How is subsidence best described?

Subsidence is best described as the process that occurs when the withdrawal of groundwater leads to a decrease in the volume of the soil and rock above it, causing the ground surface to sink. This phenomenon is primarily the result of the extraction of groundwater from aquifers, which can create voids in the subsurface and reduce the support that the soil and rock provide to the surface.

In contrast, the other options present aspects that do not accurately define subsidence. The first option suggests elevation changes due to water use, which does not capture the essence of subsidence as a sinking process. The third option discusses a reduction in groundwater levels without surface effects, which fails to address the observable sinking that is a direct consequence of groundwater extraction. Finally, the fourth option mentions consistent land elevation in relation to rainfall, which is unrelated to the mechanics of subsidence and ignores the typical downward shift in land elevation that occurs due to excessive groundwater withdrawal. Thus, the best choice that encapsulates the definition of subsidence is the one that focuses explicitly on the act of withdrawing groundwater causing surface sinking.