Urbanization and global warming impacts of Indonesia's future capital of Nusantara on air temperature and urban heat island.

Indonesia is developing a new capital, Ibu Kota Nusantara (IKN), which is expected to become a megacity in Southeast Asia. Although promoted as a sustainable city integrated with tropical ecosystems, its potential impact on future temperature increases remains unclear. This study uses mesoscale climate projections with the official land-use plan and the SSP5-8.5 scenario to assess surface air temperature changes in and around IKN. The model simulated urban heat islands (UHIs) in the western and eastern parts of IKN, with the western UHI being strongest and slightly extending northward to rural areas owing to the southerly background wind. Results show that the global warming exerts a larger effect on temperatures than urbanization. Early nighttime temperatures increase by up to 0.78 °C from urbanization alone, 1.9 °C from global warming, and 2.54 °C when both effects are simulated in the mid-twenty-first century. Low wind conditions further amplifies the warming, especially in upwind regions. The finding provides critical insights for mitigating potential heat stress and refining spatial planning in IKN and its surrounding regions.