From Colorado River Studies at Utah State University (Jack Schmidt, David Rosenberg, Jian Wang, Kevin Wheeler, and Eric Kuhn):
An essential question that drives discussion about the future of the Colorado River is, “How much water do we need?” The human body must have water to survive, and water is needed to grow crops, but the amount of water used by different societies varies greatly. In the Colorado River basin, our sense of the amount of water that we “need” is not just driven by basic survival, but is also affected by our preferences in urban and suburban landscaping, the crops that we grow, the technology and practices associated with irrigation, and the industry that exists. Thus, the question of “need” unavoidably becomes mixed with the question of “want,” and our sense of “want” is strongly affected by our aspirations for the future.
Obviously, any consideration about future water use depends on projections of population growth and anticipated agricultural and industrial uses of water. Depending on one’s vision of the future, including preferences about landscaping, agriculture, and in-stream flows to benefit aquatic and riparian ecosystems and river recreation, one might expect different future water projections in different parts of the Colorado River basin. In planning for future consumptive water use, it is important to distinguish between the amount of water we “need” to maintain the present urban areas and the existing agriculture and industry and the amount of water we “want.”
In the book Science Be Dammed, Kuhn and Fleck (2019) described how the original negotiators of the Colorado River Compact overestimated their projected future needs of water supply from the Colorado River. If one adds together the estimates of future water use made by each state in the 1920s, the total anticipated use in the Upper Basin was 8.1 million acre feet, more than twice the actual amount the Upper Basin is currently using a century later (Kuhn and Fleck, 2019, table 1). We are left to speculate as to whether these were well-intentioned over-estimates or political gamesmanship. Making such overestimates today, regardless of motive, complicates negotiations of the future of the Colorado River, because negotiators must sort need from want. Watershed runoff is decreasing as the regional climate warms (Udall and Overpeck, 2017; Milly and Dune 2020), and the pie that must be divided among the states is getting smaller.
Since the 1980s, Reclamation and the Upper Colorado River Commission (UCRC) have made many estimates of future water use. Sometimes, negotiators treat those projections as if they are precise and accurate predictions. In fact, every estimate is its own scenario—a possible trajectory of future consumptive water use. Each scenario is based on assumptions about population, cities, agriculture, and industry. Despite our best efforts, the scenarios do not necessarily enumerate all possible future conditions.
We see a disparity when comparing past projections to the actual consumptive use in the Upper Colorado River basin (Figure 1, dashed colored lines; UCRC 2007 and 2016; Bureau of Reclamation (BOR) 1981, 1984, 2012). Each recently-proposed scenario of future water depletion was higher than the actual consumptive use reported by Reclamation in its semi-decadal Colorado River Consumptive Use and Loss Reports (Figure, solid black line). In fact, since at least 2000, the actual Upper Basin uses and losses have been stable or slightly decreasing, not increasing. The retirement of thermal power plants and reduced irrigated areas may further decrease future Upper Basin depletions (see the analysis by Kuhn 2020).
Overestimation of future water needs is not unique to the Colorado River basin—many other water systems also have consistently overestimated their demands. Motives for overestimation are many (Heberger and Cooley, 2016; Kindler and Russell, 1984). Water managers may define scenarios of high future use so they can prepare for future unknown demand increases by securing enough water, while simultaneously communicating their political intentions to competing users. Overstated future depletions have the potential to focus attention on new infrastructure needs. However, managers must also avoid building expensive water supply infrastructure that goes unused should future water use be less than was anticipated. If there is a rush to build water-diverting or water-consuming infrastructure that subsequently becomes obsolete due to a changing climate, emerging technologies, or over-anticipated demands, those investments can easily become stranded assets (Kalin et al, 2019).
Scenarios help us plan for a diverse set of uncertain future conditions, even though most or all of the scenarios may never come to pass. Thus, we can consider scenarios that focus on aspirational growth as well as scenarios of continuing stable use or aggressive conservation.
As we move forward in negotiating the allocation of water supply that comes from the Colorado River, Figure 1 suggests that basin stakeholders should also consider scenarios of stable use that reflect continuing historical trends of no growth in total Upper Basin consumptive water use. Basin stakeholders should also consider scenarios where future use of water decreases due to changes in landscaping and irrigation practices.
The question then is: How should Colorado River stakeholders manage the future Colorado River in the face of these water demand uncertainties? For insight, read our white paper “Managing the Colorado River for an Uncertain Future.”
All data used in this blog can be found at Wang (2020). Future of the Colorado River Project. Link: https://github.com/JianWangUSU/Future_of_the_Colorado_River_Project/tree/master/UpperBasinConsumptiveUses
Bureau of Reclamation. (1981). Projected Water Supply and Depletions Upper Colorado River Basin. Salt Lake City, Utah.
Bureau of Reclamation. (1984). Projected Water Supply and Depletions Upper Colorado River Basin. Salt Lake City, Utah.
Bureau of Reclamation. (2012). Colorado River Simulation System Model, Demand Management Input Tool Current Trends and Other Scenarios. v4. Link: http://bor.colorado.edu/Public_web/CRSTMWG/CRSS/
Heberger, M. and Cooley, H. (2016). 21st Century Water Demand Forecasting. Pacific Institute. Link: https://pacinst.org/rethinking-future-water-demand-blog/
Kindler, J. and Russell, C. (1984). Modeling Water Demands. London: Academic Press. ISBN 0-12-407380-8 Link: http://pure.iiasa.ac.at/id/eprint/2392/
Kuhn, E., and Fleck, J. (2019). Science Be Dammed: How Ignoring Inconvenient Science Drained the Colorado River. University of Arizona Press.
Milly, P. C., and Dunne, K. A. (2020). Colorado River flow dwindles as warming-driven loss of reflective snow energizes evaporation. Science, 367(6483), 1252-1255.
Udall, B., and Overpeck, J. (2017). The twenty‐first century Colorado River hot drought and implications for the future. Water Resources Research, 53(3), 2404-2418.
Upper Colorado River Commission. (2016). Upper Colorado River Division States, Current and Future Depletion Demand Schedule. Salt Lake City, Utah. Link: http://www.ucrcommission.com/RepDoc/DepSchedules/CurFutDemandSchedule.pdf
Upper Colorado River Commission. (2007). Upper Colorado River Division States, Current and Future Depletion Demand Schedule. Salt Lake City, Utah. Link: http://www.ucrcommission.com/RepDoc/DepSchedules/Dep_Schedules_2007.pdf