High-elevation Hydropower Research Articles

Climate change impacts on high-elevation hydroelectricity in California

While only about 30% of California's usable water storage capacity lies at higher elevations, high-elevation (above 300 m) hydropower units generate, on average, 74% of California's in-state hydroelectricity. In general, high-elevation plants have small man-made reservoirs and rely mainly on snowpack. Their low built-in storage capacity is a concern with regard to climate warming. Snowmelt is expected to shift to earlier in the year, and the system may not be able to store sufficient water for release in high-demand periods. Previous studies have explored the climate warming effects on California's high-elevation hydropower by focusing on the supply side (exploring the effects of hydrological changes on generation and revenues) ignoring the warming effects on hydroelectricity demand and pricing. This study extends the previous work by simultaneous consideration of climate change effects on high-elevation hydropower supply and pricing in California. The California's Energy-Based Hydropower Optimization Model (EBHOM 2.0) is applied to evaluate the adaptability of California's high-elevation hydropower system to climate warming, considering the warming effects on hydroelectricity supply and pricing. The model's results relative to energy generation, energy spills, reservoir energy storage, and average shadow prices of energy generation and storage capacity expansion are examined and discussed. These results are compared with previous studies to emphasize the need to consider climate change effects on hydroelectricity demand and pricing when exploring the effects of climate change on hydropower operations. (C) 2013 Elsevier B.V. All rights reserved. (Less)

Response of California Summer Hydroelectricity Generation to Spring Temperature

Regions depending on winter snowpack for hydroelectricity generation may be adversely affected if spring temperatures increase. An inverse relationship between spring temperature and summer hydroelectricity generation is complicated by changing statistical properties of the variables involved. We use simple approaches to quantify, within broad limits, the effect of a change in spring temperature on hydroelectricity generation in subsequent months over a political entity as large and geographically diverse as the state of California, incorporating variables that are highly nonstationary in the mean and in covariances with each other. Looking at data from several simple perspectives provides insight and a physically realistic explanation of the observations. California’s high-elevation hydropower reservoirs mitigate effects of dry winters; precipitation is limiting and spring temperature has no detectable effect. Following wet winters, however, warm springs can lead to earlier snowmelt and increased spillage so that water storage is limited by high-elevation reservoir capacity; during cold springs the snowpack melts more slowly, allowing it to act as a water reservoir for a longer period of time so that water can be supplied as needed. Following winters with over 70 cm of Research Article British Journal of Environment & Climate Change, 3(3): 316-332, 2013 317 precipitation, water supply is abundant and hydropower seems limited by generation capacity. Our results demonstrate limitations of California’s high-elevation hydropower system, especially if climate warms, and our findings should also aid in the development of more complex, physically based, hydrologic models to aid water managers.

Simulating High-Elevation Hydropower with Regional Climate Warming in the West Slope, Sierra Nevada

Water systems in snowmelt-dominated hydroregions such as California's Sierra Nevada mountains are sensitive to regional climate change, hydropower systems in particular. In this study, a water resources management model was developed for the upper west slope Sierra Nevada to understand the potential effects of regional climate warming on hydropower at the watershed scale, a scale that has been largely neglected but is important for hydroregional planning. The model is developed with the Water Evaluation and Planning system (WEAP) and includes most water management infrastructure in the study region. Hydropower is simulated assuming historical long-term electricity demand and a spill minimization rule. The method is suitable for simulating generation for most of the main watersheds in the region. To assess the potential effect of climate warming, uniform air temperature increases of 0°C, 2°C, 4°C, and 6°C were considered, with no change in precipitation, to approximate regional warming through 2100. The highly productive northern Sierra Nevada sees large re- ductions in hydropower generation with decreases in annual runoff. The central watersheds see less reduction in annual runoff and can adapt better to changes in runoff timing. Generation in southern watersheds, which are less productive, decreases. Results from this study can help identify which watersheds might easily adapt to climate change, where hydropower is likely to conflict with other uses, and where more detailed operational studies are needed. DOI: 10.1061/(ASCE)WR.1943-5452.0000373. © 2014 American Society of Civil Engineers.

