ABSTRACT
Arid and semi-arid vadose zones are on the frontier of hydrological understanding. This challenge has generally been ignored by soil physicists, who have concentrated on agricultural applications, as well as by hydrologists, who have generally emphasized more humid environments. The increasing pressures on water supplies in desert regions due to burgeoning populations, together with the ever-increasing use of arid vadose zones for hazardous and radioactive waste disposal, have now directed an enhanced research effort towards a better understanding of hydrological processes in this environment.
