A conceptual model of deep unsaturated zones with negligible recharge

When net recharge is less than about 0.03 mm/yr, moisture movement in deep unsaturated zones at steady state will be dominated by upward movement of vapor driven by the geothermal gradient. With zero net recharge there will be a downward flow of liquid water equal to the upward vapor flux. This will produce a profile of suction potential versus depth qualitatively similar to that expected if recharge is not negligible. Consequently, the existence of a region of uniform potential is not in itself evidence of recharge.