  This paper proposes a new thermodynamic hypothesis that states that a
nonlinear natural system that is not isolated and involves positive feedbacks
tends to minimize its resistance to the flow process through it that is imposed
by its environment. We demonstrate that the hypothesis is consistent with flow
behavior in saturated and unsaturated porous media, river basins, and the
Earth-atmosphere system. While optimization for flow processes has been
previously discussed by a number of researchers in the literature, the unique
contribution of this work is to indicate that only the driving process is
subject to optimality when multiple flow processes are simultaneously involved
in a system.
