Irrigation is the artificial supply of water to agricultural land.
It is practiced by more than half the farmers in the world because they need more water for their crops than is available from rainfall. Irrigation projects must also allow for removal of excess water. Modern irrigation and the associated practice of drainage, together with the application of fertilizers and mechanization, have resulted in an unprecedented increase in farm productivity. Even in regions with adequate annual rainfall, irrigation may be necessary if the seasonal distribution is such that a dry period comes during the growing season. In parts of India and China, heavy monsoon rains fall in summer, but crops grown before the rains begin each year must be irrigated.