Agriculture and water resources management

Agriculture remains the largest consumer of freshwater on the planet. According to the Food and Agriculture Organization of the United Nations (FAO), the agricultural sector accounts for approximately 70% of global water withdrawals, and in some countries in the Middle East and Central Asia, this share exceeds 90%. This figure is based on water withdrawals from rivers, lakes, and groundwater aquifers.

Consumption below the intake. Some of the water withdrawn flows back from the fields through drainage and returns to the watercourse, while some is lost irretrievably. The term "evapotranspiration" describes the water loss by crops: evaporation from the soil surface plus transpiration, where water passes through the plant and exits the stomata. This portion of the water loss is considered irretrievable.

According to the global AQUASTAT database, irrigated lands approach 300 million hectares. This is approximately one-fifth of the world’s arable land. According to the same organization, they provide approximately 40% of the world’s food. The remaining lands are rainfed: harvests there depend on the rainfall of a given season. These figures fluctuate from year to year.

Rainfed agriculture feeds the majority of the planet’s population and is the first to feel any disruption in the monsoon.

Historical roots of irrigation

Ancient systems

Irrigation predates written language. In Mesopotamia, canals diverted the waters of the Tigris and Euphrates to fields, according to archaeological evidence, as early as the 6th and 5th millennia BC. Egyptian farmers made do with the Nile’s flooding for centuries: they dammed their fields into basins, releasing the floodwaters, nourishing the soil, fertilizing the silt, and draining any excess back into the river through slits.

A karez is an underground gallery that carries groundwater from the foothills by gravity, with virtually no evaporation. Such aqueducts were built in Iran, Central Asia, Afghanistan, and Xinjiang. The oldest are estimated to be two to three thousand years old; some systems still water gardens today.

The Chinese Dujiangyan Dam, built in 256 BC, divides the flow of the Minjiang River with a stone dam without a dam in the riverbed and still irrigates hundreds of thousands of hectares of the Chengdu Plain. In Sri Lanka, cascades of small reservoirs transferred water from reservoir to reservoir, irrigating rice fields along the way. The cascades served village communities and were maintained by the villagers themselves.

Distribution rules

The dispute over water began along with its division.

The Code of Hammurabi (18th century BC) contained provisions for punishment for negligence that resulted in a dam bursting or flooding a neighboring field. Similar regulations appeared wherever canals were built: without enforcement, the network would die out after the first season.

Everyone needs order.

In Valencia, Spain, a water tribunal meets on Thursdays at the Apostolic Gate of the cathedral. Judges representing local irrigation canals hear the parties without lawyers or papers, rendering verbal verdicts immediately. The tradition’s origins date back to the Umayyad era; in 2009, UNESCO recognized the tribunal as an Intangible Heritage of Humanity. Its mechanics explain its persistence: the court is close, the decision is immediate, and the fine is meted out immediately.

Similar institutions developed independently: aflaj councils in Oman, elders of qanat communities in Iran, and mirob distributors in the Central Asian khanates.

Irrigation technologies

Irrigation efficiency is measured by the proportion of water reaching the root zone. The difference between delivery methods is significant.

Surface irrigation

Water flows by gravity: along furrows between ridges, wide strips, or flooded checks. This method is ancient, inexpensive, and requires no pressure or energy systems. According to FAO estimates, it accounts for between four-fifths and nine-tenths of the world’s irrigated area, primarily in Asia.

The price of simplicity is losses. Typically, no more than half of the applied water reaches the roots; the rest percolates below the root zone, runs off the field’s tailings, or evaporates from the wet surface. The exact percentage depends on the soil, slope, and the discipline of the irrigator.

Improvements reduce wastefulness. Laser leveling adjusts field slope to within two centimeters, distributes water more evenly, and in experiments on the Indo-Gangetic Plain, consumption dropped by approximately a quarter. Pulsed water application distributes water along the furrow in a series of waves: alternating wetting and idle periods compacts the bottom, the front reaches the end faster, and seepage along the way is reduced. Both methods are several times cheaper than a complete technology change.

