The American Southwest is blessed with land and sunlight to spare, but in order to maintain the growth of billions of dollars of crops, support local flora and fauna, provide 4200+ megawatts of hydropower to cities, and quench 40 million residents' thirst, the supply of fresh water must be carefully monitored and allocated. 

The Colorado River is an integral natural resource that provides water for domestic and agricultural uses. Its state of flow is paramount to the health of southwestern US states as well as Mexico. This fortified essay uses the question of

to explore the potential consequences of water scarcity in the American Southwest.

## **The river's history**

The Colorado River is the major waterway in the American Southwest. In 1869, John Wesley Powell, a geologist and future director of the USGS, surveyed the majority of the river, which begins in Colorado within the Rocky Mountain National Park and terminates in the Gulf of California in Mexico about 2330km later. What Powell saw was a hard-charging, aqua-blue river stippled with whitewater rapids, often fenced in by canyons. Historically, the river was a lifeline for indigenous peoples in an otherwise harsh arid climate. American settlers were immediately drawn to the river, recognizing its potential to transform the surrounding terrain. Brigham Young, a Mormon leader and the first governor of the Utah territory, predicted the building of an empire in the desert.

By the early 20th century, that empire of farms, orchards, and cities came to pass. The river was aggressively diverted and parceled to the point that the seven states which relied on its water required a process to apportion it fairly. The [Colorado River Compact of 1922](https://www.usbr.gov/lc/region/pao/pdfiles/crcompct.pdf) and a handful of other agreements and court decisions (including the [Mexican Water Treaty of 1944](https://www.usbr.gov/lc/region/pao/pdfiles/mextrety.pdf) ) created what's called "The Law of The River." The river was divided into three sections based on usage: the upper basin (Colorado, Wyoming, and parts of Utah, New Mexico, and Arizona), the lower basin (California, Nevada, and parts of Utah, New Mexico, and Arizona), and Mexico. Each basin received an allotment of 7.5 million acre-feet of water per year, and Mexico received 1.5 million acre-feet per year. For perspective, one acre-foot of water is 326,000 gallons, which is enough water to supply 2-3 families annually.

The majority of the river's storage infrastructure was built shortly after the compact. The Hoover Dam was completed in Nevada in 1935, creating Lake Mead, the largest artificial reservoir in the country at the time, with the ability to hold several years' worth of Colorado River flow. The Glen Canyon Dam was constructed upriver in Utah several decades later, creating Lake Powell, another large artificial reservoir. Both lakes serve as valuable water storage facilities, but they also generate billions of kilowatt hours of low carbon hydropower energy each year. In years of plenty, these reservoirs are used to 'bank' extra water. In years of drought, the water can then be released to make up for allocation shortfalls.

## **Allotments**

To determine how much water could be allotted to each state, the compact calculated how much water typically runs through the Colorado River. Lees Ferry is considered the midway point of the river (and it also marks the beginning of Grand Canyon National Park). It divides the drainage areas of the upper and lower basins, and its water gauges are used to determine water allocations. Using a range from 1905-1922, the compact estimated that the river's annual flow at Lees Ferry was on average 16.4 million acre-feet. It’s worth noting that annual runoff volume from year to year varies greatly, with a peak of 22.2 million acre-feet in 1984 to a nadir of 3.8 million acre-feet in 2002. Ground rules were set to determine priority in high and low flow years. 

It might be surprising to learn that the 1922 Colorado River Compact's annual flow estimate was inaccurate. A century's worth of data and tree ring analyses have since [refined the annual flow estimate](https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2005WR004455) to 13-15 million acre-feet. This means that the river's allotments are already over-budget by more than 1 million acre-feet. Furthermore, the compact assumes that these conditions will remain relatively unchanged over time, a concept called [stationarity](https://en.wikipedia.org/wiki/Stationary_process). As we'll discuss below, the river's inputs should not be considered unchanging.

The Colorado River basin is currently experiencing the Millennium Drought, two decades of below-average flows. Currently, the water levels at Lake Mead and Powell are at historic lows. Recently, the dams holding these reservoirs installed hydraulic turbines designed to operate in lower flow. There's concern that these lakes, especially Lake Mead, could reach 'deadpool' levels in which the water is too low to generate power. In 2019, the US Congress passed the [Colorado River Drought Contingency Plan Authorization Act](https://www.congress.gov/bill/116th-congress/house-bill/2030/all-info), a plan to manage Colorado River's reservoir shortages. 

In 2021, Metaculus users said it was [more likely than not](https://www.metaculus.com/questions/7246/water-shortage-in-the-us-2021/) that the country would declare a water shortage, which it did in August 2021. This declaration triggered Tier 1 of the Drought Contingency Plan, which requires significant cuts to Arizona's allotment next year. 

