Cooling efficiency of urban green spaces affected by heat, humidity and solar radiation
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Updated: May 13, 2026

Façade-Level Monitoring of CO2 Variability under Urban Heat Island Conditions using Low-Cost Sensor Data Loggers
Published on: December 12, 2025
Eva Beele1, Raf Aerts2, Maarten Reyniers3
1Division Forest, Nature and Landscape, Department of Earth & Environmental Sciences, KU Leuven, Celestijnenlaan 200E-2411, BE-3001, Leuven, Belgium; KU Leuven Urban Studies Institute, KU Leuven, Parkstraat 45-3609, BE-3000, Leuven, Belgium; KU Leuven Plant Institute, KU Leuven, Kasteelpark Arenberg 31-2437, BE-3001, Leuven, Belgium.
Abstract:
The urban heat island effect poses considerable risks for public health, especially during prolonged heat events. Urban green spaces can help reduce temperatures through evapotranspiration and shading, yet their cooling performance under extreme meteorological conditions remains poorly understood. This study examines the cooling efficiency of urban green spaces in a compact Belgian city using a three-year (2022-2024), quality-controlled dataset from 125 consumer grade citizen science weather stations. We quantified daily day- and night-time cooling efficiency as the slope between green space cover (trees versus grasses and shrubs) and mean temperatures and related these efficiencies to weather variables describing heat intensity, heat excess, humidity, radiation, and soil moisture. Models were run for the full growing season and for the 25% hottest days. As expected, tree cooling was strongest during the day, while grasses and shrubs cooled most at night. However, daytime tree cooling declined under humid atmospheric conditions and limited soil moisture, and in combination with high solar radiation and low heat intensity. Night-time cooling by grasses and shrubs weakened under humid atmospheric and cloudy conditions, and with higher heat intensity. Across the hottest days, high soil moisture was essential to sustain cooling. These novel insights show that green space cooling efficiency is highly context-dependent and highlight the need for soil-water management to maintain cooling benefits under increasing climate extremes.
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