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Why Water Cuts Are Coming to Arizona, Nevada, and Mexico (Correct)

Sept. 1, 2021, 8:01 AMUpdated: Sept. 1, 2021, 9:20 PM

The Bureau of Reclamation, the agency charged with water resources management for the West at the federal government level, announced unprecedented Tier 1 cuts in water deliveries from Lake Mead on the Colorado River to Arizona, Nevada, and Mexico in 2022. The Tier 1 cuts will reduce water deliveries due to historic low water levels in Lake Mead.

California deliveries are not impacted by this announcement due to senior water rights, but they could be coming if water levels continue to drop. The Colorado River watershed and most western river watersheds that feed reservoirs with snowmelt are not producing as much runoff as they have historically due to the warming atmosphere affecting snow elevations and dryer and warmer soil and air temperatures.

Warmer Temperatures Reduce Show Pack Reservoir

Warmer temperatures are, on average, raising the snow level, which reduces the snow pack reservoir that we rely on to slowly melt through the spring and early summer to fill our storage reservoirs like Lake Mead. Warmer soil and air temperatures raise the elevation at which snow accumulates and results in less snow meltbecoming runoff as it is instead absorbed by the warmer, dryer soils or evaporates directly through a process known as sublimation. The poor runoff efficiency due to these factors created low reservoir storages in California and on the Colorado River.

The snow moisture content, known as snow water equivalent (SWE), typically measured on April 1 by water resource managers within each watershed, is used to predict watershed runoff volumes for the following spring and summer based on the historic record. The surprise in 2021 was that, due to the warmer than normal temperatures, the runoff volume that was anticipated based on the 2021 April SWE, did not show up. The runoff volumes were well below the anticipated volumes based on historic values.

100 Years of Hydrology Upended

This difference caused major problems for water management, particularly regarding allocations to agricultural and municipal uses. The bureau cut agricultural allocations for the Central Valley Project in California from 5% percent of normal to 0%.

While this may not sound like much of a reduction, it results in zero allocation to agricultural users who do not have guaranteed water rights. Zero, as in no surface water at all, for irrigating crops.

What this means is that over 100 years of hydrology that is used to predict runoff from our watersheds based on SWE may now be unreliable due to climate change. The condition of the snowpack and the watershed soils, air and soil temperatures, and weather patterns between April and June are now in play. And the kingpin, climate change, is driving these changes.

The new normal will challenge water managers to develop new metrics for estimating runoff volumes from our watersheds that are utilizing reduced snow pack, SWE, air temperatures, and soil moisture conditions. Businesses that depend on water, particularly agriculture, will become more risky in terms of crop choices, planting decisions, and crop management.

Will Hydrology Change Lead to Policy Change?

How will this change in hydrology translate into policy and new legislation is a legitimate question. Policy changes can be fairly quickly developed based on the science.

There is typically a lag, however, between the science and the updating or development of new legislation to deal with the impacts of either the policy decisions or competition for shared resources such as water. State agencies charged with water management such as the State Water Resources Control Board in California and the Bureau of Reclamation will make decisions on how much water is available to each group of users.

They do this using the water rights allocations and contracts with users. Water rights holders have precedence over contractual users, which is why the Tier 1 decision did not affect California users.

Even water rights holder’s access to water, however can be curtailed by an agency empowered to do so such as the action by the Water Resources Control Board this summer to stop water rights holders from withdrawing water from the Sacramento-San Joaquin Delta watersheds.

Legislative action to manage surface water rights, which are very ingrained into the fabric of state law, is not as likely as continued legislative work on groundwater rights. There remains, however, the possibility that a new normal could push states to reconsider their existing surface water rights systems, which is a complete game-changer.

This column does not necessarily reflect the opinion of The Bureau of National Affairs, Inc. or its owners.

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Cordie Qualle just completed a one-year term as the interim director of the California Water Institute at Fresno State. He is also a lecturer in the Lyles College of Engineering, teaching there for the last 12 years while also pursuing a 40 year career as a profession civil engineer.

(The headline and top summary were corrected to say Mexico, instead of New Mexico.)

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