GROUNDWATER DEPLETION: APPROACHES AND CONSIDERATIONS FOR THE FUTURE

Worldwide, the magnitude of groundwater depletion from storage may already be large enough to constitute a measurable contributor to sea-level rise, and severe groundwater declines in many parts of the world are likely to continue in the future. As social and physical landscapes evolve, so will approaches for managing aquifer depletion.

A key to successful management is to quantify the problem. Improvements in collection and telemetry of water-level data, database management, and information system networking will facilitate future efforts to map water-level changes more comprehensively. Sequential gravity surveys conducted from satellites may directly measure changes in groundwater storage efficiently and accurately over large regions. This technique has the potential to offer comprehensive assessments of subsurface hydrologic changes, to which water managers can respond accordingly. Well-calibrated three-dimensional models will be available for more aquifer systems, making it easier to track and forecast changes in the volume of groundwater in storage. Groundwater depletion from confining units, which affects water quality as well as quantity, also will likely garner more attention.

Global climate change will profoundly affect hydrologic systems. Long-term temperature rises are expected to melt snowpacks earlier, potentially increasing the need to store water for distribution during longer dry seasons. Unchecked, groundwater depletion can exacerbate the impacts of global climate change; conversely, controlled management of groundwater depletion can contribute to its mitigation. For example, in some areas, an integrated solution may be achieved by artificially recharging early runoff, transforming depleted aquifers into subsurface “reservoirs.”

Societies respond to water-resource depletion by shifting management objectives along a continuum, from locating and developing new supplies to augmenting, conserving, and reallocating existing supplies. At the same time, societies are beginning to value water for nontraditional uses, such as maintaining instream flows for aquatic ecosystems. The challenge for hydrogeologists is to develop and apply innovative technical approaches that inform society of the impacts and tradeoffs among competing management options.