Spatio-temporal identification of urban heat hotspots in Seoul using Google Earth Engine and Landsat imagery

Climate change intensifies heatwave frequency and severity, creating a critical environmental and public health challenge in urban environments. This study conducts a time-series analysis of heat-vulnerable areas (Cumulative Hotspot) in Seoul, South Korea, from 2014 to 2023 (May-September). Leveraging Google Earth Engine (GEE), Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI) were systematically derived from Landsat 8 and 9 datasets. Annual hotspots were identified using specific criteria (LST ≥ 33°C and NDVI ≤ 0.45). To overcome single-year analysis limitations and investigate structural urban heat vulnerability, this research innovatively introduces the concept of 'Cumulative Hotspot', an area experiencing heat vulnerability consecutively for three or more years or that recurs three or more times within a 10-year period. These criteria enable identification of persistent thermal stress, distinguishing it from transient phenomena. Analysis revealed Nowon-gu (10.21 km2), Dobong-gu (7.41 km2 ), and Gangseo-gu (6.56 km 2) as the consistently largest cumulative hotspot areas, with Nowon-gu approximately 5.9 times larger than the Seoul area district average. These cumulative hotspots indicate distinct, persistent heat vulnerability patterns, differing significantly from general hotspots. This long-term, time-series analysis provides valuable foundational data for developing effective and targeted urban heatwave response and adaptation policies.