Agricultural Water Use in California

This 2011 Center for Irrigation Technology Report reaffirms that overall water use by California agriculture is highly efficient and that large volumes of “new” water available through continued agricultural water conservation do not exist, despite claims to the contrary. When it comes to water supplies, claims that California farmers are wasteful and inefficient are inaccurate.

“Agricultural Water Conservation in California with Emphasis on the San Joaquin Valley” (DH Report), by David C. Davenport and Robert M. Hagan and published in 1982 by the Department of Land, Air, and Water Resources at the University of California at Davis, came to the same conclusions. In part, their reasons for writing the paper were as follows.

Water conservation is suggested by some as being a totally adequate solution to overcoming the state’s water deficit (now reflected mainly as groundwater overdraft). Others feel conservation is only a partial solution, and still others believe that past and present conservation practices have reached their practical limits, so the state’s projected deficit can only be met by further development and diversion southward of northern California water. These divergent views occur partly because of special interests, but mainly because of 1) misunderstandings over the uses, reuses, and final destinations of water, and 2) disregard for the impacts of water conservation/development actions on economic and environmental factors. This report attempts to clarify these issues (Davenport and Hagan 1982).

As in 1982, there are still major misunderstandings regarding irrigation.

“Agricultural Water Use in California: A 2011 Update” (The 2011 Update) combines a thorough review of published research and technical data in State of California publications to assess the overall potential for agricultural water use efficiency to provide new water supplies. The 2011 Update also concludes that there is little potential for new water unless large areas of agricultural land are taken out of production, which technically is not water use efficiency.

The intent of the 2011 Update is to provide an important addition to the ongoing discussions about California water and specifically what decisions must be made to assure adequate supplies for the future. The scientific and technical information presented provides a valuable tool in moving the discussions forward.

Among the 2011 Update’s key findings:

  • The Department of Water Resources’ (DWR) latest California Water Plan Update 2009 provides estimated reductions in both recoverable and irrecoverable fractions that may be attained based on specific levels of investment. Projection Level 5, which includes all “locally cost-effective projects,” will require $650 million total, over and above Proposition 50 funding, from 2005 through 2030. Estimated potential new water from these additional agricultural water use efficiency measures is about 330,000 acre-feet (AF) per year. This represents about 1.3% of the estimated current amount consumptively used by the State’s farmers (about 25.8 million acre-feet, or MAF, per year) and only about 0.5% of California’s total water use of 62.66 MAF. (All numbers are from the DWR Water Plan Update 2009 and use “dedicated water” as the basis, which includes environmental uses; source: “Agricultural Water Use Efficiency”).
  • Groundwater overdraft, with estimates from NASA satellite data suggesting a range of 3.45 MAF per year, continues to be a serious problem, especially in the San Joaquin Valley. Without development of new supplies and/or significant reductions in agricultural activity, this cannot be sustained (Buis 2009).
  • Changes in irrigation practices, such as switching from flood irrigation to drip, have the effect of rerouting flows within a region (or basin), but generally do not create new water outside of the basin.
  • Previous reallocations of agricultural water supplies for environmental purposes have significantly reduced diversions to irrigation. These reallocations include the Central Valley Project Improvement Act of 1992 (CVPIA), the Trinity River Restoration decision of 2000, two Biological Opinions regarding the Delta Smelt and salmon protection, and the San Joaquin River Restoration Program. The results of these actions include accelerated adoption of conservation strategies, increased groundwater extractions, and land fallowing/retirement.
  • On-farm water conservation efforts can affect water distribution patterns, with potential impacts on plants, animals, and recreation, as well as human and industrial consumptive uses. The effects can be positive or negative, and also inconsistent (e.g., on-farm conservation could reduce a city’s water supply but improve a nonpoint source pollution situation).
  • The 2011 Update points out that other impacts occur from irrigation water diversions and use, beyond the issue of consumptive uses such as evaporation. Therefore, it is an ongoing imperative for agriculture to improve on-farm efficiency. The 2011 Update identifies major shifts in the types of irrigation systems being used (including a 150% increase in the acreage under micro irrigation from 1994 through 2008 from 934,000 acres to 2, 336,000 acres) and cropping patterns (including a 69% decrease in cotton acreage and a 49% increase in orchard acreage between 1978 and 2007). This information is based on “Land Irrigated by Method of Water Distribution” (US Department of Agriculture, National Agricultural Statistics Service).

The 2011 Update is presented in sections, including an Introduction, and Conclusions and Findings. The Conclusions and Findings are supported by sections 2 through 4, which are summarized here:

Section 2. This section presents and explains key physical concepts that support the estimates for the future limitations of water savings from agricultural water conservation. Much of the surface runoff and deep percolation fractions that result from irrigation are recoverable fractions–they can be picked up (or pumped) and reused. These subsequent uses could include additional irrigation but also for use in wildlife habitat or, as is common with deep percolation to usable groundwater, as a city’s water supply. There are also irrecoverable fractions that may occur when surface runoff or percolation flows to a salt sink or whose quality is impaired to a point of being unusable. Reducing irrecoverable fractions can result in “new” water supplies.

