A thin layer of soil at the surface of the unsaturated zone supports much of the life on Earth. Processes occurring in the unsaturated zone affect the environment on a global scale. For instance, modifications to the soil nitrogen and carbon cycles may contribute to global climatic change. Characterizing flow and transport in the unsaturated zone is vital to understanding the hydrologic cycle.
A wide variety of scientists and engineers ply their trades within the unsaturated zone. Interests range from studying agricultural sustainability to bioremediation of contaminated soils. Regardless of their discipline, all workers in this field require a solid background in the physical, chemical, and biological aspects of unsaturated zone hydrology.