GROUNDWATER DEPLETION & SEA LEVEL RISE
An interview with Leonard Konikow, USGS- 5/23/13
Author, Groundwater Depletion 1920-2008
A natural consequence of groundwater withdrawals is the removal of water from subsurface storage. Groundwater depletion not only can have negative impacts on water supply, but also lead to land subsidence, reductions in surface-water flows and spring discharges, and loss of wetlands.
A USGS study by Leonard Konikow published in January 2013 evaluates the long-term cumulative depletion volumes in 40 separate aquifers or areas and one land use category in the United States.
According to Konikow, estimated groundwater depletion in the United States during 1900-2008 totals approximately 1,000 cubic kilometers (km3), or twice the volume of water contained in Lake Erie. Furthermore the rate of depletion from 2000 to 2008 was roughly three times the rate of depletion for the entire study time frame.
The rate of depletion also varies from aquifer to aquifer.The three individual aquifers that represent the largest contributors to groundwater depletion are principal aquifers, the High Plains aquifer, the Mississippi embayment aquifer system, and the Central Valley aquifer in California, where in some areas of the San Joaquin Valley and Tulare Basin, water levels had declined nearly 122 m, depleting groundwater from storage and lowering water levels to as much as 30 m below sea level.
"Irrigation in high intensity agricultural areas is the main cause of groundwater depletion. Climate change only plays a role inasmuch as it contributes to more frequent drought", says Konikow.
In the US, about 50% of the drinking water comes from groundwater sources as compared with Canada where 30% of the poulation draws its drinking water from groundwater.
" There is no widespread groundwater depletion in Canada because there is so much surface water, sasy Konikow. " Only a few areas in Alberta and Saskatchewan have had any serious depletion issues".
However, groundwater depletion is not limited to the United States. According to a GlobalPost article (8/11/12), researchers in Canada and the Netherlands found that while 80 percent of the world's aquifers were being used sustainably, heavy exploitation of water in other areas of the world, such as Saudi Arabia, Iran, northern India and parts of northern China, are threatening the livelihoods and sometimes lives of millions.
Konikow notes that cumulative long-term groundwater depletion around the world also contributes directly to sea-level rise and may contribute indirectly to regional relative sea-level rise as a result of land subsidence issues such as in the Gulf coast.
"Water has to go somewhere, says Konikow, "oceans represent the ultimate sink for essentially all depleted groundwater.
If the estimated volumes of depletion were spread across the surface of the oceans, it
would account for approximately 2.2 mm of sea-level rise from 1900 through 2000 and 2.8 mm of sea-level rise from 1900 through 2008."
"It is a small contributor to global sea-level rise, he says, but sufficiently large that it needs to be recognized as a contributing factor and accounted for when explaining long-term global sea-level rise."
According to Konikow, groundwater depletion was not factored in to previous Sea Level Rise estimates but will be in the next IPCC report.
Conservation and improved irrigation planning and processes can alleviate if not reverse groundwater depletion. According to Knonikow, in Texas new regulation has given the water development board the authority to set long-term goals about how groundwater should be used. In Arizona, new irrigation methods which reduce the amount of water needed are also being adopted.
Groundwater Depletion 1920-2008 - Leonard Konikow USGS, 2013
Sea Level Rise Report
- Water Today