Impacts of Energy Transition on Life Cycle Carbon Emission and Water Consumption in Japan's Electric Sector

The United Nations (UN) proposed the Sustainable Development Goals (SDG 17) in 2015, together with The Paris Agreement endorsed by 195 signatories and state parties, to address sustainable development-related issues through ambitious and dynamic actions. The transition of the energy system is at the heart of greenhouse gas (GHGs) mitigation which is required to achieve those goals and the electric sector is the core of energy system of interest while the GHG with the largest contribution to rising temperature is carbon dioxide. However, in addition to being centrally relevant for carbon emissions, the electric sector is also an important water consumer. This study applied a hybrid life cycle assessment (LCA) model with the disaggregated electric sector to investigate the impacts on carbon emission and water consumption of the energy transition in Japan under the Sixth Strategic Energy Plan. The results indicate that the electricity mix under the Nationally Determined Contribution (NDC) scenario can cut 50% of existing carbon emissions while intensifying the water consumption by 36% from the life cycle perspective in which 30% are foreign water footprints. The Kaya identity analysis confirmed this conclusion and explained the impacts of four driving factors (population, economy, electricity intensity, and electricity mix) qualitatively and quantitatively showing that the development of technologies and continuous efforts in energy saving can provide a substantial contribution to sustainable development. The results confirmed that the efforts proposed by Japan's NDC for emission reduction through an energy transition in the electric sector can meet the expectation of achieving the Paris Agreement goals but will also pose greater challenges to the future global water demand in the energy system and regional water stress.