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Peak oil has generated headlines in recent years, but the real threat to our future is peak water. There are substitutes for oil, but not for water. We can produce food without oil, but not without water.

We drink on average four quarts (4.5 litres) of water per day, in one form or another, but the food we eat each day requires 2,000 quarts of water to produce, or 500 times as much. Getting enough water to drink is relatively easy, but finding enough to produce the ever-growing quantities of grain the world consumes is another matter.

Grain consumed directly supplies nearly half of our calories. That consumed indirectly as meat, milk, and eggs supplies a large part of the remainder. Today roughly 40% of the world grain harvest comes from irrigated land. It thus comes as no surprise that irrigation expansion has played a central role in tripling the world grain harvest over the last six decades.

During the last half of the 20th century, the world's irrigated area expanded from 232m acres (93m hectares) in 1950 to 706m in 2000. This tripling of world irrigation within 50 years was historically unique. But since then the growth in irrigation has come to a near standstill, expanding only 9% between 2000 and 2010.

Farmers get their irrigation water either from rivers or from underground aquifers. Historically, beginning with the Sumerians some 6,000 years ago, irrigation water came from building dams across rivers, creating reservoirs that then enabled them to divert the water onto the land through a network of gravity-fed canals. This method of irrigation prevailed until the mid 20th century, but with few remaining sites for building dams the prospects for expanding surface irrigation faded. Farmers then turned to drilling wells to tap underground water resources.

In doing so, they learned that there are two types of aquifers: those that are replenishable through rainfall, which are in the majority, and those that consist of water laid down eons ago, and thus do not recharge. The latter, known as fossil aquifers, include two strategically important ones, the deep aquifer under the North China Plain and the Ogallala aquifer under the US Western Great Plains.

In looking at water and our future, we face many questions and few answers. Could the world be facing peak water? Or has it already peaked?

Tapping underground water resources, which got seriously underway in the mid-20th century, helped expand world food production, but as the demand for grain continued climbing the amount of water pumped continued to grow. Eventually the extraction of water began to exceed the recharge rate of aquifers from precipitation, and water tables began to fall. In effect, overpumping creates a water-based food bubble, one that will burst when the aquifer is depleted and the rate of pumping is necessarily reduced to the rate of recharge from precipitation.

Today some 18 countries, containing half the world's people, are overpumping their aquifers. Among these are the big three grain producers – China, India, and the United States – and several other populous countries, including Iran, Pakistan and Mexico.

During the last two decades, several of these countries have overpumped to the point that their aquifers are being depleted and their wells are going dry. They have passed not only peak water, but also peak grain production. Their aquifers are being depleted, their wells are going dry, and their grain harvests are shrinking. Among the countries whose use of water has peaked and begun to decline are Saudi Arabia, Syria, Iraq and Yemen. In these countries peak grain has followed peak water.

Nowhere are falling water tables and the shrinkage of irrigated agriculture more dramatic than in Saudi Arabia, a country as water-poor as it is oil-rich. After the Arab oil export embargo in 1975, the Saudis realised they were vulnerable to a counter-embargo on grain. To become self-sufficient in wheat, they developed a heavily subsidised irrigated agriculture based largely on pumping water from fossil aquifers.

After being self-sufficient in wheat for over 20 years, the Saudis announced in early 2008 that, with their aquifers largely depleted, they would reduce wheat planting by one-eighth each year until 2016, when production would end. By then Saudi Arabia projects it will be importing some 15m tons of wheat, rice, corn and barley to feed its Canada-sized population of 30 million. It is the first country to publicly project how aquifer depletion will shrink its grain harvest.

Syria, a country of 22 million people riddled by civil war, is also overpumping its underground water. Its grain production peaked in 2002 and during the decade since then has dropped 30%. It, too, is becoming heavily dependent on imported grain.

Grain production in neighbouring Iraq peaked in 2004. By 2012 it had dropped 33%, forcing the government to turn to the world market to feed its people. In addition to aquifer depletion, both Syria and Iraq are also suffering to a lesser degree from a reduced flow in the Tigris and Euphrates rivers, as upstream Turkey claims more water for its own use.

In Yemen, a nation of 23 million people that shares a long border with Saudi Arabia, the water table is falling by roughly 4ft a year as water use outstrips aquifer recharge. With one of the world's fastest-growing populations and with water tables falling everywhere, Yemen is fast becoming a hydrological basketcase. Grain production has fallen by half over the last 35 years. By 2015 irrigated fields will be a rarity and the country will be importing virtually all of its grain. Living on borrowed water and borrowed time, Yemen could disintegrate into an area of tribes warring over water.

Thus in the Arab Middle East the world is seeing the collision between population growth and water supply at the regional level. For the first time in history, grain production is dropping in a geographic region with nothing in sight to arrest the decline. Because of the failure of governments in the region to mesh population and water policies, each day now brings 10,000 more people to feed and less irrigation water with which to feed them.

Other countries with much larger populations, such as Iran, Pakistan and Mexico, are also near or beyond peak water. In Iran, a country with 81 million people, grain production dropped 10% between 2007 and 2012 as its irrigation wells started to go dry. One quarter of its current grain harvest is based on overpumping. With its population growing by over a million per year, it too faces a day of reckoning

Peak oil has generated headlines in recent years, but the real threat to our future is peak water.

vtsnowedin wrote:If you look at the water situation in Iran then any water shortage in the UK becomes trivial.
http://www.ncr-iran.org/en/news/society ... risis.html

kenneal - lagger wrote:The Punjab is just one such highly populated food growing area that will be affected, as has been pointed out earlier in the thread, so the mass starvation or mass migration will make current migrations look minuscule. People can put up with economic hardship much more than food and water hardship.

RenewableCandy wrote:The Met Office rainfall map shows the Western Isles get 8 times the rainfall of the SE of England. That's a heck of a difference.

biffvernon wrote: Water is constantly recycled through a giant purification system and global warming actually results in a faster throughput.

biffvernon wrote:But in the grand scheme of things such 'fossil' waters represent a very small part of the water that humanity makes use.

In my own part of the world...