Water for Agriculture: A Limited Resource

The Economist recently published a special report on water, which summarizes the difficulty of ensuring adequate clean water supplies for a growing global population. (It also touches on the related challenge of sanitation, which affects water quality.) Agriculture accounts for nearly 70% of the world's water use, although that number varies by region. In the US, 41% of water goes to agriculture; in India, the number is close to 90%.

India also has the distinction of being the country that draws the most groundwater, the Economist reports. With most areas subsidizing electricity, it's relatively cheap for individual farmers to sink private tubewells and run them with electrical pumps. As these wells proliferate, water levels are falling in several regions. One state that's seeing its groundwater disappear is advancing a sustainable solution.

The southeastern Indian state Andhra Pradesh relies on annual monsoons to replenish its groundwater, but its rocky composition means only about 12% of the rainfall ends up in the aquifers. Nine NGOs there are organizing a project - involving nearly a million people in 650 villages - to monitor and manage the state's limited water resources. The Economist describes how it works:

At Mutyalapadu and round about, this comes from the Rev V. Paul Raja Rao's Bharati Integrated Rural Development Society, which also runs a clinic, an orphanage and a microcredit organisation. One of the first water-management tasks for an organisation such as this is to map the locality and define its hydrological units, each of which is an area drained by a single stream with one inlet and one outlet. The region encompasses 11 hydrological units, one containing 41 villages. Some are much smaller.

The farmers taking part in the project measure and record rainfall, the water table, withdrawals and other data for their land. They calculate how much water will be available if the table is not to fall, decide which crops to grow and estimate how much water they will use, bearing in mind that about half will go in evapotranspiration. They then sit down together in a group--there are several of these for each hydrological unit--and draw up a water budget. Details of the eventual agreement, showing who should grow what and how, are displayed on a wall in the village and updated over the year with information about rain, harvests and even revenues.

No one is compelled to take part; the enterprise is voluntary and collaborative. But so far most farmers, and their families, seem pleased. The local diet has become more varied, since 13 crops are now grown in the area, compared with eight in the past. Those that need most water-- bananas, rice and cotton--have yielded to others that need less, such as peanuts and a locally bred variety of green lentils. Chemical fertilisers have been replaced by compost, a change welcomed for both health and financial reasons. Mulch, manure and organic weedkillers are also used. The upshot is that although incomes have not risen--most of the crop is eaten, not sold for cash--the cost of inputs has fallen and those involved feel they are engaged in a sustainable activity.

The result sounds impressive: "The relentless drilling of wells has abated ... Overdrawing is judged to be under control."

The World Bank is funding a similar project in several parts of China, although this effort aims specifically to reduce evapotranspiration (ET). When thinking about water inputs for agriculture, it's important to consider not only how much water a plant must get in order to grow, but how much will evaporate from the plant and the surrounding soil. Unlike water that remains in the soil, ET is essentially water lost to the local user. ET is the focus of the China project the Economist describes:

In a project that covers several parts of arid and semi-arid China--Beijing, Hebei, Qingdao and Shenyang, as well as the Hai basin and the smaller Turpan basin--the World Bank has been promoting water conservation. Elements of the approach are similar to that in Andhra Pradesh: farmers gather in water-users' associations to plan and operate irrigation services, for example. But the aim here is specifically to reduce ET, at the same time increasing farmers' incomes without depleting the groundwater.

This is high-tech stuff that involves not just drip irrigation and condensation-trapping greenhouses, but remote sensing by satellites which provide ET readings for areas of 30 by 30 metres. This tells farmers how much water they can consume without adversely affecting the ecosystems in their river basin. If the project is successful, as a pilot has been, it will also establish the use of an internet-based management system, mitigate losses from flooding and increase the supply of water to industry.

Many people are already aware that we need to reduce the amount of water we use for lawn care, showering, laundry, etc. - not to mention to protect existing water resources from contamination. We should also remember that what we eat and wear has implications for whether the global population will have enough water to live.