 A key factor in increased food supplies in the past 50 years has been irrigation, often pumped using fossil fuel energy. About 70% of all water use is for irrigation. Population growth implies that we will need much more irrigation, but in fact water supplies in many areas are falling. As demand for water has increased, aquifers have been overpumped in many parts of the world and some have collapsed and will not refill with water.
Many fossil aquifers that hold water from thousands of years ago are emptying and cannot be replenished. Land that feeds from them then reverts to low yield, dry land farming or in arid regions it stops being useful altogether. Fossil aquifers under great pressure include the U.S. Ogallala Aquifer and the deep North China Plain Aquifer.
Farmers and cities in North China, having depleted shallow supplies, are now pumping water from the deep aquifer under Heibei Province at great cost and causing water levels to drop by 3 metres a year according to the Geological Environmental Monitoring Institute (GEMI).
Some areas such as the Western U.S. are tapping rivers when underground supplies become scare but then rivers are also being overused.
In many parts of the world where rivers run through two or more countries, bitter disputes arise as each country extracts more and more water. Cities and industry compete with agriculture and even in the U.S., cities sometimes buy up the water extraction rights from farmers who then abandon the land.
Water is usually the deciding factor as to whether land can be used for farming or not. Some areas are fortunate enough to have sufficient natural rainfall to produce high yields but more often lack of water at the right time limits yield. That’s not surprising considering that over 600 litres of water is taken up by a corn crop to produce 1 kg of grain and around 4000 litres for 1 kg of rice.
There have been many reports documenting the water shortage crisis for cities and industry but remarkably little attention given to the devastating effect on food production. Water use is increased as people move onto diets with more meat and the worldwide demand for water is doubling every 21 years according to the World Bank. Countries that are unable to meet the irrigation needs of agriculture are importing more and more grain and will be in a perilous position when those supplies are no longer available. As with all our natural resources, the big problem is that as the population rises to 8 billion by 2025 the amount of water per capita will decrease and less water per person inevitably means less food per person.