The development of the Nusantara Capital City (Ibu Kota Nusantara/IKN) in East Kalimantan, Indonesia, poses significant challenges to local climate stability due to rapid changes in land cover. This study aimed to analyse the spatiotemporal patterns of land cover change and the resulting thermal dynamics driven by IKN development using remote sensing data and GIS-based spatial mapping. Landsat 8/OLI imagery from 2018 and 2022 was used to classify land cover, estimate biomass using the Global Ecosystem Dynamics Investigation (GEDI) dataset, and calculate land surface temperature (LST) and urban heat island intensity (UHII). The results revealed a direct correlation between land cover change and increased LST in IKN. Between 2018 and 2022, land cover changes led to an increase in UHII from 0.09 to 1.19, transitioning from a weak to a strong heat island. The average biomass decreased from 74.25 Mg/ha in 2019 to 66.21 Mg/ha in 2022 due to massive development. Open land and dryland agriculture exhibited the highest thermal intensification, whereas mangrove forests and plantations demonstrated thermal stability. These findings highlight the need for strategic management and expansion of vegetated areas, particularly green open spaces, to mitigate urban heat and enhance climate resilience. Urban planners should integrate ecological datasets and thermal monitoring into regulations and management to ensure the successful realisation of the forest city concept underpinning the development of IKN.