Sprinkling

The systems spray water under pressure, simulating rain. The efficiency is higher than that of gravity-fed irrigation: 65–85%, according to industry estimates. This method is suitable for light soils and uneven terrain, where leveling for gravity-fed irrigation is too expensive. Weaknesses include droplet drift, evaporation during flight, and a high energy and consumable consumption rate.

The most common type of machine in this class is a center pivot sprinkler with wheeled carts that move in a circle around the water intake point. The design was devised by American farmer Frank Zibach in the late 1940s; modern machines cover a circle with a radius of approximately 400 meters, or about fifty hectares. From an airplane, the Great Plains of the United States appear as a checkerboard of green and yellow circles.

Drip lines

The idea was sparked by a leak. In the 1930s, gardener Simcha Blass noticed that a tree near a leaking water pipe was growing taller than its neighbors. In 1965, the Israeli kibbutz Hatzerim launched the industrial production of drip tape under the Netafim brand; today, such systems are installed in fields across dozens of countries.

Water flows from the drippers in small doses directly into the root zone, keeping the surface between plants dry, preventing leaves from becoming wet and reducing fungal infections. Field measurements show that the effective water consumption rate reaches 90–95%. Fertilizer is added to the tapes along with the water; this combination is called fertigation, and it allows for the dosage of nutrients to be adjusted according to growth phases.

The disadvantages are also clear. Capital costs per hectare are higher than with any other method. Drippers clog without filtration and periodic flushing, and used drip lines become waste, requiring collection points in California. The subsurface method buries the lines 20-50 centimeters deep: water flows directly to the root zone, without wetting the soil above. This method irrigates a significant portion of California’s almond orchards and tomato fields.

Water Paths: Channels and Losses

The delivery network consumes its share before the field does. In the old irrigation systems of South Asia, losses from the water intake to the farm boundary, according to surveys by irrigation agencies, reach a third or more: earthen channels are filtered, overgrown, and evaporate.

Lining canals with concrete or film reduces filtration, while piping completely prevents evaporation. China and Uzbekistan have been implementing lining programs for main canals for years. In Indian states, distributor repairs are financed by fees collected from water user associations.

Irrigation planning

Water balance of the field

The irrigation regime is based on a moisture balance. Income is the sum of precipitation and irrigation, while expenditure is equal to evapotranspiration. Reference evapotranspiration is calculated using the Penman-Monteith equation from weather station data, and the FAO-56 manual provides crop coefficients that convert this conventional value into the requirement for a specific crop in a given week.

Soil meters measure water reserves directly. A tensiometer measures the tension with which a root draws water from the soil; a capacitive probe scans the moisture profile across horizons. A simple technique using a probe and your palm, with practice, provides acceptable accuracy and is still widely used.

A mistake costs money twice. Overfilling leaches nitrogen, breeds fungal diseases, and increases the pump bill. Underfilling reduces the yield.

Scarcity strategies

A crop’s full requirement doesn’t have the status of law. The controlled deficit strategy deliberately dehydrates the plant during periods when water stress has the least significant impact on the yield.

In vineyards in Australia and California, a moderate deficiency has become a standard practice: the berries accumulate more sugars and phenols, while the field requires tens of percent less water. Partial root zone drying goes even further: only half the roots are watered, alternating the sides of the rows. The dry half synthesizes abscisic acid, the stomata close, and the plant transpires less with almost no loss of photosynthesis.

There are limits to this approach. Deficiencies during the flowering or grain-filling phases of wheat and corn are more costly than the water saved. Protocols are tailored to the crop, soil, and region.

Varieties and crop substitutions

Breeding works toward the same goal. A short growing season delays ripening from the peak of drought, and drought-resistant corn and sorghum hybrids maintain their leaves firm longer without irrigation. Genetically modified drought-resistant corn has been registered in the US, but field gains have been modest, and acreage under it is growing slowly. Crop substitution alters the water balance more radically than any hose: sorghum instead of corn in arid states and rice instead of corn in Punjab, India are examples of such conversions.

Rice systems

Rice has historically been kept submerged to help suppress weeds. The crop itself doesn’t require a continuous layer of water.

Alternating moistening

The AWD method, developed by the International Rice Institute in the Philippines, requires keeping paddies dry for several days. Irrigation is resumed when the water level drops approximately 15 centimeters below the surface, as indicated by a perforated tube buried in the field. Savings reach up to a quarter, and in some places up to a third, of the total water consumption. Methane emissions from waterlogged soils are significantly reduced. Yields do not decline.

