The cooling effect of urban green infrastructure: From how to where

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandlingForskning

  • Zhaowu Yu
Global climate change and ongoing urbanization is increasing the challenges of heatwaves andthe urban heat island (UHI) effect. The cooling effect of urban green infrastructure (UGI) is oneof the important strategies that has been paid growing attention. However, the quantitative andgeneral role of UGIs is still uncertain, which limits the ability to make specific recommendationsfor land use optimization and climate adaptive decision-making. In this Ph.D. project, based on astudy of the literature, two essential aspects of the cooling effect of UGIs – “how” (coolingmechanism) and “where” (spatial pattern), are generally separated and considered. I proposed theconcepts of the urban cool island (UCI) effect (UCI extent, intensity, and efficiency) of UGIsand the threshold value of efficiency (TVoE), and highlighted the value of the TVoE-relatedstudy. Through the Ph.D. project, we found that: (1) the land surface temperature (LST) variationis not only associated with the dominant land-cover types but is also affected by the land-covertransfer pattern and dynamics. The substantially increased LST occurred mostly in areas wherethe green space areas had been transformed into built-up lands and other lands. (2) There is alogarithmic functional relationship between UGI area and cooling effect, which means thatlarger-sized UGIs produce a higher cooling effect, while there exists a threshold value. Beyondthis TVoE, the cooling efficiency drops rapidly. (3) The relationship between the shape indexand the cooling effect needs to be further analyzed. In general, the compact shape (circular andsquare) of UGIs has a stronger cooling effect, and this law is applicable to different latitudes andclimate zones. However, if the UGI area is large enough (we still cannot determine the minimumarea), an area with complex shape has a more significant cooling effect. (4) The urban forest cankeep cool/warm in summer/winter, which is generally a better way for mitigating than a body ofwater or grassland in high-latitude cities. (5) The local background climate stronglycontributes to the cooling effect of UGIs, which deserves further investigation (6) Theidealized model we proposed – an urban thermal security pattern (TSPurban) for heat controlpurposes – could help us better understand and maximize the cooling effect of UGIs and apply itin practice. In summary, the concepts we proposed and results of this Ph.D. project could deepenthe understanding of the cooling effect of UGIs, as well as provide practical information forclimate adaptive planning and management.
ForlagDepartment of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen
StatusUdgivet - 2018

ID: 201149559