What is subsidence in the context of land and water use?

Subsidence refers to the sinking or settling of the ground surface, which can occur as a result of various geological and human activities. In the context of land and water use, subsidence is primarily associated with the extraction of groundwater. When water is removed from aquifers—especially at a rate faster than it can be replenished—the soil and rock that were previously supported by the water can compact, leading to a decrease in elevation of the ground surface. This process can cause significant issues, including damage to structures, changes in drainage patterns, and increased flooding risk in areas that already face water scarcity.

The other options do not accurately depict the phenomenon of subsidence as it relates to water extraction. The expansion of the earth's surface or the raising of ground levels after drought do not address the settling or sinking aspect of subsidence, while the formation of new aquifers is a different geological process and is not a direct result of groundwater extraction. Therefore, the correct understanding of subsidence is tightly linked to the settlement of the ground due to the withdrawal of underground water.