Global patterns and drivers of summertime surface urban heat island cohesion

With the advancement of urbanization globally, the surface urban heat island (SUHI) effects have become increasingly pronounced, posing substantial challenges to both urban livability and public health. SUHI cohesion (SUHIC) quantifies the spatial aggregation and connectivity patterns of SUHI effects, providing critical insights into their structural organization and identifying strategic priority points for thermal regulation. However, spatial distribution and temporal tendency of SUHIC remain largely unknown, and their controls are still unclear. Therefore, spatial characteristics and temporal patterns of SUHIC from 2003 to 2022 across global cities were quantified and their drivers were further explored. There are two major findings summarized as follows. (1) The high level of SUHIC accounts for 75 % and 65 % of global cities at daytime and nighttime, respectively. The geographical distribution of SUHIC indicates significant spatial variations and climate differences, with the lowest cohesion is observed in the arid climate. SUHIC is negatively correlated to △EVI while positively correlated with △ISA and SUHII during both day and night. (2) Temporally, SUHIC of global cities shows an increasing trend from 2003 to 2022. The increasing, decreasing and stable trend account for 61 %, 25 % and 14 % at daytime worldwide, compared to 55 %, 24 % and 21 % at nighttime, respectively. The similar tendency between SUHIC and SUHII accounts for 55 % and 51 % at daytime and nighttime, respectively. About 55 % of cities exhibit an opposite trend between daytime SUHIC and △EVI (Enhanced Vegetation Index). Namely, higher vegetation difference between urban and rural areas results in greater intensity and cohesion of daytime SUHI within urban areas. This work is proposed to enhance the understanding of the aggregation and connectivity patterns of SUHI and to provide theoretical support for optimizing urban planning for sustainable city development.