GROWING MORE FOOD WITH LESS WATER.
Expectations for the population to grow by 40 per cent to more than 9 billion by the year 2050 have raised the global question of how to grow more food with less water. With agriculture responsible for 70 per cent of all freshwater withdrawals, efficient and sustainable water use is needed for our own generation and future generations.
With our global water crisis in mind, we have created this resource to provide factual water news and information.
Blue water is made up of fresh surface water and groundwater. So let's take a look at each:
Surface water refers to bodies of water like streams, rivers, lakes, reservoirs and oceans. Surface water makes up only 0.25 per cent of the total water found on earth. Continually replenished by precipitation or rain runoff, surface water is a body of water easily seen as it flows downhill to where it collects.
Surface streams have an effect on the groundwater table. Influent streams recharge groundwater supplies. 80 per cent of the earth's water is surface water; the other 20 per cent is either ground water or atmospheric water vapor. Surface water is made up of saltwater and freshwater. Salt water constrains great amounts of salt, but freshwater has a dissolved salt concentration of less than 1 per cent. Only fresh water can be used as drinking water.
- The over-pumping of groundwater is causing water tables to fall across large areas of northern China, India, Pakistan, Iran, the Middle East, Mexico, and the western United States.
- The United States is the world's third largest irrigator (after China and India).
- The Ogallala Aquifer, which spans parts of eight states from southern South Dakota to northwest Texas, is steadily being depleted. The Ogallala provides 30 percent of the groundwater used for irrigation in the U.S., and as of 2005, a volume equivalent to two-thirds the water in Lake Erie had been depleted.
- The Largest use of ground water is to irrigate crops.
When it rains, some water seeps into the ground, some of it clings to particles of soil or to roots of plants just below the land surface. This moisture provides plants with the water they need to grow. Water not used by plants moves deeper into the ground. The water moves downward through empty spaces or cracks in the soil, sand, or rocks until it reaches a layer of rock through which water cannot easily move. The water then fills the empty spaces and cracks above that layer. The top of the water in the soil, sand, or rocks is called the water table and the water that fills the empty spaces and cracks is called ground water.
Water seeping down from the land surface adds to the ground water and is called recharge water. Ground water is recharged from rain water and snowmelt or from water that leaks through the bottom of some lakes and rivers. Ground water also can be recharged when water-supply systems (pipelines and canals) leak and when crops are irrigated with more water than the plants can use.
At least some ground water can be found almost everywhere. The water table may be deep, such as under a hillside, or shallow such as under a valley. The water table may rise or fall depending on several factors. Heavy rains or melting snow may increase recharge and cause the water table to rise. An extended period of dry weather may decrease recharge and cause the water table to fall.
Aquifer is the name given to underground soil or rock through which ground water can easily move. The amount of ground water that can flow through soil or rock depends on the size of the spaces in the soil or rock and how well the spaces are connected. The amount of spaces is the porosity. Permeability is a measure of how well the spaces are connected.
Aquifers typically consist of gravel, sand, sandstone, or fractured rock such as limestone. These types of materials are permeable because they have large connected spaces that allow water to flow through. The spaces in a gravel aquifer are called pores. The spaces in a fractured rock aquifer are called fractures. If a material contains pores that are not connected, ground water cannot move from one space to another. These materials are said to be impermeable. Materials such as clay or shale have many small pores, but the pores are not well connected. Therefore, clay or shale usually restrict the flow of ground water. The next illustration shows how the connections between the pores or fractures control how water moves through an aquifer.