Climate change impacts on two high-elevation hydropower systems in California

This paper describes research to estimate the effects of climate change on two high-elevation hydropower systems in California: the Upper American River Project, operated by the Sacramento Municipal Utility District, and the Big Creek system, operated by Southern California Edison. The study builds on a previous model of the Upper American River Project, which is here modified and extended for use to simulate two hydropower systems under various conditions. Future operations of the two high-elevation systems are simulated using climate change scenarios provided for the Second California Assessment. These scenarios suggest reduced precipitation and reduced runoff for both systems, and a shift toward runoff earlier in the year. The change in the hydrograph is somewhat greater for the Upper American River Project system, because its basins lie at a lower elevation. Reduced runoff directly reduces energy generation and revenues from both systems. Because the Upper American River Project system is projected to have greater spills with warmer climate conditions, it also has greater reduction in energy generation and revenues. Both systems continue to meet peak historical power demands in summer under most climate projections. However, if the number of heat waves increases in the late summer (September), reservoir operating strategies may need to be modified.

Estimated impacts of climate warming on California’s high-elevation hydropower

California’s hydropower system is composed of high and low elevation power plants. There are more than 150 high-elevation power plants, at elevations above 1,000 feet (300 m). Most have modest reservoir storage capacities, but supply roughly 74% of California’s in-state hydropower. The expected shift of runoff peak from spring to winter due to climate warming, resulting in snowpack reduction and increased snowmelt, might have important effects on power generation and revenues in California. The large storage capacities at low-elevation power plants provide flexibility to operations of these units under climate warming. However, with climate warming, the adaptability of the high-elevation hydropower system is in question as this system was designed to take advantage of snowpack, a natural reservoir. With so many high-elevation hydropower plants in California, estimation of climate warming effects by conventional simulation or optimization methods would be tedious and expensive. An Energy-Based Hydropower Optimization Model (EBHOM) was developed to facilitate practical climate change and other low-resolution system-wide hydropower studies, based on the historical generation data of 137 high-elevation hydropower plants for which the data were complete for 14 years. Employing recent historical hourly energy prices, the model was used to explore energy generation in California for three climate warming scenarios (dry warming, wet warming, and warming-only) over 14 years, representing a range of hydrologic conditions. The system is sensitive to the quantity and timing of inflows. While dry warming and warming-only climate changes reduce average hydropower revenues, wet warming could increase revenue. Re-operation of available storage and generation capacities help compensate for snowpack losses to some extent. Storage capacity expansion and to a lesser extent generation capacity expansion both increase revenues, although such expansions might not be cost-effective.

Climate change impacts on high elevation hydropower generation in California’s Sierra Nevada: a case study in the Upper American River

Climate change is likely to affect the generation of energy from California’s high-elevation hydropower systems. To investigate these impacts, this study formulates a linear programming model of an 11-reservoir hydroelectric system operated by the Sacramento Municipal Utility District in the Upper American River basin. Four sets of hydrologic scenarios are developed using the Variable Infiltration Capacity model combined with climatic output from two general circulation models under two greenhouse-gas emissions scenarios. Power generation and revenues fall under two of the four climate change scenarios, as a consequence of drier hydrologic conditions. Energy generation is primarily limited by annual volume of streamflow, and is affected more than revenues, reflecting the ability of the system to store water when energy prices are low for use when prices are high (July through September). Power generation and revenues increase for two of the scenarios, which predict wetter hydrologic conditions. In this case, power generation increases more than revenues indicating that the system is using most of its available capacity under current hydrologic conditions. Hydroelectric systems located in basins with hydrograph centroids occuring close to summer months (July through September) are likely to be affected by the changes in hydrologic timing associated with climate change (e.g., earlier snowmelts and streamflows) if the systems lack sufficient storage capacity. High Sierra hydroelectric systems with sufficiently large storage capacity should not be affected by climate-induced changes in hydrologic timing.