By Ellen Hanak, senior policy fellow at the Public Policy Institute of California; Richard Howitt, professor and department chair of agricultural resource economics at UC Davis; and Ariel Dinar, professor and director of the UC Riverside Water Science and Policy Center
This commentary appeared in the Sacramento Bee on July 16, 2011
In the contentious debates over California's water management policy, one of the most misunderstood issues is agricultural water use efficiency. For decades, people have mistakenly assumed that improving agricultural irrigation techniques is a simple way to free up water supplies for other uses. In fact, policies that subsidize or mandate the adoption of more efficient irrigation methods often inadvertently increase the amount of water farmers use. To generate real savings, state policies need to reduce barriers to the water market, to encourage farmers growing low-value crops to sell some of their water to other users.
Although it seems counterintuitive, improving irrigation efficiency usually does not produce significant water savings. Efficient techniques such as drip irrigation allow farmers to farm their fields more intensively and to expand irrigated acreage with the water they "save." This often actually increases net farm water use – the amount consumed by crops – because it reduces the amount of water returned to the environment.
In contrast, most of the excess irrigation water used in "inefficient" techniques like furrow irrigation is returned to streams or aquifers, where it becomes available for reuse somewhere else in the system. Multiple studies in California and around the world have come to this same conclusion. Most of the water that replenishes aquifers in the Central Valley comes from irrigation runoff that seeps into the ground, for example. In only a few areas of the state, such as the Imperial Valley, can farmers save large amounts of water by adopting more efficient techniques. In such areas, excess irrigation water flows into saline water bodies or contaminated aquifers, where it becomes unavailable for reuse.
There are indeed good reasons to improve irrigation efficiency. For one, it can provide economic benefits for farmers. Farmers usually pay for the amount of water they apply to their fields, not the amount consumed by crops. When they face limited supplies, farmers often have an incentive to adopt more efficient techniques, such as drip irrigation, to make use of every possible drop on their farms.
These techniques, often combined with laser leveling of fields and more precise doses of fertilizers and pesticides, can improve crop productivity and quality and raise profits. In recent decades, many San Joaquin Valley farmers have made such changes, which have enabled them to plant more acres of higher-value fruit, nut and vegetable crops.
Improving irrigation efficiency can also provide environmental benefits. Agricultural runoff sometimes contains harmful salts and other contaminants, and more efficient irrigation can help reduce these discharges. This is another reason for the rise in more efficient irrigation techniques on the west side of the San Joaquin Valley, where farmers are required to limit runoff of selenium, a toxin to wildlife. Similarly, by reducing diversions, irrigation efficiency may allow higher stream flows on particular stretches of rivers, improving conditions for aquatic life.
Given the benefits and limitations of using more efficient irrigation techniques, how should California approach conserving agricultural water use?
The best policy is to let market forces work. Real conservation usually requires either shifting to crops that use less water or reducing crop production by fallowing farmland. Agriculture still accounts for nearly 75 percent of all human water use in California, and most of that water is still devoted to relatively low-value crops.
In our recent book "Managing California's Water," we show that the value of water differs dramatically across agricultural regions of the state because of different growing conditions and cropping patterns. Water markets are a flexible and efficient way to encourage farmers to create real water savings by selling some of the low-valued water to cities and to other farmers with higher-valued uses.
Unfortunately, California's water market has been faltering in recent years because of too many market barriers, including a cumbersome state approval process and local restrictions on farmers' ability to sell water they've conserved. Relaxing these barriers will give farmers better price signals.
Regulating irrigation technologies is not an effective way to go. Policies that impose particular technologies, or even ban specific crops, are likely to impose higher costs on farmers and society, while failing to save real water. Likewise, policies that subsidize irrigation technologies may benefit farmers, but will generally fail to achieve the societal goal of saving water.
If the goal is to reduce polluted agricultural runoff or improve stream flows, the best policy is to adopt regulations that directly address pollution discharges or flow levels and allow farmers to choose the most cost-effective way to meet these requirements. Often, farmers will adopt more efficient irrigation techniques in response, but policymakers should not micromanage these business decisions.
Agricultural water conservation is an essential part of California's water future. But our water system is complex. Not every approach that sounds like it would reduce water usage by farmers ends up making more water available to other users. It is time to take water conservation seriously by relying more on markets and science to achieve our goals.