Spatio-temporal patterns and driving forces of surface urban heat island in Taiwan

The urban heat island (UHI) phenomenon, a well-documented consequence of urbanization and industrialization, is one significant anthropogenic alteration to the Earth system. The surface UHI (SUHI) has been the subject of extensive study in recent decades owing to easy access to spatially continuous satellite data observations. However, there is a lack of comprehensive SUHI studies to understand possible underlying mechanisms and drivers of SUHI's spatial variation over Taiwan. Therefore, we aim to investigate the diurnal, seasonal, and spatial patterns of SUHI intensity (SUHII) and its driving factors over eleven cities in Taiwan from 2003 to 2020. We employed Stepwise multiple regression, Pearson's correlation technique, and land surface temperature (LST) from Aqua/Terra MODIS data to explore the relationship between SUHII and its factors. Our findings reveal that the SUHII was more intense in the daytime (from 2.21 to 6.78 °C) than at night (from 0.52 to 1.63 °C), and more intensive SUHIIs were observed in northern cities (day and night: 4.99 and 1.09 °C) than in southern cities (3.35 and 1.01 °C). The SUHII exhibited significant seasonal variation, with greater variation in the day than at night. The spatial pattern of daytime SUHII was highly correlated with normalized difference latent heat index (NDLI), vegetation, built-up intensity, and anthropogenic heat emissions. In contrast, the nighttime SUHII was closely related to built-up intensity, nighttime light, and vegetation. The factors considered in this work explained a greater fraction of the SUHII variation in the daytime (79.5 to 89.0%) than at night (44.9 to 77.0%), indicating that the underlying mechanism of the spatial patterns of nighttime SUHII was more complicated, especially in spring (day vs. night: 81.5% vs. 50.3%) and winter seasons (85.3% vs. 44.9%). This study provides crucial information on the spatio-temporal patterns and driving forces of SUHI that can aid in developing heat mitigation strategies.