What characteristic defines an unconfined aquifer?

An unconfined aquifer is characterized by its direct connection to the surface, allowing it to be readily recharged by surface water. This means that precipitation, lakes, rivers, and other surface water bodies can infiltrate directly into the aquifer without any barriers. This open connection differentiates unconfined aquifers from confined aquifers, which are typically overlain by impermeable materials that prevent water from easily moving into the aquifer.

Additionally, the nature of unconfined aquifers allows for more significant variability in their water levels, reflecting changes in climate and surface water availability. This characteristic is essential for understanding how groundwater supplies can be replenished in areas that rely on unconfined aquifers for drinking water and agriculture.