Wet soil sinks heat: spatial planning of irrigated trees to address heat vulnerabilities

Urban populations face increasing heat hazards driven by urbanisation and climate change, with the impacts disproportionately affecting vulnerable groups—those with greater sensitivity and limited adaptive capacity. Urban trees can offer a practical climate adaptation strategy, mitigating heat through evaporative cooling and shade mechanisms while providing outdoor heat relief for at-risk populations. In previous research, we employed ENVI-met microclimate and WRF mesoclimate models to explore how soil moisture, built environment, and tree patch sizes affect human thermal comfort under average and extreme summer conditions in Zurich, Switzerland. Building on this work, we now present a replicable framework for global application to optimise urban tree planting locations by creating a spatial score for planting priority. The framework combines opportunities mapping, identifying areas with higher rainfall runoff or reuse water availability for irrigation, with challenges mapping, targeting zones of heightened heat vulnerability. Our work emphasises the role of water resources and the limitations of passive cooling in urban climate adaptation, while offering actionable tools for urban planners and green space managers to enhance thermal comfort for those most at risk from heat-related hazards.