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Report says federal forecasts of Lake Powell’s level may be too optimistic

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Hydrologists recently updated the model that forecasts the level of Lake Powell. These projections are critical for planning for an increasingly dry future in the Colorado River Basin, but a new paper from Utah State University says the model may still underestimate the risk. KNAU’s Melissa Sevigny reports.

The model is based on weather conditions over a thirty-year span. That reference period is updated once a decade; it now begins in the 1990s. But a long-term drying trend began in the year 2000.

Jian Wang of Utah’s Center for Colorado River Studies says that means the projections may be too optimistic. "It’s always good to plan for the worst, right? We need to get ourselves prepared," he says. Wang suggests updating the reference period more frequently or using the last 20 years as the baseline.

But the 30-year period is the standard reference worldwide and captures more variability, according to Paul Miller of the Colorado Basin River Forecast Center. "I would be reluctant to limit it to years just since 2000, because I think there is some value in acknowledging the variability that goes on in our basin," he says.

These long-term projections help water managers plan for future shortages, which are increasingly likely in the Colorado River Basin, in part because of warmer temperatures brought on by global climate change. Scientists say the current drought is the driest on record in the last twelve hundred years.

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Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.