The “Grain-for-Green” project on the Loess Plateau is the largest revegetation program in the world. However, revegetation-induced land use changes can influence both water and carbon cycles, and the diverse consequences were not well understood. Therefore, the reasonability and sustainability of revegetation measures are in question. This study quantifies the impacts of revegetation-induced land use conversions on the water and carbon cycles in a typical watershed on the Loess Plateau and identifies suitable areas where revegetation of forest or grassland could benefit both soil and water conservation and carbon sequestration. We used a coupled hydro-biogeochemical model to simulate the changes of a few key components in terms of water and carbon by designing a variety of hypothetical land use conversion scenarios derived from revegetation policy. Compared to the baseline condition (land use in 2000), both sediment yield and water yield decreased substantially when replacing steep cropland with forest or grassland. Converting cropland with slopes larger than 25°, 15°, and 6° to forest (CTF) would enhance the carbon sequestration with a negligible negative effect on soil water content, while replacing cropland with grassland (CTG) would result in a decline in net primary production but with a substantial increase in soil water content (3.8%–14.9%). Compared to the baseline, the soil organic carbon would increase by 0.9%–3.2% in CTF and keep relatively stable in CTG. Through testing a variety of hypothetical revegetation scenarios, we identified potential priority areas for CTF and CTG, where revegetation may be appropriate and potentially beneficial to conserving soil and water and enhancing carbon sequestration. Our study highlights the challenges in future water and carbon coupling management under revegetation policy, and our quantitative results and identification of potential areas for revegetation could provide information to policy makers for seeking optimal management on the Loess Plateau.

黄土高原“退耕还林”工程是世界上最大的植被恢复计划。然而，重新植被引起的土地利用变化会影响水循环和碳循环，而各种后果尚不清楚。因此，植被恢复措施的合理性和可持续性受到质疑。本研究量化了黄土高原典型流域中重新植被引起的土地利用转换对水和碳循环的影响，并确定了森林或草地重新植被可能有利于水土保持和碳固存的合适区域。我们使用耦合水文-生物地球化学模型，通过设计源自重新植被政策的各种假设土地利用转换情景，模拟水和碳方面几个关键成分的变化。与基线条件（2000 年土地利用）相比，以森林或草地代替陡峭农田时，产沙量和产水量均显着下降。将坡度大于 25°、15° 和 6° 的农田转化为森林 (CTF) 将增强碳固存，对土壤含水量的负面影响可以忽略不计，而以草地替代农田 (CTG) 将导致净碳排放量下降初级生产，但土壤含水量大幅增加（3.8%–14.9%）。与基线相比，CTF土壤有机碳增加0.9%~3.2%，CTG保持相对稳定。通过测试各种假设的重新植被情景，我们确定了 CTF 和 CTG 的潜在优先领域，重新植被可能是适当的，并且可能有利于保护水土和加强碳固存。我们的研究强调了重新植被政策下未来水和碳耦合管理的挑战，我们的定量结果和对潜在重新植被区域的识别可以为政策制定者提供信息，以寻求黄土高原的最佳管理。