Grain buyers and consumers increasingly evaluate their potential grain purchases in terms of “sustainability metrics” such as carbon or water “footprints.” In the future, grain growers’ access to markets and the prices they receive for their crops may depend increasingly on how crops are produced in terms of such sustainability metrics.
This study estimated a number of sustainability measures for water use in Arizona small grain production including: water application intensity, water productivity, water economic productivity, and water footprint. The study also evaluated how grain production, particularly as part of grain-vegetable crop rotations, enhances the regional sustainability of local agricultural production in the arid Southwest. Finally, the study evaluated estimates of Arizona durum wheat’s water footprint (water consumed per bushel produced) reported in popular water footprint calculators. It identified several methodological and data errors in these calculators that lead to an over-estimate of the water footprint of Arizona’s durum wheat production.
Findings
Among all crops grown in Arizona, wheat and barley have relatively low water application rates. According to recent USDA survey data, only 3.1 acre-feet (AF) / acre of water are applied to wheat and barley. This is 26% lower than the state average application rate of 4.2 AF / acre across all crops.
Over the last 30 years, the amount of water that growers apply to produce a bushel of wheat has fallen by 18%, while the amount of water applied to produce a bushel of barley has fallen 17%. Put another way, the amount of Arizona wheat produced per acre-foot of water applied has increased by 22% over the last 30 years. Arizona barley has seen a similar increase in “crop per drop” (bushels per acre foot of water applied) of 21% over the same time.
Over the last 30 years, water applied annually per acre to wheat and barley fell by 10%. Given 2013 acreage of these crops, growers were applying 37,066 fewer acre-feet of water than if they were applying water at the higher rates of 1984. This reduction in water applications is equivalent to the annual residential water use of 376,029 people in Tucson, Arizona. Put another way, this reduction in applications is equivalent to 40 percent of water deliveries Tucson Water makes to all customers (residential, commercial, and industrial) over its entire service area, which encompasses more than 700,000 people.
In 2013, Arizona growers of all crops (not just grains) spent $53.3 million on new irrigation equipment, facilities, land improvements, and computer technology. This amounted to investments in irrigation improvements of $151 per acre and $42,939 per farm. Of this $53.3 million, $12.2 million were investments primarily to conserve water, while another $1.1 million was devoted to conserving energy.
Recent research on irrigation efficiency in Yuma County, Arizona highlights the important role of wheat planted in rotation with vegetables, both in terms of (a) reducing absolute consumptive use of water and (b) improving economic water productivity. Since 1970, many Yuma County acres have shifted from continuous and long-season crops to vegetable-wheat rotations. Multi-cropped systems use less water because wheat following vegetables matures in late spring, eliminating the need to irrigate in the latter half of the summer, when there is high evaporative demand. The shift to wheat-vegetable rotations has reduced per acre water use (measured in terms of crop evapotranspiration) by 24% - 56% compared to previous cropping patterns. The shift to rotations has also dramatically improved economic water productivity – the dollar value of crop production per acre-foot of water consumed. Compared to older cropping patterns, wheat-vegetable rotations increase economic water productivity 9 to 21 times.
Environmental groups have increasingly called for shifts within agriculture toward relatively more wheat production in the Lower Colorado Basin as a means of both conserving water and preserving the sustainability of agriculture in the region.
Some recent reports have suggested that Arizona durum wheat has a substantially larger water footprint (water used per unit of crop output) than wheat production in other areas. Some of the data reported in these studies and reports, however, do not match the original data sources that they cite, with unexplained omissions and changes to data that overstate water footprint of durum production in Arizona, while understating it elsewhere.
This study adjusted water footprint estimates for Arizona durum wheat production by making use of more accurate and relevant data available on regional rainfall patterns, planting season length, and crop consumptive water use. Prior estimates either underestimate Arizona durum wheat yields, overestimate water available for use by crops, or both. Both types of errors mistakenly suggest that Arizona durum production has a larger water footprint than production in most other regions. However, using better data to develop more accurate estimates, we find that Arizona durum wheat production has a water footprint that is lower (in some cases much lower) than many other durum production regions.
Finally, estimates of crop water footprints, in general, often base their calculations on estimated water use on harvested acreage only. This approach ignores three critical facts of crop production:
- Many crop acres are regularly abandoned (not harvested at some point after planting).
- Although significant amounts of water and other inputs (such as fertilizers and seed) are applied to these abandoned acres, they yield no output.
- Irrigation is a key factor in reducing rates of crop abandonment.
Water footprint measures that do not account for water used on abandoned acreage can understate the true water footprint of crop production. This is important when comparing Arizona with other regions because abandonment rates are usually much lower in Arizona than elsewhere. Properly accounting for the effects of abandonment would increase measures of the true water footprint in all regions. This increase, however, would be negligible in Arizona, where abandonment rates are very low. The increase in the true water footprint in high-abandonment areas could be much higher. This study has developed and presents a formula to adjust water footprints for the effects of abandonment.
Methods
This report used data from various years of the US Department of Agriculture’s (USDA’s) Farm and Ranch Irrigation Survey (FRIS). FRIS data are collected roughly every five years as a follow-up survey to the Census of Agriculture. The most recent survey was conducted for 2013. FRIS data were used to compare water application intensity and water productivity over time.
To construct measures of economic water productivity, the study combined data on consumptive use of water by cropping pattern from the report A Case Study in Efficiency – Agriculture and Water Use in the Yuma, Arizona Area with production and economic data from Annual Statistical Bulletins of the USDA National Agricultural Statistics Service (NASS) Arizona Field Office.
The study next examined water footprints estimated for durum wheat production in Arizona and other regions as reported by the Water Footprint Network (WFN)–a non-governmental organization based in The Hague, Netherlands that develops and reports water footprints for (among other things) specific commodities. WFN provides one of the most widely-used water footprint calculators in the world. Data from this website were compared with water footprint estimates published by other studies and compared with more locally specific data available for durum wheat production in Arizona. Because the water footprint calculators are adapted from more general water use models and are applied at a more general geographic scale, their application does not necessarily fit production conditions in the main durum wheat growing areas of Arizona.
Finally, the study developed a simple formula to estimate biases in water footprint calculations that fail to account for land abandonment. The degree of bias increases with the percentage of acres abandoned and the amount of water consumed before abandonment.