Remapping carbon storage change in retired farmlands on the Loess Plateau in China from 2000–2021 in high spatiotemporal resolution

Abstract. The soil organic carbon pool is a crucial component of carbon storage in terrestrial ecosystems, playing a key role in regulating the carbon cycle and mitigating atmospheric CO2 concentration increases. To combat soil degradation and enhance soil organic carbon on the Loess Plateau, the Grain-for-Green Program (GFGP) has been implemented. Accurately quantifying change in soil organic carbon stock (ΔSOC) resulting from farmland retirement is essential for informing land use management. In this study, the spatial and temporal distribution of retired farmlands on the Loess Plateau was analyzed using Landsat imagery from 1999–2021. To assess the effects of the years since retirement, climate, soil properties, elevation, and other factors on ΔSOC, climate-zone-specific multivariable linear regression models were developed based on field-sampled soil data. These models were then used to map ΔSOC across the retired farmlands. Results indicated that a total of 39 065 km2 of farmland was retired over the past two decades, with 45.61 % converted to grasslands, 29.75 % to shrublands, and 24.64 % to forestlands. The years since retirement showed a significant positive correlation with ΔSOC, and distinct models were developed for different climatic zones to achieve high-resolution (30 m) ΔSOC mapping. The total ΔSOC from retired farmland on the Loess Plateau was estimated at 21.77 Tg in carbon equivalent, with grasslands contributing 81.10 %, followed by forestlands (11.16 %) and shrublands (7.74 %). The associated datasets are freely available at 30 m resolution from 2000 to 2021 (Yang, 2025, https://doi.org/10.6084/m9.figshare.28785971).