The Agricultural Water Use Efficiency Strategy in Update 2009 of the California Water Plan outlines several estimates of attainable savings in both recoverable and irrecoverable water at different levels of investment (Projection Level). Projection Level 5 (which requires a significant investment in on-farm and district-level improvements) results in only an estimated 1.3% savings in water compared to total agricultural consumptive use.

Other factors in evaluating different Project Levels include:

  • The cost of water conservation versus savings of irrecoverable fractions (i.e., new water) is not a linear function. The marginal costs of each acre-foot savings increases exponentially as the desired savings increase.
  • The grant funding assumptions beyond Proposition 50 funding do not consider whether the measures implemented are cost effective at the farm level. It could reasonably be assumed that without additional available funding many of the investments required at the different Projection Levels would not be made.
  • The cost estimates for developing new water through agricultural water conservation need to be compared to cost estimates from other sources of new water. Several options are available in California that would result in new water (e.g., increased storage capacity, increased use of groundwater conjunctive management, desalinization, etc.). The benefits and costs (both tangible and intangible) of water conservation must be compared to all other options for developing new water.
  • The needs of the State for water reliability may not be able to wait for the time required to implement the changes contemplated in the conservation Projection Levels.

The 2011 Update stresses that agriculture must continue attempts to reduce irrecoverable fractions. The main options for doing so are:

  1. Reducing irrigated acreage. This is not a conservation measure but a transfer of water out of agriculture.
  2. Reducing crop consumptive use. This could be done in a variety of ways. One option is to change cropping patterns. The report points out that agriculture has made cropping changes. These have occurred over a long period of time and as a result of market forces (whether these forces were the result of court decisions, production system changes, or consumer preferences).
  3. Improving irrigation efficiency. This can be done through improved irrigation event management or possibly by changing to a system type that makes it easier to achieve the potential efficiency. The 2011 Update discusses how choosing an irrigation system involves many factors, including initial and ongoing maintenance costs of the system; crop economics (i.e., commodity prices versus production costs); physical restrictions on irrigation practices created by the soil, terrain, or crop; water supply quality, flexibility, and reliability; labor availability and ability; support infrastructure for a particular type of system; and management ability. While one system may have an inherently higher potential field efficiency than another (e.g., micro-spray versus furrow), all of these factors may combine so that in a given situation a furrow system may provide the same irrigation efficiency as micro irrigation and may also be the better business decision.

Section 3. In explaining the concept of recoverable and irrecoverable losses the report shows that the different water users in a basin or water use area are very often inextricably interconnected. The actions of one water user can affect others in the system. Another important finding is that diversions of water to irrigation, regardless of recoverable and irrecoverable fractions, can cause other impacts as well–to recreation, fisheries, natural habitats, overall water quality, and energy use.

Water allocation decisions primarily pertaining to the Central Valley Project (CVP) and the California State Water Project–but also during the era when the Hetch Hetchy system for the City of San Francisco, Mokelumne Aqueduct for the East Bay, and the Owens Valley system for the City of Los Angeles were constructed starting over 100 years ago–were made during an era when the natural environment was not as important an issue as it is now. Some of these decisions have been revisited and have resulted in major reallocations back to the environment.

These reallocations include:

  • Mono Lake Settlements of 1994- diverts 30,800 AF per year from Los Angeles supplies to the environment as Mono Lake elevation stabilizes.
  • Lower Owens River Settlement of 1997- further reductions in diversions from Owens River and groundwater pumping in the Owens Valley to Los Angeles
  • CVPIA of 1992- 800,000 AF per year from agriculture to the Sacramento and San Joaquin Valley’s environment and 340,000 AF per year from agriculture to the Trinity River.
  • Trinity River Restoration of 2000-  increased the return to the river system from 340,000 AF per year under CVPIA to 647,000 AF per year in a normal water year.
  • Biological Opinion (BiOp) regarding Delta Smelt (final rules still pending) first issued in December 2008 and Biological Opinion regarding Salmon Migrations (also under challenge) issued in June 2009- no final estimate of total diversions from agriculture due to overlapping actions and the effect of different water years. National Marine fisheries estimated a 330,000 AF per year reallocation from agriculture for the Salmon BiOp.
  • San Joaquin River Restoration Program issued 2009- 247,826 AF per year in a normal water year from CVP contractors to the environment.

Water reallocations back to the environment to alleviate pressures on fisheries and other natural habitats do not come without impacts. The original allocation decisions (no matter whether right or wrong) resulted in new environments, including major investments in irrigation and municipal & industrial (M&I) facilities resulting in jobs and an increase in State Gross Product.

