Irrigation is often studied together with drainage, which is the removal of surface and sub-surface water from a given area.
Irrigation has been a central feature of agriculture for over 5,000 years and is the product of many cultures.
Sophisticated irrigation and storage systems were developed by the Indus Valley Civilization in present-day Pakistan and North India, including the reservoirs at Girnar in 3000 BCE and an early canal irrigation system from circa 2600 BCE.
Large scale agriculture was practiced and an extensive network of canals was used for the purpose of irrigation.
Irrigation also has other uses in crop production, including frost protection, In contrast, agriculture that relies only on direct rainfall is referred to as rain-fed or dry land farming.
Irrigation systems are also used for cooling livestock, dust suppression, disposal of sewage, and in mining.
Historically, it was the basis for economies and societies across the globe, from Asia to the Southwestern United States.
Archaeological investigation has found evidence of irrigation where natural rainfall was insufficient to support crops for rainfed agriculture.
These were constructed using relatively simple excavation tools, without the benefit of advanced engineering technologies, and achieved drops of a few feet per mile, balancing erosion and siltation.Ancient Persia (modern day Iran) used irrigation as far back as the 6th millennium BCE to grow barley in areas where natural rainfall was insufficient.The Qanats, developed in ancient Persia in about 800 BCE, are among the oldest known irrigation methods still in use today.The lake swelled annually from flooding of the Nile.In the Zana Valley of the Andes Mountains in Peru, archaeologists found remains of three irrigation canals radiocarbon dated from the 4th millennium BCE, the 3rd millennium BCE and the 9th century CE.