Flood forecasting with a watershed model: a new method of parameter updating

Flood forecasting is of prime importance when it comes to reducing the poss ible number of lives lost to storm-induced floods. Because rainfall-runoff models are far from being perfect, hydrologists need to continuously update outputs from the rainfall-runoff model they use, in order to adapt to the actual emergency situation. This paper introduces a new updating procedure that can be combined with conceptual rainfall-runoff models for flood forec asting purposes. Conceptual models are highly nonlinear and cannot easily a ccommodate theoretically optimal methods such as Kalman filtering. Most met hods developed so far mainly update the states of the system, i.e. the cont ents of the reservoirs involved in the rainfall-runoff model. The new param eter updating method proves to be superior to a standard error correction m ethod on four watersheds whose floods can cause damage to the greater Paris area. Moreover, further developments of the approach are possible, especia lly along the idea of combining parameter updating with assimilation of add itional data such as soil moisture data from field measurements and/or from remote sensing.