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Hydropower and water scarcity: the growing climate risks of a climate solution

December 17, 2022

Even as a scorching, dry summer fades toward winter, the specter of drought has refused to exit the stage. While drought is defined as a lack of water resources–as typified by the historically low levels of the Mississippi River last month–it can easily metastasize as a lack of electricity. Water is the “fuel” for hydropower, still the leading source of renewable electricity generated on the planet, and a drought is like an embargo on that fuel.

Water managers on the Colorado River just warned of a looming “doomsday scenario” where continued drought would halt electricity generation at Glen Canyon Dam. That scenario has already arrived for Kariba Dam, the second largest hydropower project in southern Africa, which provides more than half of the electricity used by Zambia and Zimbabwe. Kariba’s reservoir—built in 1959 it is the largest reservoir in the world by volume—is at the lowest level in its history, resulting in extreme power cuts to Zimbabwe and power rationing in Zambia.

Because water crises become energy crises, they are now also crises for climate action. To help achieve the decarbonization of energy that is central to meeting climate targets, many countries are planning on a dramatic expansion of hydropower, and global energy agencies forecast a doubling of global capacity by 2050. Yet due to the level of climate change that is already baked in, drought-driven embargos on hydropower’s water fuel are likely to become more frequent and more widespread in the coming decades.

In other words, one of the most touted solutions to the climate crisis is becoming less reliable due to the negative impacts from climate change that are already under way. That complicated reality has important implications for how we manage existing water and energy systems, and for the climate change solutions coming out of the recently concluded United Nations Climate Change Conference (COP27).

This past summer, Europe and China endured historic droughts that lowered rivers and drained reservoirs that hydropower systems use to generate electricity. Hydropower provides 80% of the electricity for China’s Sichuan province and the extended drought cut generation by half. A heat wave compounded the challenge, so at the same time as generation was declining, demand for electricity for air conditioning was spiking: electricity demand in Sichuan was up 25% compared to the same period in 2021. As a result, tens of thousands of commercial consumers in Sichuan were told to shut down for ten days in August.

In Europe, drought drove down hydropower generation in Italy, Austria, Spain and Portugal.

a dry reservoir in Spain
Extreme low reservoir levels on the Guadiana River in Spain due to the drought of the summer of … [+]AFP VIA GETTY IMAGES
The southwestern United States appears to be shifting toward an overall drier climate, signaling long-term challenges for both water supplies and hydropower. Hydropower dams on the Colorado River provide electricity to 5 million people and their reservoirs have been declining for decades. The Bureau of Reclamation reported that there is a nearly one in three chance that reservoir levels will fall so low by 2024 that its 1.3 gigawatt Glen Canyon Dam will stop generating. Further down the Colorado River, the drought has diminished annual generation from Hoover Dam by 22% as its reservoir also declines toward its “dead pool” (no generation) level.

California normally gets about 13% of its electricity from hydropower, but during a drought that decreased to just 6%. That level of reduction poses challenges for places like California and Europe, but with diversified grids they can adapt. What about countries where hydropower dominates the grid? A 2015 drought diminished hydropower generation in Zambia to a similar extent as in California, except hydropower provides nearly all of Zambia’s electricity! That means drought caused national electricity generation to decline by 40%, causing rolling blackouts and immense economic disruption. This year is shaping up to be worse.

These examples demonstrate how drought can reveal vulnerabilities in energy and economic systems that currently depend on hydropower. What should really grab our attention are future forecasts: that global hydropower will double to help avoid climate change, but also that the future will see more drought and water scarcity because of the impacts from climate change that are now unavoidable (minimizing future warming is crucial to avoid even greater disruptions).

The International Energy Agency projects that southern Africa will face increased drought risk due to climate change, with associated disruptions to hydropower. In addition to periodic drought, climate change will make Zambia drier overall, with declines in average river flows and a 20% reduction in hydropower generation.

This rising risk is not limited to Africa. A recent study in Nature Climate Change found that, even under the most optimistic climate scenario, more than 60% of existing hydropower projects are in “regions where considerable declines in streamflow are projected” by 2050, rising to 74% of projects with greater warming. I was lead author on a study that found that approximately one-third of global hydropower projects are in regions projected to have increased risk for water scarcity. The two studies identified similar regions most at risk, with both pointing to China, the southwestern United States, Mexico, southern Europe and the Middle East.

Meanwhile, a quarter of all planned hydropower dams are in regions with medium to very high levels of water scarcity risk.

These current and rising risks for drought and water scarcity should inform plans for tackling climate change, including those emerging from COP27. Countries should plan their low-carbon power systems for the level of drought and scarcity risks that are already “baked in” and/or likely under current trajectories. The impacts of drought on grids in southern Africa illustrates the system-level vulnerability of power systems that are highly dependent on a source so susceptible to climate disruptions

Diversification of generation sources and climate resilience should become major objectives of energy planners. For example, solar panels generally operate near their peak capacity during hot, sunny drought periods when other generation sources are stressed (aside from hydropower dams, nuclear and thermal plants also can see generation curtailed during droughts due to depletion of cooling water sources).

Hydropower is often proposed as a way to stabilize grids that are heavily dependent on renewables like wind and solar, which fluctuate based on variables like weather and the day-night cycle. Pumped storage hydropower–which lifts water from a lower reservoir to an upper reservoir “battery” ready to generate when needed–can provide that same service, with both lower risk from droughts and scarcity as well as generally far lower negative impacts to rivers, fisheries and communities compared to conventional hydropower.

Hydropower has a role in solving the climate challenge, but it is imperative to understand that hydropower is itself far more vulnerable to climate-driven disruptions compared to other renewables like wind and solar. Diversified, low-carbon grids provide greater resilience in the face of shifting climate and hydrology–and we need new government policies, power planning and financial flows to support their future development.

by Jeff Opperman


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