The Impact of Urbanization Scale on Ecological Conditions and Surface Heat Patterns: A Comparative Study of Jakarta - Semarang City

Abstract

Urbanization alters the composition and spatial distribution of built-up and vegetated surfaces, influencing urban thermal conditions. However, comparative assessments across different urbanization scales that link these surface characteristics with energy partitioning remain limited. This study compares Jakarta and Semarang City to examine differences in surface thermal and ecological conditions associated with contrasting urbanization scales. Landsat 9 imagery was used to derive land surface temperature (LST), Normalized Difference Vegetation Index (NDVI), Normalized Difference Built-up Index (NDBI), and Urban Thermal Field Variance Index (UTFVI). Random Forest classified land-cover, while Surface Energy Balance Algorithm for Land (SEBAL) estimated surface energy balance components. Regression analysis examined NDVI and NDBI relationships with UTFVI, and Mann–Whitney U tests assessed differences between cities. Jakarta had greater mean NDBI (-0,046) and lower NDVI (0,225) than Semarang City (-0,180 and 0,402, respectively). Jakarta exhibited higher mean LST (28,7 °C), with 17,95% of its area classified as very good, compared with 26,2 °C and 74,68% in Semarang City. NDBI showed a stronger relationship with UTFVI (R² ≈ 0,56) than NDVI (R² ≈ 0,32), while multiple regression indicated a stronger association between NDBI and higher UTFVI in Jakarta and between NDVI and lower UTFVI in Semarang City. Despite comparable mean net radiation, Jakarta had higher mean sensible heat flux (141,41 W/m²), whereas Semarang City had higher mean latent heat flux (142,91 W/m²). These findings demonstrate that urbanization scale affects thermal conditions through contrasting surface composition, spatial distribution, and energy partitioning, supporting context-specific heat mitigation.