The soil organic carbon pool can strongly affect the carbon cycle and future global warming. However, the dependence of carbon storage on climate is currently not well understood. The uncertainties related to future soil C dynamics are relatively high and should be reduced. Different ways have been identified to improve the prediction of Earth system models. In particular, improving the role of texture and the representation of erosion on the soil organic carbon (SOC) balance are considered as important avenues of research. Both are in turn strongly dependant of the soil nature that evolves permanently throughout time under the action of climate on time scale as short as a few tens of years. Therefore we propose, i) to evaluate the changes in soil carbon and associated properties at the 2100 horizon over Mediterranean regions; ii) to implement an erosion module into the land surface model ORCHIDEE-CROP to better represent the lateral carbon, nitrogen and phosphorous fluxes in croplands over this region due to erosion; iii) to perform experiments to better understand the C dynamics of eroded soils during transport. To do so we will i) develop a statistical approach, to evaluate the link between soil classes and climate and to derive from this analysis the potential soil changes at Mediterranean scale; ii) derive the changes in carbon storage in soils for each grid cell from the obtained soil projections, and associated soil characteristics, using simulations by LPJmL and ORCHIDEE-CROP models over Mediterranean regions. iii) We will develop and evaluate an erosion module in ORCHIDEE-CROP based on the literature. Validation will be performed using a monitoring done on a site network around the Mediterranean Sea in the framework of the MASCC project. iv) Then, we will estimate, using the erosion module, the gain or the losses of nutrients and thus the quantify of inputs required to maintain fertility at those places undergoing a net decrease of nutrients due to erosion. v) To totally close the carbon budget of agricultural sector, we will estimate the C emissions due to fertiliser productions needed to compensate the effect of erosion or the modifications of fertility due to modifications of soil properties. We will also perform some experiments to better constraint the C emission from eroded soils during transport. Finally, based on these estimations, we will calculate the economic cost of inaction (nothing done to prevent soil erosion) vs. action (modification of practices to reduce erosion)

The main objective of the project is therefore to better understand the impact of soil erosion on the C balance of croplands over Mediterranean regions associated with its economic impacts. To do so, it will bring together researchers from different disciplines (agronomists, economists, land surface modellers, soil scientists, life cycle assessment specialists) and different countries (Tunisia, France, Algeria) to propose a broad view of the soil C cycle and its impact on other sectors.