Irrigation & Agricultural Water

Archaeological evidence places some of the earliest use of irrigation in Khuzistan, south-west Iran, in the 6th millennium BCE, in areas lacking rainfall sufficient for rainfed agriculture. The site of Choga Mami, in present-day Iraq near the Iranian border, is believed to show the first canal irrigation in operation at about 6000 BCE. This marks the origin of deliberately engineered water conveyance for crops.

Irrigation was used to manipulate water in the Indus plains from around 4500 BCE, drastically increasing the size and prosperity of agricultural settlements. Artificial reservoirs at Girnar date to 3000 BCE and an early canal irrigation system to about 2600 BCE, supporting large-scale agriculture through an extensive canal network. This combined storage and conveyance represents one of the earliest integrated irrigation systems.

Archaeologists found remains of three irrigation canals in the Zaña Valley near Nanchoc in northern Peru, radiocarbon dated to the 4th millennium BCE, the 3rd millennium BCE and the 9th century CE, with traces of a possible 5th-millennium BCE canal beneath. Radiocarbon dating places the oldest at least 3400 BCE and possibly 4700 BCE. The canals irrigated peanuts, squash, manioc, chenopods and later maize, and provide the earliest record of irrigation in the New World.

Farmers in the Mesopotamian plain used irrigation from at least the third millennium BCE. They developed perennial irrigation, watering crops regularly throughout the growing season by coaxing water through a matrix of small channels formed in the field. This shifted irrigation from flood-dependent to continuous supply.

Irrigation began in Nubia between the third and second millennia BCE, relying largely on flood waters of the Nile and other rivers in what is now Sudan. The Nubians developed a waterwheel-like lifting device called a sakia. Mechanical lifting extended irrigation beyond the reach of gravity flooding.

Irrigation reached the Niger River region cultures and civilizations by the first or second millennium BCE. The methods were based on wet-season flooding and water harvesting rather than permanent canal works. This marks the spread of agricultural water management into sub-Saharan Africa.

Ancient Egyptians practised basin irrigation, using Nile floods to inundate diked plots and returning surplus water to the watercourse after sediment settled. Under Amenemhet III in the twelfth dynasty, around 1800 BCE, the natural lake of the Faiyum Oasis was used as a reservoir to store water surpluses for dry seasons. It is an early documented case of on-scheme storage.

A canal system discovered by Desert Archaeology, Inc. at Marana, Arizona in 2009 dates to between 1200 BCE and 800 BCE. It predates the Hohokam culture by two thousand years and belongs to an unidentified culture. It is the oldest known agricultural irrigation canal system in what is now the United States.

Qanats, developed in ancient Persia about 800 BCE, comprise networks of vertical wells and gently sloping tunnels driven into cliffs and hillsides to tap groundwater. They are among the oldest irrigation methods still in use, now found across Asia, the Middle East and North Africa. Persia had used irrigation to grow barley in low-rainfall areas as early as the 6th millennium BCE.

The noria, a water wheel with clay pots around the rim powered by stream flow or by animals, first came into use among Roman settlers in North Africa around the same era as the qanat. By 150 BCE the pots were fitted with valves to allow smoother filling as they were forced underwater. This improved the efficiency of continuous mechanical water lifting.

Sunshu Ao of the Spring and Autumn period and Ximen Bao of the Warring States period are the oldest known hydraulic engineers of China. Both worked on large irrigation projects. They represent the beginning of state-organised hydraulic engineering in China.

The irrigation works of ancient Sri Lanka date from about 300 BCE in the reign of King Pandukabhaya and were under continuous development for the next thousand years. They included underground canals and artificial reservoirs to store water, used primarily to irrigate water-hungry paddy fields. Much of the system survives undamaged at Anuradhapura and Polonnaruwa.

The Qin hydrologist and irrigation engineer Li Bing devised the Dujiangyan Irrigation System in the Sichuan region in 256 BCE. It was built to irrigate a vast area of farmland and still supplies water today. It is among the longest continuously functioning irrigation headworks in the world.

By the 2nd century CE, during the Han dynasty, the Chinese used chain pumps to lift water from lower to higher elevations. They were powered by manual foot-pedal, hydraulic waterwheels or rotating mechanical wheels pulled by oxen. The water served urban quarters and palace gardens, but mostly irrigation of farmland canals and field channels.

