Deciphering the Roles of 2-D and 3-D Urban Landscape Metrics in Diurnal Surface Thermal Environment Along Urban Gradients

The urban heat island phenomenon has posed detrimental effects on urban climate and human well-being. Various influencing factors, such as urban morphology, have been applied to reveal their influences on land surface temperature (LST). However, there exists a lack of comprehension regarding how two-dimensional (2-D) and 3-D urban morphologies influence diurnal LSTs across urban gradients. In this article, Nanjing, China was taken as the study area. Using multisource remote sensing data, we investigated the relative contributions and marginal effects of 2-D/3-D urban morphology on diurnal LSTs along urban gradients. The following results have been shown. 1) The overall impact of 2-D urban morphology on daytime LST surpassed that of 3-D urban morphology. Conversely, 3-D urban morphology exhibited a greater impact on nighttime LST. 2) During the day, the percent of building (PER_B), the percent of tree (PER_T), and the sky view factor (SVF) were the main contributors in most urban gradients. At night, SVF and PER_B ranked among the top four factors for all areas. 3) PER_T was negatively related to daytime LST, and when PER_T exceed 30%, it contributed to a stronger cooling effect. PER_B was positively correlated with daytime LST, while the correlation was reversed at night. An SVF greater than 0.9 decreased daytime LST within gradients 4 to 8, while an SVF exceeding 0.8 lowered nighttime LST across all gradients. Our findings provide crucial insights for decision-makers to develop effective strategies in mitigating the diurnal urban thermal environments.