  In this paper, we apply sensitivity methods to nonlinear PDEs like Burgers
and KPZ equations. These equations are known to have analytical solutions which
make easier the analysis of the sensitivity of their solutions to initial
conditions. The main result stands in the fact that the most the solution is
sensitive to the initial condition, the most it is decorrelated in space, i.e.
the values of the initial condition participate to the solution at all
distances of the wave front. This finally reveals a particular aspect of the
Burgers turbulence.
