Low-carbon transition pathways of power systems for Guangdong-Hongkong-Macau region in China

China has announced its ambitious targets towards carbon neutrality by 2060. The Guangdong-Hongkong-Macau (GHM) region, as a pilot demonstration area for China's reform and opening-up, faces dual pressures on providing low-carbon electricity for meeting its surging demand while limiting carbon emissions. Here, we develop an energy system optimization model with high spatio-temporal resolution that integrates investment planning and operation optimization to explore transition pathways for the GHM power system under various decarbonization scenarios. Power system operations in hourly resolution are included to quantify spatio-temporal variability of generation and demand. We show that reducing carbon emissions by 70%, 85%, and 100% in 2050 requires a total system cost of 619.1, 628.3, and 653.1 billion USD (values in 2021 USD), with an average decarbonization cost of 4.79, 5.27, and 7.11 USD per ton, respectively. Accelerating transition to carbon neutrality by 2035 incurs a total system cost of 686.9 billion USD and an average decarbonization cost of 9.11 USD per ton. Moreover, nuclear, offshore-wind, and imported electricity cover over 80% of electricity demand when achieving carbon neutrality and thus serve as cornerstones for supporting the GHM power system transition. Furthermore, we observe that a high fossil fuel price benefits emission mitigation, while reinforcing transmission networks considerably reduces system transition costs. Combing low renewable and storage prices, a high electricity import ratio, and transmission network expansion delivers a lower bound for system transition and a negative average decarbonization cost for the GHM region. Nuclear, offshore-wind, and imported electricity are essential for decarbonizing the GHM power system. Achieving carbon neutrality in the GHM power system by 2050 requires an average annual expense of 21.8 billion USD.