| Climate change & hydropower
first dry year following wet years faces an immediate and notable decrease in hydropower generation, demonstrating the system’s vulnerability to drastic changes in water availability. Wet extremes can momentarily benefit power generation, but do not result in longer-term system resilience.
Varying degrees Different basins exhibit varying degrees of resilience
and performance. For instance, the northern basins (Stanislaus and Tuolumne) have large storage capacities and show some buffer in the first dry year after wet years, with approximately half the generation losses compared to preceding and subsequent dry years (Figure 2). The Stanislaus still generally requires two wet years to reach above-average storage values (Figure 3). During the wet rebounds, the basin shows increased
hydropower generation especially in late winter and spring (Jan-May), while losses in multi-year droughts are year-round and more apparent in late spring (May- Jun). The Tuolumne basin also has a large storage capacity and shows a more stable response to drought with losses in storage averaging around -30% in most dry years, compared to historical averages. Major losses in generation occur between the winter and summer (especially in Feb-Jul), while benefits from wet years are mostly seen in the winter of the second wet year (Jan-Mar). The Merced and Upper San Joaquin basins, on the other hand, have lower storage capacity. The Merced shows the widest range of variation in generation due to its dependency on the water stored in the terminal reservoir in the basin’s outlet. Therefore, generation ranges on average from approximately +40% in wet years to below -60% during prolonged droughts, compared to historical averages, and major losses concentrate in the summer when water is needed downstream for agricultural demands. Notably, the Upper San Joaquin basin performs the worst during droughts even though it is the most regulated river basin, due to the low storage capacity in its multiple reservoirs, leading to significant generation losses. Gains in generation in the wet year(s) are already lost in the first subsequent dry year. Losses during droughts and gains during wet years are both concentrated in the winter and summer.
Impacts To lessen or alleviate these impacts, planners can invest
in advanced forecasting and monitoring systems, adopt adaptable operational and storage strategies, and explore compensatory sources of power generation. For instance, California is actively advancing Forecast Informed Reservoir Operations to enhance flood control strategies. This approach relies on short-term forecasts of atmospheric rivers to determine when to release water (or not) for flood control, rather than following outdated and inflexible protocols from the mid-1900s of always preemptively emptying reservoirs. Additionally, there is growing interest in integrating
alternative energy sources with hydropower, such as taking advantage of the complementarity of solar energy. This includes utilising floating solar photovoltaics (PV) and solar PVs over canals, where possible, which not only reduces evaporation but also boosts solar energy efficiency and ensures greater energy security.
www.waterpowermagazine.com | May 2024 | 69
The concept of managed aquifer recharge is also being extensively researched; this approach aims to mitigate flood risks, counteract groundwater depletion, and meet agricultural water demands simultaneously. Given the vulnerability of existing hydropower systems to increases in hydrologic whiplash, bolstering climate resilience with more adaptable water resource infrastructure and management is paramount.
References
Facincani Dourado, Gustavo; Rheinheimer, David E; Abatzoglou John T; and Viers, Joshua H. Stress testing California’s hydroclimatic whiplash: Potential challenges, trade-offs and adaptations in water management and hydropower generation. Water Resources Research Journal. ESS Open Archive. April 18, 2024. [Article currently under review]
https://essopenarchive.org/users/651166/ articles/659313-stress-testing-california-s- hydroclimatic-whiplash-potential-challenges- trade-offs-and-adaptations-in-water- management-and-hydropower-generation
Above: Figure 2. Average annual relative change in generation compared to the historical mean (1951-2010 water years) during the longest sequences of 5 dry- year long spells (D5) interspaced by one or two wet years (W1 or W2) in the Stanislaus (STN), Tuolumne (TUO), Merced (MER) and Upper San Joaquin (USJ) basins. Wet years are shaded in light blue Below: Figure 3. Average annual relative change in storage compared to the historical mean (1951-2010 water years) during the longest sequences of 5 dry- year long spells (D5) interspaced by one or two wet years (W1 or W2) in the Stanislaus (STN), Tuolumne (TUO), Merced (MER) and Upper San Joaquin (USJ) basins. Wet years are shaded in light blue
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