Between the 7th and 14th centuries the Hohokam built and maintained irrigation networks along the lower Salt and middle Gila Rivers rivalling in complexity those of the ancient Near East, Egypt and China. Using simple excavation tools they achieved drops of a few feet per mile, balancing erosion and siltation, and combined canals with weirs. By CE 1300 their irrigation supported the largest population in the Southwest and enabled aggregation of rural populations into stable urban centres.

The ancient Sri Lankan irrigation system was extensively restored and further extended during the reign of King Parakrama Bahu. The works reinforced a thousand-year-old network of tanks and canals serving paddy cultivation. Their precise engineering has allowed much of the system to remain functional.

Under the direction of King Sejong the Great, the Korean engineer Chang Yŏngsil invented the uryanggye, the world's first rain gauge, in 1441. It was installed in irrigation tanks as part of a nationwide system to measure and collect rainfall data for agriculture. Planners and farmers could use the resulting survey information to manage water supply.

The scale of global irrigation increased dramatically over the 20th century: 8 million hectares were irrigated in 1800, 94 million in 1950 and 235 million in 1990. By 1990, 30% of global food production came from irrigated land. The expansion relied on canals redirecting surface water, groundwater pumping and diversion from dams.

Modern irrigation in Egypt began with Muhammad Ali Pasha, who sought independence from the Ottomans through increased cotton trade with Europe. His administration proposed replacing traditional Nile basin irrigation, which used the river's annual ebb and flow, with irrigation barrages in the lower Nile better suited to cotton. Egypt devoted 105,000 ha to cotton in 1861, a figure that increased fivefold by 1865 as the American Civil War cotton scarcity cemented Egypt as England's supplier.

Congress passed the Desert Land Act in 1877 and the Carey Act in 1894 in attempts to expand irrigated farmland by granting land and expecting farmers to find water. Both only marginally increased irrigation. Their failure set the stage for direct federal construction of irrigation works.

Irrigated land in the United States rose from 300,000 acres in 1880 to 4.1 million in 1890 and 7.3 million in 1900. Two thirds was sourced from groundwater or small ponds and reservoirs and one third from large dams. A key attraction was its dependability relative to rainfed agriculture, which proponents argued made farmers more creditworthy.

As of November 2019 a Glasgow-based startup had helped a Scottish farmer establish edible salt marsh crops irrigated with seawater. It represents the use of non-conventional water sources for agriculture alongside treated wastewater, desalinated water, drainage water and fog collection. Such sources broaden where irrigated production is physically possible.

The global land area equipped for irrigation rose from 289 million hectares in 2000 to 355 million in 2023, a 23% increase and more than twice the area of the 1960s. Asia held 71% of the total in 2023, where irrigation was a key component of the green revolution, with the Americas at 16% and Europe at 8%. China and India recorded the largest net gains, of 21 and 15 million hectares respectively.

Russia's expansion of irrigation began to decline in the late 1980s, with irrigated hectares in Central Asia peaking at 7 million. Gorbachev cancelled a proposed scheme to reverse the Ob and Yenisei rivers for irrigation in 1986. The breakup of the USSR in 1991 ended Russian investment in Central Asian cotton irrigation.

By 1975 the USSR used eight times as much water as it had in 1913, overwhelmingly for irrigation. Dams on the Don and Kuban Rivers had removed freshwater flow from the Sea of Azov, making it much saltier, while depletion and salinization affected other areas. It marks the peak phase of Soviet hydraulic expansion.

Italian oil drillers had discovered Libya's underground water resources during the colonial period, but the water lay dormant until 1969, when Gaddafi and the American Armand Hammer built the Great Man-Made River to deliver Saharan water to the coast. The water largely contributed to irrigation. It cost four to ten times more than the crops it produced were worth.

In the 1960s the small Perth company Hugall & Hoile invented a system they called reticulation, dividing a garden's irrigation system into segments with solenoid electronic valves connected to a mechanical timer. Robert Hugall became known as the father of backyard irrigation. Former cricketer Wally Edwards, who founded Holman Industries in 1966, later targeted the DIY garden watering market in the early 1990s.

Arizona sued California for increased access to the Colorado River on the grounds that its groundwater supply could not sustain an almost entirely irrigation-based agricultural economy, and won. The Colorado River irrigates more than 4.5 million acres in the lower basin states of Arizona, Colorado and Nevada. It also feeds California's Imperial Valley via the All-American Canal, built under the National Reclamation Act.

