Agricultural water use efficiency

As the state’s largest water using sector, many look to agriculture as a way to free up water supplies for environmental and other uses.  However, estimates of how much water could be saved vary widely, and oftentimes don’t result in ‘new’ water

California is unarguably the nation’s leading agricultural producer with the state’s 76,400 farms and ranches producing more than 400 agricultural commodities and providing nearly half of the fruits, nuts, and vegetables grown in the US.  In a typical year, about 9.6 million acres are irrigated with about 34 MAF of water, which is about 40% of the state’s supplies.  As the state’s largest water-using industry, many look to agriculture as a way to increase supplies for environmental and urban uses.

California agriculture has made great strides in improving water use efficiency while increasing output.  Since 1970, many water providers have modernized their water delivery systems, and farmers have moved to higher value crops and are utilizing technologies to save water and increase crop yields; this has significantly increased the economic value of the state’s agricultural production.  However, quantifying the efficiency improvements made, assessing irrigation efficiencies, and planning further improvements is hampered by a lack of surface water delivery and groundwater use data.

In an effort to address water use efficiency and conservation, in 2009 the state legislature passed the Water Conservation Act (SB X7-7), requiring both urban and agricultural water suppliers to increase water use efficiency.  For the agricultural sector, the Act mandated that water suppliers providing water to 10,000 acres or more of irrigated land must measure the volume of water delivered and adopt a pricing structure based at least in part on the quantity delivered.  The legislation also required certain agricultural water suppliers to prepare agricultural water management plans and to implement a set of efficient water management practices if they are cost-effective and technically feasible.

IMPROVING AGRICULTURAL WATER USE EFFICIENCY

The California Water Code (CWC) Section 10817 defines ‘water use efficiency’ as “the efficient management of water resources for beneficial uses, preventing waste, or accomplishing additional benefits with the same amount of water.”  Water efficiency can be a cost-effective and flexible tool to adapt to drought as well as to address longstanding water challenges.

Agricultural water efficiency can be improved through hardware upgrades, better water management, and the use of agricultural technologies.  However, in order to make use of many water efficient practices, growers need flexible water delivery systems that can deliver water at the time, quantity, location, and duration required; this often requires modernization of the water supplier’s delivery systems.

Farmers are increasing their use of drip irrigation and micro-sprinklers; a survey of growers in 2010 found that the irrigated acreage using drip irrigation and micro-sprinklers increased 16% between 2001 and 2011, while the acreage of land irrigated using surface irrigation methods decreased by 13%.

However, conversion of traditional irrigation systems to pressurized systems and installing advanced technologies requires significant investment in facilities and equipment, as well additional energy that increases costs for both the water supplier and the growers.  The California Farm Water Coalition reports that from 2003-2008, San Joaquin Valley farmers invested $1.5 billion in high efficiency irrigation equipment; considerably more has been spent in recent years.  These additional costs can be a challenge for many water suppliers and growers.

Besides drip and micro-irrigation, growers are also employing other technologies to be more water efficient, such as utilizing real-time communications networks, satellite weather information, ET and soil moisture sensing systems.  Furrow, basin, and border irrigation methods have been improved to limit runoff and deep percolation, and organic or plastic mulch can be used to reduce evaporation of applied water, minimize weed growth, and improve crop growth and productivity.  Additionally, agricultural land stewardship practices can reduce water and improve on-farm management.

At the water supplier level, water suppliers are upgrading and automating their systems to meet the needs of growers, as well as optimizing their systems by lining canals, developing spill recovery and tail water return systems, using regulating reservoirs, and managing surface water conjunctively with groundwater.

HOW MUCH WATER CAN BE SAVED?

While agriculture has done much to improve efficiency, many say there is still room for improvement.  How much improvement, however, is the subject of a broad and ongoing debate.  At the high end, some researchers say potential savings could be as much as 5 million acre-feet per year, while others have determined the potential to be only about 330,000 acre-feet per year, and that the only way to free up large volumes of water in the agricultural sector is to take land out of production, which they note technically does not fit the definition of water use efficiency.

Others caution that any approach to any approach to estimating the potential of developing new water supplies through agricultural water conservation must acknowledge the different between recoverable flows such as surface water runoff and deep percolation to groundwater and irrecoverable flows, such as those lost to transpiration, saline sinks, and non-beneficial evaporation.

