Global analysis of sub-daily urban impacts on atmospheric variables and thermal comfort in a climate change scenario

Source abstract

Urban areas are responsible for around 70% of global greenhouse gas emissions, which contribute to climate change. At the same time, cities, and urban populations in particular, are affected by climate change. Additionally, temperature, and other atmospheric variables, such as wind and humidity, are directly influenced by urban areas and affect human thermal comfort. The urban impacts vary by city, time of day, and may be influenced by climate change. However, a global analysis of these effects is still rare for a climate change scenario. Using climate simulations of the global Conformal Cubic Atmospheric Model (CCAM) for the RCP8.5 scenario, urban impacts on the diurnal cycles of atmospheric variables were investigated. CCAM uses a state-of-the-art parameterization for the subgrid-scale urban effects. Results show significant changes in urban impacts on temperature, wind speed, and humidity, in some urban areas for individual seasons and time of the day. In the northern extra-tropics, there is a tendency for an increase in urban impacts on nighttime temperature in summer, resulting in an increase in the nighttime urban heat island intensity. In contrast, the urban impact is reduced around noon during this season in both the northern and southern extra-tropics, along with changes in humidity and wind speed which affect the thermal comfort, with a tendency towards a reduction during daytime and a smaller and less robust increase during nighttime. These results highlight the importance of global climate models with urban representation to understand the climate change impacts on the meso climate of urban areas.