Under Pressure: Common Governance of Arizona’s Groundwater

By Kyle Rose

As noted in our last article, Arizona’s water usage is unsustainable. Cuts from the Colorado River and lower levels of rainfall and snowpack due to climate change are forcing Arizona residents and businesses to cut back on water use. However, as 72% of Arizona’s water is used by agriculture, these cuts are largely inefficient and insufficient to meet the state’s growing water crisis. However, there is also another side of water use that needs to be addressed if cuts must be made: groundwater.

Groundwater is the second biggest source of agricultural water after surface water, and its importance is growing. A 2020 agricultural profile by the University of Arizona found that between 2010 and 2015, Arizona agriculture’s use of groundwater increased by 305,329 acre-feet, or 6.4%, even while agriculture’s overall water usage decreased by almost 39,000 acre-feet. In contrast, Arizona agriculture’s surface water use, which includes imports from the Colorado River, decreased by almost 360,000 acre-feet. Reliance on groundwater is already causing substantial ground sinking, also referred to as subsidence, with parts of Cochise County sinking at rates of almost half a foot a year. Even in Irrigation Non-Expansion Areas (INAs) and Active Management Zones (AMZs)  such as the Douglas INA, the ground is sinking at the rate of almost 4 inches per year. In comparison, most areas of metropolitan Phoenix have subsidence rates of less than an inch. This, however, is only one set of outcomes. To truly understand the greater impact groundwater overuse has on agriculture and the rest of the state, a review of the geology and the environmental and economic consequences is in order. 

First, Arizona has two main aquifer types, unconsolidated sand and gravel aquifers and permeable rock aquifers. Arizona’s unconsolidated sand and gravel aquifers, a subset of the interstate Basin and Range basin-fill aquifer system, are the primary holding medium for groundwater for around 96% of the state’s population and around 92.7% of its agricultural GDP. These kinds of aquifers are highly susceptible to pollution due to their high permeability. 

Second, although these aquifers are recharged by current natural water sources, they also contain large quantities of fossil water that has been trapped for thousands or millions of years. Fossil water takes tens of thousands of years or more to replenish naturally due to the depths at which they are found, and sometimes can never be replenished as the water sources that created them no longer exist. In other words, fossil water, at least on human time-scales, is a non-renewable resource. 

Finally, overpumping of groundwater can destroy aquifers due to subsidence. Once water is taken out of the rock layers in which it is held, the fissures that originally held the water compact under the weight of the surrounding earth. The process both lowers the ground itself and decreases the permeable rock layers’ ability to store water, permanently reducing the capacity of the aquifer and lowering the water level for the entire area. 

Taken together, these three traits make Arizona’s aquifers acutely sensitive to overuse. Drill deep enough and pump long enough, and you eventually will hit fossil water that cannot be replenished and risk collapsing the aquifer if too much is pumped. Aquifers also play an important role in feeding springs that flow into major rivers like the Gila and Salt Rivers. Simply pumping water back into them risks polluting the aquifer and eventually the springs with runoff unless it is treated first, an expensive process that not all rural communities can afford.

Besides the environmental impacts, these environmental costs also produce broader economic and social costs. For example, a 2014 study of subsidence in Phoenix found that houses located in subsiding areas were worth almost 10% less on average compared with those in non-subsiding areas. This is primarily due to extra repair costs for fixing cracked foundations, sloping floors, and distorting wood framing. Communities that exclusively use groundwater for their water supply are also at risk of running dry, which will ultimately force them to either build infrastructure to import water from other parts of Arizona or run out of water completely. Heavily-subsided land is also more vulnerable to floods, something that will become a greater concern as monsoons gain in strength due to climate change.

However, despite numerous negative consequences, farmers keep pumping at unsustainable rates. This paradoxical behavior can be explained by the fact that groundwater is a common-pool resource. Unlike private goods, common-pool resources are defined as goods whose use cannot be excluded and can be competed over. Because of these two aspects, free-riding is encouraged because even if one cuts back on the use of the good, others will just use it up anyway. Over time, a tragedy of the commons situation occurs, where the resource is used at unsustainable levels, eventually destroying it entirely and leaving everyone worse off. This kind of behavior is reinforced by lack of information about resource stocks and other users. If no one knows who is exploiting a resource or how much anyone else is taking, users have no way of knowing how to change their behavior. It also gives users the incentive to cheat on any agreements they have to regulate the resource, since an agreement cannot be enforced if no one knows who is breaking it. 

Using this framework, we can start to make sense of Arizona agriculture’s use of groundwater.

As the state’s aquifers often cross property lines, no person can exclude others from using it except the government, so multiple farmers can tap into the same aquifer. Despite this, almost 87,000 square miles of Arizona, or 75.7% of the entire state’s land, is either unprotected or has very few protections for its groundwater. These include major agricultural areas such around Yuma and lands around the southern Gila River. Outside of protected areas, farmers can drill wells without any restrictions on their number or capacity. Since no one farmer has any idea which other users are pumping or how much, nor an incentive to tell others, they free-ride and pump as much water as necessary to grow their crops. Over time, as outside water sources decrease or become more expensive, groundwater usage increases and with it all the previously mentioned negative consequences. 

Farmers know this but also fail to cooperate due to the risk of cheating. In other words, as the water table lowers over time and cuts from other water sources deepen, the only incentive farmers have is to drill deeper. Eventually, the wells run dry or the cost of their construction and maintenance becomes prohibitive for smaller farmers and local communities. In the long term, everyone loses. 

Despite these dire long term consequences, relying on government regulation in this area is not practical due to politics. Attempts to create water conservation and irrigation non-expansion areas in rural areas where aquifers are at risk have been repeatedly obstructed by entrenched interest groups. However, even if these conservation areas were passed, loopholes to get around the limits would spring up such as grandfathered wells or farmers would simply dig illegal wells. Pure market solutions are also elusive due to lack of groundwater ownership permitting individual profit without individual responsibility. Ultimately, lack of information hinders everyone from coming to a solution.

In other words, the most effective solution needs to be a mix of private and public measures that increase the availability and transparency of information. For instance, water from the CAP Canal and other pumped water resources is metered, crops take a certain amount of water to grow, and production output from farms is recorded by the USDA and local regulatory agencies. Combined, these three pieces of information could produce estimates as to how much groundwater a farm is currently using without metering wells. This information can then be made publicly available and advertised. Information on subsidence, which can also be used to calculate groundwater usage, could be gathered by the Arizona’s Department of Water Resources remote-sensing program. This program is currently restricted to AMZs and small sections surrounding them, but there is nothing to stop them from expanding it to all of Arizona’s agricultural areas. 

By doing this, local communities and, more importantly, other agricultural businesses, can know how much water everyone else is using. Communities can then target political pressure and negotiations towards the most egregious water users instead of the entire agricultural community. It would also allow other companies to put pressure on high groundwater users to cut back on water use, since they would be directly impacted by lowering water levels via higher drilling and maintenance costs for wells. Farmers could then come to reliable agreements about water use and reduce the appeal of free-riding. Furthermore, if combined with a variable rate system that is tied to seasonal water demand, these agreements could be directly tied into farmers’ overall water usage.

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