Abstract
Soil erosion is a major pathway of physical soil organic carbon (SOC) loss and a critical threat to the permanence of land-based carbon dioxide removal (CDR). Biochar is widely recognised as a durable carbon sink, yet its hydrological effects and erosion-mitigation potential remain undervalued in CDR frameworks. Here we synthesise global evidence and long-term Mediterranean experiments to show that hydrological improvements—an enhanced soil sponge function—are not ancillary co-benefits but a core mechanism supporting carbon durability. A global meta-analysis indicates that biochar reduces runoff by 25 % and soil erosion by 16 % on average. In Mediterranean vineyards, we observed up to 65 % soil erosion rate reduction (fine-earth and coarse fragment (gravel) erosion), up to 73 % increases in stored water (up to 300 % in dry conditions), and 85 % increases in SOC with 4 % (w/w) biochar amendments. These findings imply that soil erosion reduction should be formally integrated into Monitoring, Reporting, and Verification (MRV) methodologies and/or considered in forthcoming IPCC methodology reports on CDR, carbon capture and storage (CCS), and carbon capture and utilisation (CCU) for biochar-based CDR. Explicitly accounting for erosion-mediated carbon retention would reduce permanence uncertainty and strengthen the credibility of soil-based CDR credits in emerging compliance and voluntary carbon markets. By protecting carbon stocks in topsoils and enhancing crop and vegetation productivity, biochar provides a scalable strategy for climate-resilient land management and durable carbon removal with the added benefit of preserving existing soil C stocks.