Farmland Irrigation
Agriculture drinks about seventy percent of the fresh water humans use, and a great deal of it evaporates before it reaches a root. Pumping it takes energy. The fix does both.
The effect compounds within years. Put it in place and it keeps working.
Origins
Irrigation built civilisation and it has also destroyed several.
The oldest large-scale human engineering projects on Earth are irrigation works: the canals of Sumer, the qanats of Persia, the terraces of the Andes and Bali, the flood management of the Nile. Wherever people learned to move water onto land, cities followed, and armies, and writing, and taxes.
And wherever they moved water onto land without adequate drainage, salt followed. Irrigation water carries dissolved minerals. It evaporates. The minerals stay. Over centuries the salt accumulates in the topsoil until the ground goes white and nothing will grow. Sumerian records show wheat being progressively replaced by more salt-tolerant barley, and then barley yields declining, and then the fields being abandoned. The fertile crescent is substantially salt pan now, and it was done by farmers watering their crops.
The twentieth century did it again, faster and larger. The Aral Sea was the fourth-largest lake in the world; Soviet planners diverted its rivers to irrigate cotton, and it is now mostly desert, with the rusting hulls of fishing boats sitting on sand two hundred kilometres from any water. It is one of the largest environmental catastrophes ever caused deliberately by an engineering decision.
The lesson has been available for four thousand years and we keep having to relearn it.
What it actually is
Most irrigation is flood irrigation: water is run across a field and gravity does the rest. It is ancient, cheap, and enormously wasteful. A large share of the water evaporates, runs off, or percolates below the root zone before any plant drinks it.
The alternatives are well understood and unevenly adopted.
Drip irrigation delivers water directly to the root zone, drop by drop, through a network of tubes. It can cut water use dramatically while increasing yields, because the plant gets a steady supply rather than a flood followed by a drought.
Sprinklers and precision systems apply water where it is needed and at rates the soil can absorb rather than run off.
Sensors and scheduling mean irrigating when the crop actually needs it, rather than on a calendar. Soil moisture probes cost very little and routinely reveal that a farmer is watering twice as much as necessary.
And the drainage. Nobody talks about drainage, and it is what killed Sumer. Irrigation without drainage brings salt to the surface. This is not a historical curiosity; it is happening now, across the Indus, the Murray-Darling, the Central Valley of California.
The climate angle is the energy. Pumping water is one of the largest electricity uses in agriculture, and in much of India and the Middle East it is pumped from ever-deeper wells with subsidised or free electricity, which is a machine for emptying an aquifer. Using less water directly means burning less fuel.
The numbers
The share. Agriculture accounts for roughly 70% of global freshwater withdrawals. Nothing else comes close.
The waste. In flood irrigation, a large fraction of applied water never reaches a plant. Efficiency improvements can cut application substantially while maintaining or increasing yields.
The energy. Pumping is a major agricultural electricity load, particularly in South Asia, where groundwater irrigation runs on heavily subsidised power. Reducing water use cuts emissions directly and immediately.
The aquifers. The Ogallala under the American High Plains, the North China Plain aquifer, and the aquifers of Punjab and Gujarat are all being drawn down faster than they recharge. These are not renewable on human timescales. When they are gone, the agriculture built on them ends.
The salt. Irrigation-induced salinisation affects a very large area of the world’s irrigated land, and it is functionally irreversible without expensive drainage. This is the oldest known failure mode in agriculture and it is still happening.
The honest paradox. Efficient irrigation frequently increases total water consumption, and this is one of the least-known and most important findings in the field. Give a farmer drip irrigation and he may irrigate more land, or switch to a thirstier crop, because water is now cheaper per hectare. This is Jevons’ paradox, it is well documented, and any programme that does not account for it may achieve nothing at all.
Why it matters
The most valuable thing on most farms is not the soil. It is the water, and we behave as though it is free.
In much of the world it literally is. Electricity for pumping is subsidised to zero for political reasons, and so the water underneath is pumped up and sprayed across a field in the middle of the afternoon, in July, where most of it evaporates before it touches a root. Nobody is being wicked. The price is telling them to do it.
And the water under the High Plains, under the Punjab, under the North China Plain, is not being replenished. It fell as rain during the last ice age. It is, in the exact sense of the word, fossil water — the same category as fossil fuel, formed over geological time, spent within a single human lifetime, and gone.
Your grandchildren will farm that ground or they will not, and the difference is being decided now, by pumps, on land where nobody is paying attention.
There is a version of this that every farmer already understands, because farmers are the people who watch the water table. The well that used to be at forty feet is at ninety. The neighbour drilled deeper and now yours is dry. This is not an abstraction and it does not need an environmentalist to explain it. It needs a price that tells the truth, and technology that is already sitting on the shelf.
What it actually takes
Confronting the subsidy. Free or near-free electricity for pumping is the single largest driver of groundwater depletion in South Asia, and it is politically almost untouchable. Any honest account has to say this, and any workable solution has to find a way through it — which usually means paying farmers for the power they do not use, rather than trying to charge them for what they do.
Capital, which smallholders do not have. Drip irrigation systems cost money up front and pay over years. Financing, not conviction, is the barrier.
