Are grand tree planting initiatives meeting expectations in mitigating urban overheating during heat waves?

<p dir="ltr">Numerous cities undertakes substantial tree planting initiatives for heatwave mitigation, driven by model predictions indicating a positive mitigation impact. However, emerging studies suggest that the transpiration behavior of trees during heatwaves significantly deviates from normal. This divergence, overlooked in current climate models, introduces the possibility of inaccuracies in predicting transpiration cooling during heatwaves. In this research, 1) The universality of changed transpiration in heat wave is revealed: the study of over 700 trees of various species indicates that the transpiration of at least 65 % of the sampled trees is overestimated by conventional model during heat waves. 2) The transpiration scheme within climate model is revised to represent the new pattern. Comparison shows that conventional model overestimates the peak hour cooling efficiency of trees in heatwave by 60 %. Consequently, the effectiveness of large-scale tree-planting as a heatwave mitigation strategy may not meet expectations, emphasizing the need for strategy refinement during heatwaves.</p>