The natural defence that could help cities beat extreme heat

In a study published in Environment International, leading researchers from Surrey’s Global Centre for Clean Air Research (GCARE) monitored temperatures across Guildford for three years to understand how different urban environments cope with heat. The team compared six types of green and blue infrastructure – woodland, lakeside, grassland, a pocket park, riverside and a green wall. They then compared temperatures with a built-up area between June 2023 and August 2025. 

During peak summer hours, all six of the green and blue sites were cooler than the built-up location. The woodland site recorded the greatest difference, at around 2.5°C cooler, followed by grassland at 2.3°C and lakeside at 2.1°C. 

Across ten extreme heat events that were analysed during the study, the woodland site was on average 4.5°C cooler during the daytime than the built-up site, with differences frequently exceeding 5-6°C during the most severe heatwaves. Grassland and lakeside were around 4°C cooler on average. 

Researchers also compared how often each location experienced heatwave conditions, defined in Surrey as temperatures reaching at least 28°C for three consecutive days. Over the three summers, the built-up site experienced 54 heatwave days, with heatwave conditions accounting for 19.6 per cent of summer daytime observations. In comparison, all six green and blue spaces experienced significantly less extreme heat. The green wall recorded the highest exposure of the six at 8.7 per cent, while the woodland area recorded no heatwave periods at all. 

As part of GCARE’s Guildford Living Lab, the study used a network of sensors to record temperature and humidity every minute at the seven locations across Guildford over three years, alongside satellite data to provide a broader picture of urban temperatures. Satellite observations also showed substantial differences in summer surface temperatures, particularly between the built-up, woodland and lakeside areas. 

While woodland showed some of the largest and most consistent temperature differences, the research team cautions that each type of green and blue infrastructure was represented by one location, meaning local conditions may have influenced the results. Future studies could examine multiple examples of each type and how their cooling effects extend into surrounding streets and neighbourhoods. 

The work was supported through RECLAIM Network Plus, GP4Streets, GreenCities, GREENIN and University Global Partnership Network-funded projects. 

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Reference: 

Khalili, S., Jones, L., & Kumar, P. (2026). Microclimatic performance of greening against urban overheating: a multiseasonal analysis using in-situ monitoring and satellite data. Environment International 215, 110452.

Notes to editors 

• Professor Prashant Kumar is available for interview; please contact mediarelations@surrey.ac.uk to arrange. 
• The full paper can be found here: https://doi.org/10.1016/j.envint.2026.110452
• Images are available upon request