Irrigation consists of artificially bringing water to cultivated crops to increase their yield. Irrigation can compensate for a lack of rainwater, but necessitates the removal of groundwater, and water from rivers and lakes. Not all arable land is irrigated: only 17% was in 2003, but this land could provide up to 40% of the world’s harvest. (1)
Water as a Resource
Water is a renewable resource: the amount present on Earth is virtually constant. At any one time, water is flowing in the ocean, evaporating, and falling again over the earth. However, certain water stores, in particular aquifers (beds of water-bearing rock), take somewhere on a timescale of thousands of years to replenish. On a human timescale, they could therefore be depleted before they can regenerate, and come to be missed.
Furthermore, only 2.5% of total water reserves are fresh water. Fresh water from watercourses and subterranean groundwater for...