Intensive rice

A neighboring school of thought came from Madagascar in the 1980s: young seedlings, sparse planting, and alternating watering instead of a constant layer. Field results vary between countries and seasons; the methodology is still being tested in various agroclimatic zones.

Soil as a moisture storage device

Humus holds water. Every percent of organic matter increases the soil’s water retention; specific factors vary in the literature, but the general consensus is that organic matter retains moisture many times better than a mineral matrix of the same weight.

Conservation agriculture relies on three techniques: minimal tillage, a constant layer of plant residue on the surface, and crop rotation with cover crops. Mulch and stubble reduce evaporation, root canals channel rainfall deeper, legumes accumulate nitrogen and reduce the need for commercial fertilizers. Shelterbelts dampen winds over the field, reducing evaporation.

The Sahel provides illustrative examples. In Burkina Faso, zai pits filled with manure catch the first rainfalls directly beneath the plants, while crescent-shaped terraces retain runoff on slopes. Using these techniques, farmer Yacouba Sawadogo raised a grove on a burned-out plot of tens of hectares and won the international Right Livelihood Award in 2018.

Collection and retention of local water

Local runoff collection doesn’t require main channels. Everything that falls on the farm is included: roofs, yards, slopes, and seasonal riverbeds.

Rajasthan, an Indian state with a semi-arid climate, has been home to several dozen dams, or johads, built by the Tarun Bharat Sangh community movement and villages since 1985. According to the organization itself, the number of these structures runs into the thousands. The Arvari and Ruparel rivers, which had been drying up, returned to a steady flow by the late 1990s, and water levels in the reservoirs rose.

Kenya’s sand dam works differently. A stone wall across the dry riverbed slows the floodwaters, allowing the water to seep through and be stored within the sand. The structure is extremely simple, and evaporation from the sand is virtually zero; the village draws water year-round from wells dug in the sand near the wall.

Ancient techniques have survived to this day in Asia: cascades of tanks in South India distribute monsoon runoff between villages, and Andean terraces hold rainfall on slopes without causing soil to slide.

Groundwater

Inexpensive pumps have turned grain-producing nations to aquifers. The International Water Management Institute, together with the World Bank, estimates that there are twenty to thirty million tube wells in India. A well saves crops during droughts and draws the aquifer dry if operated without meters or limits.

A classic example of overdrafting is the Ogalla aquifer beneath the US Great Plains. The aquifer feeds a significant share of American grain and livestock; in some areas of Texas, the level has dropped by tens of meters, and natural replenishment is taking centuries.

Subsidized electricity is fueling pumping. In Punjab, India, free electricity has been the norm since the 1990s; according to the Central Groundwater Board, water levels in the central regions of the state are falling by tens of centimeters annually. Solar pumps are eliminating the last remaining expense, the energy bill; the PM-KUSUM program is testing a new approach: farmers sell surplus solar power to the grid, transforming the pump from an unlimited supply into a source of income.

Artificial recharge of aquifers diverts floodwaters into infiltration basins or directly into wells. In Arizona, similar water banks have been in operation since the 1990s. In Gujarat, India, hundreds of thousands of small dams have significantly raised water levels beneath villages over the past decade, according to independent field surveys.

Drainage and salinization

Irrigation water carries dissolved salts. Plants drink and deposit these salts in the soil; without leaching and drainage, the soil profile degrades. According to a common estimate, one in five irrigated hectares on the planet already suffers from salinization or waterlogging.

The Central Asian example is well-known worldwide. Since the 1960s, cotton fields have been consuming the Amu Darya and Syr Darya rivers, the Aral Sea has lost its flow, and its water area has shrunk by approximately nine-tenths. Winds carry salt from the dried seabed to nearby fields, and the surrounding cropland suffers from secondary salinization.

The remedy has long been known. Drainage pipes at a depth of one and a half to two meters collect groundwater and divert it away from the soil. Leaching rates are calculated to displace salts below the roots without raising the groundwater level. Sodium-rich soils are loosened with gypsum, and salt-tolerant crops are sown during the transition years.

