Soil organic carbon maps and associated uncertainty at 90 m for peninsular Spain

Abstract. Human activities have significantly disrupted the global carbon cycle, leading to increased atmospheric CO₂ levels and altering ecosystems' carbon absorption capacities, with soils serving as the largest carbon reservoirs in terrestrial ecosystems. The complexity and variability of soil properties, shaped by long-term transformations, make it crucial to study these properties at various spatial and temporal scales to develop effective climate change mitigation strategies. However, integrating disparate soil databases presents challenges due to the lack of standardized protocols, necessitating collaborative efforts to standardize data collection and processing to improve the reliability of Soil Organic Carbon (SOC) estimates. This issue is particularly relevant in peninsular Spain, where variations in sampling protocols and calculation methods have resulted in significant discrepancies in SOC concentration and stock estimates. This study aimed to improve the understanding of SOC storage and distribution in peninsular Spain by focusing on two specific goals: integrating and standardizing existing soil profile databases, and modeling SOC concentrations (SOCc) and stocks (SOCs) at different depths using an ensemble machine-learning approach. The research produced four high-resolution SOC maps for peninsular Spain, detailing SOCc and SOCs at depths of 0–30 cm, 30–100 cm and the effective soil depth, along with associated uncertainties. These maps provide valuable data for national soil carbon management and contribute to compiling Spain's National Greenhouse Gas Emissions Inventory Report. Additionally, the findings support global initiatives like the Global Soil Organic Carbon Map, aligning with international efforts to improve soil carbon assessments. The soil organic carbon concentration (g/kg) maps for the 0–30 cm and 30–100 cm standard depths, along with the soil organic carbon stock (tC/ha) maps for the 0–30 cm standard depth and the effective soil depth, including their associated uncertainties, —all at a 90-meter pixel resolution— (SOCM90) are freely available at https://doi.org/10.6073/pasta/48edac6904eb1aff4c1223d970c050b4 (Durante et al., 2024).