The prediction of the in-service behavior and durability of composite materials reinforced with natural fibers is a challenge when they are subjected to simultaneous multi-physical inputs, such as water exposure combined to mechanical loadings. Understanding the response of the material may require an accurate description of its microstructure at different scales. This work proposes an original approach devoted to generate realistic virtual microstructures in order to predict numerically the hygroscopic behavior of composites reinforced with natural fibers.