Across-Scale boundary layer processeS in complex URban Environments: the ASSURE/urbisphere/UrbanAIR observation network in Bristol, UK.

Climate change already affects most of the world’s urban population. Developing resilient urban environments requires improving both weather and climate modelling. Heterogeneity exists from street (100 m) to neighbourhood (1 km) to city (10 km) scales due to urban form and function. Hectometric-scale numerical weather prediction (NWP) may be starting to resolve neighbourhood-scale heterogeneity but how can observation networks be designed to capture spatial variation in urban climates (horizontally and vertically) to evaluate these model predictions robustly?

To address these challenges, we combine city-scale field observations, resident interviews, high-resolution numerical (Large Eddy Simulation, NWP) and wind-tunnel modelling. Three research projects (ASSURE, urbisphere, and UrbanAIR) have collaborated to design and maintain an urban observation network in the UK. The focus is on Bristol as it is compact, has representative land-use, is close to the coast, and lies in relatively low-lying complex terrain. Bristol City authorities had previously used Met Office climate simulations at 2.2 km resolution to plan for urban heat vulnerability. Both partners were engaged in our design of a network of over 40 lamp-post mounted automatic weather stations that has run since spring 2024. A network of ground-based remote sensing (Doppler wind lidars, automatic lidar ceilometers) was deployed at six sites across the city to observe boundary layer development in response to the urban surface and orography. Other observations included indoor climate, radiation, vegetation, and tracer gas dispersion experiments. The core Bristol field campaign ran from spring 2024-2025 but a sub-set of measurements is ongoing. This follows other year-long urbisphere campaigns in Berlin, Paris, Freiburg, and Heraklion.

This talk provides an overview of the observation network in the Bristol project and the data-set obtained. Key findings will be presented where field and modelling approaches were combined to design the deployment, e.g., a Virtual Doppler Lidar approach using LES, lessons learned from a testbed of a high-resolution NWP ensemble.