The work presented in this paper shows an estimate of the impacts of climate change on two high-elevation hydropower systems in California: the Upper America River Project, operated by Sacramento Municipal Utility District in Northern California, and the Big Creek system, operated by Southern California Edison in Southern California. The study builds on previous work modeling the Upper American River Project System. The model presented here includes methodological improvements to better simulate historical operations and more accurately project future operations of both hydropower systems. The operations of these two highelevation systems were simulated using historical and climate change scenarios. Hydrologic scenarios under climate change imply an average reduction in runoff for both systems (with a greater reduction for the Big Creek systems) and a change in the hydrograph towards earlier timing of runoff. The change in the hydrograph is greater for the Upper America River Project system because of the lower elevation of the basins where the system is located. The simulation results show that associated with the reduction in runoff there is a reduction in energy generation in both systems. However, due to the greater change in the hydrologic conditions for the Upper America River Project system, spills are greater in that system, and hence the reduction in energy generation (and associated revenues) is greater as well. In both systems the ability to meet peak historical power demands in the summer months would remain basically unaltered. However, an increase in the occurrence of heat waves especially later in the summer period (September) would increase peak power demand at times when these systems might not be at peak power capacity unless operating strategies are modified.

The work presented in this paper shows an estimate of the impacts of climate change on two high-elevation hydropower systems in California: the Upper America River Project, operated by Sacramento Municipal Utility District in Northern California, and the Big Creek system, operated by Southern California Edison in Southern California. The study builds on previous work modeling the Upper American River Project System. The model presented here includes methodological improvements to better simulate historical operations and more accurately project future operations of both hydropower systems. The operations of these two high-elevation systems were simulated using historical and climate change scenarios. Hydrologic scenarios under climate change imply an average reduction in runoff for both systems (with a greater reduction for the Big Creek systems) and a change in the hydrograph towards earlier timing of runoff. The change in the hydrograph is greater for the Upper America River Project system because of the lower elevation of the basins where the system is located. The simulation results show that associated with the reduction in runoff there is a reduction in energy generation in both systems. However, due to the greater change in the hydrologic conditions for the Upper America River Project system, spills are greater in that system, and hence the reduction in energy generation (and associated revenues) is greater as well. In both systems the ability to meet peak historical power demands in the summer months would remain basically unaltered. However, an increase in the occurrence of heat waves especially later in the summer period (September) would increase peak power demand at times when these systems might not be at peak power capacity unless operating strategies are modified

This research is part of a spectrum of studies of the California water system to assess impacts of climate change on urban and agricultural water agencies. This report describes preliminary work on methods for measuring current water supply reliability and methods for projecting changes in supply reliability caused by climate change, including: (1) a review of recent climate change literature in California; (2) a summary of criteria for evaluating water resource models; (3) an assessment of CALSIM-II water supply reliability forecasts and (4) an assessment of the accuracy of April-June flow forecasts performed by the California Department of Water Resources (DWR). The literature review showed that climate change will affect Californian hydrology in several ways, including an earlier start of spring snowmelt, an increase in winter runoff as a fraction of total runoff, and an increase in winter flood frequency. The study’s evaluation of three models used to estimate the water supply impacts of changing climate scenarios—CALSIM-II, CALVIN, and CVMod—revealed each model strengths and weaknesses. The CALSIM-II studies revealed differences in water supply reliability among user groups and showed that supply reliability at the aggregate basin level differs markedly from reliability at the levels of Depletion Study Area (DSA) and other sub groups within basins. Additionally, the distribution of reliability is different between annual and monthly terms. Finally, analysis of DWR data showed a positive correlation between forecast accuracy and watershed elevation, and showed wet year forecasts to be significantly more accurate than dry year forecasts. This finding implies a strong correlation between snowpack and ability to predict streamflow, and thus a reduction in forecast reliability under most climate change scenarios.

This paper is among the first to report on the full integration of basin-scale models that include projections of the demand and supply of water and energy for residential, commercial, industrial, and agricultural sector users. We link two widely used regional planning models that allow one to study the impact of rising climate variability on water and electricity use in Sacramento, California. Historic data combined with the current energy and water system configuration was used to assess the implications of changes in temperature and precipitation. Climate simulations suggest that electricity imports to the region would increase during hot dry spells, when regional power production is most constrained. In particular, regional imports of electricity would increase over 35 % in hot dry years, assuming a 4 °C increase in average temperature and a 25 % decrease in average precipitation.