Strong contributions of local background climate to the cooling effect of urban green vegetation

TLDR

Urban green vegetation is a promising strategy to mitigate the urban heat island effect, yet the influence of local background climate on its cooling performance remains poorly understood. This study proposes and applies a cooling‑effect framework to examine how local climate conditions affect UGV cooling in eight temperate‑monsoon and Mediterranean cities. The framework was implemented across eight representative cities, integrating climatic data from temperate‑monsoon and Mediterranean regions to assess UGV cooling. Results show that increased rainfall and irrigation boost grassland cooling, high humidity limits UGV cooling, wind speed strengthens tree‑covered but weakens grass‑covered UGVs in Mediterranean cities, and that a tree area of about 0.5 ha maximizes cooling efficiency, offering guidance for UGV planning.

Abstract

Abstract Utilization of urban green vegetation (UGV) has been recognized as a promising option to mitigate urban heat island (UHI) effect. While we still lack understanding of the contributions of local background climate to the cooling effect of UGV. Here we proposed and employed a cooling effect framework and selected eight typical cities located in Temperate Monsoon Climate (TMC) and Mediterranean Climate (MC) demonstrate that local climate condition largely affects the cooling effect of UGV. Specifically, we found increasing (artificial) rainfall and irrigation contribute to improving the cooling intensity of grassland in both climates, particularly in the hot-dry environment. The cities with high relative humidity would restrict the cooling effect of UGV. Increasing wind speed would significantly enhance the tree-covered while weakening the grass-covered UGVs’ cooling effect in MC cities. We also identified that, in order to achieve the most effective cooling with the smallest sized tree-covered UGV, the area of trees in both climate zones’ cities should generally be planned around 0.5 ha. The method and results enhance understanding of the cooling effect of UGVs on larger (climate) scales and provide important insights for UGV planning and management.