Irrigation

• 1. Introduction

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  Irrigation has shaped how people grow food for over 5,000 years, applying controlled amounts of water to land that rain alone cannot sustain. The earliest known canal irrigation flickered into operation at Choga Mami, on the present-day border of Iraq and Iran, at about 6000 BCE. Today the practice feeds the planet on a scale those first canal-builders could not have imagined. By 2023-23 percent of all croplands were equipped for irrigation, and in 2025 those lands produced 48 percent of all crops measured in value. That makes irrigated land 3.2 times more productive than rainfed land. How did a technique born in dry river valleys spread to nearly every populated corner of the world? Why does watering a field still threaten to dry up rivers, poison soil, and drain aquifers that took millennia to fill? And how do farmers move water onto a field at all, from a single drop at a plant's root to a wheel of pipe rolling across an entire strip of land? These are the questions this documentary follows.

• 2. Moving Water To The Field

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  Surface irrigation, also called gravity irrigation, is the oldest method and has been in use for thousands of years. Water simply moves across the land following the slope, wetting the surface and soaking in, divided into furrow, border strip, or basin forms. It carries low capital costs and modest energy needs, which makes it the common choice for developing nations, low-value crops, and large fields. In terraced rice paddies, dikes plugged with soil flood or hold water in each distinct field. Surface irrigation even waters urban gardens in and around Phoenix, Arizona, where a berm surrounds the plot and water arrives on a schedule set by a local irrigation district.

  Sprinkler irrigation pipes water to central points in a field and throws it overhead under high pressure. Rotating sprinklers called rotors are driven by a ball drive, gear drive, or impact mechanism, while guns operate at very high pressures of 275 to 900 kPa and flows of 3 to 76 liters per second. A water reel travelling sprinkler unwinds polyethylene tubing from a steel drum, pulling itself across the field until it returns to the reel and shuts off. These travelling systems water small farms, sports fields, parks, pastures, and cemeteries unattended.

  Micro-irrigation distributes water under low pressure through a piped network, applying a small discharge to each plant. Drip irrigation, its best-known form, delivers water at or near the root zone one drop at a time, with field water efficiency typically between 80 and 90 percent when managed correctly. Paired with plastic mulch, it doubles as a delivery system for fertilizer, a process called fertigation. Run too long, though, a drip system pushes water below the root zone in what engineers call deep percolation.

• 3. Machines That Walk The Land

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  Center pivot irrigation joins galvanized steel or aluminum pipe segments on wheeled towers, fed from a pivot point and sweeping the field in a circle. Crops are often planted in a circle to match it. Newer systems hang drops from a U-shaped pipe so the sprinkler heads sit just above the crop, limiting evaporation, a design known as LEPA, or Low Energy Precision Application. The earliest pivots ran on water power before hydraulic and electric-motor-driven systems took over, and many modern pivots now carry GPS devices.

  Lateral move systems, also called side roll or wheel line, take a different approach. A series of pipes, each with a wheel about 1.5 meters across fixed at its midpoint, couples together and applies water in a stationary strip. When that strip is watered, the hose comes off, the system drains, and the whole line rolls to a new position before reconnecting. It costs less to install than a center pivot but demands far more labor. Most lines use 100 or 130 millimeter aluminum pipe that serves as both water channel and axle, suited to small, oddly-shaped, or hilly fields.

  Subirrigation raises the water table artificially to moisten soil from below the root zone, often on permanent grasslands in lowlands or river valleys tied to drainage infrastructure. In commercial greenhouses it feeds potted plants from beneath, flooding a trough for ten to twenty minutes before pumping the solution back to a holding tank for reuse. A humbler version is the self-watering container, a planter suspended over a reservoir with a wicking material like a polyester rope that draws water up by capillary action.

• 4. Where The Water Comes From

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  Groundwater drawn from springs and wells, surface water taken from rivers, lakes, and reservoirs, and non-conventional sources such as treated wastewater, desalinated water, drainage water, and fog collection all feed irrigation. In the vineyards at Lanzarote, humid night air condenses onto stones to yield water, and fog collectors are also built from canvas or foil sheets. In large urban areas, condensate from air conditioning units is becoming a more popular source.

  Seawater itself can grow food. A Glasgow-based startup helped a farmer in Scotland establish edible salt marsh crops on an acre of previously marginal land, flood irrigated twice a day to simulate tidal flooding with water pumped from the sea using wind power. The plants, samphire, sea blite, and sea aster, yield a higher profit than potatoes, and the project also brings soil remediation and carbon sequestration.

  Different crops demand vastly different volumes across a growing season. Sugarcane needs 1500 to 2500 millimeters over its total growing period, banana 1200 to 2200, and citrus 900 to 1200. Potato sits far lower at 500 to 700, while onions range from 350 to 550 and peas from 350 to 500. Irrigation can be supplementary to rainfall, the common pattern worldwide, or full irrigation where crops rarely rely on rain at all, found only in arid landscapes or in semi-arid areas outside the rainy season.

• 5. A Practice As Old As Cities

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  Some of the earliest known use of irrigation dates to the 6th millennium BCE in Khuzistan in south-west Iran. In the Indus Valley Civilization, irrigation of the alluvial plains is estimated to have begun around 4500 BCE, with artificial reservoirs at Girnar dated to 3000 BCE and an early canal system from about 2600 BCE. Farmers in the Mesopotamian plain developed perennial irrigation by at least the third millennium BCE, coaxing water through a matrix of small channels to water crops throughout the growing season.

