Climate change & hydropower | The whiplash effect
Gustavo Facincani Dourado gives an insight into research looking at the phenomenon known as climate whiplash and its impact on hydropower and water management
Above: Gustavo Facincani Dourado is a PhD candidate in Environmental Systems in the Hydrology and Water Resources Engineering programme at the University of California, Merced Email:
gdourado@ucmerced.edu
THE AREA UNDER STUDY consists of four major basins in the central part of the Sierra Nevada in California: the Stanislaus, Tuolumne, Merced and Upper San Joaquin river basins, which contribute the most to the San Joaquin River flow. They host various hydropower projects, including the expansive Big Creek hydropower system which is ranked among the world’s largest complexes of its kind. Collectively these projects generate approximately 25% of California’s hydroelectric energy, with a total generation capacity of over 2700MW. In addition to the largest climate variability in the US, the Mediterranean climate regime found in California gives the state a more extreme mismatch in water availability and demands. Electricity and especially agricultural water needs are greater during California’s hot, dry summers, while most of the precipitation arrives primarily as a few atmospheric river events in the northern part of the state, in particular in the Coast and Sierra Nevada mountain ranges during the winter. Climate change – warming in particular – further complicates that dynamic with a shift in hydrology towards less snow accumulation, earlier snowmelt and more precipitation contributing to streamflow as rain. Meanwhile, climate change is also causing increased climate “whiplash,” which refers to extreme annual shifts from one climate extreme to another, such as from severely dry to wet or wet to dry conditions. Climate whiplash is primarily driven by rapid climate change, which intensifies the hydrological cycle and therefore climate variability. That rapid change impacts specific components of the climate system, such as causing disruptions in the polar vortex, which in turn affects the jet stream (fast-flowing air currents flowing
Right: Figure 1. Time series showing the different combinations of synthetic hydrological sequences used in this study, formed by 25 combinations of two periods of 2-5 dry years (D2 to D5) interspaced by either 1 or 2 wet years (W1 or W2) that result in 5-to-12 year-long sequences for the Stanislaus (STN), Tuolumne (TUO), Merced (MER) and Upper San Joaquin (USJ) basins
west to east). These effects are especially noticeable in the US West Coast, but climate whiplash has also been recognised and is projected to intensify in parts of Europe and Asia. The research on whiplash impacts on hydropower
production underscores the challenges in managing extremes, revealing system vulnerabilities due to limited surface water storage capacity, and emphasising the need for adaptive strategies to enhance climate resilience in hydropower operations. To simulate the impacts of whiplash events, we used a daily water system simulation model (CenSierraPywr) to stress test the water and power projects in the Central Sierra Nevada, and also constructed 200 synthetic hydrologic sequences by sampling the hydrological data derived from future climate projections for the years 2030 through 2060 (Figure 1). We sampled the wettest (>80th percentiles) and driest (<40th and 20th percentiles) water years across projections of ten Global Circulation Models. Then, we combined these water years into 2-to-5-year long dry spells interspaced by 1-2 wet years, to be used as climate-perturbed hydrological inputs to the CenSierraPywr model.
Our findings show that whiplash impacts on
hydropower production are significant due to increased spillage. Even though the basins examined are highly regulated, they can be affected due to their smaller surface water storage capacity. Storage capacity constrains the ability of these systems to absorb hydrologic shocks. A very wet year can alleviate the stress caused by droughts by bringing storage or energy generation levels close to or even above average historical averages. However, the
68 | May 2024 |
www.waterpowermagazine.com
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