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University of Colorado scientists say reservoir evaporation a concern

Study says conservation efforts must include reducing water loss
The Animas River flowing southeast of Durango. A new University of Colorado study on water conservation says reservoir evaporation should be measured and losses reduced.

DENVER – A focus should be placed on measuring and reducing reservoir evaporation in an effort to meet Colorado’s growing water supply demands, according to a study by the University of Colorado Boulder.

The report, unveiled on Monday, focused on conservation, a popular theme touted by water managers across Colorado. The conservation push is featured in a statewide plan finalized in November that aims to map the future of water in the state.

Supply shortfalls are expected by 2050 or sooner in the state, with results that could lead to agricultural dry-up and fish and wildlife extinction, as well as increased demands and pressure on municipalities.

Colorado’s Water Plan calls for achieving 400,000 acre-feet of municipal and industrial water conservation by 2050.

The CU Boulder study says that water managers should focus on addressing reservoir evaporation as part of their efforts.

“Evaporation of water from open reservoirs in the arid Western U.S. cannot be neglected anymore, especially with the possibility of precipitation decreases occurring as a result of a changing climate,” said associate professor Katja Friedrich, a faculty member in the Department of Atmospheric and Oceanic Sciences. “We need to try to plan for both short-term needs and to make sure we have enough water over the coming decades.”

The state can’t rely on groundwater alone, as the natural rate that water enters an aquifer is low. Groundwater is considered a nonrenewable resource.

“While groundwater storage has its advantages, such as lack of evaporation, it also has its challenges, including slow recharge rates and challenges associated with controlling the recharged water, retrieving the water and delivering the water to the customer,” Colorado’s Water Plan says.

Climate projections show Colorado warming by an additional 2.5 degrees to 5 degrees by mid-century, with temperatures in summer increasing more than those in winter. Warming temperatures drive evaporation, which could result in an earlier runoff, a longer irrigation season and a decrease in annual stream flow.

If the population of Colorado rises while the climate warms – a scenario already taking place – the state would need nearly 1 million acre-feet of water per year by 2050, according to Colorado’s Water Plan.

The CU Boulder researchers pointed out that water managers have little information about evaporative loss, relying on methods developed in the 1920s. Instead, new tools should be adopted, including using techniques that not only estimate evaporation but also forecast it, the researchers said.

Water managers will never be able to eliminate reservoir evaporation. But there are techniques to reduce it.

A strategy could include covering surface water with thin films of organic compounds, reflective plastics or extremely lightweight shades to reduce evaporation. Other proposals include moving reservoir water underground into new storage areas, or building new storage reservoirs at higher elevations where less evaporation occurs.

“We can no longer afford to lose this amount of water. Once it is lost it is gone,” said retired Department of Atmospheric and Oceanic Sciences scientist Bob Grossman, who helped organize a recent conference on reservoir evaporation. “The neglect of evaporative loss as the cost of doing business in a water-abundant world will likely cut into the bottom line as scarcity looms.”

pmarcus@durangoherald.com

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