SEMINAR | Julien Lerat (CSIRO, Australia)

As an indispensable operational tool, hydrological modeling nonetheless struggles to simulate extreme events such as the 2022 floods in Australia or the 2026 drought in France. Improving these capabilities requires a fundamental revision of the structure of hydrological models — a complex task given the mathematically fragile formulation on which many models rely.

This presentation explores the possibility of formulating an entire complex hydrological model as a system of differential equations and solving it efficiently for operational use. This approach is based on the QuaSoARe analytical solution method, which approximates the model's incoming and outgoing flux functions as piecewise-linear functions. QuaSoARe also enables the computation of the gradients of the model outputs with respect to its parameters and inputs, thereby embedding the model in a differentiable framework.

The presentation presents three practical applications of the method: (1) improving the structure of the GR2M model to simulate low-flow conditions in Australia, (2) exploring changes in the parameterization of the GR4J model, and (3) computing the elasticity of discharge to climate forcings for the GR4J model.