Growing Water in the Desert

Image above: Lettuce farming in Yuma County, Arizona. An estimated 90 percent of US lettuce consumed in the winter comes from this area (courtesy of Kurt Nolte, University of Arizona)

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In my last blog I emphasized both the imperative and the opportunities for ‘growing water’ on irrigated farms in water-scarce regions. As I come across more real-world examples from my research, I’ll share them through this blog (and please share your own stories).

I recently became aware of an analysis conducted by the Yuma County Agriculture Water Coalition that discusses the water-saving efforts of farmers in the far southwestern corner of Arizona.

Yuma County is one of the hottest and driest regions of the US, and it is also one of the most agriculturally productive. Yuma County ranks in the top 0.1 percent among US counties in vegetable and melon sales, the top 0.5 percent in sales of all crops, and in the top 1 percent in sales of all crop and livestock products combined. This strong agricultural productivity is made possible by fertile alluvial soils along the lower Colorado River, an abundance of sunlight and a nearly frost-free growing season, and some of the highest-priority rights to the waters of the Colorado, held by the six agricultural entities pictured below.

Irrigation districts in Yuma County, Arizona
(map courtesy of Yuma County Agricultural Water Coalition)

Historical growth in water productivity

Importantly, the water productivity – measured here as crop sales per acre-foot (AF) of water withdrawn from the Colorado River – of these Yuma County farmers is now substantially higher on average than other Arizona counties using the river’s water. In Yuma County, gross crop receipts average $681 per AF of water, while receipts ranged from $162-$520 per AF in the five other Arizona counties that utilize Colorado River water.

The story of water use in Yuma County caught my attention not just because of this water productivity, but because of the fact that water required by these farms has decreased by 18% since 1975, which helps bolster their water productivity (i.e., if you use less water to grow a crop and the dollar value of the crop remains the same, the index of water productivity increases).

Even more impressive is that fact that the water not delivered to Yuma farms is simply left in the river for other water users, or to benefit the aquatic environment. In my last blog I highlighted the opportunity for farmers to implement various water-saving measures and then market their surplus water to other water users, or to environmental interests interested in enhancing environmental flows, thereby ‘growing water’ as a new source of income to supplement their crop revenues. This opportunity remains available to Yuma farmers should they choose to implement additional water-saving strategies going forward. But historically, the water savings in Yuma County have been motivated by other factors.

Less water is now required on Yuma County farms due to improved irrigation practices and shifting into multi-crop systems
(graph courtesy of Yuma County Agricultural Water Coalition)

As illustrated in the water graph above, water deliveries to Yuma farms declined substantially between 1975 and 1985 in response to growing concerns regarding the salinity of Colorado River water. The US Salinity Control Act of 1974 was passed to provide financial incentives to farmers to lessen salt runoff. Within the Wellton-Mohawk Irrigation and Drainage District, 10,000 acres of farms on sandy, high infiltration rate soils were retired from production. Irrigation improvements were made on other farmlands, including leveling of 44,000 acres to improve water application and reduce salty runoff, concrete lining of 263 miles of farm canals, and the construction of 10,600 on-farm water control structures to enable farmers to better measure and control their water applications. Also important was the provision of irrigation scheduling assistance to growers, provided by the US Bureau of Reclamation. The combined benefit of these programs totaled to reduced water deliveries of 145,000 AF from 1975-85.

However, as the above graph shows, water use again shot up in the five years from 1985-90, swallowing up almost all the water gains made over the previous decade. This resulted from a 50% jump in vegetable production and the water-intensive practice of germinating newly planted vegetable fields using ‘subbing,’ in which furrows are filled with water for 7-10 days to facilitate uniform germination and early season crop development. This subbing practice typically consumes two to three feet of water!

Yuma farmers quickly learned how to become more efficient in growing vegetables, however. They shifted from flooding their furrows to sprinkler irrigation, and reduced the water required for vegetable establishment to only nine inches.

Saving water by shifting crops

During 1990-2010, as more and more Yuma farmland was converted from water-intensive crops such as alfalfa and citrus trees to multi-crop production systems including vegetables, the farmers again realized substantial water savings, lowering their overall water deliveries by 15% from 1990 levels. These water savings were made possible by the fact that vegetables and other crops incorporated into multi-crop systems (such as durum wheat or melons) are grown during cooler times of the year, avoiding the high evapotranspiration months of July, August, and September (see chart below).

By shifting to crops that don’t require irrigation during hot, dry summers, Yuma farmers have been able to reduce their overall water needs
(diagram courtesy of Yuma County Agricultural Water Coalition)

Because wheat, melons, and vegetables all consume less than half the volume of water used by alfalfa, crop switching makes a great deal of sense in a hot desert like Yuma. And in a broader region facing severe water scarcity challenges, the lessons learned in Yuma can help many other farmers interested in growing water.

(Many thanks to Meghan Scott and Wade Noble of the Noble Law Office in Yuma for alerting me to this story, and for helping to ensure its accuracy)