Climate sensitivity of hydrological models. Impact of evapotranspiration calculation on the simulation of recent hydrological trends in France.

Hydrological models are now widely used to simulate the impacts of global warming on water resources. They are therefore credited with the ability to represent the evolution of the hydrological cycle under the effect of the increase in temperature, and in particular that of the evapotranspiration term. However, the analysis of recent hydrological trends in a large number of French basins already highlights the effect of the increase in temperature and evapotranspiration on river runoff. We are therefore seeking to evaluate and understand the climatic sensitivity of the MORDOR-SD hydrological model developed and used at EDF (Garavaglia et al. 2017). The capacity of the model to reproduce the hydrological trends observed over a large catchment dataset is analysed for different calculations and formulations of potential evapotranspiration. The results obtained suggest that, beyond the choice of formulation (very simplified as a function of temperature or complete as a function of all the climatic variables), it is the consideration of trends in solar radiation and surface albedo that makes it possible to explain the evolution of evapotranspiration and flows in France. The evolution of vegetation cover also appears to be a sensitive factor, rarely taken into account and promising for future studies.