How Droughts Threaten the Future of Hydropower

Hydropower is the largest source of renewable energy in the United States, accounting for 54% of the country’s renewable electricity generation.

However, dry conditions and droughts intensified by climate change are beginning to stress hydropower generation in some regions, casting a shadow of doubt over its future.

The above infographic sponsored by the National Public Utilities Council explores how prolonged dry conditions in some U.S. regions are threatening hydropower generation. This is part two of two in the Hydropower Series.

The U.S. Megadrought

According to a recent study, the American Southwest is currently experiencing its worst megadrought—defined as a drought that lasts two decades or longer—in 1,200 years.

The multi-decade drought that began in 2000 was exacerbated by extreme-dry conditions and a hot summer in 2021. Based on the soil moisture data (covering nine states) used in the study, the 22-year period was the region’s driest spell since 821 AD.

While climate change alone did not cause this, it accounted for 42% of the intensity of the 2000–2021 megadrought. Furthermore, it also made the year 2021 20% drier than it would have been.

As of 2022, California, Nevada, Arizona, Utah, and New Mexico were among the hardest-hit states by dry conditions, which has affected both their hydropower generation and reservoir storages.

Hydropower’s Droughtful Future

In most drought-hit states, hydropower’s share of electricity generation has fallen over the last two decades.

For instance, California’s hydropower generation dropped from 25.5 million megawatt-hours (MWh) in 2001 to 17.3 million MWh in 2022. Over that same period, hydropower’s share of California’s electricity generation fell from 13% to 8%.

Besides the long-term declines in hydroelectric generation, water levels at some reservoirs are precariously low. Here’s a look at the water storage levels of select Southwestern reservoirs as of March 15, 2023:

Notably, Lake Mead (Hoover Dam) and Lake Powell (Glen Canyon Dam)—the top two largest U.S. reservoirs by capacity, respectively—have alarmingly low storage levels with less than one-third of total storage filled.

To put that into perspective, these satellite images from NASA show a bird’s eye view of the Overton Arm, a part of Lake Mead, in 2000 compared to 2021 and 2022:

Similarly, prolonged dry conditions have pushed the storage levels of many other Southwestern reservoirs to well below their long-term averages.

The risks from these falling water levels are clear—if a reservoir’s elevation falls below a certain threshold (known as the minimum power pool), it can no longer support power generation. This occurred in 2021 when California’s Edward Hyatt Power Plant was shut down due to historically low water levels at Lake Oroville. Although the plant has resumed operations since then, the emergency shutdown is a recent example of hydropower’s vulnerability to drought.

Mitigating the Risks to Hydropower

Hydropower is one of the most reliable sources of renewable electricity and can operate at all times of the day. Furthermore, hydropower plants are important “black start” resources because they can independently kick-start electricity generation in the event of a blackout.

Consequently, a threat to the future of hydropower also poses risks for the power grid. In fact, in the summer of 2022, the NERC found that all U.S. regions covered by the Western grid interconnection were at risk of energy emergencies in the event of an extreme heat occurrence, because of dry conditions threatening hydropower.

Besides fighting climate change and working to reduce the frequency of intense droughts, here are three ways to combat the challenge facing hydropower while advancing decarbonization:

• Large-scale backup battery storage systems can be built to compensate for falling hydropower generation during severe droughts.
• Buildings and homes can be retrofitted and built with energy-efficient technologies to curb the overall demand for electricity and load on the grid.
• The power grid can be made more climate-resilient by expanding long-distance transmission lines and deploying more solar and wind power in interconnected regions.

Click here to learn more about how electric utilities and the power sector can lead on the path toward decarbonization.

Visualizing the State of Climate Change

The recent influx of wildfires, droughts, and hurricanes serves as a warning sign of the impact of climate change.

In order to identify ways to mitigate the crisis, it’s important to understand the historical drivers and current state of climate change.

This infographic sponsored by the National Public Utilities Council (NPUC) explores how human activities have influenced the climate crisis and how decarbonizing the power sector can help.

The Human Drivers of Climate Change

Global warming, the phenomenon driving climate change, is a result of increasing greenhouse gas (GHG) emissions.

GHGs in the atmosphere increase the Earth’s temperature through the greenhouse effect. This refers to the natural warming of the Earth that occurs when GHGs trap the sun’s heat.

Since the Industrial Revolution, human activities like energy generation and consumption from fossil fuels have accelerated GHG emissions and the greenhouse effect. The atmospheric concentration of carbon dioxide is now nearly 415 parts per million (ppm), up from around 280 ppm prior to the Industrial Revolution. As a result, the Earth is warming faster.

For a better understanding of how humans have contributed to the crisis, here’s a look at historical CO₂ emissions by sector:

Electricity and heat by far accounts for the largest share of emissions since 1990. This is because of the dominance of fossil fuels in our energy mix over the last few decades.

The transport sector is the second-largest contributor largely due to the reliance on internal combustion engines, oil-fired ships, and other fossil fuel products like jet fuel.

Limiting the temperature rise and ultimately the impacts of climate change will require emissions reductions across all sectors, starting with electricity generation.

How Decarbonizing the Power Sector Can Help

A decarbonized energy system with clean electricity generation is an essential building block for the road to net-zero emissions.

There are two factors that emphasize the importance of a clean power sector. First, all sectors of the modern economy rely on electricity for daily functions. If this electricity comes from clean sources, it can help reduce the consumer’s carbon footprint. Second, global power demand is charging up with the electrification of sectors like transport and industry. As a result, supplying clean electricity will be more important than ever.

In Part 2 of the Road to Net Zero series, we will explore pathways to decarbonize the U.S. economy, beginning with the power sector.