Water
All agricultural production requires fresh water. Unfortunately water resources are under increasing pressure as a result of growing demand, using up non-renewable resources, and climate change.
Climate Change
A recent paper by the Intergovernmental Panel on Climate Change (IPCC) looked at the impact of climate change on water and its availability to agriculture. Tara Garnett of the Food Climate Research Network prepared a short summary which includes the following:
- By the middle of the 21st century, annual average river runoff and water availability are projected to increase as a result of climate change4 at high latitudes and in some wet tropical areas, and decrease over some dry regions at mid-latitudes and in the dry tropics.
- Increased precipitation intensity and variability are projected to increase the risks of flooding and drought in many areas.
- Water supplies stored in glaciers and snow cover are projected to decline in the course of the century Higher water temperatures and changes in extremes, including floods and droughts, are projected to affect water quality and exacerbate many forms of water pollution
- Globally, the negative impacts of future climate change on freshwater systems are expected to outweigh the benefits (high confidence). By the 2050s, the area of land subject to increasing water stress due to climate change is projected to be more than double that with decreasing water stress.
- Changes in water quantity and quality due to climate change are expected to affect food availability, stability, access and utilisation.
Non-renewable resources
As Lester Brown points out,
Scores of countries are overpumping aquifers as they struggle to satisfy their growing water needs. The drilling of millions of irrigation wells has pushed water withdrawals beyond recharge rates, in effect leading to groundwater mining. The failure of governments to limit pumping to the sustainable yield of aquifers means that water tables are now falling in countries that contain more than half the world’s people, including the big three grain producers—China, India, and the United States.
Most of the world’s aquifers are replenishable, so that when they are depleted, the maximum rate of pumping will be automatically reduced to the rate of recharge. Fossil aquifers, however, are not replenishable. For these—including the vast U.S. Ogallala aquifer, the deep aquifer under the North China Plain, or the Saudi aquifer, for example—depletion brings pumping to an end. Farmers who lose their irrigation water have the option of returning to lower-yield dryland farming if rainfall permits. But in more arid regions, such as in the southwestern United States or the Middle East, the loss of irrigation water means the end of agriculture.
Saudi Arabia recently announced that it was abandoning its highly-subsidised farming operations. This was widely attributed to the depletion of the non-renewable acquifer that had been used to irrigate that farming. Closer to home, the Spanish province of Almeria is the heart of the production of many of the lettuces and tomatoes now consumed in the UK; but this production is increasingly challenged by the depletion of groundwater and creeping desertification of the area.