Hydropower is drying up, putting additional strain on power grids

Shigh temperatures are baking the American Southwest this Labor Day weekend. And amid neighborhood pool parties and backyard barbecues, residents wonder what will break first: their heat or their power.

Extreme, prolonged heat waves put a strain on power grids because everyone spins theirs energy-intensive air conditioners at the same time, it increases energy demand. Meanwhile, coal, natural gas and nuclear power plants operate less efficiently and have less capacity when temperatures are high. The stress on the power grid this weekend is so troubling that the California Independent System Operator (ISO), which oversees the state’s power system, asks the residents not charging electric vehicles, setting thermostats to 78°F or higher, and reducing overall energy use. The goal, as they say, is to prevent energy shortages.

One thing that certainly doesn’t help this situation is the disappearing hydropower in the region that makes up for it nearly a quarter from the electricity production of the region. While the entire western United States is experiencing dry conditions, the southwest, and California in particular, is two decades of megadrought which severely limited the state’s hydroelectric sources. As the chart below shows, hydropower has dropped from about 15%-20% of California’s electricity in the early 2000s to just 7.5% last year.

Hydroelectric power is generated from dammed reservoirs, and when the reservoirs fall below a certain threshold, the plant can no longer generate power. This can worsen the strain on the power grid during extreme weather. “If you’re in the middle of a terrible drought and you have a lot less hydropower than normal, it makes it harder to meet demand,” said Jordan Kern, an assistant professor in the College of Natural Resources at North Carolina State University. “But usually system operators have deputies. There will be electricity that is produced at the natural gas plants. It’s dirtier, it’s more expensive, but it keeps the lights on.”

Read more: The Colorado River drought is a climate cautionary tale

In California, solar and other renewables have grown over the past decade, filling the void in hydroelectric power generation. But renewable energy sources do not have all the advantages of hydropower. And 2021 Department of Energy (DOE) report. found that hydropower is a key factor in the overall reliability of the grid as it operates at all times of the day and can offer greater and long-term storage than batteries. What’s more, hydroelectric power can very quickly restart the power grid after a blackout.

A 2019 DOE analysis found that hydropower—despite only 10% of the nation’s total generating capacity—provides about 40% of the so-called black start resources. which start transmission to the grid and help switch on other generators after an outage. Solar PV and wind generators, according to the report, “cannot be relied upon” to operate in this manner.

A US government map as of late August 2022 showing extreme and exceptional drought conditions in the western half of the country.


Due to dry conditions that “threaten the availability” of hydroelectric power, North American Electric Reliability Corporation said in May, all areas of the US that are part of the western grid system are “at risk of power failures”. This network serves 80 million people in 14 states, two Canadian provinces and a small part of northern Mexico.

Last summer, Lake Oroville, California’s second-largest reservoir, fell to the minimum levels needed for hydroelectric power, forcing The Hyatt power plant shuts down. This is the first time this has happened since the plant went into operation in 1967. What happened there could happen to other large reservoirs in the coming years. There is a 10 percent chance that Lake Powell will fall below operating levels as early as next year and a 30 percent chance by 2024, according to August forecasts from the Bureau of Reclamation. This reservoir spans the states of Arizona and Utah, holds water for Glen Canyon Dam, and typically supplies power to customers in Wyoming, Utah, Colorado, New Mexico, Arizona, Nevada, and Nebraska. It is currently only about 25% full, the lowest level since it was first filled.

Read more: China’s extreme drought is making the country even more reliant on coal

Lake Mead, another massive reservoir located further down the Colorado River system on the Nevada-Arizona border, is 28 percent full. According to the same Bureau of Reclamation projections, there’s a 23 percent chance its levels will drop to 1,000 feet by 2024 and a 7 percent chance they’ll drop to 950 feet by 2026 — the point at which the water will be too low to flows through the Hoover Dam Pipes, which take water from the reservoir. The Hoover Dam’s capacity, which is enough to serve 1.3 million people, is distributed primarily in California, but also in Nevada and Arizona. “They could stop producing electricity,” Kern says of the two iconic dam structures. “It’s something that people are increasingly concerned about.”

The graph below shows the water levels in the western reservoirs. It should be noted that Lake Mead and Lake Powell are well below full and also well below what they were for this time of year based on a 30-year average, but many others are in similar conditions.

As summers get longer and hotter due to climate change, the US grid will become busier. And in many countries, the loss of hydroelectric power means more reliance on fossil fuels that contribute to climate change and worsen drought conditions—a vicious, paradoxical cycle.

Other drought-stricken countries are in a similar boat. The dry conditions in Sichuan Province, China, for example constrained hydropower generation — which accounts for 80% of the region’s electricity — and caused blackouts. Similar overstrains of power have occurred throughout Europe this summer, when low water levels reduced hydropower, along with making it difficult to cool nuclear reactors and transport coal on rivers.

But conditions are not so dire in the US this year. And experts like Jack Schmidt, director of Utah State University’s Colorado River Research Center, say hydropower shouldn’t be at the center of the broader drought problem. His view is that the country will find ways to fill the energy gaps. But there is no easy solution if drinking water and irrigation water for agriculture are scarce.

“Water supply is more important than energy,” says Schmidt. “That doesn’t mean strength isn’t important. The power of the Hoover Dam is important. But American society does not fall apart if we lose it. This is not equivalent to water loss.

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