Data Dump: Hydropower dries up along with the rest of the West

As hydropower wanes, dirtier energy sources take up the slack

In the summer of 1881, a 28-year-old Ohioan named Lucien L. Nunn, smarting from a string of failed restaurant ventures in Colorado’s mining country, left the budding burg of Durango and hiked 70 miles over high mountains to Telluride, where he hoped to strike it rich. That he eventually did, although it was not by mining, but by replacing coal-power with clean energy. 

Shortly after he arrived in Telluride, Nunn opened a law firm, and in 1889 his client, the owner of the Gold King Mine (not to be confused with the Gold King Mine near Silverton, which famously blew out in 2015), asked Nunn to whip his venture into shape. The mine had tapped some rich veins, but the cost of hauling coal up to its lofty, 12,000-feet-above-sea-level perch to power the mill’s steam engines ate up the profits. 

Nunn took the dilemma to his younger brother Paul, an engineer. And Paul had an answer: electricity. Using the nascent technology being developed—and fought over—at the time by the likes of Thomas Edison and Nikola Tesla, they found they could harness the power of a cascading mountain stream to generate electricity and move it via copper wire to a motor in the mill. “Everything was extremely simple from water wheels to motors,” Paul Nunn wrote in an article years later about the first of many such generators they would install, “and except for lightning, the plant ran smoothly and steadily thirty days and more without a stop.”

And with that, the Nunn Brothers had sown the seeds of the modern power grid, one that would sprout and spread from the Telluride region to other mining regions of the West and beyond. Up until the 1950s, most of the power flowing through that ever-expanding grid was generated by the force of falling water, which is simple to harness, readily available, and requires no dirty or dangerous mining or drilling for or burning of fuels1.

But what happens when the water stops flowing and when this “limitless” source of energy hits its limits, due to drought and overuse? The Southwest is about to find out. 

Today, hydropower provides a far smaller share of the Southwestern energy mix than it once did, yet it still plays an important role on the grid2. First, it serves as an always-on, baseload power that can displace much dirtier coal- or natural gas-burning. Plus, and maybe just as important, the power output from a hydroelectric dam can be ramped up or down quickly, like that from a giant battery, meaning it can be used to stabilize the grid and to fill in when solar or wind generation drops suddenly or a fossil fuel generator goes offline. 

When reservoir levels fall, however, the generating capacity of the associated hydropower plants decreases, as well. Even when reservoirs are full, dam operators may be reticent to release large amounts of water for power generation during dry years. And if levels drop below power-plant intakes, then power generation halts altogether.

And so, hydropower—or the potential lack thereof—is yet another reason that the apparent long-term aridification of the West is so worrying. As the amount of hydropower flowing into the grid wanes, grid operators must turn to other readily “dispatchable” power sources such as natural gas to meet power demand (which also is likely to increase due to an uptick in air-conditioning use resulting from warmer and warmer temperatures).

Note that the total hydropower output line and the natural gas-fired output line are almost reverse mirror images of one another: When hydropower goes up during wet years, natural gas burning goes down, and vice versa for dry years. Data source: California Energy Almanac.

Burning natural gas emits carbon dioxide, while extracting, processing, and transporting natural gas emit methane. Meanwhile, heightened demand for the fuel is likely to raise the price of natural gas, which may sway utilities to revert back to burning even dirtier coal. All of those added emissions will only further exacerbate the warming of the climate that the planet has been experiencing for the last century and some and that is now coming home to roost in the form of permadrought, wimpy river flows, mega-wildfires—and reduced hydropower output (thereby starting the whole nasty cycle all over again).

California has nine dams exceeding 200 megawatts of generating capacity in addition to dozens of smaller hydroelectric plants. During the last severe dry spell, (2012-2015), power output from the state’s collective dams plummeted and natural gas generation—and emissions—shot up (a trend that was magnified by the 2011 closure of San Onofre nuclear plant). The last 12 months have been drier than any other year on record and Lake Shasta, the state’s largest hydropower generator, is facing its worst season in 44 years and is less than half of capacity at a time of year when it should be filled to the brim.

Power output at Devil Canyon dam, east of Los Angeles, closely tracks drought conditions. California last experienced extreme drought back in 2012-2015. Last year the state entered dry-times once again. Source: Energy Information Administration.

The good news is that the day-to-day output of Hoover and Glen Canyon Dams aren’t significantly affected by reservoir water levels, so generation doesn’t plummet during dry years like it can at other dams. The bad news is that a much larger problem looms for both reservoirs: The water levels are slowly but surely approaching the minimum power pool, or the level of the intakes for the power plants. If and when the lake surface drops below that level, all power generation will come to a screeching halt, having massive ramifications for the Southwest power grid.

Lake Powell’s surface level is just four feet above its low-point thus far, hit in 2005, and less than 70 feet above the minimum level for the power plants to operate. Lake Mead, meanwhile, is currently just 24 feet above minimum power pool level. Source:

That won’t happen this year, most likely, but if the current dry spell isn’t broken in dramatic fashion soon, then grid operators could be scrambling for big new power sources in the not-so-distant future.

Oh, and that power-grid seed planted by the Nunn Brothers 130 years ago? It’s known as the Ames plant and it continues to generate power to this very day.


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That said, hydroelectricity isn’t necessarily emission-free, since rotting vegetation in reservoirs can emit methane, sometimes in significant amounts (depending largely on where the reservoir is located). Those emissions will occur whether the associated dam is generating power or not, however, so hydropower-generation can be considered carbon-free.


Another drawback of hydropower: In order to generate it on a large-scale, a dam is usually necessary. Dams wreck rivers and ecosystems. Indeed, resistance to new, big hydroelectric dams from environmentalists and the coal industry—which was scared of losing more market share—is one reason that hydropower lost its dominant position on the Southwestern grid (hydro still reigns in the Northwest, where the dams on the Columbia River are some of the biggest power generators in the nation).