The Thermal Footprint of Urbanisation: Surface Urban Heat Island and Land-Use Dynamics in Sakarya Province

This study investigates the spatial and temporal variation in Surface Urban Heat Island (SUHI) intensity and its relationship with land use across the districts of Adapazarı, Serdivan, Erenler, and Arifiye in Sakarya Province, Türkiye. The analysis draws on Landsat 5 TM, Landsat 7 ETM+, and Landsat 8 OLI/TIRS Collection 2 Level-2 imagery acquired under comparable day-and-time conditions during June, July, and August of 2000, 2006, 2012, 2018, and 2024. Using geographic information systems (GIS), median composites were generated for each study period in the Google Earth Engine environment. Land Surface Temperature (LST), the Normalized Difference Vegetation Index (NDVI), and the Normalized Difference Built-up Index (NDBI) were then calculated at a spatial resolution of 30 m. SUHI intensity was determined as the difference between the mean LST values of urban and rural areas. The findings show that built-up areas expanded over the study period, while agricultural and forested areas became increasingly fragmented. Mean LST increased from 31.77 °C in 2000 to 38.15 °C in 2024, whereas urban LST rose from 34.79 °C to 45.38 °C. Over the same period, rural LST increased from 29.84 °C to 36.11 °C, and SUHI intensity rose from 4.95 °C to 9.27 °C. The negative correlation between mean LST and NDVI (r=-0.42) and the positive correlation between mean LST and NDBI (r=0.48) highlight the contrasting effects of vegetation cover and built-up surfaces on the thermal environment. These findings underscore the need to conserve land cover, strengthen green infrastructure, and promote climate-sensitive urban development that accounts for the thermal impacts of the built environment in rapidly urbanizing, medium-sized cities. Future research using datasets with higher temporal resolution may yield more precise results. Nevertheless, this study provides a useful case study for examining SUHI dynamics and developing climate-resilient planning approaches in medium-sized cities with similar characteristics.

Surface urban heat island, land surface temperature, Landsat, NDVI, NDBI, green spaces.

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