Unveiling Divergent Trends of in Soil Erosion and Soil Organic Carbon Displacement in Response to Climate and Land-Use Changes over China

Soil erosion is a widespread form of soil degradation in terrestrial ecosystems, and plays a crucial role in the dynamics of soil carbon pools. Assessing soil erosion affected by climate and land-use changes is essential for evaluating future risks and impact on soil organic carbon (SOC) displacements. The Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations have provided the basis for most such assessments, but are gradually being superseded by more recent simulations from Phase 6 (CMIP6). However, a quantitative comparison of the differences between CMIP5 (RCP8.5) and CMIP6 (SSP5-8.5) models and their impacts on soil erosion and SOC simulations has not been conducted. Therefore, this study aims to compare changes in soil erosion in response to climate change and land-use change in China based on CMIP5 and CMIP6 simulations, and assesses the impact of erosion on SOC stocks. Combining the effects of climate and land use change, the CMIP5 ensemble model projects an increase in soil erosion rates over most of China, while CMIP6 models project an average soil erosion reduction of 39 t·km−2·a−1 for the years 2031–2050 compared to the reference period. Climate and land-use changes contribute to the increased soil erosion rate by 51.75% and −28.85%, respectively, based on CMIP5, and by 32.75% and −54.01%, respectively, based on CMIP6. The CMIP6 results demonstrate less rainfall erosivity due to climate change and more pronounced mitigating effects from beneficial land-use changes on soil erosion compared to CMIP5. However, the average change in SOC displacement rate is projected to be −0.02 t·km−2·a−1 for CMIP6. The CMIP5 results suggest that soil erosion in areas other than the Tibetan Plateau will result in a rising rate of soil organic carbon displacement by 0.03 t·km−2·a−1. Therefore, it is recommended that decision-makers consider multiple dimensions such as different models and influencing factors when updating impact studies for water and soil conservation.