Water and the high-desert vineyard

The Verde Valley averages under 14 inches of rain a year, less than half what the weather stations in the high country to its north, east and south record. In the Willcox basin, the growing season from March to October brings about eight and a half inches, and more than two thirds of that arrives in July and August. Grapevines can be stubborn about drought, but not that stubborn, and the growers’ own petitions for both regions treat irrigation as a necessity.

Wells, almost everywhere

In the Willcox petition to the federal government, growers were blunt about their source. The basin is closed: no river drains it, and no canal or aqueduct brings water in. Irrigation comes from wells and from what little rain falls, which is why the petition says vineyard owners must manage their water carefully, with drip irrigation and other water-saving methods.

The Verde Valley has a river running through it, yet its growers told the same agency much the same thing. Their petition said groundwater inside the region was sufficient for irrigation, and that vineyard owners saved it with drip systems and with reclaimed water approved for farm use.

A University of Arizona survey of 56 grape growers around the state, run from December 2022 to May 2023, put numbers on the pattern. Wells were the most common source, domestic wells for 49 percent of respondents and commercial wells for 35 percent. Drip was the main irrigation system for 91 percent. When growers were asked which subjects mattered most for extension programs, irrigation came first, with 84 percent calling it very important, ahead of pests and disease.

The monsoon’s part

Southern Arizona’s summer storms come when the large-scale circulation shifts and humid air flows north from the Gulf of Mexico and the Gulf of California. For a vine, the timing matters as much as the volume. May and June are the hard months: the air is dry, the winter’s soil moisture is gone, and in heat above about 90 degrees the leaves close their pores to save water, which slows the vine’s growth and the ripening of its fruit. When the monsoon arrives, humidity lets the leaves stay open longer, the cloud cover takes the edge off the sun, and some of the rain soaks down to recharge the aquifer the wells draw on. It does not replace irrigation. It makes the late summer, when the grapes are ripening, a little easier.

Willcox becomes an AMA

Arizona manages groundwater most tightly inside Active Management Areas, where new irrigated farmland is off the table. In November 2022, voters in the Douglas basin chose to create one. Voters in the Willcox basin turned theirs down.

Two years later the state acted anyway. On December 19, 2024, the director of the Arizona Department of Water Resources ordered the Willcox Groundwater Basin designated as an AMA, finding that active management was needed to preserve the existing supply and that land subsidence or fissuring threatened property or storage. The public process drew testimony from 38 people and 423 written comments. The designation took effect on January 8, 2025, making Willcox the state’s seventh AMA and the first created by the director’s own decision.

Under the order, irrigation of new acreage in the basin is prohibited, and non-exempt wells must be measured and their withdrawals reported. Farmland keeps its right to irrigate only if it was legally irrigated at some point in the five years before designation. For a grower, that fixes the map: a new vineyard in the basin has to go on ground that was already watered.

What growers say they will do

The same university survey asked about the future. Eighty-six percent of growers said they were at least somewhat concerned about water availability. Asked how they were responding, the most common answer was drilling another well, at 17 percent, followed by passive water harvesting, improved efficiency and taking part in water legislation. Only 5 percent reported using deficit irrigation, deliberately giving vines less water than they could use, to manage canopy growth.

The concern was already on the record in 2020. When the Verde Valley was proposed as a wine region, one public comment questioned whether grapes could be grown at all in an area so prone to long droughts. The federal answer was that they already were, with water-saving irrigation.