Overdrafting

Overdrafting is the process of extracting groundwater beyond the safe yield or equilibrium yield of the aquifer.

Since every groundwater basin recharges at a different rate depending upon precipitation, vegetative cover and soil conservation practises, the quantity of groundwater that can be safely pumped varies greatly among regions of the world and even within provinces. Some aquifers require a very long time to recharge and thus the process of overdrafting can have consequences of effectively drying up certain sub-surface water supplies. Subsidence occurs when excessive groundwater is extracted from rocks that support more weight when saturated. This can lead to a capacity reduction in the aquifer.^[1]

Effects on climate

Aquifer drawdown or overdrafting and the pumping of fossil water may be a contributing factor to sea-level rise.^[2] By increasing the amount of moisture available to fall as precipitation, severe weather events are more likely to occur. To some extent moisture in the atmosphere accelerates the probability of a global warming event. The correlation coefficient is not yet scientifically determined.

Accelerated decline in subterranean reservoirs

According to a 2013 report by research hydrologist, Leonard F. Konikow, ^[3]at the United States Geological Survey (USGC), the depletion of the Ogallala Aquifer between 2001–2008, inclusive, is about 32 percent of the cumulative depletion during the entire 20th century (Konikow 2013:22)."^[3] In the United States, the biggest users of water from aquifers include agricultural irrigation and oil and coal extraction.^[4]"Cumulative total groundwater depletion in the United States accelerated in the late 1940s and continued at an almost steady linear rate through the end of the century. In addition to widely recognized environmental consequences, groundwater depletion also adversely impacts the long-term sustainability of groundwater supplies to help meet the Nation’s water needs."^[3]

According to another USGS study of withdrawals from 66 major US aquifers, the three greatest uses of water extracted from aquifers were agriculture (68%), public water supply (19%), and self-supplied industrial (4%). The remaining about 8% of groundwater withdrawals were for “self-supplied domestic, aquaculture, livestock, mining, and thermoelectric power uses.”^[5]

Socio-economic effects

Scores of countries are overpumping aquifers as they struggle to satisfy their growing water needs, including each of the big three grain producers—China, India, and the United States. These three, along with a number of other countries where water tables are falling, are home to more than half the world’s people.^[6]

Water is intrinsic to growth, and overdraft limits its available supply. According to Liebig's law of the minimum, growth is therefore impeded.^[7] Deeper wells must be drilled as the water table drops, which can become expensive. In addition, the energy needed to extract a given volume of water increases with the amount the aquifer has been depleted. Saltwater intrusion is another consequence of overdrafting, leading to a reduction in water quality.^[8]

See also

• Groundwater recharge
• Groundwater-related subsidence
• Drinking water
• Water crisis

References

External links

• The Perils of Groundwater Pumping, Issues in Science and Technology