جريان المياه السطحية
Rainfall/runoff relationship are well defined within the field of hydrology. Surface runoff in hydrologic systems is generally conceptualized as occurring from pervious and impervious areas. It is the pervious runoff that is affected by antecedent moisture conditions, as runoff from impervious surfaces such as roads, sidewalks, and roofs will not be significantly affected by preceding moisture levels. Pervious surfaces (such as fields, woods, grassed areas, and open areas) are highly affected by antecedent moisture conditions, as they will produce a greater rate of runoff when they are wet than when they are dry.