The Water Resources Research Center of the University of Arizona has just published “Arroyo 2018″ which is devoted to the title subject. You can download the 16-page report at:
Here are some excerpts and highlights:
Archeological evidence suggests that irrigated agriculture first arrived along the Santa Cruz River in southern Arizona around 1200 BCE. During this time, irrigation canals were constructed along the river near the current Interstate-10 corridor just west of Tucson. These early farmers irrigated corn, tobacco, and squash.
Between 300 BCE and 1450 AD, native people constructed a network of canals near the Salt and Gila Rivers in South Central Arizona, where they developed a distinct culture known as “Hohokam”. Evidence of these canals exists today near the sites of the Pueblo Grande Village on the east side of Phoenix, and the Casa Grande village west of Florence. The disappearance of this civilization may have been due to changes and variability of the local climate.
Following the demise of the Hohokam, the Xalychidom Piipaash (Maricopa) and Onk Akimel O’odham (Pima) tribes became established in southern and central Arizona. These tribes continued using irrigated agriculture, but with simpler canal systems.
By the mid-19th century, when American and Europeans made the trip across the deserts of the Southwest to reach the California gold fields, the Gila River people diverted water from the river to agricultural fields in the valley of the Middle Gila, creating a virtual breadbasket in Arizona. They supplied large quantities of wheat to the U.S. military and traded farm products, such as beans and squashes, to travelers and newcomers.
By the late 1800s, American settlers had diverted much of the water of the Gila and Salt Rivers that supported native agriculture, causing the Pima and Maricopa tribes to lose their livelihood and ushering in an era of extreme hardship for the tribes.
According to the Arizona Department of Water Resources, agriculture accounts for 68 percent of water use in Arizona. A 2017 study by University of Arizona economists estimated that agriculture contributes $23.3 billion to the Arizona economy.
Arroyo 2018 discusses the milestones in water use and development:
The Reclamation Act of 1902 allowed the federal government to fund construction of dams and other irrigation projects.
The Central Arizona Project (CAP), initiated in 1968, diverts water from the Colorado River for use in agriculture and municipalities.
The Groundwater Management Act of 1980 regulated extraction of groundwater. Southern Arizona was divided into Active Management Areas where extraction of groundwater for agricultural use is limited. Agriculture has transitioned to more CAP water. By 2014, groundwater accounted for 40 percent of the state’s annual water use.
Arroyo 2018 notes that farmers have been able to reduce water use, while increasing yields, by making improvements to irrigation systems. Several of those improvements are discussed.
Also, the introduction of genetically modified crops that are resistant to herbicides has made possible the adoption of no-till farming in Arizona. With no-till agriculture, farmers can leave biomass from harvested crops on fields, which lowers soil temperature, reducing soil evaporation and soil salinity. It can also prevent soil erosion.
Arizona farmers are also exploring new crops which use less water: Agave can be marketable for tequila, fiber, and biofuel. Industrial hemp can provide fiber. Guayule can yield rubber and biofuel.
The report concludes:
The agricultural industry has a significant impact on Arizona’s economy, and it is a dominant force in many rural communities across the state. Because different regions have different water conditions, farmers must consider location-specific factors in their water management decisions. Along the Colorado River and Lower Gila River, growers hold some of the oldest and most secure water rights in the state. With this water they have developed a nationally important region for vegetable production. In Central Arizona, CAP water has alleviated groundwater overdraft problems, but the potential for shortage in CAP’s supply is increasing uncertainty in this region. Here, farmers and irrigation districts face the real possibility of being forced to go back to the groundwater pumps or to take lands out of production. Beyond the reach of the CAP, agriculture reliant on groundwater is watching water levels fall as communities struggle to find acceptable regulatory solutions to the threat of depletion.
Growing demands for water, food, and fiber, coupled with near-term likelihood of Colorado River shortage, have led to increased focus on Arizona’s agricultural water use. Water efficiency gains have been substantial in recent decades, reducing total water use while increasing agricultural production statewide. There is still room for efficiency improvements, with the help of science and technology and financial assistance. As they continue to grow, cities and other water users will continue to look for ways to supplement their water supplies through voluntary water transactions with farmers that include attention to impacts on rural communities. Although sometimes contentious, this process can yield mutual benefits. The need for food and fiber will grow locally and globally; and because it is more reliable and productive than dryland farming, irrigated agriculture will supply this need. Finding the right balance among competing water demands in Arizona will take continued collaborations among growers, government, the scientific community, and concerned citizens.
Guayule, a desert rubber plant