Decarbonizing the electricity sector requires massive investments in generation and transmission infrastructures that may impact both water and land resources. Characterizing these effects is key to ensure a sustainable energy transition. Here, we identify and quantify the unintended consequences of decarbonizing the China Southern Power Grid, China’s second-largest grid. We show that reaching carbon neutrality by 2060 is feasible; yet, doing so requires converting 40,000 km2 of land to support solar and wind as well as tapping on rivers to build 32 GW of hydropower. The impact of wind and solar development would span across multiple sectors, since crop and grassland constitute 90% of the identified sites. The construction of new dams would carry major externalities and trickle down to nearby countries, as most dams are located in transboundary rivers. Curbing the international footprint of this decarbonization effort would require additional investments (12 billion USD) in carbon capture technologies.