Adapting cities to heat: an umbrella review of the effectiveness of urban cooling measures across climates

Abstract Urbanisation and global warming have increased heat in cities. Adaptation measures such as green (e.g. parks, street trees, green walls), blue (e.g. water bodies, misting), and grey (e.g. reflective materials, urban design) infrastructures can reduce urban air temperatures. However, their effectiveness depends on the surrounding climate. Here we conduct an umbrella review of 64 systematic reviews to identify the key factors influencing urban heat and to assess how the effectiveness of different adaptation measures varies across tropical, arid, continental, and temperate climates. Results indicate that adaptation measure effectiveness is primarily driven by background climate, alongside measure size, composition and surrounding urban morphology. Evidence remains limited for several measures, including cool materials, permeable pavements, shading devices and water misting. Pedestrian-level air temperature reductions reported in the reviews were analysed using multilevel meta-regression models, assessing the effects of measure type, climate zone, and their interaction. Water bodies and parks provide consistent pedestrian level daytime air temperature reduction of 2 ∘ C–2.5 ∘ C and 2.5 ∘ C–3 ∘ C regardless of temperature or precipitation. Green walls perform better in arid climates (4 ± 1.4 ∘ C) than in temperate climates (2.4 ± 0.8 ∘ C). Narrow streets perform better in tropical (5.6 ± 1.8 ∘ C) and temperate (4.7 ± 0.9 ∘ C) climates than in arid (2.6 ± 1.6 ∘ C) climates. Vegetation-based solutions perform best in hot climates but involve trade-offs between water availability and evapotranspiration efficiency. Overall, adaptation effect is stronger in hot-summer than in warm-summer climates. Key recommendations include further research on nighttime cooling, the influence of urban morphology, standardised metrics to improve comparability across studies and under-represented but promising solutions such as water misting, shading devices and cool materials. These findings can help decision-makers in selecting the most suitable solutions in the future making of cities based on each urban and climatic context.