## **Water trends**

How does the water get into the Colorado River basin in the first place? Most of it originates as snowpack at the river's headwaters. Historically, the bulk of precipitation arrives via winter storms that are caused by frontal systems from the North Pacific Ocean. Summer thunderstorms from the Gulf of California/Mexico also supply appreciable moisture. The region often experiences extreme fluctuations in precipitation year over year influenced by the "[atmospheric circulation patterns and sea-surface temperature (SST)](https://pubs.usgs.gov/fs/2004/3062/) of the tropical and North Pacific Oceans." However, [analysis conducted by the Colorado Climate Center](https://watercenter.colostate.edu/wp-content/uploads/sites/33/2021/06/ColoradoWater_V38-1v-r15-web.pdf#page=37) found that precipitation trends are potentially shifting—total precipitation has stayed relatively constant, but with a little less snow in the winter and a little more rain in the summer. This shift in precipitation seasonality is potentially significant because snowmelt is how [most water enters alpine streams](https://pdf.sciencedirectassets.com/287972/1-s2.0-S2214581818X00032/1-s2.0-S2214581817304639/main.pdf?X-Amz-Security-Token=IQoJb3JpZ2luX2VjELD%2F%2F%2F%2F%2F%2F%2F%2F%2F%2FwEaCXVzLWVhc3QtMSJHMEUCIAtPpdL6CjBQtAt%2F8LPtzDseIevSNxLXVunwUTN9TT8GAiEAkBN%2Bj0KOCss82w9jMb%2BeJG2qFM1FmWwsbYS29DoxOIUq%2BgMIGRAEGgwwNTkwMDM1NDY4NjUiDLpeVl0WP1uINHuLTSrXA9DdflFv4vNK9Mt2qT0WWVgGfXvGstvSW%2BTHuVtQlDN5asKCb%2BnpP4VGFXRtIkk0b0KQPjAPWSZkumqAWlMtL%2Bft317z9ui2L5FTBDt1gIp3ooS%2F5Jk6ltbqQWbb%2BNKG%2FsNywdewYqMNFHNUrryZcWhWzU7hkkVpoegaEh0pJoaolfRrdG%2BCYPOQK5yjBBEX8iNLXBUf6iOhy%2BcUgfagjXjsEnzQIwqlNxfbGVChvfAzW1m%2F%2FCZgyS9g4yPrOKcK0B%2FLb3GoYODfJZ6HgObxgu%2FPZpBjt7YuPgFdwbid0BvsHojalhs%2F3pOqqADc2tTM56XO%2Ff%2FuuBYnaSfVgzDkn5gLuVELjXzuMq9BsSIuK2w3%2BqSxzkjlRu4VwdTOZ9ckJSkdFfSVQZDQ8XAN0PWLIoSeAg6iao4wFLDvFVKxfrMxdEsNRUoQ0e0klEwYz1EecYpvP%2BqeMjKWRg1gZ%2FKOIO6eqjMufLuiF0L4YU8nmbxstpduOg9sUmyKpNAGDjFz%2F%2BZyP1Ab4UpOYB6s%2FgTebUd6s6IDx7rQYtWH3iGVInINfYRFpedT4Mzxp4JCQ1gith4GLC0TX87zLvJ7zEPQwy7kWVg3ULhxp6YuycKJpim9eFu1NL6H7jD0nq2KBjqlAbE2GXtcCizhB%2FqWGE33dqdszJKz8gOzu2zy3YUJ9aJGH6YWPTblIqKEqZwGvGEti2S73m4HWn0GBM7t%2Berl6obWIQ753OiYQt4t05e60l8BglERqeM9GaJYmNO7ApC%2BHam%2Fquak5K5GVT8p8vgYNkVhP6MHJjHOvV5AFgCbGWruYEoSaQSdhwk6Id0GXeuIpt6LSlJVwN4ItSerzKh14VBI4yEYiA%3D%3D&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20210922T163716Z&X-Amz-SignedHeaders=host&X-Amz-Expires=300&X-Amz-Credential=ASIAQ3PHCVTYREPJOMMD%2F20210922%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=6c5188432b98fc919f0d8a8d47cc455b916ed891295fcffe9338a90ee44a2dc5&hash=5a96f922e6c52c342267450c3aaa07827e668ef3c183c5b89b1926f5b3135fbd&host=68042c943591013ac2b2430a89b270f6af2c76d8dfd086a07176afe7c76c2c61&pii=S2214581817304639&tid=spdf-3a6bdb6e-6c09-4ce0-bd03-d227d2dad60a&sid=0b1acae17c2cf84b099ab2f84ca01d604349gxrqa&type=client). A [USGS study on loss of snow cover](https://www.usgs.gov/mission-areas/water-resources/science/atmospheric-warming-loss-snow-cover-and-declining-colorado?qt-science_center_objects=0#qt-science_center_objects) explains:


> Snow cover, because of its high albedo, is a shield that reduces the amount of solar radiation absorbed by the basin. In years when the snow cover is low, more radiation is absorbed, and that extra energy drives more evaporation. Conversely, an extensive cover of snow suppresses evaporation. When more water is consumed by evaporation, less remains behind to supply the river, and the flow of the river decreases, as does the availability of water to the users downstream.

