Estimation of water requirements in agriculture at a basin scale: the case of the Aude basin

The Mediterranean area, a renowned climate change "hotspot," faces increasing water scarcity that poses a significant threat to its vital agricultural sector. As a contribution to the TALANOA-WATER project, a European-funded PRIMA project, this thesis aims to quantify the future evolution of agricultural water requirements and assess climate-driven impacts on crop yields in the Aude basin, a representative Mediterranean watershed in southern France. To achieve this, an enhanced R-based agronomic model based on the SIMETAW framework was developed, validated, and applied. The model simulates the daily soil water balance for key regional crops—including wine grapes, cereals, and fruit orchards—across 33 distinct pedoclimatic zones, driven by an ensemble of downscaled climate projections for the RCP 2.6, 4.5, and 8.5 scenarios. Crucially, the framework assesses crop performance across a range of water availability scenarios, from rainfed to fully irrigated conditions, and incorporates regulated deficit irrigation strategies for quality-oriented crops like PGI and PDO wine grapes. Results indicate a strong divergence in future irrigation demand that is highly dependent on the emissions pathway, with the basin-wide area-weighted requirement projected to increase significantly under the RCP 8.5 scenario throughout the 21st century. The analysis of yield-water production functions reveals that crop resilience to water stress is highly dependent on soil characteristics. For the near-future period (2030-2060), soil type was found to be a more dominant factor in determining yield outcomes than the differences between climate scenarios, with deep, high-capacity soils providing a crucial buffer against drought stress. These findings highlight the compounded risk of climate change and soil vulnerability in the Aude basin, underscoring the critical need for integrated, adaptive water management strategies. The developed model proves to be a robust tool for supporting policymaking by delivering key agronomic inputs for a broader and integrated hydro-agro-economic modeling framework.