Microclimatic performance of greening against urban overheating: a multiseasonal analysis using in-situ monitoring and satellite data

Green-blue infrastructure (GBI) is increasingly promoted as a nature-based solution for mitigating urban overheating and managing heatwave events, highlighting the need for long-term monitoring evidence to support its effective implementation. This study compares cooling contrasts observed at six monitored GBI sites - woodland, lakeside, grassland, pocket park, riverside, and green wall - relative to a selected built-up reference site, using a three-year in-situ sensor network integrated with satellite-derived Land Surface Temperature (LST) data. The largest summer air temperature contrasts relative to the built-up reference during peak hours (12:00-16:00 h) were observed at the woodland, grassland, and lakeside sites, ranging from 2.1 to 2.5 °C. During the same period, air temperature contrasts of 2.1 °C were observed at the pocket park and riverside sites, while the contrast at the green wall was 1.8 °C. Satellite-based mean summer LST provided a complementary surface thermal perspective, revealing pronounced spatial contrasts, with the largest reductions observed at the woodland and lakeside extraction areas. During peak temperature events, cooling benefits declined across all GBI sites. Air temperature contrasts between the monitored GBI sites and the built-up reference varied across regional wind regimes, with contrasts at the woodland, grassland, and lakeside sites generally remaining within 2-3 °C, while greater variability was observed at the smaller monitored GBI sites. Over the three-year study period, the built-up reference recorded the highest heatwave threshold occurrence (19.6% of the summer period), while considerably lower occurrences were recorded across the monitored GBI sites (0.0-8.7%). This study provides long-term microclimatic evidence on the capacity of selected GBI settings to buffer high ambient temperatures. Although no direct epidemiological or individual exposure assessment was conducted, the observed reductions in high ambient temperatures, particularly during daytime heat peaks, provide policy-relevant microclimatic evidence for urban heat-health adaptation.