Unsaturated hydraulic conductivity

From Glossary of Meteorology

unsaturated hydraulic conductivity

The proportionality constant between the volumetric flux of water and the hydraulic gradient in a porous medium for cases of water content less than saturation.

Often expressed as a function of soil-water pressure head and/or water content, it includes the effects of the water-filled pore structure and the viscosity and density of the water.