Water Efficiency June 2012 : Page 47
• Previous reallocations of agricultural water supplies for environmental purposes have signifi cantly reduced diversions to irrigation. Th ese real-locations include the Central Valley Project Improvement Act of 1992 (CVPIA, www.usbr.gov/mp/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. Th e results of these actions include accelerated adoption of conservation strategies, increased groundwater extractions, and land fallowing/retirement. • On-farm water conservation eff orts can aff ect water distribution patterns, with potential impacts on plants, animals, and recreation, as well as hu-man and industrial consumptive uses. Th e eff ects 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). • Th e 2011 Update points out that other impacts occur from irrigation water diversions and use, beyond the issue of consumptive uses such as evapo-ration. Th erefore, it is an ongoing imperative for agriculture to improve on-farm effi ciency. Th e 2011 Update identifi es major shift s in the types of irrigation systems being used (includ-ing 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). Th is 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 Conclu-sions and Findings. Th e Conclusions and Findings are supported by sections 2 through 4, which are summarized here: Section 2. Th is section presents and explains key physical concepts that sup-port the estimates for the future limita-tions of water savings from agricultural water conservation. Much of the surface runoff and deep percolation fractions that result from irrigation are recoverable frac-tions—they can be picked up (or pumped) and reused. Th ese subsequent uses could include additional irrigation but also for use in wildlife habitat or, as is common with deep percolation to usable ground-water, as a city’s water supply. Th ere are also irrecoverable fractions that may occur when surface runoff or percolation fl ows to a salt sink or whose quality is impaired to a point of being unusable. Reducing irrecoverable fractions can result in “new” water supplies. Th e Agricultural Water Use Effi ciency Strategy in Update 2009 of the California Water Plan outlines several estimates of attainable savings in both recoverable and irrecoverable water at diff erent levels of investment (Projection Level). Projec-tion Level 5 (which requires a signifi cant investment in on-farm and district-level improvements) results in only an estimat-ed 1.3% savings in water compared to total agricultural consumptive use. Other factors in evaluating diff erent Project Levels include: • Th e cost of water conservation versus savings of irrecoverable fractions (i.e., new water) is not a linear function. Th e marginal costs of each acre-foot savings increases exponentially as the desired savings increase. • Th e grant funding assumptions beyond Proposition 50 funding do not consider whether the measures implemented are cost eff ective at the farm level. It could reasonably be as-sumed that without additional avail-able funding many of the investments required at the diff erent Projection Levels would not be made. • Th e 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 avail-able in California that would result in new water (e.g., increased storage capacity, increased use of ground-water conjunctive management, desalinization, etc.). Th e benefi ts and costs (both tangible and intangible) of water conservation must be compared to all other options for developing new water. • Th e needs of the State for water reli-ability may not be able to wait for the time required to implement the changes contemplated in the conser-vation Projection Levels. The 2011 Update stresses that agriculture must continue attempts to reduce irre-coverable fractions. The main options for doing so are: 1. Reducing irrigated acreage. Th is is not a conservation measure but a transfer of water out of agriculture. 2. Reducing crop consumptive use. Th is could be done in a variety of ways. One option is to change crop-ping patterns. Th e report points out that agriculture has made cropping changes. Th ese 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 con-sumer preferences). 3. Improving irrigation effi ciency. Th is can be done through improved irriga-tion event management or possibly by changing to a system type that makes it easier to achieve the potential ef-fi ciency. Th e 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 produc-tion costs); physical restrictions on irrigation practices created by the soil, terrain, or crop; water supply quality, fl exibility, and reliability; labor avail-ability and ability; support infrastruc-ture for a particular type of system; and management ability. While one system may have an inherently higher potential fi eld effi ciency 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 JUNE 2012 WATER EFFICIENCY 47
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