effects are then expressed as inner-outer ring contrasts relative to a rural baseline, providing a simple, reproducible “urban-effect intensity” metric that is directly comparable across cities, seasons and model configurations.

Across the 14 megacities analysed so far, the urban core (0-15 km) is consistently warmer, more deeply mixed and less windy than the rural ring (45-60 km), with a much stronger signal over non-coastal cities. Averaged over inland sites, near-surface temperature is enhanced by ~1.8 °C during the day and ~3.6 °C at night (~12-28 % above rural), compared with only ~1.1-1.4 °C (5-8 %) over coastal cities. Daytime PBLH in non-coastal urban cores is ~230 m higher than in rural surroundings (~30 % increase), and nocturnal PBLH can be nearly doubled (~80 %), whereas coastal cities exhibit more modest enhancements (~50-90 m; ~13-18 %).

At the individual-city scale, Delhi and Moscow show the clearest extremes: daytime PBLH enhancement reaches ~526 m in Delhi and ~441 m in Moscow, with nocturnal PBLH nearly tripled (~274 %) and more than doubled (~206 %), respectively. Night-time T_2m difference is also strongest in Delhi (~6 °C), followed by Beijing, Mexico City and Moscow (>3-4 °C, >30 % above rural), while all cities show similar urban wind slow-downs of ~0.7-0.9 m s⁻¹ (~15-20 %).

Considered jointly, the temperature, PBLH and wind-speed diagnostics reveal a consistent urban signal of sustained warming, enhanced mixing depths and reduced low-level winds in urban cores, strongest in large inland megacities and muted but still evident in coastal cities. These meteorological changes are expected to strongly influence urban air quality, which we will investigate explicitly in future work.

Keywords: Megacity, Urbanisation, Meteorology, UHI and WRF