Drought Threatens The Future Of Hydropower

When I was in hiatus between my undergraduate and graduate work, I drove cross country in a 4-cyclinder Plymouth Horizon. The trip opened up many perspectives to me: how disparate the intellectual lives are of people across the US, how the National Parks offer a glimpse back to the US wilds of 300 years ago, how complicated urban and rural planning is. I also had a chance to visit Hoover Dam, a majestic example of built structure, indeed, with its arch design and precipitous sheer drop. Yet I now understand that drought has changed the aspect and function of its Lake Mead’s reservoir. It’s at a historically low level and, as a result, Hoover Dam is generating less electricity than ever.

If Lake Mead’s end-of-2022-year elevation is at or below 1,075 feet, Lake Mead will operate in a shortage condition in the upcoming year. As of February, Lake Mead, which provides the dam water, was sitting at an elevation of 325 meters. The dam is expected to stop producing power at around 289.56 meters.

The dam, home to one of the largest hydropower plants in the country, supplying power to around 1.3 million people in Nevada, Arizona, and California, is not alone in its struggle to produce electricity.

According to the United States Bureau of Reclamation (USBR), many other dams affected by drought are seeing similar effects. With the likelihood of a hydropower crisis in the coming decade, climate change adaptation strategies are now necessary to keep the water flowing.

3 Case Studies of Drought

Hoover Dam is often used to balance large solar operations in California and Arizona. When the sun is high during the day and loads are relatively low, Hoover doesn’t produce much power. But when the sun begins to set and loads increase with people returning home, watching TV, and making dinner, solar doesn’t produce as much power, and the dam produces more. This would be lost with Lake Mead, according to a report from Ars Technica.

Lake Powell, a reservoir on the border of Arizona and Utah, is also slowly but surely drying. It’s situated behind the 1,320-megawatt Glen Canyon Dam and power station. With the role of providing power for some 3 million customers in Arizona, Colorado, New Mexico, Utah, and Wyoming, this news is startling. Lake Powell has lost 4% of its potential storage capacity since 1986, when the last survey was completed, and 6.79% since 1963, when the diversion tunnels of Glen Canyon Dam closed and the reservoir began to fill.

“Conducting repeat surveys with the most up-to-date technology is critical to understanding water storage capacity in Lake Powell,” said Dan Jones, USGS scientist and co-author of a March, 2022 USBR study. New comparative data indicate the rate of reservoir storage capacity loss observed continues to be consistent with previous studies. USGS scientists used high-resolution multibeam bathymetry and lidar to create the equivalent of an underwater topographic map of the reservoir. The data were then combined to create a topobathymetric digital elevation model (TBDEM), a continuous representation of submerged bathymetry and subaerial topography.

California’s Trinity Mountains, due to lack of precipitation and winter snowpack, is an example of the repercussions of drought on ecosystems and habitat. The area has a 2022 flow schedule scaled for a critically dry water year. Critically dry is one of 5 water year types used by the Trinity River Restoration Program to determine how much reservoir water will be released in support of the program’s goals to improve habitat for anadromous fish — fish that migrate to fresh water from salt water to spawn — like salmon and steelhead. This year, according to the USBR, marks the third critically dry year in the last 5 years for the Trinity watershed. The planned release schedule attempts to maximize benefits to the physical and biological character of the Trinity River, given the constraints of the limited amount of water available.

Climate change is a direct causal factor for the historic dam low levels due to ongoing drought conditions.

The Feds Acknowledge the Trouble with Hydropower

In October, 2021,  Assistant Secretary for Water and Science at the US Department of the Interior Tanya Trujillo spoke before the House Natural Resources Subcommittee on Water, Oceans, and Wildlife. “I  want to reiterate something I and my colleagues across the Administration are focused on every day: climate change is real,” Trujillo affirmed. Trujillo described how the Colorado River Basin had seen its driest 22-year period recorded in more than 100 years of record-keeping. In 2000, the reservoir system was 95% full, but that September 28th saw the Colorado River system reservoirs at just 39%. That decline in volume meant that combined hydropower generation had declined 13% to an annual average of 10.5 million MWh.

