Cooling down urban green spaces in a future climate

The intensification of urban heat due to climate change poses risks to both human populations and biodiversity. Urban green spaces (UGS), such as parks and gardens, have been demonstrated to be cooler than surrounding areas. However, in a future hotter climate, it is unclear whether UGS will maintain sufficiently cool conditions to support both species and human tolerances. The study aims to investigate how climate change will affect the microclimate conditions of UGS and evaluate the effectiveness of different strategies to maintain their cooling benefits. We applied a microclimate model (UT&C) to simulate air temperature, thermal comfort and other relevant variables within 15 urban green spaces across three Swiss cities (Zurich, Geneva and Lugano) under historical and future climate conditions. All models show good predictive performance for air and surface temperatures (R² = 0.61–0.97). Future climate data for the 2080 decade was obtained from the COSMO-CLM convection permitting model under RCP 8.5 and bias-corrected to the station scale. Scenarios incorporating these vegetation parameters most relevant to thermal comfort were developed and assessed for their effectiveness in mitigating temperature increases in a future climate.

Preliminary results for Zurich show that the thermal comfort within UGS, as represented by Universal Thermal Climate Index (UTCI), is expected to increase by an average of 2.2°C by 2080 if the existing vegetation configuration in urban green spaces remains unchanged. Increasing the fraction of ground vegetation is the most effective solution, further cooling by up to 0.8 °C, although unable to offset the negative impact on thermal comfort due to climate change. Future work will confirm the generalizability of these findings with a comparison across all UGS and cities. Overall, this study provides insights into the adaptive management of green infrastructure in cities for both humans and biodiversity in the face of climate change.