Progress, knowledge gap and future directions of urban heat mitigation and adaptation research through a bibliometric review of history and evolution.

[Display omitted] • UHMA research are booming in publications, authors, institutions, and research areas. • UHMA has evolved into a transdisciplinary research field, covering many emerging areas, beyond the built environments. • UHMA research covers: (i) UHI impact assessment and cause identification, (ii) microclimate regulation and human thermal comfort, (iii) climate-related health impact and adaptation, and (iv) urban heat mitigation strategies and techniques. • This study highlights UHMA knowledge gaps in seven dimensions and UHMA development in five aspects. • This study proposes 13 suggestions for promoting the transformation from UHMA research to practice. This paper presents a bibliometric review of the history and evolution of Urban Heat Mitigation and Adaptation (UHMA) from 1989 to 2021 to identify its research progress, knowledge gaps, and future research directions. The results indicate that research on UHMA is booming and that the field has diversified over time. Existing studies have examined UHMA from the environmental, technical, health, economic, and social perspectives. Over time, UHMA has evolved into a transdisciplinary research field, covering many emerging areas beyond built environments, including materials, computer sciences, physiology, chemistry, and geosciences. Relevant UHMA topics can be divided into four research clusters: (i) UHI impact assessment and cause identification, (ii) microclimate regulation and human thermal comfort, (iii) climate-related health impact and adaptation, and (iv) urban heat mitigation strategies and techniques. This study highlights some knowledge gaps in UHMA research, including (i) overfocusing on urban heat causes, effects, and mitigation solutions; (ii) more focus on mitigation, overshadowing adaptation, and preparation; (iii) highlighting materials and vegetation, but overlooking water features and urban form; (iv) incomplete understanding of heat-related impacts; (v) focusing more on microclimate and heat islands rather than extreme heat; (vi) unsound policy, social, and economic support; and (vii) lack of actual UHMA implementation. There are also some challenges in UHMA development, including (i) the uneven distribution of publications, authors, and affiliations; (ii) topic, affiliation, and nation aggregation and bias; (iii) slow evolution in key disciplines, publications, and authors; (iv) knowledge isolation owing to tendentious academic collaboration and communication; and (v) limited journal scope and restricted methodological approaches. To overcome such challenges and enhance UHMA research and policy, 13 suggestions were made. Overall, by promoting transdisciplinary UHMA research informed by climatic sciences, scientific models, policy-relevant techniques, and socio-economic support, this study is expected to better frame UHMA research and bridge science and policy. [ABSTRACT FROM AUTHOR]