Accounting for the rebound. This is the hard one. Efficient irrigation often expands irrigated area or shifts to thirstier crops, and total water use goes up. Programmes must cap total extraction, not just improve efficiency, or they may make the aquifer situation worse while congratulating themselves.
Drainage, which nobody funds. Salinisation destroyed the first agricultural civilisation on Earth and it is destroying farmland now. Drainage is expensive, invisible, and the only thing that prevents it.
Measuring extraction. In most of the world, groundwater pumping is unmetered. You cannot manage what nobody counts, and nobody is counting.
Where it matters most
The Indus and Gangetic plains are the epicentre: the largest groundwater irrigation system on Earth, running on subsidised power, depleting aquifers at a rate visible from space via satellite gravity measurement.
The High Plains and the Ogallala aquifer are the American equivalent. Some counties have already pumped themselves out and reverted to dryland farming, which is a preview.
The Central Valley of California is subsiding measurably as the groundwater is withdrawn, and the land surface is dropping, permanently reducing the aquifer’s capacity to ever refill.
The North China Plain feeds a very large population from an aquifer being drawn down hard.
The Aral Sea basin remains the standing monument to what happens when nobody says stop.
How to tell it’s being done well
Is total extraction capped, or only efficiency improved? This is the question that separates a genuine programme from a counterproductive one. Efficiency without a cap frequently increases total water use.
Is anyone metering the groundwater? Most of the world does not. Everything else is guesswork.
Is there drainage? Irrigation without drainage brings salt to the surface. This destroyed Sumer and it is still destroying farmland.
Who pays for the power? If pumping electricity is free, no technology will fix the depletion, because the price is telling the farmer to keep pumping.
What you can do
Anyone
- Most of the water we use is used to grow our food, not in our homes. Household water saving is worthwhile and it is a rounding error against irrigation.
- Know where your food's water comes from. A great deal of it comes from aquifers that will not refill.
Farmers
- Soil moisture sensors are cheap and almost always reveal you are watering more than you need to.
- Drip pays for itself in water, energy and often yield, but the capital cost is real and financing is the obstacle.
- Watch your water table, and talk to your neighbours about it. Aquifers are a commons and they fail collectively.
Policymakers
- Meter the groundwater. You cannot manage what nobody counts, and almost nobody counts.
- Cap total extraction, do not just subsidise efficiency. Efficiency without a cap can increase total use.
- Pay farmers for the power they do not use, rather than trying to charge them for what they do. It is politically survivable and it works.
- Fund drainage. It is invisible, unglamorous and it is what prevents salinisation.
Business and investors
- Agricultural supply chains dependent on depleting aquifers have a material, mostly unpriced, long-term exposure.
- Drip irrigation finance for smallholders is a large and underserved market with a clear payback.
Who is working on this
We are researching which organizations in our directory of 8,493 actively work on this solution, and we only list an organization once we have verified it. That research is ongoing. In the meantime, search the directory yourself:
Questions
How much water does agriculture use?
Roughly 70% of all freshwater withdrawn by humans. Nothing else comes close, which means that household water conservation, while worthwhile, is a rounding error against irrigation.
Why is efficient irrigation a climate solution?
Because pumping water takes energy, and in many regions a great deal of it. Groundwater irrigation in South Asia runs on heavily subsidised electricity, and reducing water use directly reduces the fuel burned to move it. It also reduces methane from flooded fields where rice is involved.
What is the paradox with efficient irrigation?
That it often increases total water consumption, which is one of the least-known and most important findings in the field. Give a farmer drip irrigation and he may irrigate more land or switch to a thirstier crop, because water is now cheaper per hectare. Efficiency without a cap on total extraction can make the aquifer situation worse.
What is salinisation?
Irrigation water carries dissolved minerals. It evaporates and the salt stays behind, accumulating in the topsoil until nothing will grow. It destroyed Sumerian agriculture and it is currently affecting a very large area of the world's irrigated land. Drainage prevents it, and drainage is expensive, invisible and almost never funded.
What is fossil water?
Groundwater that fell as rain thousands of years ago and is not being replenished on any human timescale. The Ogallala aquifer under the American High Plains and the aquifers of the Punjab and the North China Plain are all being drawn down faster than they recharge. When they are gone, the agriculture built on them ends.
What is the single biggest obstacle?
The price of electricity for pumping, which in much of South Asia is subsidised to nearly zero for political reasons. No technology fixes depletion when the price is telling the farmer to keep pumping. The workable route is usually to pay farmers for the power they do not use rather than trying to charge them for what they do.
Sources
- Project Drawdown - Improve Irrigation Efficiency (Drawdown Explorer) Framework and classification. Cited, not reproduced.
- FAO AQUASTAT - global water use in agriculture
- Grafton et al. (2018), Science - The paradox of irrigation efficiency
- NASA GRACE - satellite measurement of groundwater depletion
- IPCC (2019) - Special Report on Climate Change and Land
The solution taxonomy follows the framework popularised by Project Drawdown. The analysis above is our own; for their carbon modeling and rankings, visit them directly.