After the construction of the Aswan High Dam, Egypt lost its annual floodwaters. Constant irrigation raised groundwater levels, and the delta had to be drained for decades; eventually, most of it is now covered with pipes. Pakistan has been addressing the same issue with borehole drainage under the SCARP program since the late 1950s.

Reuse of wastewater

Treated sewage is a proven irrigation resource.

Israel returns approximately 85-87% of its treated wastewater to its fields, a feat no other country has yet achieved. The Shafdan junction receives sewage from the Tel Aviv metropolitan area, purifies it by filtering it through the sands of the coastal aquifer, and then distributes it to the irrigation networks of the desert Negev. Recycled water is cheaper than desalinated water, and farmers use it entirely. WHO guidelines determine the degree of treatment depending on the crop and delivery method; a subsurface drip line eliminates contact between the water and leaves and fruits, and sanitary requirements for this system are more relaxed.

In southern Spain, recycled water for greenhouses in Almería is mixed with desalinated seawater. Desalination for agricultural irrigation remains expensive: a cubic meter costs approximately $0.50 to $1.50, depending on energy prices. Not everyone can afford it. This water is effective for high-quality crops such as greenhouse tomatoes, berries, and flowers.

Digital tools

Landsat satellites have been continuously imaging the surface since 1972. Thermal channels are used to calculate the actual evapotranspiration of each field; the American OpenET project publishes these maps openly, and agencies in western states use them to verify their declared water intake. The Normalized Vegetation Index (NVI) highlights crop stress before it’s noticed by agronomists on the road.

The field is equipped with sensors and meters. Strain gauges and capacitive probes transmit moisture via radio, meters with telemetry record canal intake, and a controller opens a valve according to a schedule or a sensor signal. The meter maintains discipline for both the farm and the water management organization. A variable-rate sprinkler switches nozzle sections between field zones; in heterogeneous areas, tests show savings of approximately one-fifth of irrigation water. The data is sent to the cloud, from where it is read by both the agronomist and the pumping station.

Indian mobile services send farmers irrigation dates compiled from weather data and forecasts. An inexpensive smartphone replaces an agronomist in areas where advisory services are physically out of reach.

Economic mechanisms

When water is free, over-irrigation is rational: the farm’s only expenses are the pump and electricity. Tariff reform pegs fees per cubic meter instead of per hectare, making metering itself profitable. Irrigation systems in Spain, Morocco, and Mexico are moving toward this model; raising tariffs is politically difficult, so reforms are dragging on for years.

Transferring networks to users is the second lever. In the early 1990s, Mexico transferred the operation of state irrigation districts to water user associations, and by the middle of the decade, the associations managed the majority of the country’s irrigated areas, and payments for canal maintenance began to be made more regularly than under state control. Around the same time, Turkey transferred large tracts of land from the DSI structure to cooperatives and associations, with comparable results.

Subsidies for drip irrigation equipment operate differently. If not linked to metered water, the subsidy purchases the equipment without upgrading the water intake; if linked to cubic meters, it upgrades the water intake as well.

Pumps for tens of dollars lower the entry barrier for smallholder farmers in Africa. A treadle pump lifts water from depths of up to seven meters and irrigates up to half a hectare; sales in Kenya and Zambia have been established by NGOs in collaboration with local plumbers.

Virtual water

The term came into use in the early 1990s thanks to London geographer Tony Allan. Water used to produce grain, meat, or fabric ends up in the goods themselves. Middle Eastern countries have been buying it secretly for decades, along with imported wheat.

Mekkonen and Hoekstra’s calculations yield an average global footprint of about 1,800 liters per kilogram of wheat and about 15,000 liters per kilogram of beef. The variation between farms is enormous. The methodology has been criticized for mixing rainwater (green) and river water (blue); in calculations for stressed basins, it is the blue portion that is taken into account.

The economics of losses are simple. According to FAO estimates, approximately a third of all food produced never reaches consumers. Every lost tonne requires irrigation, fertilizer, and transportation; reducing losses frees up water from the river without removing a single cubic meter.

