Remapping Carbon Storage Change in Retired Farmlands on the Loess Plateau in China from 2000 to 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 sequestration on the Loess Plateau, the Grain-for-Green Program (GFGP) has been implemented. Accurately quantifying carbon capture and storage (CCS) 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 to 2021. To assess the effects of the length of farmland retirement, climate, soil properties, elevation, and other factors on CCS, climate-zone-specific linear regression models were developed based on field-sampled soil data. These models were then used to map the dataset of CCS across the retired farmlands. Results indicate 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 length of farmland retirement showed a significant positive correlation with CCS, and distinct models were developed for different climatic zones to achieve high-resolution (30 m) CCS mapping. The total CCS from retired farmland on the Loess Plateau was estimated at 21.77 Tg in carbon equivalent according to the dataset, with grasslands contributing 81.10 %, followed by forestlands (11.16 %) and shrublands (7.74 %).