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.

Groundwater is the fresh water that can be found underground, it is also one of the largest sources. Groundwater depletion can be comparable to ¨money in a bank¨, The primary cause of groundwater depletion is pumping or the excessive pulling up of groundwater from underground aquifers.

The ranking is based on the amount of groundwater each country uses for agriculture. This issue is becoming quite large in the United States (most notably California) but it is also worth noting that it has been a problem in other parts of the world, as was documented in Punjab, India in 1987

According to a 2013 report by research hydrologist, Leonard F. Konikow, at the United States Geological Survey (USGS), 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)." In the United States, the biggest users of water from aquifers include agricultural irrigation and oil and coal extraction."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."

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