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How does infiltration move precipitation into the ground?

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Diagram illustrating Earth's environmental spheres, with labeled sections showing the geosphere (land and crust), biosphere (living things), atmosphere (air), and hydrosphere (water), each extending vertically from the Earth's surface. — hydrosphere Earth's environment includes the atmosphere, the hydrosphere, the lithosphere, and the biosphere.

In the context of the hydrosphere, infiltration is the process by which precipitation enters the soil profile and moves downward.1

This movement is governed by the infiltration rate, which represents the speed at which water enters the soil. Initially, this rate is typically high, especially after a dry spell, but it decreases as rainfall continues. This reduction occurs because soil pores become clogged by particles carried down by the water and because colloidal soil particles swell as they absorb moisture.1

The efficiency of this process depends on several factors:
* Soil Texture: Infiltration rates decrease more rapidly in clay-rich soils compared to sandy soils.1
* Permeability: The ease with which water moves through soil or rock is determined by its permeability, which is influenced by grain size, pore structure, and the presence of aggregates.23
* Saturation: If the precipitation rate exceeds the soil's infiltration capacity, the surface becomes saturated, leading to overland flow rather than infiltration.12

Once water has infiltrated the soil, it may be held as moisture or continue to percolate downward due to gravity to replenish groundwater supplies.14