Tip Sheets

‘Overdrawing the system’: Western water supply lags demand

Media Contact

Jeff Tyson

With severe drought impacting the Western U.S. — including the Colorado River and its reservoirs — the federal government announced this week it is keeping more water in one of the river’s reservoirs, Lake Powell, instead of releasing it downstream to Lake Mead. The decision is meant to maintain hydropower production as well as electricity supply, and comes as Southern California prepares to implement emergency water conservation measures.

Flavio Lehner

Climate scientist and assistant professor of earth and atmospheric science

Climate scientist Flavio Lehner has monitored water supply in the Southwest for about a decade, and his studies show the region is trending toward more frequent and deeper droughts. Lehner says both the Lake Mead and Lake Powell reservoirs had robust water availability in the 1980s and around the year 2000. But now, both reservoirs combined are down to the equivalent of one year’s worth of natural streamflow.

Lehner says:

“That doesn’t mean we’re running out of water in one year, because the Colorado River is not completely dry by any means. It just means that current supply is not keeping up with demand. Fundamentally, we’re clearly overdrawing the system. We do, however, have less than a one-year buffer in our reservoirs when we look at how much water usually comes down the Colorado River in a year.

“What you’re seeing in the Colorado River is that we are having a long term, slow and gradual change in our climate. The river responds to rising temperatures, changes in precipitation, and other factors with an enduring decline in flow and increasingly frequent drought conditions.

“These long-term trends are hard to reverse. Thus, water resource planning for the future might need to include the possibility of continuing low flows.”

Media note: A graphic developed by Flavio Lehner showing Upper Colorado River storage and flow trends can be viewed and downloaded here: https://cornell.box.com/v/UpperColoradoRiver. For additional information, see this Cornell Chronicle story.

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