This book introduces groundwater science in the larger context of our water cycle, also called the hydrologic cycle. The hydrologic cycle is the continuous movement of water on, above, and below the surface of the Earth as portrayed in Figure 1.
This book explains that, although groundwater accounts for 99% of our liquid fresh water, only a fraction of groundwater is accessible without over-pumping aquifers. Consequently, only a small portion of the huge groundwater reservoir can be used annually without depleting this vital resource. Yet, global groundwater extraction has increased more than fourfold in the last 50 years and has caused approximately 25% of the current 3.1 mm/year rise of the oceans (Wood and Hyndman, 2018).
Groundwater shapes the Earth through weathering and geomorphologic processes. Rivers, lakes and wetlands are surface manifestations of groundwater, exchanging flow with the groundwater reservoir that feeds them when they need water and takes some of their flow when surface water is present in excess. This book draws attention to the ways in which the surface water that we can see is connected to and supported by the hidden groundwater reservoir that is continually flowing and replenishing the hydrologic cycle. This continual flow of groundwater is a conveyor belt for natural, as well as anthropogenic (human-made), chemicals. The distribution of such chemicals governs where groundwater is suitable to drink and the capability for soil to grow crops is largely dependent on how subsurface water interacts with the soil.
This book takes the broad view of the subject “groundwater in our water cycle” to include the natural and anthropogenic chemicals transported by groundwater flow and introduce many topics that are explained comprehensively in other Groundwater Project books. Groundwater provides multiple services by: regulating surface water flow, supporting ecosystems, and providing water for all life on Earth. In short, groundwater is the Earth’s life support system.