Europe: URBan environments and Regional Climate Change (URB-RCC)

Cities play a fundamental role on climate at local to regional scales through modification of heat and moisture fluxes, as well as affecting local atmospheric chemistry and composition, alongside air-pollution dispersion. Vice versa, regional climate change impacts urban areas and is expected to more severely affect cities and their citizens in the upcoming decades. Simultaneously, the share of the population living in urban areas is growing, and is projected to reach about 70% of the world population up to 2050. This is especially critical in connection to extreme events, for instance heat waves with extremely high temperatures exacerbated by the urban heat island effect, in particular during night-time, with significant consequences for human health. Additionally, from the perspective of recent regional climate model developments with increasing resolution down to the city scale, proper parameterization of urban processes is starting to play an important role to understand local/regional climate change. The inclusion of the individual urban processes affecting energy balance and transport (i.e. heat, humidity, momentum fluxes) via special urban land-use parameterization of distinct local processes becom es vital to simulate the urban effects properly. This will enable improved assessment of climate change impacts in the cities and inform adaptation and/or mitigation options by urban decision-makers, as well as adequately prepare for climate related risks (e.g. heat waves, smog conditions etc.). Cities are becoming one of the most vulnerable environments under climate change. In 2013, the CORDEX community identified cities to be a prime scientific challenge. Though, until now no major collaborative efforts have happened, therefore increased cooperation dedicated to these aspects is highly relevant to the CORDEX community.

The main goal of this FPS is to understand the effect of urban areas on the regional climate, as well as the impact of regional climate change on cities, with the help of coordinated experiments with urbanized RCMs. This clearly complies with the first CORDEX FPS criterion to address regional to local scales problems and effects with local impacts, which cannot be addressed by the GCMs and is not included in the standard CORDEX framework. The proposed activities require the specific data, both for specific land-use parameterization and the observational data, which are available from the previous campaigns, to make the expected simulations and their validation complying with the second CORDEX FPS criterion. This FPS action can be supported by – and contributing to – Special IPCC Assessment Report planned for cities after AR6, WCRP Grand Challenges – Weather and Climate Extremes – on local scale, and SDG (Sustainable Development Goal) on sustainable cities (#11), climate action (#13) and health (#3), providing information for risk management in these aspects to urban stakeholders, which corresponds to the third CORDEX FPS criterion. As for the fourth criterion, urbanization is important for many groups participating in CORDEX activities and going across the CORDEX domains as big cities appear in each of them. Clearly, careful selection of targeted coordinated simulations have to be performed.