RECENT ANALYSIS ON AGRICULTURAL WATER USE EFFICIENCY

In the 2006 CalFed Water Use Efficiency Comprehensive Evaluation considered what the potential water savings would be for different levels of investment in water efficiency programs, and estimated the potential savings to be from 34,000 to 190,000 acre-feet per year of irrecoverable water and 150,000 to 927,000 acre-feet per year of recoverable water.

The 2009 Pacific Institute report, Sustaining California Agriculture in an Uncertain Future, estimated that the potential savings from utilizing efficient irrigation technologies, improved irrigation scheduling, and regulated deficit irrigation could yield potential water savings ranging from 4.5 MAF to 5.9 MAF, depending on if the hydrology is wet, average, or dry.  It is important to note that the report did not separate its quantitative estimates between recoverable and irrecoverable water savings, and thus the potential water savings are applied water savings only.

A 2011 report from the Center for Irrigation Technology, Agricultural Water Use in California: A 2011 Update, refuted much of the Pacific Institute’s findings, estimating the potential of new water from agricultural water use efficiency to be far less at 1.3%, or approximately 330,000 acre-feet per year.  The report also stated that the only way to free up large volumes of ‘new’ water would be to take large acreages of farmland out of production, which technically is not water use efficiency.

BUT IS IT ‘NEW’ WATER?

It’s important to recognize that saved or conserved water in agriculture may or may not mean ‘new’ water available for instream flows or other purposes.  Saved water is only ‘new’ water when it is prevented from evaporating, or from flowing to salt sinks or to the ocean.  In California, irrigation water applied in excess of crop requirements most oftentimes provides water to another field below it, either directly through surface flows or indirectly via groundwater recharge and pumping.  Much of the water in an agricultural setting is used and reused many times over; this is why on-farm improvements will not result in regional water savings.  Indeed, some efficiency improvements may actually increase water use as a result of larger plants, higher yields, and increased irrigated acreage.

Therefore, in agriculture, it is necessary to focus on net water savings and not on applied water reductions.  Net water savings is achieved by reducing the irrecoverable flows; a reduction of applied water that results in the reduction of recoverable flows often does not save water, but nonetheless may have other benefits, such as improvements in water quality, flow, and timing, as well as conserving energy.  It should also be noted that much of the recoverable flows in California go to wetlands and managed wetlands and provide the only source of water for such wetlands.

Water use efficiency actions can benefit aquatic habitat through changes to instream flow and timing; additional benefits could include water quality improvements such as reducing subsurface drainage flows and reducing contaminant loads.  However, depending on the timing of the flow changes, there can be impacts such as reduced runoff to downstream water users and increased concentration of pollutants in drainage water.

IN CONCLUSION …

Farmers are business people; they are striving to maximize agricultural profits without compromising economic vitality, water quality, or the environment.  Successful implementation of efficiency measures depends on the technical feasibility, the cost-effectiveness, the availability of funds, and the willingness of water suppliers, as well as the soils, topography, climate, markets, available surface and groundwater supplies, and crop choices.

Click here to download this resource management strategy from the California Water Plan.

 

FOR MORE INFORMATION

Reports and other documents …

• Water for Farms, from the Public Policy Institute of California
• Sustaining California Agriculture in an Uncertain Future, from the Pacific Institute
• Agricultural Water Use in California: A 2011 Update, from the Center for Irrigation Technology at CSU Fresno
• From Storage to Retention: Expanding California’s Options for Meeting Its Water Needs, from the California Roundtable for Water and Food Supply
• Irrigation and Water Use, from the USDA Economic Research Service

Agencies and organizations working in this area …

• The California Agricultural Irrigation Association:  The California Agricultural Irrigation Association (CAIA) is a network of irrigation professionals throughout California whose goal is to promote common ideals, standards, and business practices.
• The California Farm Water Coalition: CFWC was formed to increase public awareness of agriculture’s efficient use of water and promote the industry’s environmental sensitivity regarding water.
• The California Farm Bureau Federation: California Farm Bureau Federation is a nonprofit organization of farmers and ranchers consisting of county Farm Bureaus from nearly every county in California, established in 1919 to work for the betterment of family farmers and ranchers in California.