The relation between near surface soil moisture (s) and the similar media scaling factor (&agr;) is shown to follow a power law in four limiting cases: long time flux limited infiltration, short time flux limited infiltration into dry soil, long time soil limited evaporation, and long time soil limited transpiration. The exponents of these relations are derived from dimensional analysis of approximate solutions to the Richards equation. Numerical simulations of moisture fluxes indicate that a power law also describes the relation between s and &agr; at intermediate times, with exponents bounded by the short time flux limited infiltration and the long time transpiration solutions. The relative magnitudes of the derived exponents imply an increasing coefficient of variation of soil moisture during drydowns, consistent with observations from field experiments. ¿ 1998 American Geophysical Union