Towards a Heat-Resilient Pärnu: Integrating Sensor Networks, Satellite Data and Microscale Modelling

The Regions4Climate project, funded under Horizon Europe, supports transformative adaptation by co-developing and testing tailored climate resilience solutions in 12 European regions. One of these is Pärnu, Estonia’s coastal “summer capital,” which—by Nordic standards—is particularly vulnerable to heat due to its unique geographic and climatic setting. The case study focuses on mitigating urban heat-related risks.

Urban heat island (UHI) conditions in Pärnu had not been systematically studied before. To fill this gap, we applied a threefold methodological and approach: (1) deploying a dense real-time weather sensor network, (2) analysing satellite-derived land surface temperatures, and (3) simulating thermal comfort under various climate and land use scenarios using microscale modelling. Together, these methods allow us to observe and understand heat dynamics from regional to street level.

Since June 2023, SEI Tallinn and partners have operated 50 sensors measuring temperature and relative humidity every 10 minutes across a 10×15 km area. Sensor density is highest around the city centre with its diverse microclimatic conditions—residential areas, parks, commercial districts, and beaches—and decreases towards rural surroundings. Locations were selected following the Local Climate Zone framework, considering critical social infrastructures. Results reveal strong daytime UHI heterogeneity, with cooler temperatures in parks and coastal areas and warmer conditions in (often close-by) built-up zones. At night, a more spatially extensive UHI develops, peaking around the city centre. Real-time data are publicly accessible via a dedicated visualization tool.

To complement these measurements, 15 clear-sky warm days between 2013 and 2024 were processed using Landsat 8 data to generate 100 m resolution land surface temperature maps for midday conditions. These maps identify heat hotspots as well as the cooling influence of green and blue infrastructure, guiding hotspot selection for microscale modelling.

Four representative sites—plus a planned new train station area—were selected for ENVI-met simulations at 1 m resolution. Using the Physiological Equivalent Temperature index, we assessed current and future thermal comfort conditions and detected resilience opportunity areas in the city. Simulations quantify heat exposure and mitigation potential of increased vegetation, shade, and urban form changes under climate change.

By integrating data across scales, our approach offers specific, place-based recommendations for heat-resilient urban planning in Pärnu. It underscores the value of existing green and blue spaces, supports their expansion, advocates for heat-conscious building standards, and promotes strategies to reduce daytime heat uptake—particularly in central areas—to protect vulnerable groups and strengthen the climate resilience of Estonia’s “summer capital.”