A mealy-mouthed reaction to cutting off groundwater to new subdivisions

We need to move beyond governance by hubristic computer models.

I’m not necessarily opposed to the decision by the Arizona Department of Water Resources to stop accepting local groundwater pumping as satisfying the 100-year water supply requirement for new residential subdivisions in the Phoenix metro area.

However, such a significant policy decision shouldn’t be based on a computer model projecting a 4% shortfall in groundwater supplies for existing and already approved new homes … a hundred years from now. The attention that has been paid to the results of this model, nationally and locally, is silly and overwrought.

We live in an era of computer model hubris. Boffins claim to have created computer programs that duplicate the real world and human behavior in all its complexity: for the global and regional climate; for global, national, and local economies. And how much groundwater Valley residents will be consuming a hundred years from now.

The only thing we know for sure about these computer models is that they will be wrong, and often by orders of magnitude.  

The ADWR model is a straightforward projection based upon existing usage patterns. But the things that can affect demand for groundwater over the next 100 years are close to infinite and incalculable. 

Most obvious are things that would change existing usage patterns, efficiencies that would reduce consumption by existing and already approved future consumers. 

Most important are the potential substitution effects. The Valley has been easing off reliance on groundwater and increasing reliance on surface water, from the Colorado, Salt, and Verde rivers. This has been particularly the case within our large municipalities. So, over the next 100 years, how much flow is going to be available from those three rivers to continue substituting for groundwater? What are going to be the relative costs of each over time? What will electricity rates do over the next 100 years, which affects the relative cost of groundwater pumping versus alternatives?

Even more imponderable, what other substitution alternatives may become available over the next 100 years? There are groundwater basins outside the Valley designated for extraction and transportation to other places, particularly to the Valley. But there are political and infrastructure obstacles to overcome.  

I think reclaiming wastewater to drinking water standards is the most likely big, new source. The City of Phoenix says it is serious about constructing a treatment plant to do that. How big of a new source might it be, and how quickly? 

And, over the next 100 years, maybe what I regard as the white elephant dream of desalinated water for the Valley could become a reality.

The ADWR decision has serious consequences, particularly a reduction in supply of middle-class, single-family homes over time. In fact, there is a subtext of a debate about urban form at work here. 

Our large cities generally have a designation as meeting the assured water supply requirement. It is the exurbs, such as Queen Creek and Buckeye, where the ADWR decision could limit the construction of new homes. There are those who want to use water as leverage for infill and greater density. However, infill projects don’t deliver the same home for the value. And a sizable segment of the market prefers the elbow room available in the exurbs.

To the extent the decision delays the conversion of farmland to residential subdivisions, it might actually make the groundwater overdraft worse rather than better. Farms use more groundwater than homes. Moreover, new subdivisions using groundwater have to replace it with other water via the Central Arizona Groundwater Replenishment District.  

So, with the problem of imponderables in the model and known adverse consequences of the decision, why the mealy-mouthed “not necessarily opposed” formulation?

In significant part, due to the imponderables. 

To be sustainable, eventually groundwater pumping in the Valley has to achieve an equilibrium between what nature produces and what we extract. The Valley is approaching what is called safe-yield, but significantly through artificial recharge, banking excess surface water.

The future availability of excess surface water, particularly from the Colorado, is very much up in the air. Critics of allowing continued use of groundwater for new subdivisions focus on that. They assert that there is considerable doubt that the replenishment district will be able to secure the alternative supplies necessary to offset the additional groundwater pumping. It's not a concern to be shrugged away. 

Under the Groundwater Management Act, the director of ADWR may not have had a choice but to make the decision he made. And that illustrates the problem of an excessively regulatory approach to achieving a balance between supply and demand for water. It requires attempting the impossible, such as predicting the demand for a particular source of water 100 years from now.

Policy should consider the water supply holistically, not divided by source or location. The holistic supply over time is what really matters. A home built in one of the large cities will use pretty much the same amount of water as one built in Queen Creek. In terms of the security of the Valley’s future water supply, which bucket the water comes from isn’t as important as how much remains in all the buckets. 

Policy should be to move water to where people want to live, not require people to accept suboptimal housing choices because of artificial divisions of water sources and geography. Some people prefer more dense, urban living. Some prefer the elbow room and more value for the buck in the exurbs. Our management of water should facilitate both choices. 

We’ve learned that supply and demand for Colorado River water could be brought into balance through price. At a high enough price, enough high-priority users were willing to forbear so that shortages didn’t exclusively fall on lower-priority users. The use of price, rather than regulation, to allocate shortages and bring supply and demand into balance needs to be more broadly deployed. 

Because water markets are so underdeveloped, we are stuck with regulators making decisions with known and immediate adverse consequences based upon a highly speculative and distant need. I don’t know that Arizona, or the Valley, has the leadership up to the task, but that should change.  

Reach Robb at robtrobb@gmail.com.