Cost-effectiveness analysis of climate mitigation measures to achieve greenhouse gas reduction targets in the water sector: a case study of South Korea

The water sector remains underrepresented in climate policy despite its role in greenhouse gas mitigation. This study develops a facility-level cost-effectiveness analysis framework for South Korea's water sector by harmonizing system boundaries, capital expenditure/operation and maintenance expenditure, energy savings, grid emission factors, and technology lifetimes. By using a measure-level database, we evaluate five implementation scenarios. Results show substantial heterogeneity in cost-effectiveness. Scenario D provides the least-cost economic benchmark, achieving high reductions at negative net cost, whereas Scenario E offers a renewables-inclusive and policy-feasible roadmap, achieving a 71% reduction at 10,762 KRW/tCO2eq with a total program cost of 32.7 billion KRW. The sensitivity analysis indicates that cost-to-effectiveness ratio is most responsive to installation cost, technology lifetime, and energy-saving benefits. The proposed framework supports transparent, budget-feasible mitigation portfolio design and can be adapted to other countries by replacing country-specific emission factors, costs, facility inventories, and policy thresholds.