Climate change | j longest on record, hydropower in the northwest


region (which includes Oregon, Washington, Idaho, Wyoming, Montana, northern Nevada, Utah, and Colorado) continued to far outpace other renewable energy sources across western states. It delivered 26% of total electricity generated, demonstrating that even with reduced water levels due to drought, hydropower remains a cornerstone of the existing grid and a necessary building block for the transition to a low-carbon grid.


Acknowledging that hydropower is, and should remain, a pillar of the clean energy transition does


not mean simply carrying on with business as usual, Schneider cautioned. “While climate models differ on the predicted


frequency of droughts or periods of increased precipitation, it is clear that climate change is water change,” she added, “and we must adopt new strategies to ensure that the hydropower of the future is responsive and resilient in the face of an evolving climate.” Schneider believes that it is clear that the effects of


climate change are ongoing and that “through these extreme and varied weather conditions, hydropower remains a critical means to a stable grid”.


Drought impacts on Western US hydropower


According to a new report from the Pacific Northwest National Laboratory (PNNL) in the US, characterising the contribution of hydroelectric power to the western generation portfolio during drought is crucial to understanding the resilience of the power grid to climate risk, both now and in the future. In a wet year, like 2011, hydropower can meet 30% of annual western electricity demand. That contribution can drop below 20% during severe drought years. The report analyses the impacts of historical western droughts on hydroelectric power by combining two decades’ worth of annual generation— recorded at more than 600 hydroelectric power plants—with historical climate data developed for distinct hydropower climate regions of the west. The most extreme impacts of drought on hydroelectric power are found at individual dams where reservoir levels are so low that released water – and thus power generation – becomes severely restricted. According to the report, these isolated cases often receive widespread attention in national media, leading to a possible misconception that hydroelectric power is an unreliable technology whose role and contribution will diminish over time if the western climate produces longer and more severe droughts. Yet, when aggregated to the scale of


the west, the observational records of hydropower generation tell a different story, the report continues. Even during the most severe droughts experienced since the turn of the century, the western hydropower fleet sustained 80% or more of its typical annual generation. This translates to approximately 140–150TWh of renewable energy in a severe drought year, which is of similar magnitude to annual output from all other renewable electricity sources in the west combined (renewables excluding hydro contributed 140TWh in 2020 and 159TWh in 2021). Drought in 2021 led to the worst year for


hydropower generation in the west since 2001, with total generation approximately 16% below the 21st century average. The year 2021 was particularly severe in California (second worst hydro year of the last two decades, ~48% below average) and Oregon (worst hydro year of the last two decades, ~16% below average), while generation in Washington and Idaho was affected to a lesser degree (~12% below average for combined region). The main reason for the relative stability


in total western annual hydropower generation is diversity of weather conditions across the region; drought rarely impairs hydropower generation across all western river basins at the same time. To support an analysis of drought impacts


on hydroelectric generation that considers the west’s climatic diversity, the report introduced eight hydropower climate regions of the west, each unique in the drought conditions it experiences, water storage capacities and operations of its dam and reservoir fleet. These hydropower climate regions are: ● Mid to Upper Columbia (accounting for 51% of western generation on average).


● South Cascades/California (18%). ● Snake River Basin (11%). ● North Cascades/Puget Sound (10%). ● Lower Colorado Projects (6%). ● Missouri Headwaters (2%). ● Colorado Rockies (1%). ● Utah Wasatch Range (< 1%). “When studying and characterising drought, the instinct is to look at it from a regional or state level, but state boundaries might not be the most relevant for understanding the impacts of drought on hydropower,” says Sean Turner, water resources modeler at PNNL and main author of the report. “Grouping them by climate conditions leads to a cleaner assessment of the impact of drought on hydropower.” According to the report, total western


hydropower generation in 2022 is likely to rebound from 2021, despite continuation


of drought over much of the region. This projection is based on a forward extrapolation of hydropower generation informed by a seasonal precipitation outlook for the remainder of the current water year. The rebound in generation from 2021 levels has been driven by increased output in the northwest regions which experienced a relatively wet spring and held above-average snow levels going into summer dry months. Generation in California and in the Lower Colorado Projects will remain very low in 2022. However, hydropower dams with very


large multi-year storage, such as the Lower Colorado Projects (Glen Canyon and Hoover) have sustained relatively stable generation through multi-year drought so far but are at risk of breaching critical reservoir thresholds within the next few years. Such risks are unique to the Lower Colorado Projects and do not reflect the status of western hydropower in general, the authors state. “When people read stories about one particular dam during a drought, like Glen Canyon Dam, or one particular state, like California, they’re left with the impression that hydropower will not be very reliable in the future, but one dam represents just a small portion of overall capacity,” said Turner. “This means that total western hydropower will still be a major source of power supply even during the worst drought years.” The full report can be read at www. pnnl.gov/main/publications/external/ technical_reports/PNNL-33212.pdf


REFERENCES: Drought Impacts on Hydroelectric Power Generation in the Western United States. A multiregional analysis of 21st century hydropower generation by Sean W.D. Turner, Nathalie Voisin, Kristian Nelson and Vince Tidwell. September 2022. PNNL-33212 https://www.pnnl.gov/news-media/ face-drought-hydropower-still-delivers- electricity


46 | November 2022 | www.waterpowermagazine.com


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