  Ancient Egyptians practiced basin irrigation, letting the flooding Nile inundate diked plots until fertile sediment settled before returning the surplus to the watercourse. The pharaoh Amenemhet III, in the twelfth dynasty around 1800 BCE, used the natural lake of the Faiyum Oasis as a reservoir to store water for dry seasons. The Ancient Nubians turned a waterwheel-like device called a sakia, beginning irrigation between the third and second millennia BCE and depending on floodwaters of the Nile.

  The Qanats of ancient Persia, developed about 800 BCE, remain among the oldest irrigation methods still in use, a network of vertical wells and gently sloping tunnels tapping groundwater. In the Zana Valley of the Peruvian Andes, archaeologists radiocarbon-dated irrigation canals at least to 3400 BCE and possibly as old as 4700 BCE, the oldest known canals in the Americas, watering peanuts, squash, manioc, and chenopods. The irrigation works of ancient Sri Lanka, beginning about 300 BCE in the reign of King Pandukabhaya, grew over the next thousand years into one of the most complex systems of the ancient world, later restored and extended under King Parakrama Bahu between 1153 and 1186 CE.

• 6. Engineers Of The Ancient World

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  Sunshu Ao of the 6th century BCE and Ximen Bao of the 5th century BCE stand as the oldest known hydraulic engineers of China, both working on large irrigation projects. In the Sichuan region of the state of Qin, the hydrologist Li Bing built the Dujiangyan Irrigation System in 256 BCE to water a vast area of farmland that still draws water today. By the 2nd century CE, during the Han dynasty, the Chinese used chain pumps to lift water uphill, powered by foot-pedal, hydraulic waterwheels, or oxen-pulled wheels.

  The earliest agricultural irrigation canal system known in the present-day United States dates to between 1200 BCE and 800 BCE, discovered in 2009 by Desert Archaeology, Inc. at Marana, Arizona, next to Tucson. It predates the Hohokam culture by two thousand years and belongs to an unidentified people. The Hohokam themselves were the only culture in North America known to rely on irrigation canals, supporting the largest population in the Southwest by 1300 CE. Between the 7th and 14th centuries they built extensive networks along the lower Salt and middle Gila Rivers, cultivating cotton, tobacco, maize, beans, and squash, and later growing agave through dry-farming.

  Korea produced a different kind of breakthrough. Chang Yongsil, also known as Jang Yeong-sil, an engineer of the Joseon dynasty working under the direction of Sejong the Great, invented the world's first rain gauge, the uryanggye, in 1441. Installed in irrigation tanks as part of a nationwide system, it let planners and farmers measure and collect rainfall data for agriculture.

• 7. The Twentieth Century Surge

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  The scale of irrigation exploded across the 20th century. In 1800, 8 million hectares were irrigated worldwide; by 1950 that reached 94 million, and by 1990 it stood at 235 million, when 30 percent of global food production came from irrigated land. National governments led most schemes, though the United States, China, and European countries like the United Kingdom funded projects in other nations. Anxiety over the American cotton monopoly fueled empirical projects abroad: Britain developed irrigation in India, the Ottomans in Egypt, the French in Algeria, the Portuguese in Angola, the Germans in Togo, and the Soviets in Central Asia.

  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. On the Great Plains, Euro-American farmers drew groundwater first with wind-powered pumps, then with gas-powered pumps in the mid-1930s that pushed wells deep into the Ogallala Aquifer. The center-pivot sprinkler arrived after World War II and made irrigation far easier, but by the 1970s farmers drained the aquifer ten times faster than it could recharge, and by 1993 had removed half the accessible water. Congress passed the National Reclamation Act in 1902, channeling western land-sale money into dams like the Hoover Dam, though frustration with the Reclamation Service led to the Reclamation Extension Act of 1914.

  When the Bolsheviks conquered Central Asia in 1917, the native Kazakhs, Uzbeks, and Turkmens used minimal irrigation. Driven by fears of the American cotton monopoly, Soviet leaders pursued ambitious hydraulic projects, and in the 1950s began diverting the Syr Darya and Amu Darya that fed the Aral Sea. Before diversion the rivers delivered 55 cubic kilometers of water to the sea each year; afterward only 6. The Aral Sea shrank to less than half its original seabed, sharpening the regional climate and spreading airborne salinization. Mikhail Gorbachev killed a plan to reverse the Ob and Yenisei in 1986, and the breakup of the USSR in 1991 ended Russian investment in Central Asian cotton irrigation.

• 8. The Price Of Abundance

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  Negative impacts frequently follow extensive irrigation. Diverting surface water has dried up the very sources it drew from, leading to more extreme regional climates, while overpumping groundwater has caused subsidence and salinization that damages crops and seeps into drinking water. Still water in canals and ponds let pests and pathogens thrive, producing regional outbreaks of malaria and schistosomiasis. Some governments used irrigation schemes to encourage migration of more desirable populations, and some vast national schemes never paid off, costing more than the crop yields they gained.

  In the mid-20th century, diesel and electric motors let pumps draw groundwater faster than drainage basins could refill, threatening the future of food production in the North China Plain, the Punjab region of India and Pakistan, and the Great Plains of the US. Salinity is a parallel danger: in Australia, over-abstraction of fresh water for intensive irrigation has put 33 percent of the land area at risk of salination. Under-irrigation gives poor salinity control and lets toxic salts build on the surface where evaporation is high, requiring leaching and drainage to carry the salts away.

  The global land area equipped for irrigation reached 355 million hectares in 2023, up 23 percent from 289 million in 2000, with 71 percent of it in Asia where irrigation was central to the green revolution. India and China hold the largest equipped areas at 76 and 75 million hectares, far ahead of the United States at 25 million. Until the 1960s there were fewer than half as many people as in 2024, and they drew a third of the river water humans take now. With more than seven billion people competing for water against industry, cities, and biofuel crops, the pressure that built these systems has not eased.