Even with the release of extra water from upstream reservoirs, Lake Mead outside Las Vegas is forecast to continue dropping in 2015 and into 2016, according to the U.S. Bureau of Reclamation’s latest monthly “24-Month Study” (pdf). At this point, as Lake Mead drifts deeper into record emptiness, it goes without saying that the big reservoir, the key to supply water for urban-suburban Nevada, Arizona and Southern California, along with the vast agricultural empires of the southwestern deserts, is heading into record territories.

Storage in Lakes Mead and Powell. Data source: USBR, graph by John Fleck

But for the record, the current forecast end-of-water-year level for Sept. 30, 2015, is 1,075.32 feet above sea level, which would be a record low for the end of a water year. Forecasting into 2016 should be taken as little more than median flow arm-waving, but for the record, 2016’s 1,070.64 would be, yup, another record. The forecasted drops would happen even with an anticipated release of surplus water from upstream, according to the Bureau’s analysis.

Faced with serious risks if dropping reservoir levels continue, the board of the Southern Nevada Water Authority last week voted in favor of spending another $650 million to build a new pumping plant capable of sucking water out of the reservoir at very low levels. Brett Walton reported the details:

The water authority’s two existing intakes will be exposed to desert air if the lake’s elevation drops below 1,000 feet above sea level. A third intake is currently under construction, but it would require a separate pumping station — like the one that the committee recommended — to operate at the lowest water levels, those below the 1,000-foot mark.

This is not Las Vegas expecting Lake Mead to drop that far, but rather buying some extremely expensive insurance against an enormous downside risk. To senior managers at SNWA, that risk has to appear in the realm of possibility. Since 1998, Mead’s elevation has dropped 133 feet. The 1,000-foot mark – the point at which a major U.S. city’s water supply is gone – is just another 81 feet away.

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