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Nighttime light (NTL) imagery provides valuable information for monitoring urban development, human activity, and, consequently, urban thermal environments. However, only a few studies have attempted to directly draw linkages between NTL and urban heat island (UHI) formation. Establishing associations between NTL and UHI indicators could potentially ease the process of identifying heightened thermal environments and thus pinpointing urban hotspots in need of policy interventions and strategic mitigation measures. In the present study, through clustering and correlation analysis, we study ties between NTL, surface urban heat island intensity (SUHII) and atmospheric urban heat island intensity (AUHII) in Seoul. NTL data was derived from the Suomi National Polar-Orbiting Partnership-Visible and Infrared imager/Radiometer Suite (SNPP-VIIRS), while SUHII data was obtained from the moderate resolution imaging spectroradiometer (MODIS) satellite instrument. Additionally, AUHII was computed from archived weather data collected from multiple automatic weather stations (AWSs) in Seoul. Our results show that NTL is highly positively correlated with SUHII (R > 0.86, p < 0.05) and AUHII (R > 0.68, p < 0.05). The findings highlight the potential usage of NTL as a proxy for UHI formation, simplifying the process of identifying heightened thermal areas in Seoul that may require rapid policy intervention. [ABSTRACT FROM AUTHOR]

The effects of heat waves (HW) are more pronounced in urban areas than in rural areas due to the additive effect of the urban heat island (UHI) phenomenon. However, the synergies between UHI and HW are still an open scientific question and have only been quantified for a few metropolitan cities. In the current study, we explore the synergies between UHI and HW in Seoul city. We consider summertime data from two non-consecutive years (i.e., 2012 and 2016) and ten automatic weather stations. Our results show that UHI is more intense during HW periods than non-heat wave (NHW) periods (i.e., normal summer background conditions), with a maximum UHI difference of 3.30°C and 4.50°C, between HW and NHW periods, in 2012 and 2016 respectively. Our results also show substantial variations in the synergies between UHI and HW due to land use characteristics and synoptic weather conditions; the synergies were relatively more intense in densely built areas and under low wind speed conditions. Our results contribute to our understanding of thermal risks posed by HW in urban areas and, subsequently, the health risks on urban populations. Moreover, they are of significant importance to emergency relief providers as a resource allocation guideline, for instance, regarding which areas and time of the day to prioritize during HW periods in Seoul. [ABSTRACT FROM AUTHOR]

• Extensive dataset used to study influences of wind speed and cloud coverage on UHI. • Impact of land-use and land cover characteristics on UHI are assessed. • Changes of 0.5 m/s in wind speeds are estimated to reduce UHII by 0.20 K. • Changes of 1 octa in cloud coverage are estimated to reduce UHII by 0.24 K. • Peak diurnal UHII of 1.2 K between densely built and scarcely built areas is found. Prevailing weather conditions and urban morphology are among the fundamental drivers of the radiative and turbulent exchange processes that inherently result in an urban heat island (UHI). The influence of such drivers varies with temporal changes and must be estimated using recent and sufficiently large meteorological and land-use datasets. We used the most recent in-situ temperature observations collected from a spatially extensive network of 54 automatic weather stations (AWS) gathered over a period of nine years to quantify the influence of wind speed, cloud coverage and land use characteristics on the magnitude of UHI in Seoul city. Through an analysis of variance and combined clustering techniques, we found increased UHI intensities (UHII) under low wind speeds, clear skies and densely built areas. Changes of 0.5 m/s in wind speeds and 1 octa in cloud coverage corresponded to 0.20 °C and 0.24 °C reductions in UHII, respectively. Also, statistically significant differences in peak diurnal UHII values of 1.2 °C were estimated between densely built and sparsely built areas. The obtained results shed light on the factors likely to influence UHI development in Seoul city, and fuel scientific discourse on the development of sustainable cities and effective policies for the management of the built environment. [ABSTRACT FROM AUTHOR]

• Interactions between UHI and air pollutant concentrations are explored. • UHI is positively correlated with common primary air pollutants. • UHI is negatively correlated with ground-level O 3 concentrations. • Seasonal effects are stronger in autumn and winter season than in spring. • The relationship between UHI and air pollutant concentrations is weakest in summer. Urban environments face two challenging problems that are parallel in nature but yet with compelling potential synergistic interactions; urban heat island (UHI) and air pollution. We explore these interactions using in-situ temperature and air pollution data collected from 13 monitoring stations for nine years. Through regression analysis and analysis of variance (ANOVA) tests, we found that carbon monoxide (CO), nitrogen dioxide (NO 2), sulfur dioxide (SO 2), and particulate matter (PM) show positive correlations with UHI intensity (UHII). At the same time, Ozone (O 3) was negatively correlated with UHII. Moreover, there was a substantial seasonal effect on the strength of the correlations between UHI and air pollution, with some air pollutants showing strong associations with UHI during certain seasons (i.e., winter and autumn). The strongest interactions were observed for NO 2 (R² = 0.176) and PM10 (R² = 0.596) during the wintertime and for SO 2 (R² = 0.849), CO (R² = 0.346), PM2.5 (R² = 0.695) and O 3 (R² = 0.512) during autumn. Understanding such interactions is essential for urban climate studies and our study provides a basis for scientific discussions on integrative mitigation strategies for both UHI and air pollution in Seoul city. [ABSTRACT FROM AUTHOR]