Interactions between energy, water and carbon cycles: A new agro-eco-hydrological model to study impacts of global changes in the agropastoral Sahel

To project the future of natural resources, the modeling of continental surfaces is identified as a key tool. In this study, an emphasis is given to the modeling of water and vegetal resources, whose interactions cannot be finely apprehended by current models. To this end, an agro-eco-hydrological model is proposed to quantify both the energy, water and carbon exchanges and the plant productivity of natural and agricultural ecosystems encountered in the agropastoral Sahel: millet cultivation and shrub fallow. This model is based on the physically-based SVAT model, SiSPAT (Braud et al., 2005). It mechanistically simulates vertical energy and water transfers in the continuum, and its high capability in the Sahelian zone has been fully demonstrated (Velluet et al., 2014). Processes specific to plant functioning and to carbon cycle were now added to the model: photosynthesis, stomatal regulation, seasonal plant phenology, and organ carbon allocation. This step was carried out for the millet crop using the formalisms described in the agronomic models SARRA-H from CIRAD (Dingkuhn et al., 2003) and STICS from INRAE (Brisson et al., 1998). Similarly, the description of natural ecosystems will soon be drawn from the ecological models STEP (Mougin et al., 1986) and TREEGRASS-2 (Boulain et al., 2014); all these models dedicated to vegetation having successfully been tested in the Sahelian context. The new version of the model has now the ability to simulate the seasonal development of agrosystems as a function of climate and energy and water availability. A first phase of exploitation of the integrated model has just been carried out in order to evaluate the robustness and relevance of the developments. It was conducted at the scale of a millet plot and with the support of multi-year observations acquired at the Wankama site (Cappelaere et al., 2009). The presentation will focus on the results as well as some perspectives of applications in future climatic changes.