Water is held on the leaf surface until it either drips off as through fall or trickles down the leaf stem finally reaching the ground as stem flow. Interception of falling rain buffers the surface against erosion. Coniferous trees tend to intercept more water than deciduous trees on an annual basis because deciduous trees drop their leaves for a period of time. Upon reaching the ground, some water infiltrates into the soil, possibly percolating down to the ground water zone or it may run across the surface as runoff. Infiltration refers to water that penetrates into the surface of soil.
Infiltration is controlled by soil texture, soil structure, vegetation and soil moisture status.
High infiltration rates occur in dry soils, with infiltration slowing as the soil becomes wet. Coarse textured soils with large well-connected pore spaces tend to have higher infiltration rates than fine textured soils. However, coarse textured soils fill more quickly than fine textured soils due to a smaller amount of total pore space in a unit volume of soil. Runoff is then generated quicker than one might have with a finer textured soil. Vegetation also affects infiltration.