Irrigation and agriculture. Irrigation means artificial watering of agricultural land. Artificial watering is required when natural supply does not suffice. Usually natural supply obtains from precipitation mainly in the form of rainfall or snowfall. The proverbial long-staple lustrous Egyptian cotton grows with the help of irrigation. Moreover, because of the uncertainty in occurrence and amount of rainfall, the success of agriculture greatly depends on irrigation in many prosperous agricultural regions of the world. In fact, with the exception of year round humid conditions of the equatorial region of the world, irrigation is resorted to in varied forms and degrees in all the major agricultural regions of the world. Irrigation is also developed to fill up the gap in the water supply between the wet and dry seasons.
For the purpose of irrigation, water is usually drawn from the flowing rivers, lakes and reservoirs. In the drier regions, the underground water source is tapped with the help of wells and tube-wells. In some regions of the world the courses of the perennial rivers are diverted to develop irrigation in the drier parts. For example, attempts are being made to connect the north-flowing Pechora River with the Volga by diverting the flow of the former river through nuclear blasting. In some countries, water is painstakingly collected from fog and dew droplets. In Peru rainfall is caused by driving the fog inland. In Israel and Australia, irrigation is also performed by collecting water from dew. In extremely dry regions water is made to flow through tunnels to eliminate any loss through evaporation. These irrigation tunnels are called Karrez and are found
to occur in Iran and Pakistan.
The development of irrigation dates back to the antiquity. In fact, irrigation as a technology is believed to have originated from the glorious Egyptian or the better-known Nile valley civilization. There are evidences of the utilization of the Tigris and Euphrates waters for irrigation in the Babylonian, Chaldean and Assyrian civilizations. Irrigation was not unknown to the great Indus valley civilization.
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