Water Market: Australia and Chile

The Murray-Darling Basin experienced the "millennium" drought of 1997-2009. The 2012 Basin Plan set caps on total withdrawals; by then, water rights had already been separated from land parcels, and quota trading had migrated to electronic trading platforms. Farmers decide based on the weather: whether to water their own crops or sell water to someone with a higher yield per cubic meter. In a dry year, they sell water, not cut back their gardens.

The scheme has its critics. Environmental releases are delayed, rights are becoming more expensive, and small farms are leaving the valleys.

Chile has been selling and mortgaging water rights like real estate since 1981. The northern basins also demonstrated their risks: rights were concentrated in the hands of mining companies, and minimum water releases were poorly regulated.

Climate variability and insurance

Precipitation in the main grain-growing belts comes in waves. The warm phase of El Niño intensifies drought over Australia and Southeast Asia, while rain patterns in East Africa change. Mountain snow acts as a seasonal reservoir: the Indus and its tributaries are fed by meltwater from the Hindu Kush and Karakoram during the summer breaks between monsoons. Heat during peak weeks increases crop evapotranspiration by tens of percent, compressing the irrigation schedule.

Index-based insurance links the payout to a measurable event: a rainfall shortfall at a weather station or a satellite-based dryness index, eliminating the need for an appraiser or disputes over the stage. Crop insurance schemes are in place in Kenya and India; in Mongolia, a similar principle is used to insure livestock against jute.

Regional strategies

Israel: A Closed Loop

Water in the country has been subject to a state quota since a 1959 law; every intake is licensed and accounted for. Most fields are irrigated using drip irrigation, tariffs are linked to a cubic meter and a seasonal quota, and water quality is categorized into fresh, recycled, and brackish. Five large desalination plants on the Mediterranean coast shut down most of the city’s water supply, and natural freshwater is being redistributed to agriculture and natural areas.

Negev gardeners irrigate with secondary water through subsurface lines, and remove salts through leaching with controlled drainage.

India: More harvest from every drop

The PMKSY irrigation program, launched in 2015, includes a subsidized subprogram with this slogan: the state reimburses up to half of the costs of micro-irrigation, with more for small farms. According to the Ministry of Agriculture, the total area under micro-irrigation in the country has approached 15 million hectares.

Punjab shows a different side. The state feeds the country with rice in an arid climate; free electricity has fed wells for decades, and groundwater levels in the central regions are falling by tens of centimeters per year. State diversification programs encourage the replacement of rice with corn, legumes, and cotton through subsidies and procurement.

Everyone is waiting for the monsoon. Its two-week delay rewrites the plans of entire districts.

The Netherlands: Greenhouses and Tips

The greenhouse sector operates with a nearly closed water circuit. Drainage from the mats is collected, disinfected with ultraviolet light, and returned to the roots, while rainwater from the roofs is stored in reservoirs. According to measurements by the Wageningen Agricultural University, a kilogram of greenhouse tomatoes requires only a few liters of water, compared to tens of liters in the open field.

Approximately eight thousand cubic meters of rain are collected per hectare of roofs in the country annually; reservoirs are designed to accommodate the entire seasonal runoff. After disinfection, the runoff is tested for salts and nitrates, and any excess is discharged only after inspection.

Water is managed by councils (waterschappen), bodies elected by residents and endowed with their own tax. They are responsible for canal levels, drainage, and runoff quality; the first councils are over seven centuries old. Their plans determine the fate of fields below sea level. An experimental farm on the island of Texel is testing potatoes and green crops irrigated with brackish water; coastal farms prone to flooding are adopting this method.

Accounting, quality and stock

Accountability is the primary requirement for management: how much is taken, how much is delivered to the field, how much is used productively. Satellite-based evapotranspiration estimates track water consumption even where meters are unavailable; in Australia, such data is already linked to trading quotas.

Agricultural runoff carries away nitrates, phosphorus, and pesticide residues; the traces are visible in algal blooms and dead zones in estuaries. Coastal buffer strips of grasses and shrubs prevent runoff, settling basins capture the runoff, and precise application of fertilizers reduces the source itself. Drainage water is distributed through a chain of crops: tomatoes receive the first irrigation, cotton or barley the next, and at the end of the chain is an evaporation basin with halophytes — plants accustomed to salt. This system is used in California’s San Joaquin Valley and the lower Nile.