  We study the effect of disordered ripples on the conductivity of monolayer
graphene flakes. We calculate the relaxation times and the Boltzmann
conductivities associated with two mechanisms. First, we study the conductivity
correction due to an external in-plane magnetic field $B_\parallel$. Due to the
irregular local curvature found at graphene sheets deposited over a substrate,
$B_\parallel$ can be mapped into an effective random magnetic field
perpendicular to the graphene surface. Second, we study the electron momentum
relaxation due to intrinsic pseudo magnetic fields originated from deformations
and strain. We find that the competition between these mechanisms gives rise to
a strong anisotropy in the conductivity tensor. This result provides a new
strategy to quantitatively infer the strength of pseudo-magnetic fields in
rippled graphene flakes.
