Front Range cities in Colorado are facing an alarming vulnerability to possible cuts in water supply from the beleaguered Colorado River, according to a recent study conducted by Hydros Consulting on behalf of the Colorado River Water Conservation District.

As competition for the state's limited water resources increases, the study found that 96% of Front Range water use from the Colorado River is subject to potential cuts under an interstate agreement.

The study, part of a seven-year effort to analyze the potential impacts of water cuts under the Colorado River Compact, highlights the disproportionate vulnerability of Front Range cities compared to the Western Slope.

While 30% of Western Slope water use shares the same vulnerability, 96% of Front Range water use is at risk. This is concerning considering that the Front Range accounts for only 23% of the state's overall use of the river but represents 48% of the state's curtailable Colorado River water use.

The vulnerability of Front Range water rights stems from their relative newness compared to the Colorado River Compact, which was signed in 1922.

In Colorado water law, water rights receive priority during shortages based on their age, meaning that water rights newer than the compact can be curtailed. Under the compact, if flows to the Lower Basin states (California, Arizona, and Nevada) fall below the agreed amount, these states can call on Colorado to reduce its water use, potentially subjecting water users with newer rights to cuts.

While the study suggests that Colorado's growing water demand is not likely to trigger this situation under current hydrologic trends and reservoir operations, a sustained period of severe drought could change the scenario.

Over the past 20 years, the Colorado River's average flow dropped to 11 million acre-feet for a period of seven years, lower than the longer-term norm of 13 million acre-feet. If this becomes the new normal, river flows would drop below the lower basin's entitlement, potentially leading to water cuts.

Even without a natural drop in river flows, rising water demand in Colorado could cause interstate issues on the river.

Projections for 2050 show that the upper basin may fail to meet its obligation of sending additional water downstream to Mexico. This increasing demand also poses a threat to critical water levels at Lake Powell, the country's second-largest reservoir. If water levels drop below the federally established critical elevation of 3,500 feet above sea level, it could jeopardize hydropower infrastructure at the dam.

It is important to note that these predictions assume the continuation of existing operation guidelines for federal reservoirs like Powell. Negotiators from federal, state, and tribal entities are expected to agree on new operating guidelines to be implemented after 2026.

In the ongoing discussions surrounding the Colorado River Compact, upper basin states commonly argue that they should not be held responsible for the effects of climate change. Becky Mitchell, Colorado's interstate negotiator on the Colorado River, supports this interpretation of the compact.

Critics, however, believe that Colorado and other upper basin states are not obligated to deliver 75 million acre-feet to the lower basin over 10 years, but rather the upper basin cannot cause flows into the lower basin to fall below that amount.

The study also provides data that seems to support the argument that Colorado uses less water in drought years, contrary to claims by upper basin water experts. These factors will undoubtedly shape any future attempts to curtail Colorado's water use under the compact. Nonetheless, the study highlights that even with comparative legal immunity against curtailment, the Western Slope is not entirely immune to water shortage risks.

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Front Range cities, including Denver, Colorado's largest city, receive about half of their water supply from the Colorado River basin.

As the study reveals, these cities are likely to rely on reservoir water to meet their growing water demands, potentially leading major reservoirs like Granby and Dillon to become emptier over the coming decades. If river flows drop to an 11-million-acre-foot annual average and water demands continue to increase as projected, Front Range water users may need to rely on their storage reservoirs every year to sustain their water supply.

The findings of this study serve as a wake-up call for Front Range cities and policymakers in Colorado. With the vulnerability of Front Range water rights and the potential for future water cuts, proactive measures must be taken to ensure a sustainable and secure water future for the state.