Pluri-annual water budget on the Seine basin : past, current and future trends

International audience ; The trajectory of the Seine basin water resources is rebuilt from the early 1900s to the 2000s before being projected at the end of the 21th century. In a first part, the long-term hydrological data of the Paris gauging stations are ana-lyzed since 1885, highlighting the effect of anthropogenic water management on the Seine River discharge. Then, a detailed water budget of the Seine Basin is pro-posed. It quantifies for the first time the water exchanges between aquifer units as well as the effect of water withdrawals on river-aquifer exchanges. Using this model, the trajectory of the system is evaluated based on a downscaled climate re-analysis of the twentieth century and a reconstruction of the land use in the early 1900s, as well as the choice of a climate projection which favors the model that reproduces best the low frequency of precipitation. The trajectory is synthesized in the form of average regimes, revealing a relative stability of the hydrosystem until today, and drastic changes in the discharge regime in the future, especially con-cerning low flow decreased amount and increased duration. Those expected changes will require the definition of an adaptation strategy even though they are rather limited in the Seine basin when compared to other French territories.