Abstract
Urbanization leads to distinct meteorological features of urban environments, and one the best-known is the urban heat island (UHI) effect. For megacities, these features become mesoscale phenomena (scale ≥ 10 km) that are amplified by the tropospheric feedbacks, and have substantial implications on human well-being. For the first time, a three-dimensional statistical description of the megacity-induced meteorological effects extending towards the lower troposphere for summer is acquired on a quasi-climatological timescale (a decade) based on high-resolution (1 km) simulations for Moscow with the COSMO-CLM model with and without its urban canopy model TERRA_URB. Our results confirm the features from previous observational and modeling studies, including the UHI itself, the cooling effect above established by the cross-over effect, the urban dry/moist islands and the urban breeze circulation. Particularly, the UHI shows a strong diurnal variation in terms of intensity and vertical extent between daytime (≈0.5 K/≈1.5 km) and nighttime (>3 K/≈150 m). We have discovered a systematic veering in the downwind shift of the UHI spatial pattern established by the Coriolis effect, and an enhanced stable stratification of the rural surroundings established by the urban plumes further downwind. Finally, extending the analysis to multiple summers demonstrates a substantial increase in summer precipitation (up to +25%) over the city center and its leeward side. These urban-caused mesoclimatic effects need to be taken into account in weather and climate services, including the design of future megacities.
Highlights
Essential features of urban climate are deviations of the temperature and humidity from surrounding rural environment, known as urban heat island (UHI) and urban dry/moisture islands (UDI/UMI)
Since the canopy-layer UHI and UDI/UMI intensities are considered as important for most of the studied features of urban climate, model-to-observations comparison was performed for this variables in addition to rural values of near-surface (2 m) air temperature and specific humidity
Using the COSMO-CLM mesoscale model coupled to the urban canopy scheme (UCM)
Summary
Essential features of urban climate are deviations of the temperature and humidity from surrounding rural environment, known as urban heat island (UHI) and urban dry/moisture islands (UDI/UMI). Investigation of these effects and taking them into account within the framework of different weather and climate services is especially important due to their significant environmental and social impacts. Such impacts are considered as negative due to urban-caused acceleration of climate warming in the cities [1,2,3] and amplification of the heat waves [4,5] and related heat stress [6,7]. UDI and UMI effects are described, e.g., in [15,16,17,18].
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