In the 1950s Soviet officials began diverting the Syr Darya and Amu Darya, which fed the Aral Sea, for irrigation. Inflow fell from 55 cubic kilometres a year to only 6, and the Aral Sea came to cover less than half of its original seabed. The result was a more extreme regional climate and airborne salinization that lowered nearby crop yields.

The Tana River Irrigation Scheme in eastern Kenya was completed between 1948 and 1963, opening new lands for agriculture. The Kenyan government attempted to resettle the area with detainees from the Mau Mau uprising. It illustrates how African irrigation schemes of the 20th century were shaped by colonial political aims.

Until the advent of the center-pivot sprinkler after World War II, farmers irrigated fields by laying pipes across them with sprinklers at intervals, a labour-intensive process. The center pivot made irrigation significantly easier and enabled large-scale mechanised application. Later systems hung drops from a U-shaped pipe with heads positioned just above the crop to limit evaporative losses.

Between the late 1800s and the 1930s, farmers on the Great Plains used wind-powered pumps of limited capacity to draw groundwater. The development of gas-powered pumps in the mid-1930s pushed wells deep into the Ogallala Aquifer. By the 1970s farmers drained the aquifer ten times faster than it could recharge, and by 1993 half the accessible water had been removed.

A 1918 decree by Lenin encouraged irrigation development in Central Asia, where the native Kazakhs, Uzbeks and Turkmens had used minimal irrigation before the Bolshevik conquest of 1917. Actual development began in the 1930s, when Stalin and other Soviet leaders prioritised large-scale, ambitious hydraulic projects, especially along the Volga. The drive stemmed from fears of the American cotton monopoly and a desire for cotton self-sufficiency.

Construction of the Hartbeespoort Dam began in 1916 to elevate the living conditions of 'poor whites' in the region and was eventually completed as a 'whites only' employment opportunity. The Pretoria irrigation scheme, Kammanassie project and Buchuberg irrigation scheme on the Orange River followed in the same vein in the 1920s and 1930s. These linked irrigation headworks to racialised social policy.

The Reclamation Extension Act transferred significant decision-making power over irrigation projects from the Reclamation Service to Congress. It followed growing frustration with Frederick Newell's uncompromising leadership, falling crop prices, resistance to delaying debt payments and refusal to begin new projects before old ones finished. It reflected the political unpopularity the Service had accumulated.

In 1912 the Union of South Africa established an irrigation department and began investing in water storage infrastructure and irrigation systems. The government used irrigation and dam-building to pursue social goals including poverty relief through construction jobs for poor whites and the expansion of white farming. It institutionalised state-led irrigation development in southern Africa.

Before the Bolshevik conquest, the Russian government accepted a 1911 American proposal to send hydraulic experts to Central Asia to investigate the potential for large-scale irrigation. Tsarist officials had meanwhile maintained Slavic settler irrigation techniques through the late 19th century. The survey prefigured the later Soviet hydraulic programme.

The National Reclamation Act channelled money from sales of western public lands, in parcels up to 160 acres, into irrigation projects on public or private land in the arid West. Supporters backed it to increase exports, 'reclaim' the West and resettle the Eastern poor. It was the most successful piece of federal irrigation legislation, though the Reclamation Service directed most funds to construction of large dams such as the Hoover Dam rather than settlement.

The advent of diesel and electric motors in the mid-20th century led to systems that could pump groundwater out of major aquifers faster than drainage basins could refill them. This made overdrafting of underground aquifers a structural feature of modern irrigation. It is among the principal environmental challenges associated with the capability.

National governments led most irrigation schemes within their borders, but private investors and other nations, especially the United States, China and European countries, funded and organised schemes in other nations. Global anxiety about the American cotton monopoly fuelled imperial irrigation projects: Britain in India, the Ottomans in Egypt, the French in Algeria, the Portuguese in Angola, the Germans in Togo and the Soviets in Central Asia. Irrigation was pursued to raise wheat, rice and cotton output and increase self-sufficiency.

California began irrigating in earnest in the 1870s in the San Joaquin Valley and passed the Wright Act of 1887, permitting agricultural communities to construct and operate needed irrigation works. The law created a legal vehicle for collective scheme development. It underpinned the state's subsequent irrigation expansion.

After the British occupation of Egypt in 1882, the conversion to perennial irrigation was intensified through construction of the Delta Barrage, the Assiut Barrage and the first Aswan Dam. Perennial irrigation reduced local control over water and made subsistence and non-cotton farming very difficult. It contributed to widespread peasant bankruptcy and the 'Urabi revolt of 1879–1882.