“Declining storage levels due to ongoing drought have resulted in reduced hydropower generation efficiency and concerns about approaching minimum power pool at Glen Canyon Dam,” Trujillo explained, “below which no power can be produced.” The Colorado River, an important source for many dams and power plants in the region, has been wracked by drought for the past 22 years.

Click here to see drought level data today from the US Drought Monitor. Sometimes pictures speak louder than words.

Why Drought is so Alarming for Hydropower

How they work: Hydropower plants generate electricity by releasing stored water into penstocks to drive turbines. Their reservoirs are filled naturally from river flows, replenished by rainfall and snowmelt or, in the case of pumped storage systems, artificially through pumping previously released water back into storage when energy prices are low.

Two main factors impact hydro production.

• The first is the amount of water that passes through a dam’s generators.
• The second is the depth of the body of water that feeds the dams. Deeper bodies of water have more force behind the water rushing through and spinning the turbines of a generator.

The potential energy of the water flowing through turbines with a certain vertical fall, termed hydraulic head, is converted into electricity.

Operating a hydroelectric power plant is complicated. These plants are subject to regulatory, environmental, and recreational requirements, as well as physical storage limitations and the interconnected nature of operating units within a watershed. Such systems provide humidity to the atmosphere, storage water on the surface and subsurface, and flow to the streams.

Renewable energy: Electricity production by hydropower plants harnesses the energy of flowing water, a renewable source for electricity production. In case of most hydropower plants, greenhouse gas emissions per kWh of generated electricity, mainly caused by methane emissions from reservoirs behind hydropower dams, are much smaller than emissions caused by fossil fuel-based electricity production. Hydropower has been vigorously tapped to meet the growing electricity demand while mitigating environmental impacts. Currently, hydropower contributes almost a fifth of the world’s electricity generation and more than half of global renewable electricity generation. However, as one of the pillars of future renewable energy, hydropower is highly sensitive to changing climate.

Drought: Driven by river flows, conventional hydropower is exposed to the vagaries of weather and climate, motivating drought and climate change hydropower impact studies at large spatial scales. Hydrological drought refers to negative anomalies in river discharge, groundwater levels, or lake levels or a loss of wetland area. The causes of hydrological drought are complex, involving both atmospheric and hydrological processes at different time scales.

Drought management requires an understanding of the timing, duration, severity, and spatial extent of drought events. The impact of these constraints on hydroelectric generation is increased by the sustained drought, which limits the availability of water. In simpler terms, when there is  a combination of low precipitation and extremely high temperature that produces low streamflow, the energy sector becomes challenged by a reduced potential of hydropower.

Grids: Power grids that depend on hydropower also depend on the climate to deliver water to reservoirs, thus are exposed in the short term to the threat of prolonged drought and in the long term to possible drying trends. These trends may erode generating capability over decades.

Current work being done: Several measures have been undertaken in the Colorado River Basin. At Glen Canyon Dam, the turbine runners — the part of the machine that generates power by spinning with the movement of the water — were made more efficient through a design update. The USBR also continues to monitor the river system.

Future planning: When planning hydropower projects for the future, experts say that attention must be given to the greenhouse gas contribution of the impounded waters behind storage dams and the impact of dams on water temperature. The impacts of climate change, for example, the changing water availability and temperature on usable capacity, output, and revenue of hydropower plants are worsening worldwide. That means adaptation strategies should be well integrated into hydropower planning and management in advance.

USBR is working with states, tribes, agriculture, power customers, municipalities, conservation organizations, and other stakeholder communities on projects and activities across the West to address drought conditions and impacts. Activities include leveraging a range of tools to mitigate drought impacts, including new water supply and infrastructure projects to increase drought resiliency, reduce reliance on declining water sources, and increase efficiency in deliveries.

This includes new storage projects where appropriate, groundwater recharge, diversification of supplies, water conservation and efficiency, and water reuse projects. USBR is also collaborating with partners across the West on projects to improve water management through the development of science and technologies, improved modeling and forecasting tools, and long-term planning efforts to develop innovative strategies to address hydrologic changes.