Estimation of soil organic carbon content and dynamics in Mediterranean climate regions considering long-term monthly climatic conditions

• Estimated SOC content in the EU Mediterranean climate zone in 2009 and 2018. • The long-term average monthly climate data effectively improved model accuracy. • The average SOC content increased by 2.41 g/kg from 2009 to 2018. • Changes in the SOC content of different land cover types were analysed. Soil organic carbon (SOC), an essential indicator of soil quality, is necessary for maintaining soil fertility, promoting crop growth and coping with global climate change. The unique climatic conditions of Mediterranean climate zones have a significant impact on SOC production and storage. Therefore, this study used random forest (RF) and light gradient boosting machine (LightGBM) algorithms to construct models. The validity and contribution of long-term average monthly climate data to estimating SOC content in Mediterranean climate zones were explored by comparing models using only Landsat image data and topographic parameters with models incorporating long-term average monthly climate data. The SOC content in the European Union Mediterranean climate zones was accurately estimated in 2009 and 2018, and its spatial and temporal distribution characteristics and the SOC dynamics under different land cover types were explored. Results showed that the introduction of long-term average monthly climate data significantly improved the prediction accuracy of the models. The R 2 value of the RF model was enhanced by 0.22, whilst the R 2 of the LightGBM model improved by 0.20–0.21. In addition, the contribution of long-term mean monthly climate data to SOC content estimation exceeded 60 %. Regarding spatial distribution, northwestern Spain had the highest SOC content of more than 100.00 g/kg. The lowest SOC contents were found in southern Portugal and southwestern Spain, which were below 5 g/kg. For temporal variation, the average SOC content in the study region increased by 2.41 g/kg between 2009 and 2018. The highest SOC content was found in tree cover and mixed leaf type (broadleaved and needleleaved), whereas the lowest SOC content was determined in irrigated or postflood cropland.