Street green space is relevant but not sufficient for adapting to growing urban heat in world cities

Cities face multiple growing climate-related risks. Identifying adaptation strategies and quantifying their effectiveness and limits is hence crucial. Street green space (SGS) receives significant attention in the urban heat adaptation space due to its potential to reduce heat load and provide additional ecosystem benefits. Yet, the majority of existing studies assessing the effectiveness of SGS are either global or very local, and typically rely on remotely-sensed surface temperature and green space density metrics. Limited evidence spanning across different urban and climate contexts exists. Here, we empirically estimate the heat stress reduction potential of SGS across global and local climate zones in 133 cities worldwide using air temperature and wet-bulb globe temperature (WBGT) daily outputs from UrbClim, a 100-m resolution urban microclimate
model, combined with a high-resolution SGS indicator, the Green View Index (GVI). We quantify a SGS cooling efficiency interquartile range of [-0.03, -0.01] °C
GV I for maximum WBGT, with substantial variation across global climate and local climatic zones. We design reality-bounded scenarios to explore possible evolutions of SGS until 2050. Combining these scenarios with the estimated cooling efficiencies, we show that ambitious yet locally feasible SGS expansion could offset 3-11% (cities interquartile range) of the projected increase in maximum WBGT under a current policies climate change scenario, and 2-7% under SSP5-(8.5), compared to a 2008-2017 climatology. These results highlight that SGS expansion is an effective yet insufficient strategy to adapt to the growing urban heat stress across cities worldwide. Conversely, reduced SGS from
administrative inaction or climate impacts on vegetation health may worsen urban heat. These findings inform about the global adaptation potential and limits of urban street green, and can support policymakers in framing SGS expansion programs into a broader portfolio of actions to tackle growing urban heat and its adverse consequences.