Objective China is actively promoting the integration of soil and water conservation (SWC) carbon sinks into the national voluntary greenhouse gas emission reduction trading mechanism. Scientifically and reasonably setting the baseline scenarios for such carbon sequestration projects is crucial to this endeavor. Both domestically and internationally, the potential changes in carbon stocks in the project area without implementing project measures is commonly adopted as the baseline for carbon sequestration projects, which provides the fundamental approach for setting the baseline for SWC carbon sink projects.

Methods Based on the requirements of China Certified Emission Reduction (CCER) methodology solicitation and internationally accepted practices, this study addressed the baseline issues for SWC carbon sink projects and elaborated their definition, characteristics, classification methods, and core principles. Additionally, methods for determining baseline scenarios were analyzed. Focusing on the carbon sequestration pathways of projects, the methods for setting baselines under different circumstances were elaborated in detail, and illustrated with application examples of typical measures.

Results 1) The project-level baseline established through rigorous baseline surveys was the most feasible approach. 2) Model-based prediction could enhance baseline consistency and transparency but required calibration and exhibited significant uncertainty. 3) Regional or national baselines could reduce costs and simplify demonstration, yet they lacked site-level representativeness. 4) Specific operational methods were proposed for setting baselines for each carbon sequestration pathway,categorized as "Vegetation Carbon Stock Enhancement""Erosion Reduction and Carbon Emission Abatement" and "Soil Conservation and Carbon Fixation". 5) Practical application was demonstrated through case examples.

Conclusions The project-level baseline method facilitates the quantification of the carbon sequestration benefits of SWC measures. The scientifically sound and appropriate setting of the baseline plays a decisive role in the development and integration of SWC carbon sink projects into the carbon market. Integrating SWC carbon sink projects into the carbon market contributes to climate change mitigation and lays a foundation for sustainable land management.