Neighborhood-scale reductions in heatwave burden projected under a 30% minimum tree cover scenario

Abstract

Cities pursuing nature-based solutions to mitigate heatwaves need tools to estimate cooling benefits from increased tree canopy cover. This study applied the i-Tree Cool Air model and a heatwave degree day (HWDD) metric to quantify reductions in heatwave severity if neighborhoods in 10 Italian cities achieved the recommended minimum 30% tree cover. The scenario focused on establishing functional urban forests, with additional canopy placed over permeable surfaces to enhance stormwater infiltration and evapotranspiration-based cooling. Despite dry summer conditions, the 30% tree cover scenario reduced HWDD by a median of 34% (range: 16–84%), translating into comparable reductions (median 36%) in heatwave-related mortality for those aged 65 +. The tree cover generated new ecosystem service benefits valued at $10 million per city (range: $2–$62 million) through avoided stormwater runoff, air pollution removal, and carbon sequestration. Results consider drought constraints and potential irrigation trade-offs, including exacerbation of humid heat extremes.