Another major issue facing irrigation is the impact on water quality from surface runoff and deep percolation. The 2011 Update discusses nonpoint source pollution and how agriculture must deal with its legal obligations. Irrigated agriculture now operates under new voluntary area aggregated water quality regulatory conditions that are contingent on continued improvement. Without this continued improvement it may well be that irrigated agriculture will have to operate under individually directed waste discharge permits in the future. However, the physics of irrigated agriculture dictate that some level of intentional deep percolation must occur to prevent soil salinization and subsequent loss of this important productive resource. If irrigated agriculture is to survive (along with the food and fiber it produces), society must find a way to sustain an acceptable level of water quality impact.

Section 4. The recoverable/irrecoverable concept is reintroduced to underscore that on a volumetric basis, agriculture is very efficient. However, as was pointed out and discussed in Section 3, there are many concerns other than consumptive use.

Discussion in California is shifting towards overall agricultural water stewardship–going beyond an argument that is grounded in the sciences (e.g., irrigation, environment, water quality) to one that is also socio-economic in nature. As with all public policy issues, the arguments can be objective (e.g., more economic benefit can be generated from an acre-foot of water delivered to Silicon Valley than to the San Joaquin Valley) or subjective (e.g., maintaining X miles of Wild and Scenic rivers is a moral imperative). Further, even though there may be tangible benefits associated with any one argument, the body politic (i.e., voters) may favor the intangible.

The movement towards this type of discussion is ongoing. The authors point to a recent paper presented to the California State Water Resources Control Board (SWRCB) by the Delta Watermaster calling for a re-evaluation and possibly expanded and/or more rigorous application of the State’s constitutional imperative that water be reasonably and beneficially used (Wilson 2011).

Another indicator is California Senate Bill SBX7-7, The Water Conservation Act of 2009. One of the mandates of SBX7-7 is that DWR, in conjunction with all stakeholders, is to “…develop a methodology for quantifying the efficiency of agricultural water use” (Water Conservation Act of 2009). The main question, which is still to be answered as of this paper’s writing, is whether the “efficiency” to be quantified will be one based on strict volumes of water, or whether the economic benefits and costs of irrigation should also be considered.

The Conclusion. The 2011 Update is primarily prepared as an update to the 1982 DH Report. The findings of that report are still accurate–there is limited potential for agricultural water conservation to fix the water demand needs of California.

A central tenet continues to be the need for a better understanding of the concept of recoverable versus irrecoverable fractions when examining the potential for water conservation within agriculture. Claims of excessive irrigation inefficiency, with resulting large volumes of new water available are wrong for the same basic reason that the DH Report enumerated in 1982–most of the purported agricultural inefficiency is recovered and reused by other agricultural interests, cities, industry, and the environment, or left in groundwater basins.

However, regardless of what actual amount of net water savings would result, the authors emphasize that on-farm water conservation is a continual imperative–not just to create new water, but to alleviate other, sometimes unavoidable, impacts such as impaired water quality and habitat degradation.

The authors want to make it clear that the issues facing California today have gone beyond those that prompted the DH Report. The discussion must move to one of acceptable sustainability for all stakeholders, given that there are a number of steady-state solutions available. For example, one constant and critical issue that has continued over the past 30 years is groundwater overdraft. This issue alone, if not addressed in a timely manner, may ultimately seal the fate of much of San Joaquin Valley agriculture in particular.

A 2011 paper by the Public Policy Institute of California (PPIC) lists eight myths surrounding California water management that are seen to be impeding the development of real solutions. PPIC agreed that the potential for water conservation (agricultural or M&I) to fix the situation is widely overstated. But most importantly, the PPIC paper points to the involvement of all stakeholders in creating the problems that the State faces and the absolute need for cooperation among all stakeholders to solve these problems. PPIC stated it very well in the introduction to their paper:

Often, myths serve the rhetorical purposes of particular stakeholders. And they persist because our public policy debates are not sufficiently grounded in solid technical and scientific information about how we use and manage water. In combating these myths, we hope to set the stage for a more rational and informed approach to water policy and management in the state (Hanak et al. 2011).

The authors hope that “Agricultural Water Use in California: A 2011 Update” will also help in setting that stage.

The full Agricultural Water Use in California: A 2011 Update, can be downloaded at
About the Author

Peter Canessa, Sarge Green, and David Zoldoske

Authors’ Bios: Peter Canessa is program manager at Fresno State’s Center for Irrigation Technology and a registered agricultural engineer specializing in irrigation and drainage, agricultural water, water quality, and energy management. Sarge Green is a program director at CIT; his areas of expertise include agricultural water supply, groundwater, and water quality management. David Zoldoske is the director of CIT and an irrigation systems and water management expert.