Abstract
Rapid urban expansion in Sukoharjo Regency due to spillover from Surakarta City has converted green spaces into built-up land, elevating surface temperatures and driving the Urban Heat Island (UHI) phenomenon. This study aims to analyze the spatial distribution of UHI (2015–2025) and evaluate the effects of the vegetation index (NDVI) and built-up index (NDBI) on UHI intensity. A spatio-temporal quantitative approach was applied using Landsat 8 data (2015 and 2025) processed via Google Earth Engine (GEE). Samples were gathered using stratified random sampling across a 6x6km fishnet grid and analyzed using multiple linear regression and Kappa accuracy tests. Results indicate a significant UHI expansion concentrated in the northern corridor (Kartasura, Baki, and Grogol). Statistically, the Very Strong UHI category expanded from 17.02% to 25.47%, with NDBI dominantly driving UHI (
R
2
= 0,434
B
= 26,838
p
< 0,05), achieving high accuracy (Overall Accuracy 90.62%, Kappa 0.883). These findings demonstrate that converting natural surfaces into impervious materials accelerates heat accumulation more strongly than vegetation cools it. This study highlights the need for stricter zoning and mandatory dense-canopy Green Open Spaces (RTH) for sustainable urban heat mitigation.