According to researchers at the University of Utrecht, “Groundwater depletion is fast becoming the most important contribution of terrestrial water to sea-level rise. It currently outweighs the negative contribution of storage behind dams and will be of the same magnitude as the present contribution of mountain glaciers.”
Depletion of groundwater reserves has more than doubled in recent decades as a result of population growth and the increased demand on groundwater reservoirs for drinking water and the irrigation of croplands. Most of the water pumped up from deep underground pools is not replenished; it evaporates into the air or flows into rivers that ultimately feed back into the seas.
Artificial reservoirs, such as the Hoover Dam on the Colorado River and the Three Gorges Dam on the Yangtze River in China, have the opposite effect. They lock up water that would otherwise flow into the seas.
Previously scientists had speculated these effects cancelled each other and therefore they did not consider terrestrial water a significant part of the sea level problem.
The Utrecht study however now suggests that groundwater pumping will cause a global sea level rise (SLR) of about 0.8 millimeters per year by 2050.
Another study lead by Yadu Pokhrel, suggests groundwater use is already having this great an effect and found that between 1961 and 2003 the seas rose by about 0.77 millimeters per year on this account or about 42% of the observed total.
Besides adding to SLR, aquifer pumping can lower water levels below the level of existing pumps, decrease the pumping yield of existing wells, make for longer lifts for existing pumps, thus increasing the cost to produce wells, cause land subsidence and deteriorate water quality as a result of saltwater or poorer, deeper, water intrusions.
The options for farmers that lose their irrigation water due to aquifer depletion are to either return to lower-yield dry-land farming if rainfall permits or in more arid regions, such as in the southwestern United States or the Middle East, cease to produce crops.
Saudi Arabia is water-poor. Nevertheless it developed a 30-year program to boost local wheat production in order to become self-sufficient. Relying heavily on subsidies, it developed an extensive irrigated agriculture system based largely on its deep fossil aquifer. After several years of supporting wheat prices at five times the world market level however the government was forced to cut the subsidies and harvests dropped from a high of 4.1 million tons in 1992 to 2.7 million tons in 2007.
Some Saudi farmers are now pumping water from wells that are 4,000 feet deep.
Recognizing its hydrologic limitations, in early 2008 the Saudi government announced plans to phase out wheat production entirely by 2016.
Of note is the fact, wheat shortages were believed to be a factor in the Arab Spring uprisings.
Lester Brown points out in an article, As Countries Over-Pump Aquifers, Falling Water Tables Mean Falling Harvests, “Since the over-pumping of aquifers is occurring in many countries more or less simultaneously, the depletion of aquifers and the resulting harvest cutbacks could come at roughly the same time. And the accelerating depletion of aquifers means this day may come soon, creating potentially unmanageable food scarcity.”
The situation in the U.S. southwest is exemplified by the Colorado River, which as noted above, forms Lake Mead as it is backed up behind the Hoover Dam. Recent studies have shown, the river is shrinking by as much as 7 percent each year, exacerbated by recent severe drought.
The Colorado is considered America’s most endangered river.
The Colorado River provides more than 4,200 megawatts of carbon free hydro electric power. The Hoover Dam however hasn’t run at capacity since 1983 because of lower river flows and other water demands.
Lake Mead currently sits at a level of 1,116 feet above sea level which is a drop of 90 feet below its level when drought took hold in 2000. It is projected to drop another 30 feet in the next two years and should it drop a further 60 feet the Hoover Dam would cease generating electrical power alltogether.
Unfortunately this is not an unlikely scenario. The National Oceanic and Atmospheric Administration projects wet regions of the planet will get wetter and dry regions dryer in the course of the 21st Century.
Steven Schafersman, predicts traditional rainfall amounts of 12-15 inches a year in the southwestern United States will permanently become 4-5 inches a year on account of anthropogenic climate change.
One alternative being considered by Nevada authorities to address the problem, is a multibillion-dollar pipeline to tap groundwater across eastern Nevada. As pointed out above, this will only exacerbate the problem of SLR, on top of the increase already being felt due to the the loss of terrestrial storage behind Hoover Dam. It would also be a temporary fix as this groundwater too will ultimately be depleted.
The better alternative is suggested by the events of 2011. SLR declined by 5 millimeters.
NASA referred to this phenomenon as a “Pothole on the Road to Higher Seas”
Kevin Trenberth, Distinguished Senior Scientist at the Climate Analysis Section of the National Centre for Atmospheric Research has pointed out, while previously there has been slight reductions in SLR corresponding to La Nina years, the loss of 5mm of SLR in 2011 is a prominent pothole. He explains that the rains in late 2010 and early 2011 caused a fall in global sea level of 5mm, about half of which was estimated to have fallen on Australia in this period.
The following NASA diagram demonstrates where water was taken up from the land and where it fell over the relevant span.
Most of the rainfall originated in the oceans from whence it evaporated before condensing and falling onto the land.
The American southwest is a prominent drying region in the diagram and the Arabian Peninsula as well experienced a loss of water mass.
The 2011 natural reversal of SLR demonstrates a terrestrial capacity to sequester water, at least temporarily, that otherwise adds to SLR. By using rainfall derived from the oceans to supplant water mined from aquifers and to recharge already depleted aquifers, this SLR benefit can be perpetuated.
The way to service the need in the American southwest is to divert the increases in Canada – forecast to be as much as 30 percent this century – which currently, mostly – 60 percent – flows northward into Hudson Bay or the Arctic south by any of the three corridors that have been proposed.
Each of these proposals also has a significant hydro electric component.
For the Middle East and North Africa the logical way to create additional anthropogenic sea level potholes is to transport fresh water in the ballast holds of oil tankers deadheading to their home ports.
Even though Canada currently frowns on fresh water exports, their is no prohibition with respect to ballast water.
Not only is this a SLR solution, it is a productive way to prevent unmanageable food scarcity.
The government of Canada and the relevant provincial governments, to whom the resource belongs, need to reconsider bulk water exports. Although environmental issues are claimed as the rationale of those opposing exports, the more compelling environmental evidence mitigates in favour of exports.
Canada’s current situation is untenable. The rainfall map shown below reveals the entire west coast of Vancouver island experiences in excess of 3000 millimeters of rainfall per year.
The record rainfall in Canada for a 24-hour interval is 489 millimeters in 1967 at the Brynnor mine near Tofino on the west coast of Vancouver Island. Nevertheless in 2009 the tourist town of Tofino had to impose water restrictions at the height of its summer season.
As is the case in most of Canada, which has 6 percent of the global renewable water supply, virtually all of the west coast’s plenty is simply going to waste.
If we were to sell some of it there might be sufficient funds to deal with our own domestic shortfalls.