What else beyond shifting precipitation patterns can accelerate the loss of snow cover? The Colorado River basin's temperatures increased [almost 0.8°C over the past century](https://science2017.globalchange.gov/chapter/6/). Higher temperatures in the basin cause higher rates of snowmelt, [decrease soil moisture](https://pubs.er.usgs.gov/publication/70032682), and increase [evapotranspiration](https://www.usgs.gov/special-topic/water-science-school/science/evapotranspiration-and-water-cycle?qt-science_center_objects=0#qt-science_center_objects). This trend is called [aridification](https://www.pnas.org/content/117/22/11856). Altogether this results in less precipitation reaching the river basin. Data from the USGS study quoted above resulted in [estimates that each increase of 1](https://www.science.org/doi/abs/10.1126/science.aay9187)[°](https://science2017.globalchange.gov/chapter/6/)[C will decrease river flow by 9.3%](https://www.science.org/doi/abs/10.1126/science.aay9187). Note that other studies have reported ranges between [2.5% and 15%](https://repository.library.noaa.gov/view/noaa/25440). Another [study in Science](https://www.science.org/doi/10.1126/science.aaz9600) estimates that almost half of the current Millennium Drought is caused by anthropogenic climate change. Overall, predictions of Colorado River flow range from +5% to -40% depending on precipitation and temperature. 

**What will be the Colorado River’s average annual flow volume (measured at Lees Ferry AZ) from 2025-2050?"**

Building an accurate long-term water flow model is difficult because weather and precipitation is [exceptionally hard to predict](https://scijinks.gov/forecast-reliability/). For management purposes, water managers typically use a [24-month study](https://knowyourwaternews.com/why-do-water-managers-pay-such-close-attention-to-the-24-month-study/) to make informed decisions. Various Colorado River flow models weight precipitation and temperature differently. Here are my variables (with weights) and prediction:

* Precipitation (3x): There doesn't seem to be a significant, perceptible change in precipitation volume over the past century. It's entirely possible that the drought will break or continue over the next few decades, although it does seem unlikely that it will increase to levels seen right before the Colorado River Compact in 1922.
* Temperature (2x): I feel quite certain that the Colorado River basin's temperatures will continue to increase due to climate change. How much it will change is up for debate (I predict on [this Metaculus question](https://www.metaculus.com/questions/1596/what-year-will-the-2c-climate-threshold-be-crossed/) that the +2 degree Celsius threshold will be crossed around 2035). Consequently, I believe increased evapotranspiration and decreased snow cover will continue over the next two decades. [This paper on drought implications](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016WR019638) predicts that increased temperature could cause river flow to decrease by at least 20% by mid-century.
* Dust, etc (1x): The aridification of the continent [may lead to more dust storms](https://watercenter.colostate.edu/wp-content/uploads/sites/33/2021/06/ColoradoWater_V38-1v-r15-web.pdf#page=31), which could decrease snow cover even further.
* **Prediction**: Using a baseline average of 14.5 million acre-feet of water per year, I predict that the Colorado River will average a flow of approximately 13 million acre-feet from 2025-2050.

## **Consequences**

The consequences of a Colorado River that's experiencing prolonged water scarcity issues (or abundances) are profound. How will society react? Let's take a look at a few consequences worth considering:

**Conservation**

First and foremost, the region will have to consider significantly curtailing its water usage through conservation initiatives and by improving efficiency. Currently, only states lower in priority (as stipulated by the "Law of the River") have had to seriously integrate these principles. Nevada is a particular standout: Despite a swelling population, the state decreased its water usage over the past decade after adopting stringent water usage regulations. Meanwhile, high priority states like California have voluntary water usage restrictions, which may ultimately become permanent water austerity measures.

**Pricing**

Supply constraints on water should drive water prices up, at least temporarily. The [Nasdaq Veles California Water Index](https://www.nasdaq.com/market-activity/index/nqh2o) tracks the prevailing market price for water transactions in California. The [current price of water](https://www.waterexchange.com/ca-water-index/) in September 2021 is above $900, up from $500 in September 2020 and $200 in September 2019. Clearly, the price of water is highly variable, and dependent on precipitation but also temperature. Will the price of water continue to increase?

**Innovation**

Water scarcity issues are a threat to the Colorado River basin's security. It's an important question, how Americans in the Southwest react to a shrinking Colorado River. Some states are investing in desalination facilities, [but they're pricey and environmentally unfriendly](https://e360.yale.edu/features/as-water-scarcity-increases-desalination-plants-are-on-the-rise). Large-scale climate geo-engineering projects may be seriously considered, and several Metaculus questions are already pitched at relevant questions on this topic. 

This is an opportunity, then, to forecast the future of solar radiation management, which is the intentional reflection of solar radiation from Earth's surface. This reflection is a subset of nascent and not yet proven technologies that aim to increase planetary albedo, thereby mitigating the effects of global warming without decreasing greenhouse gases. How likely is it for this kind of geo-engineering to be embraced? The drying of the Colorado River and the American Southwest provides a sobering opportunity to forecast on this question.