International audienceA sensitivity analysis is defined by some response function and the variable with respect to which the sensitivity is evaluated. In many cases the observations have errors and it is important to estimate the impact of this error, If the state of the system is retrieved through a variational data assimilation then the observation is found only in the Optimality System (O.S.). Therefore the sensitivity analysis has to be carried out on the optimality system, in that sense sensitivity analysis is a second order property and the O.S. can be considered as a generalized model because it contains all the available information. In this presentation we will see how a sensitivity analysis can be carried out. The method is applied to water pollution. The model is derived from shallow water equations and an equation of concentration of the pollutant, it is discretized using a finite volume method and the sensitivity with respect to the source term of the pollutant is studied
