Action and retroaction between climate and soil: cost in terms of global C storage in soils (CLIMSOIL)

The soil organic carbon pool can strongly affect the carbon cycle and future global warming. However, the dependence of carbon storage on climate is still not well understood. The uncertainties related to future soil C dynamic are therefore still important and different ways have been identified to improve the prediction of Earth system models. In particular, improving the role of mineralogy and the representation of erosion are considered important avenues of research. Both are in turn strongly dependant on the soil nature that evolves permanently through time under climate action. Therefore we propose: i) to assess the change in soils and associated properties at the 2100 horizon at the global scale (OT- Med); and ii) to implement an erosion module to the ORCHIDEE-CROP models to better represent the lateral carbon, nitrogen and phosphorous fluxes (BASC). To this end we will i) develop a statistical approach, to evaluate the link between soil classes and climate, and to derive the potential soil changes (OT-Med) at global scale from this analysis ; ii) derive the changes in carbon storage in soils from the obtained soil projections, and associated soil characteristics, using simulations by LPJmL (OT- Med) and ORCHIDEE-CROP models (BASC) at both French and Mediterranean scales, iii) estimate, using the erosion module, the gain or the losses of nutrients and thus the necessary inputs to maintain fertility in places facing a net decrease of nutrients due to erosion (BASC). To totally close the carbon budget of soils, 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 (BASC). 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 - BASC)

This study will provide a first investigation at broad scales of future soil properties changes beyond carbon change, and a new insight on climate change impact on carbon beyond the classically predicted direct effects of precipitation, temperature and NPP on C cycling. Moreover, it will bring together researchers from several disciplines who are not used to work on the same topic (agronomists, economists, land surface modellers, soil scientists, life cycle analysis specialists), aiming to define a broader view of the soil C cycle and its impact on other sectors. It also represents an attempt by two Labex at joining forces on joint topics as encouraged by ANR.